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a new approach to selectively reject naturally hydrophobic gangue in the flotation of base metal sulphide minerals | springerlink

a new approach to selectively reject naturally hydrophobic gangue in the flotation of base metal sulphide minerals | springerlink

Efficient separation of naturally hydrophobic gangue, such as talc and carbonaceous materials, from sulphide minerals in flotation is becoming a significant challenge in many processing plants due to the need to process lower grade and more complex ores. Considering the hydrophobic nature of these gangue minerals, prefloating them at the beginning of the flotation circuit in the absence of collectors and rejecting the concentrate is a common practice to remove these gangue minerals. However, sulphide minerals, such as chalcopyrite, can become naturally floatable due to surface oxidation and therefore may float together with naturally hydrophobic gangue. In this study, a new approach was developed to maximize the prefloat of hydrophobic gangue while minimizing the loss of sulphide minerals. The new approach introduced a prefloat cleaner stage where sulphide minerals recovered to the prefloat concentrate was depressed and separated from other hydrophobic gangue minerals at a low pulp potential with the prefloat cleaner tailing fed back to the main sulphide flotation circuit. Flotation tests were conducted using chalcopyrite and organic carbon. The results show that the proposed approach can significantly reduce the loss of valuable minerals in the prefloat flotation without affecting the reject of naturally hydrophobic gangue. Applying pulp potential control at the prefloat cleaner flotation stage also reduces the consumption of reducing agents while minimizing the effect of reducing agents on downstream rougher flotation.

Brooke K, Bullock N, Harvey R, O'sullivan R, Phan C, Tan P, Telford P, Edgar M (2013) Mount Isa and Townsville operations. In: Rankin WJ (ed) Australasian mining and metallurgical operating practices, vol 1, 3rd edn. Ausimm, Australia, p 931

Becker M, Harris PJ, Wiese JG, Bradshaw DJ (2009) Mineralogical characterisation of naturally floatable gangue in Merensky Reef ore flotation. Int J Miner Process 93(34):246255. https://doi.org/10.1016/j.minpro.2009.10.004

Lu S, Wu W Study of process mineralogy and carbon depression in carbon-bearing Cu-Co oxide ore IN DRC. In: 26th International Mineral Processing Congress, IMPC 2012: Innovative Processing for Sustainable Growth - Conference Proceedings, 2012. pp 62966304

OConnor C, Wiese J, Corin K, McFadzean B (2019) On the management of Gangue minerals in the flotation of platinum group minerals. Mining, Metallurgy and Exploration 36(1):5562. https://doi.org/10.1007/s42461-018-0026-6

Konieczny A, Pawlos W, Krzeminska M, Kaleta R, Kurzydlo P (2013) Evaluation of organic carbon separation from copper ore by pre-flotation. Physicochemical Problems of Mineral Processing 49(1):189201. https://doi.org/10.5277/ppmp130117

Zhao KL, Gu GH, Wang H, Wang CL, Wang XH, Luo C (2015) Influence of depressant foenum-graecum on the flotation of a sulfide ore which contains hydrophobic gangue. Int J Miner Process 141:6876. https://doi.org/10.1016/j.minpro.2015.06.005

Lotter NO, Bradshaw DJ, Becker M, Parolis LAS, Kormos LJ (2008) A discussion of the occurrence and undesirable flotation behaviour of orthopyroxene and talc in the processing of mafic deposits. Miner Eng 21(1214):905912. https://doi.org/10.1016/j.mineng.2008.02.023

Leung A, Wiltshire J, Blencowe A, Fu Q, Solomon DH, Qiao GG (2011) The effect of acrylamide-co-vinylpyrrolidinone copolymer on the depression of talc in mixed nickel mineral flotation. Miner Eng 24(5):449454. https://doi.org/10.1016/j.mineng.2010.12.010

Shortridge PG, Harris PJ, Bradshaw DJ, Koopal LK (2000) The effect of chemical composition and molecular weight of polysaccharide depressants on the flotation of talc. Int J Miner Process 59(3):215224. https://doi.org/10.1016/S0301-7516(99)00077-0

Chimonyo W, Fletcher B, Peng Y (2020) The differential depression of an oxidized starch on the flotation of chalcopyrite and graphite. Miner Eng 146:106114. https://doi.org/10.1016/j.mineng.2019.106114

Mierczynska-Vasilev A, Beattie DA (2010) Adsorption of tailored carboxymethyl cellulose polymers on talc and chalcopyrite: correlation between coverage, wettability, and flotation. Miner Eng 23(1113):985993. https://doi.org/10.1016/j.mineng.2010.03.025

Fu Y, Zhu Z, Yao J, Han H, Yin W, Yang B (2018) Improved depression of talc in chalcopyrite flotation using a novel depressant combination of calcium ions and sodium lignosulfonate. Colloids Surf A Physicochem Eng Asp 558:8894. https://doi.org/10.1016/j.colsurfa.2018.08.056

Deng W, Xu L, Tian J, Hu Y, Han Y (2017) Flotation and adsorption of a new polysaccharide depressant on pyrite and talc in the presence of a pre-adsorbed xanthate collector. Minerals 7(3). https://doi.org/10.3390/min7030040

Yuan D, Cadien K, Liu Q, Zeng H (2019) Adsorption characteristics and mechanisms of O-carboxymethyl chitosan on chalcopyrite and molybdenite. J Colloid Interface Sci 552:659670. https://doi.org/10.1016/j.jcis.2019.05.023

Khraisheh M, Holland C, Creany C, Harris P, Parolis L (2005) Effect of molecular weight and concentration on the adsorption of CMC onto talc at different ionic strengths. Int J Miner Process 75(34):197206. https://doi.org/10.1016/j.minpro.2004.08.012

Bakalarz A, Duchnowska M, Pawlos W (2018) Influence of hydrodynamics on preflotation process in flotation machine. Minerals and metallurgical processing 35 (1):19-23. Doi:https://doi.org/10.19150/mmp.8054

Duchnowska M, Bakalarz A, Luszczkiewicz A, Drzymala J, Kowalczuk PB, Konieczny A, Pawlos W Influence of selected frothers on pre-flotation of the kupferschiefer ore. In: IMPC 2016 - 28th International Mineral Processing Congress, 2016

Kowalczuk PB, Buluc B, Sahbaz O, Drzymala J (2014) In search of an efficient frother for pre-flotation of carbonaceous shale from the Kupferschiefer stratiform copper ore. Physicochemical Problems of Mineral Processing 50(2):835840. https://doi.org/10.5277/ppmp140233

Gredelj S, Zanin M, Grano SR (2009) Selective flotation of carbon in the PbZn carbonaceous sulphide ores of Century Mine, Zinifex. Miner Eng 22(3):279288. https://doi.org/10.1016/j.mineng.2008.08.005

Carr D, GHarbort G, Lawson V (2003) Expansion of the Mount Isa Mines copper concentrator phase one cleaner circuit expansion. Paper presented at the Eightth mill. Operators Conference, Townsville, Queensland, Australia

Ahn JH, Gebhardt JE (1991) Effect of grinding media-chalcopyrite interaction on the self-induced flotation of chalcopyrite. Int J Miner Process 33(14):243262. https://doi.org/10.1016/0301-7516(91)90056-O

Chander S (1991) Electrochemistry of sulfide flotation: growth characteristics of surface coatings and their properties, with special reference to chalcopyrite and pyrite. Int J Miner Process 33(14):121134

Zachwieja JB, McCarron JJ, Walker GW, Buckley AN (1989) Correlation between the surface composition and collectorless flotation of chalcopyrite. J Colloid Interface Sci 132(2):462468. https://doi.org/10.1016/0021-9797(89)90260-9

Jalilian H, Shafaei Tonkaboni SZ, Noparast M, Haghi H (2014) Reduction of lead and zinc loss in pre-concentration process of Koushk flotation circuit. Paper presented at the 14th international mineral processing symposium Kuadasi, Turkey, October 15-17, 2014

Xumeng Chen: conceptualization, design, methodology, software, data acquisition, analysis and interpretation, and writingoriginal draft, review, and editing. Sunfangze Liu: methodology, data acquisition, analysis, and interpretation. Yongjun Peng: conceptualization, resources, writingcritically review and editing, supervision, project administration, and funding acquisition.

Chen, X., Liu, S. & Peng, Y. A New Approach to Selectively Reject Naturally Hydrophobic Gangue in the Flotation of Base Metal Sulphide Minerals. Mining, Metallurgy & Exploration 38, 713720 (2021). https://doi.org/10.1007/s42461-020-00365-9

flotation cell - an overview | sciencedirect topics

flotation cell - an overview | sciencedirect topics

The MAC flotation cell was developed by Kadant-Lamort Inc. It can save energy comparedto conventional flotation systems. The MAC flotation cell is mainly used in the flotation section of waste paper deinking pulping, for removal of hydrophobic impurities such as filler, ash,ink particles, etc. It can increase pulp whiteness and meet the requirements of final paper appearance quality. Table11.11 shows the features of MAC flotation cell. Kadants MAC flotation cell deinking system uses air bubbles to float ink particles to the cell surface for removal from the recycled material. The latest generation of the MAC cell deinking system incorporates a patented bubble-washing process to reduce power consumption and also fiber loss. It combines small, new, auto-clean, low-pressure injectors with a flotation cell. The function of injectors is to aerate the stock before it is pumped and sent tangentially to the top of the cell. The air bubbles collect ink particles in the cell and rise up to the top to create a thick foam mat that is evacuated because of the slight pressurization of the cell. The partially deinked stock then goes to a deaeration chamber and is pumped to the next stage. Here, the operation is exactly the same as for the first stage. This stage also has the same number of injectors and same flow (Kadant,2011). This operation is repeated up to five times for a high ink removal rate. Remixing of the air coming from downstream stages of the process helps the upstream stages and improves the overall cell efficiency. Adjustable and selective losses of fiberdepend on the application and technical requirements inks, or inks and fillers. The use of low-pressure injectors in the MAC flotation cell could save about 2530% of the energy used in conventional flotation systems (ECOTARGET,2009). The benefits of the MAC flotation cell are summarized in Table11.12.

Agitated flotation cells are widely used in the mineral processing industry for separating, recovering, and concentrating valuable particulate material from undesired gangue. Their performance is lowered, however, when part of the particulate system consists of fines, with particle diameters typically in the range from 30 to 100m. For example, it was observed difficult to float fine particles because of the reduction of middle particles (of wolframite) as carriers and the poor collision and attachment between fine particles and air bubbles; a new kinetic model was proposed [34].

As an alternative to agitated cells, bubble columnsused in chemical engineering practice as chemical reactorswere proposed for the treatment of fine particle systems. Flotation columns, as they came to be known, were invented back in the 1960s in Canada [35]. The main feature that differentiates the column from the mechanical flotation cell (of Denver type) is wash water, added at the top of the froth. It was thought to be beneficial to overall column performance since it helps clean the froth from any entrained gangue, while at the same time preventing water from the pulp flowing into the concentrate. In this way, it was hoped that certain cleaning flotation stages could be gained.

Let us note that the perhaps insistence here on mineral processing is only due to the fact that most of the available literature on flotation is from this area, where the process was originated and being widely practiced. The effect of particle size on flotation recovery is significant; it was shown that there exists a certain size range in which optimum results may be obtained in mineral processing. This range varies with the mineral properties such as density, liberation, and so on, but was said to be of the order of 10100m [36].

Regulating the oxidation state of pyrite (FeS2) and arsenopyrite (FeAsS), by the addition of an oxidation or reduction chemical agent and due to the application of a short-chain xanthate as collector (such as potassium ethyl xanthate, KEX), was the key to selective separation of the two sulfide minerals, pyrite and arsenopyrite [37]. Strong oxidizing agents can depress previously floated arsenopyrite. Various reagents were examined separately as modifiers and among them were sodium metabisulfite, hydrazinium sulfate, and magnesia mixture. The laboratory experiments were carried out in a modified Hallimond tube, assisted by zeta-potential measurements and, in certain cases, by contact angle measurements.

This conventional bench-scale flotation cell provides a fast, convenient, and low-cost method, based on small samples (around 2g), usually of pure minerals and also artificial mixtures, for determining the general conditions under which minerals may be rendered floatableoften in the absence of a frother (to collect the concentrate in the side tube) [38]. This idea was later further modified in the lab replacing the diaphragm, in order to conduct dissolved air or electroflotation testssee Section 3.

Pyrite concentrates sometimes contain considerable amounts of arsenic. Since they are usually used for the production of sulfuric acid, this is undesirable from the environmental point of view. However, gold is often associated with arsenopyrite, often exhibiting a direct relationship between Au content and As grade. There is, therefore, some scope for concentrating arsenopyrite since the ore itself is otherwise of little value (see Fig.2.2). Note that previous work on pyrites usually concentrated on the problem of floating pyrite [40].

In the aforementioned figure (shown as example), the following conditions were applied: (1) collector [2-coco 2-methyl ammonium chloride] 42mg/L, frother (EtOH) 0.15% (v/v), superficial liquid velocity uL=1.02cm/s, superficial gas velocity uG=0.65cm/s, superficial wash water velocity uw=0.53cm/s; (2) hexadecylamine, 45mg/L; pine oil, 50mg/L; EtOH, 0.025%; uL=0.84cm/s; uG=0.72cm/s; uw=0.66cm/s; (3) Armoflot 43, 50mg/L; pine oil, 50mg/L; EtOH, 0.025%; uL=0.84cm/s; uG=0.71cm/s; uw=0.66cm/s [39]. The pyrite (with a relatively important Au content of 21g/ton) was a xanthate-floated concentrate. The presence of xanthates, however, might cause problems in the subsequent cyanidation of pyrites when recovering their Au value, which perhaps justified the need to find alternative collectors. In general, the amines exhibited a behavior similar to that of the xanthates (O-alkyl dithiocarbonates). The benefit of the amine was in its lower consumption, as compared with the xanthate systems.

The arsenic content of the pyrite was approximately 9% (from an initial 3.5% of the mixed sulfide ore). The material was sieved and the75m fraction was used for the laboratory-scale cylindrical column experiments. The effect on metallurgical characteristics of the flotation concentrate of varying the amount of ferric sulfate added to the pulp was studied; three collectors were used and their performance was compared (in Fig.2.2). Both hexadecylamine and Armoflot 43 (manufactured by Akzo) exhibited an increased recovery but a very low enrichment, whereas 2-coco 2-methyl ammonium chloride (Arquad-2C) showed a considerable enrichment; a compromise had to be made, therefore, between a high-grade and a low recovery.

Electroflotation (electrolytic flotation) is an unconventional separation process owing its name to the bubbles generation method it uses, i.e., electrolysis of the aqueous medium. In the bottom of the microcell, the two horizontal electrodes were made from stainless steel, the upper one being perforated. The current density applied was 300 Am2. It was observed that with lime used to control pH, different behavior was observed (see Fig.2.3). Pyrite, with permanganate (a known depressant) also as modifier, remained activated from pH 5.0 to 8.0at 80% recovery, while it was depressed at the pH range from 9.0 to 12.0. A conditioning of 30min was applied in the presence of modifier alone and further 15min after the addition of xanthate. The pure mineral sample, previously hand collected, crushed, and pulverized in the laboratory, was separated by wet sieving to the45 to+25m particle size range.

Pyrite due to its very heterogeneous surface, consisting of a mosaic of anodic and cathodic areas, presents a strong electrocatalytic activity in the anodic oxidation of xanthate to dixanthogen. It is also possible that the presence of the electric field, during electroflotation, affected the reactions taking place. In order to explain this difference in flotation behavior thermodynamic calculations for the system Fe-EX-H2O have been done [41]. It was concluded that electroflotation was capable of removing fine pyrite particles from a dilute dispersion, under controlled conditions. Nevertheless, dispersed air and electroflotation presented apparent differences for the same application.

The size of the gas bubbles produced was of the order of 50m, in diameter [21]. Similar measurements were later carried out at Newcastle, Australia [42]; where it was also noted that a feature of electroflotation is the ability to create very fine bubbles, which are known to improve flotation performance of fine particles.

In fact, the two electrodes of a horizontal electrodes set, usually applied in electroflotation, could be separated by a cation exchange membrane, as only one of the produced gases is often necessary [43]. In the lower part/separated electrode, an electrolyte was circulated to remove the created gas, and in the meantime, increase the conductivity; hence having power savings (as the electric field is built up between the electrodes through the use of the suspension conductivity). Attention should be paid in this case to anode corrosion, mainly by the chloride ion (i.e., seawater).

Microorganisms have a tremendous influence on their environment through the transfer of energy, charge, and materials across a complex biotic mineralsolution interface; the biomodification of mineral surfaces involves the complex action of microorganism on the mineral surface [44]. Mixed cationic/anionic surfactants are also generating increasing attention as effective collectors during the flotation of valuable minerals (i.e., muscovite, feldspar, and spodumene ores); the depression mechanisms on gangue minerals, such as quartz, were focused [45].

Another design of a flotation cell which applies ultrasound during the flotation process has been developed by Vargas-Hernndez et al. (2002). The design consists of a Denver cell (Koh and Schwarz, 2006) equipped with ultrasonic capabilities of performing ultrasound-assisted flotation experiments. This cell is universally accepted as a standard cell for laboratory flotation experiments. In Figure 35.25, a schematic of the Denver cell equipped with two power transducers is shown operating at 20kHz. The ultrasonic transducers are in acoustic contact with the body of the flotation cell but are not immersed in the same cell. Instead, they are submerged in distilled water and in a thin membrane that separates the radiant head of the transducer from the chamber body. The floatation chamber has a capacity of 2.7l and is also equipped with conventional systems to introduce air and mechanical agitation able to maintain the suspension of metallurgical pulp. In the upper part of the cell there is an area in which the foam is recovered for analysis by a process called skimming. The block diagram of Figure 35.25 further shows that the experimental system was developed to do ultrasonic-assisted flotation experiments. The transducers operate at 20kHz and can handle power up to 400W. In the Denver cell an acoustic probe, calibrated through a nonlinear system and capable of measuring high-intensity acoustic fields, is placed (Gaete-Garretn et al., 1993, 1998). This is done in order to determine the different acoustic field intensities with a spatial scanner during the experimentation. Figure 35.26 shows the distribution of ultrasonic field intensity obtained by a spatial scanner in the central area of the flotation chamber. The Denver cell with ultrasonic capabilities, as described, is shown in Figure 35.27. The obtained results were fairly positive. For example, for fine particle recovery it worked with metallurgical pulp under 325mesh, indicating floating particles of less than 45m, and the recovery curves are almost identical to those of an appropriate size mineral for flotation. This is shown in Figure 35.28, where a comparison between typical copper recovery curves for fine and normal particles is presented. The most interesting part of the flotation curves is the increase in recovery of molybdenum with ultrasonic power, as shown in Figure 35.29. The increase in recovery of iron is not good news for copper mines because the more iron floating the lower grade of recovery. This may be because the iron becomes more hydrophobic with ultrasonic action. According to the experts, this situation could be remedied by looking for specific additives to avoid this effect. Flotation kinetics shown in Figure 35.30 with 5 and 10W of acoustic power applied also show an excellent performance. It should be noted that the acoustic powers used to vary the flotation kinetics have been quite low and could clearly be expanded.

Figure 35.28. Compared recovering percent versus applied power in an ultrasonic-assisted flotation process in a Denver cell: (a) fine and ultrafine particles recovering and (b) normal particles recovering.

These experiments confirm the potential of power ultrasound in flotation. Research on assisted flotation with power ultrasound has been also carried out by Ozkan (2002), who has conducted experiments by pretreating pulp with ultrasound during flotation. Ozkhans objective was to recover magnesite from magnesite silts with particles smaller than 38m. Their results show that under ultrasonic fields the flotation foam bubbles are smaller, improving magnesite recovery rates. When Ozkhan treated magnesite mineral with a conventional treatment the beneficial effect of ultrasound was only manifested for mineral pretreatment. The flotation performed under ultrasonic field did not show improvement. This was because power ultrasound improves the buoyancy of clay iron and this has the effect of lowering the recovery of magnesite.

Kyllnen et al. (2004) employed a cell similar to Jordan to float heavy metals from contaminated soils in a continuous process. In their experiments they obtained a high recovery of heavy metals, improving the soil treatment process. Alp et al. (2004) have employed ultrasonic waves in the flotation of tincal minerals (borax Na O710 B4 H2O), finding the same effects as described above, i.e., that power ultrasound helps in the depression of clay. However, the beneficial effect of ultrasound is weakened when working with pulps with high mineral concentration (high density), probably due to an increase in the attenuation of the ultrasonic field. Safak and Halit (2006) investigated the action mechanisms of ultrasound under different flotation conditions. A cleaning effect on the floating particles was attributed to the ultrasonic energy, making the particles more reactive to the additives put in the metallurgical pulp. Furthermore due to the fact that the solid liquid interface is weaker than the cohesive forces of the metallurgic pulp liquids, it results in a medium favorable to creation of cavitation bubbles. The unstable conditions of a cavitation environment can produce changes in the collectors and even form emulsions when entering the surfactant additives. In general, many good properties are attributed to the application of ultrasound in flotation. For example, there is a more uniform distribution of the additives (reagents) and an increase in their activity. In fact in the case of carbon flotation it has been found that the floating times are shortened by the action of ultrasound, the bubble sizes are more stable, and the consumption of the reagents is drastically lowered.

Abrego Lpez (2006) studied a water recovery process of sludge from industrial plants. For this purpose he employed a flotation cell assisted by power ultrasound. In the first stage he made a flotation to recover heavy metals in the metallurgical pulp, obtaining a high level of recovery. In the second stage he added eucalyptus wood cones to the metallurgical pulp to act as an accumulator of copper, lead, nickel, iron, and aluminum. The author patented the method, claiming that it obtained an excellent recovery of all elements needing to be extracted. zkan and Kuyumcu (2007) showed some design principles for experimental flotation cells, proposing to equip a Denver flotation cell with four power transducers. Tests performed with this equipment consisted of evaluating the possible effects that high-intensity ultrasonic fields generated in the cell may have on the flotation. The author provides three-dimensional curves of ultrasonic cavitation fields in a Denver cell filled with water at frequencies between 25 and 40kHz. A warming effect was found, as expected. However, he states that this effect does not disturb the carbon recovery processes because carbon flotation rarely exceeds 5min. They also found that the pH of tap water increases with the power and time of application of ultrasound, while the pH of the carbonwaterreagentsludge mixture decreases. The conductivity of the metallurgical pulp grows with the power and time of application of ultrasound, but this does not affect flotation. The carbon quality obtained does not fall due to the application of ultrasound and the consumption of lowered reagents. They did not find an influence from the ultrasound frequency used in the process, between 25 and 40kHz. They affirmed that ultrasound is beneficial at all stages of concentration.

Kang et al. (2009) studied the effects of preconditioning of carbon mineral pulp in nature by ultrasound with a lot of sulfur content. They found that the nascent oxygen caused by cavitation produces pyrite over oxidation, lowering its hydrophobicity, with the same effect on the change of pH induced by ultrasonic treatment. Additionally, ultrasound decreases the liquid gas interfacial tension by increasing the number of bubbles. Similar effects occur in carbon particles. The perfect flotation index increases 25% with ultrasonic treatment. Kang et al. (2008) continued their efforts to understand the mechanism that causes effects in ultrasonic flotation, analyzing the floating particles under an ultrasonic field by different techniques like X-ray diffraction, electron microscopy, and scanning electron microscopy techniques. In carbon flotation it is estimated that ultrasonic preconditioning may contribute to desulfurization and ash removal (deashing) in carbon minerals. Zhou et al. (2009) have investigated the role of cavitation bubbles created by hydrodynamic cavitation in a flotation process, finding similar results to those reported for ultrasonic cavitation flotation. Finally, Ozkan (2012) has conducted flotation experiments with the presence of hard carbon sludge cavitation (slimes), encountering many of the effects that have been reported for the case of metallurgical pulp with ultrasound pretreatment. This includes improved flotation, drastic reduction in reagent consumption, and the possible prevention of oxidation of the surface of carbon sludge. A decrease in the ash content in floating carbon was not detected. However, tailings do not seem to contain carbon particles. All these effects can be attributed to acoustic cavitation. However, according to the author, there is a need to examine the contribution of ultrasound to the probability of particlebubble collision and the likelihood of getting the bubbles to connect to the particles. The latter effects have been proposed as causes for improvements in flotation processes in many of the publications reviewed, but there is no systematic study of this aspect.

In summary, power ultrasound assistance with flotation processes shows promising results in all versions of this technique, including conditioning metallurgical pulp before floating it, assisting the continuous flotation process, and improving the yields in conventional flotation cells. The results of ultrasonic floating invariably show a better selectivity and an increase, sometimes considerable, in the recovery of fine particles. Paradoxically, in many experiments an increase has been recorded in recovering particles suitable for normal flotation. These facts show the need for further research in the flotation process in almost all cases, with the exception perhaps of carbon flotation. For this last case, in light of the existing data the research should be directed toward scale-up of the technology.

The concentrate obtained from a batch flotation cell changes in character with time as the particles floating change in size, grade and quantity. In the same way, the concentrate from the last few cells in a continuous bank is different from that removed from the earlier cells. Particles of the same mineral float at different rates due to different particle characteristics and cell conditions.

The recovery of any particular mineral rises to an asymptotic value R which is generally less than 100%. The rate of recovery at time t is given by the slope of the tangent to the curve at t, and the rate of recovery at time t1 is clearly greater than the rate at time t2. There is a direct relationship between the rate of flotation and the amount of floatable material remaining in the cell, that is:

The process is carried out in a flotation cell or tank, of which there are two basic types, mechanical and pneumatic. Within each of these categories, there are two subtypes, those that operate as a single cell, and those that are operated as a series or bank of cells. A bank of cells (Fig. 8) is preferred because this makes the overall residence times more uniform (i.e., more like plug flow), rather than the highly diverse residence times that occur in a single (perfectly mixed) tank.

FIGURE 8. Flotation section of a 80,000t/d concentrating plant, showing the arrangement of the flotation cells into banks. A small part of the grinding section can be seen through the gap in the wall. [Courtesy Joy Manufacturing Co.]

The purpose of the flotation cell is to attach hydrophobic particles to air bubbles, so that they can float to the surface, form a froth, and can be removed. To do this, a flotation machine must maintain the particles in suspension, generate and disperse air bubbles, promote bubbleparticle collision, minimize bypass and dead spaces, minimize mechanical passage of particles to the froth, and have sufficient froth depth to allow nonhydrophobic (hydrophilic) particles to return to the suspension.

Pneumatic cells have no mechanical components in the cell. Agitation is generally by the inflow of air and/or slurry, and air bubbles are usually introduced by an injector. Until comparatively recently, their use was very restricted. However, the development of column flotation has seen a resurgence of this type of cell in a wider, but still restricted, range of applications. While the total volume of cell is still of the same order as that of a conventional mechanical cell, the floor space and energy requirements are substantially reduced. But the main advantage is that the cell provides superior countercurrent flow to that obtained in a traditional circuit (see Fig. 11), and so they are now often used as cleaning units.

Mechanical cells usually consist of long troughs with a series of mechanisms. Although the design details of the mechanisms vary from manufacturer to manufacturer, all consist of an impeller that rotates within baffles. Air is drawn or pumped down a central shaft and is dispersed by the impeller. Cells also vary in profile, degree of baffling, the extent of walling between mechanisms, and the discharge of froth from the top of the cell.

Selection of equipment is based on performance (represented by grade and recovery), capacity (metric tons per hour per cubic meter); costs (including capital, power, maintenance), and subjective factors.

Among all processing industries, only in the ore and mining industries is the accent more on wear resistance than corrosion. In mining industries, the process concerns material handling more than any physical or chemical conversions that take place during the refining operations. For example, in the excavation process of iron ore, conventional conveyer systems and sophisticated fluidized systems are both used [16,17]. In all these industries, cost and safety are the governing factors. In a fluidized system, the particles are transported as slurry using screw pumps through large pipes. These pipes and connected fittings are subjected to constant wear by the slurry containing hard minerals. Sometimes, depending on the accessibility of the mineral source, elaborate piping systems will be laid. As a high-output industry any disruption in the work will result in heavy budgetary deficiency. Antiabrasive rubber linings greatly enhance the life of equipment and reduce the maintenance cost. The scope for antiabrasive rubber lining is tremendous and the demand is ever increasing in these industries.

Different rubber compounds are used in the manufacture of flotation cell rubber components for various corrosion and abrasion duty conditions. Flotation as applied to mineral processing is a process of concentration of finely divided ores in which the valuable and worthless minerals are completely separated from each other. Concentration takes place from the adhesion of some species of solids to air bubbles and wetting of the other series of solids by water. The solids adhering to air bubbles float on the surface of the pulp because of a decrease in effective density caused by such adhesion, whereas those solids that are wetted by water in the pulp remain separated in the pulp. This method is probably the more widely used separation technique in the processing of ores. It is extensively used in the copper, zinc, nickel, cobalt, and molybdenum sections of the mineral treatment industry and is used to a lesser extent in gold and iron production. The various rubber compounds used in the lining of flotation cells and in the manufacture of their components for corrosive and abrasive duties are:

Operating above the maximum capacity can cause the performance of flotation cells to be poor even when adequate slurry residence time is available (Lynch et al., 1981). For example, Fig. 11.21 shows the impact of increasing volumetric feed flow rate on cell performance (Luttrell et al., 1999). The test data obtained at 2% solids correlates well with the theoretical performance curve predicted using a mixed reactor model (Levenspiel, 1972). Under this loading, coal recovery steadily decreased as feed rate increased due to a reduction in residence time. However, as the solids content was increased to 10% solids, the recovery dropped sharply and deviated substantially from the theoretical curve due to froth overloading. This problem can be particularly severe in coal flotation due to the high concentration of fast floating solids in the flotation feed and the presence of large particles in the flotation froth. Flotation columns are particularly sensitive to froth loading due to the small specific surface area (ratio of cross-sectional area to volume) for these units.

Theoretical studies indicate that loading capacity (i.e., carrying capacity) of the froth, which is normally reported in terms of the rate of dry solids floated per unit cross-sectional area, is strongly dependent on the size of particles in the froth (Sastri, 1996). Studies and extensive test work conducted by Eriez personnel also support this finding. As seen in Fig. 11.22, a direct correlation exists between capacity and both the mean size (d50) and ultrafines content of the flotation feedstock. The true loading capacity may be estimated from laboratory and pilot-scale flotation tests by conducting experiments as a function of feed solids content (Finch and Dobby, 1990). Field surveys indicate that conventional flotation machines can be operated with loading capacities of up to 1.52.0t/h/m2 for finer (0.150mm) feeds and 56t/h/m2 or more for coarser (0.600mm) feeds. Most of the full-scale columns in the coal industry operate at froth loading capacities less than 1.5t/h/m2 for material finer than 0.150mm and as high as 3.0t/h/m2 for flotation feed having a top size of 0.300mm feeds.

Froth handling is a major problem in coal flotation. Concentrates containing large amounts of ultrafine (<0.045mm) coal generally become excessively stable, creating serious problems related to backup in launders and downstream handling. Bethell and Luttrell (2005) demonstrated that coarser deslime froths readily collapsed, but finer froths had the tendency to remain stable for an indefinite period of time. Attempts made to overcome this problem by selecting weaker frothers or reducing frother dosage have not been successful and have generally led to lower circuit recoveries. Therefore, several circuit modifications have been adopted by the coal industry to deal with the froth stability problem. For example, froth launders need to be considerably oversized with steep slopes to reduce backup. Adequate vertical head must also be provided between the launder and downstream dewatering operations. In addition, piping and chute work must be designed such that the air can escape as the froth travels from the flotation circuit to the next unit operation.

Figure 11.23 shows how small changes in piping arrangements can result in better process performance. Shown in Fig. 11.23 is a column whose performance suffered due to the inability to move the froth product from the column launder although a large discharge nozzle (11m) had been provided. In this example, the froth built up in the launder and overflowed when the operators increased air rates. To prevent this problem, the air rates were lowered, which resulted in less than optimum coal recovery. It was determined that the downstream discharge piping was air-locking and preventing the launders from properly draining. The piping was replaced with larger chute work that allowed the froth to flow freely and the air to escape. As a result, higher aeration rates were possible and recoveries were significantly improved.

Some installations have resorted to using defoaming agents or high-pressure launder sprays to deal with froth stability. However, newer column installations eliminate this problem by including large de-aeration tanks to allow time for the froth to collapse (Fig. 11.24a). Special provisions may also be required to ensure that downstream dewatering units can accept the large froth volumes. For example, standard screen-bowl centrifuges equipped with 100mm inlets may need to be retrofitted with 200mm or larger inlets to minimize flow restrictions. In addition, while the use of screen-bowl centrifuges provides low product moistures, there are typically fine coal losses, as a large portion of the float product finer than 0.045mm is lost as main effluent. This material is highly hydrophobic and will typically accumulate on top of the thickener as a very stable froth layer, which increases the probability that the process water quality will become contaminated (i.e., black water).

This phenomenon is more prevalent in by-zero circuits, especially when the screen-bowl screen effluent is recycled back through the flotation circuit, either directly or through convoluted plant circuitry. Reintroducing material that has already been floated to the flotation circuit can result in a circulating load of very fine and highly floatable material. As a result, the capacity of the flotation equipment can be significantly reduced, which results in losses of valuable coal. Most installations will combat this by ensuring that the screen-bowl screen effluent is routed directly back to the screen bowl so that it does not return to the flotation circuit. The accumulation of froth on the thickener, which tends to be especially problematic in by-zero circuitry, is also reduced by utilizing reverse-weirs and taller center wells, as this approach helps to limit the amount of froth that can enter into the process water supply. Froth that does form on top of the clarifier can be eliminated by employing a floating boom that is placed directly in the thickener (Fig. 11.24b) and used in conjunction with water sprays. The floating boom can be constructed out of inexpensive PVC piping, and is typically attached to the rotating rakes. The boom floats on the water interface and drags any froth around to the walkway that extends over the thickener, where it is eliminated by the sprays.

Column cells have been developed over the past 30 years as an alternative to mechanically agitated flotation cells. The major operating difference between column and mechanical cells is the lack of agitation in column cells that reduces energy and maintenance costs. Also, it has been reported that the cost of installing a column flotation circuit is approximately 2540% less than an equivalent mechanical flotation circuit (Murdock et al., 1991). Improved metallurgical performance of column cells in iron ore flotation is reported and attributed to froth washing, which reduces the loss of fine iron minerals entrained into the froth phase (Dobby, 2002).

The Brazilian iron ore industry has embraced the use of column flotation cells for reducing the silica content of iron concentrates. Several companies, including Samarco Minerao S.A., Companhia Vale do Rio Doce (CRVD), Companhia Siderrgica Nacional (CSN), and Mineraes Brasileiras (MBR), are using column cells at present (Peres et al., 2007). Samarco Minerao, the first Brazilian producer to use column cells, installed column cells as part of a plant expansion program in the early 1990s (Viana et al., 1991). Pilot plant tests showed that utilization of a column recleaner circuit led to a 4% increase in iron recovery in the direct reduction concentrate and an increase in primary mill capacity when compared to a conventional mechanical circuit.

There are also some negative reports of the use of column cells in the literature. According to Dobby (2002), there were several failures in the application of column cells in the iron ore industry primarily due to issues related to scale-up. At CVRD's Samitri concentrator, after three column flotation stages, namely, rougher, cleaner, and recleaner, a secondary circuit of mechanical cells was still required to produce the final concentrate.

Imhof et al. (2005) detailed the use of pneumatic flotation cells to treat a magnetic separation stream of a magnetite ore by reverse flotation to reduce the silica content of the concentrate to below 1.5%. From laboratory testing, they claimed that the pneumatic cells performed better than either conventional mechanical cells or column cells. The pneumatic cells have successfully been implemented at the Compaia Minera Huasco's iron ore pellet plant.

This chapter presents a novel approach to establish the relationship between collector properties and the flotation behavior of goal in various flotation cells. Coal flotation selectivity can be improved if collector selection is primarily based on information obtained from prior contact angle and zeta potential measurements. In a study described in the chapter, this approach was applied to develop specific collectors for particular coals. A good correlation was obtained between laboratory batches and large-scale conventional flotation cells. This is not the case when these results are correlated with pneumatic cell trial data. The study described in the chapter was aimed at identifying reasons for the noncorrelation. Two collectors having different chemical compositions were selected for this investigation. A considerable reduction in coal recovery occurred at lower rotor speeds when comparing results of oxidized and virgin coal. The degree to which a collector enhances flocculation in both medium- and low-shear applications and also the stronger bubble-coal particle adherence required for high-shear cells must, therefore, all be taken into consideration when formulating a collector for coal flotation.

an introduction to froth flotation

an introduction to froth flotation

When I started out the information on the processing equipment was easy to come by.Over time this has changed.As a start in reversing this, I have been presenting introductions to some of the common processes and equipment used in mineral processing.Major portions of this have been excerpted from A Mining Engineers Notebook: Mineral processing (www.smartdogmining.com).

Development and use of froth flotation as a beneficiation process has been ongoing since the first part of the last century.Initial study of the flotation concept was in the late 19th century.The basic process involves the selective coating of a particle's surface to alter or enhance its surface chemical characteristics.The flotation process is widely used for treating metallic and non-metallic ores. A greater tonnage of ore is treated by flotation than by any other single process. Practically all the metallic minerals are being recovered by the flotation process and the range of nonmetallic minerals is steadily being enlarged.

Flotation, or more specifically froth flotation, is a physicochemical method of concentrating fine minerals and coal.The process involves chemical treatment of a pulp to create conditions favorable for the attachment of particles to air bubbles.Some particles are not readily wetted by water (hydrophobic), while others are readily wetted by water (hydrophilic).By the addition of chemicals these properties can be enhanced.Air bubbles are created by the rapid motion of the agitator mechanism which draws air down the hollow shaft and disperses the air into the pulp.The air bubbles carry the hydrophobic particles to the surface of the pulp and form a stabilized froth which is skimmed off while the hydrophilic particles remain submerged in the pulp.

More than any other beneficiation process, there is probably no such thing as a typical flotation circuit.Development of a flotation circuit is entirely dependent on the characteristics of the ore and what works at one operation may not work at a nearby operation.And even in one operation the requirements can and will change over time.This requires continual test work.That said there are some fairly common flotation arrangements.

One of the most common is the rougher-scavenger-cleaner arrangement; where the first couple of cells (roughers) are set to produce a high grade concentrate, which are followed by cells (scavengers) to make maximum recovery.The break between rougher and scavengers is sometimes set by concentrate grade but can vary over time.The rougher concentrate may be a final concentrate or a portion combined with the scavenger concentrate which goes to cleaner section.Often there is a regrind mill between the scavengers and the cleaners.The cleaner concentrate will often go to final concentrate while the cleaner tails and the scavenger tails are a final tail.For a complex ore, or a multi-product ore this circuitry can get to re-cleaners, secondary flotation, and even more complex circuits.All of which is beyond an introduction level article.

Most flotation cells operate in the same manner, although there are a few exceptions, but this section will deal with the general operation of the majority of cells. Later articles will deal with some of the specialized units such as column cells.

The pulp flows by gravity into each cell through the feed pipe, from which it is fed into the impeller in the mixing zone.As the pulp flows over the impeller blades it is thrown outward and upward from the impeller and diffuser by the centrifugal action of the impeller. The pulp is kept in complete circulation by the impeller action and as the flotation reaction takes place, the pulp is passed from cell to cell. Pulp flows to each succeeding cell through the tails section, which in small cells can be an overflow weir, or on larger cells be by valves controlling the outflow through the side or bottom. This gives accurate control of pulp level as the pulp passes through the machine.

It is not essential to have each individual cell with separate tails control; however, for most installations this is recommended. An alternate arrangement (for smaller rectangular type cells) is with gate control every two to four cells for pulp level control, and free pulp passage from cell to cell, by means of the ports, as well as cell to cell overflow. The arrangement is actually a "grouping" without sacrificing the positive circulation feature.

The passage of pulp through the cell and the action created in the impeller zone draws air down the standpipe (or it may be a low pressure air system). The impeller zone thoroughly mixes the air with the pulp and reagents. As this action proceeds, a thoroughly aerated live pulp is produced and furthermore, as this mixture is mixed together by the impeller action, the pulp is intimately diffused with exceedingly small air bubbles which support the largest number of mineral particles.

Aeration is accomplished by one of two methods; either natural or forced/induced aeration.Under natural aeration, the design of the impeller and diffuser natural draw air down the standpipe into the mixing zone.For some applications, this may not be sufficient or a simpler impeller design is desired, and for these a forced or induced aeration system is used, where low pressure (commonly under 10 psig (0.6 atmospheres) air is supplied to the cell.This feature is accomplished by the introduction of air from a blower or turbo-compressor through the standpipe connection into the aerating zone where it is premixed with the pulp by the impeller action. Induced air is of particular advantage for low ratio of concentration and slow-floating ores.

Throttling of air is of benefit when suppressed flotation is required. This is accomplished by cutting off or decreasing the size of air inlet on the standpipe.Suppressed flotation finds its chief use in certain nonmetallics and occasionally in cleaner or recleaner operations.

The aerated pulp, after leaving the mixing zone, passes upward by displacement to the central section of the cell. This is a quiet zone and is free from cross currents and agitation. In this zone, the mineral-laden air bubbles separate from the gangue and pass upward to the froth column without dropping their load, due to the quiescent condition. The gangue material follows the pulp flow and is rejected at the discharge weir or valve.

The mineral-laden bubbles move from the separation zone to the pulp level and are carried to the overflow by the crowding action of succeeding bubbles. To facilitate the quick removal of mineral-laden froth, some cells are equipped with froth paddles. Froth removal can be further facilitated by the use of crowding panels which create a positive movement of froth to the overflow.Cells normally have the overflow along the outside edges, while larger circular cells may have additional overflows running towards the center.These additional overflows do cause issues during agitator maintenance.

Positive circulation of all pulp fractions from cell to cell is important. Minimizing short circuiting, which can occur through the machine is important; so that every particle is subject to positive treatment. In instances where successful metallurgy demands the handling of a dense pulp containing an unusually large percentage of coarse material, the use of bottom mounted valves provides additional sand relief in the machine operation. This opening removes from the lower part of the cell the coarse fractions and passes them through the feed pipe to the impeller of each succeeding cell. The sand relief openings assure the passage of slow floating coarse mineral to each impeller and therefore it is subject to the intensive mixing, aeration and optimum flotation condition of each successive cell.The passage of the coarse fractions through each impeller minimizes short circuiting and thus, both fine and coarse mineral are subject to positive flotation.

Flotation cells are normally set up in rows or banks of equal sized cells.The size of the cells and number of cells of a flotation bank or row depends upon facts and conditions which can best be determined by test work and modified by experience. At a given/desired pulp density and reagent combination, a certain flotation contact period/residence time is required to obtain the desired recovery and grade.This contact time and pulp density determines the volume required for a given feed rate in tons per unit time.

Flotation contact time required for the ore is one of key factors in calculating capacity.If an ore is slow floating and requires twelve minute treatment time, and another ore is fast floating and requires but six minute treatment, the second ore requires only half the capacity of the first. With the residence time and knowing the pulp density and specific gravity of dry solids the cubic feet of pulp handled by the flotation machine, so are determining factors in calculating the flotation contact period.

Metallurgical results required from the flotation machine will have considerable bearing on the installed capacity. Several stages of cleaning may be required to give a high grade concentrate. Results with cells of equal volume will not necessarily be equal because they may not be equally efficient.

The volume of the flotation cell determines the time available for flotation to take place. Therefore, the capacity of any flotation machine is dependent on the volume. All flotation cells having the same volume will have approximately the same capacity, with allowance made for horsepower, the efficiency of the impeller and aeration. As the flotation contact period is very important in any flotation machine, the actual cubical content of any machine should be carefully checked as well as accurate determinations on average pulp specifications.

To determine the number of cells required, firs determine the volumetric flow (cubic feet/minute, cubic meters/minute, or similar) of pulp and multiply by the desired residence time, this gives the required flotation volume.Based on the desired operating philosophy of one, two or more rows/banks of cells divide the total volume by the number of rows/banks to get the volume per row/bank.Then divide this by the desired number of cells per row/bank.

In order to secure the maximum positive treatment of the mineral, and to produce a desired concentrate grade, it is best to have the necessary total volume divided into at least four cells and preferably five or six separate cells, so that they may be used for roughing, cleaning, or recleaning purposes.Alternatively the cleaners/recleaners can be a separate row/bank preceded by scrubbing, attrition, or modifying reagents.

Recovery in flotation is of prime importance. In studying recoveries it is essential also to investigate thoroughly the intermediate products produced. It is a simple matter to make a high recovery or a low tailing if no thought is given to the nature of the concentrate produced or circulating load.

A 'comparison of product assays does not give true and complete information with respect to the performance of a flotation machine. . Product assays for two flotation machines operating in parallel could quite conceivably be identical, yet the physical characteristics of the products recovered and discarded would be entirely dissimilar. Wide differences which would be obvious in detailed investigation might not be indicated by a cursory examination.

Higher recoveries have been possible in many instances by changes in grinding and removal of coarse primary concentrates. Recovery at a coarser grind means a decreased amount of slime mineral in the pulp. Absence of slime in concentrates is reflected in the analysis of the insoluble fraction.

silver lead zinc ore processing method using flotation

silver lead zinc ore processing method using flotation

Sulphide ore of lead and zinc containing considerable silver was submitted for testing with the purpose of determining a flowsheet for the production of separate lead and zinc concentrates for marketing at their respective smelters. It is necessary to recover as much silver as possible in the lead concentrate as a higher return for this silver is realized than for the silver in the zinc concentrate. The ore contained sphalerite, a portion of which was easily floatable but difficult to depress in the lead flotation circuit.

Also, the recovery of silver minerals occurring in a lead, zinc sulfide ore is efficiently accomplished using Flowsheet #2. The process consists of selective flotation to produce a mixed silver, lead concentrate for maximum smelter return and a separate zinc concentrate. Over-grinding of silver minerals is detrimental to efficient flotation recovery, so the Flash Flotation Unit-Cell is used in the grinding circuit to recover a large part of the silver and lead values as soon as liberated.The flowsheet is for a plant having a capacity in the range of 300 to 500-tons per day.

The crushing section of this 50-65 ton mill consists of a conventional layout of single stage crushing. The mine ore is fed from the coarse ore bin to a 9x 16 Forced Feed Jaw Crusher by means of a Apron Ore Feeder. The crushed ore is conveyed by a Belt Conveyor to the Bolted Steel Fine Ore Bin. A Adjustable Stroke Unit Flotation Cell are incorporated in the Belt Ore Feeder delivers the fine ore to the ball mill.

The Mineral Jig and the grinding circuit for immediate recovery of a substantial amount of the lead and silver at a relatively coarse grind. The 5 x 5 Steel Head Ball Mill discharges into an 8x 12 Selective Mineral Jig which in turn discharges into a small flashFlotation Cell. The tailings from the Unit Cell flow by gravity to the 30 Cross-Flow Classifier. The Mineral Jig and the flashcell treating an unclassified feed, produce high-grade concentrates of lead and silver with a minimum amount of zinc. Recovery of these important amounts of lead and silver at this point not only prevents detrimental sliming of the lead mineral and possible subsequent loss, but also increases the amount of new feed that can be fed to the ball mill. By taking advantage of recovering a clean product representing a high recovery of the lead leaves only a small amount of the lead to be recovered in the selective flotation section.

This section of the flowsheet uses two 6-cell (32 x 32) Flotation Machines. The classifier overflow is fed by gravity to the first rougher cell of the lead machine. Three rougher cells provide ample contact time for the flotation of the lead. This rougher lead flotation concentrate is then delivered by gravity to the cleaner cells. Three cleaner cells are used for triple cleaning of the lead concentrate. This triple cleaning was recommended because of the easily floatable zinc that could not be effectively depressed by conventional zinc depressant reagents. Roughing, plus triple cleaning in a 6-cell machine with no pumps or elevators is an example of flexibility a distinctive feature of Sub-A Flotation Machines.

The lead circuit tailing is then conditioned with reagents in a 6 x 6 Super-Agitator and Conditioner prior to zinc flotation. The conditioned pulp is then floated in a 6-cell No. 18 Special Sub-AFlotation Machine for the production of a cleaned zinc concentrate. This machine is arranged for four rougher cells and two cleanings of the rougher zinc concentrate.

Soda ash and zinc sulphate are fed to the ball mill by means of Cone Type Dry Reagent Feeders. Cyanide, sodium sulphite, MIBC frotherand xanthate (Z-3) are fed to the grinding circuit and lead flotation circuit using a multi-compartment Wet Reagent Feeder. Lime and copper sulphate (CuSO4) are added to the zinc conditioner and pine oil and xanthate (Z-5) are stage added to the zinc rougher circuit using Wet Reagent Feeders.

The Visual Sampler, consisting of a Suction Pressure Diaphragm Pump and a No. 13A Wilfley Concentrating Table, takes a portion of the final zinc tailing. This unit enables the operator to determine visually the results of flotation. Any necessary change of reagents is immediately indicated by observation of the concentrate streak shown on the table. Many installations of the Visual Sampler have proved this unit to be a money-saving necessity in any flotation plant.

Thickening, prior to filtration, was not recommended in this case because of the rapidity at which these concentrates filtered and the relatively small tonnage of this mill. Thickening is advisable on slower filtering ores and on larger tonnages.

The final lead-silver concentrates (including the Flash FlotationCell concentrate) are filtered on the 44-disc Filter, the filter cake discharging directly into concentrate bins. The dewatered Mineral Jig concentrate is combined with the filtered lead concentrate in the storage bin.

The above flowsheet incorporates the first rule of milling procedurerecover the mineral as soon as freedthis is accomplished by the Jig and Flash Unit Cell in the grinding circuit. Note that a high-grade lead product representing 2/3 of the total lead (very low in zinc), is recovered in the grinding circuit. This flowsheet successfully answers The Problem by recovering 84% of the total silver in the lead concentrate.

The recovery of silver minerals occurring in a lead-zinc sulfide ore is efficiently accomplished using the above flowsheet. The process consists of selective flotation to produce a mixed silver-lead concentrate for maximum smelter return and a separate zinc concentrate. Over-grinding of silver minerals is detrimental to efficient flotation recovery, so the Flash Flotation Unit-Cell is used in the grinding circuit to recover a large part of the silver and lead values as soon as liberated.The flowsheet is for a plant having a capacity in the range of 300 to 500-tons per day.

The crushing section consists of primary and secondary crushing with intermediate screening. Both crushers are located in the same building and conveniently attended by one operator. A minimum of conveying equipment is required by this arrangement. Dust collecting facilities are, likewise, limited to only one building.

The crushed ore after automatic sampling is subjected to two-stage grinding using a Rod Mill in open circuit and a Ball Mill in closed circuit with a Classifier. TheUnit Flotation Cell receives the discharge from the ball mill for recovery of a substantial amount of the granular silver minerals together with galena as soon as freed. Reagents are added to the ball mill. Tramp iron and occasional oversize gangue are removed from the circuit by the Spiral Screen attached to the ball mill and this prevents excessive wear or plugging of the unit cell. The classifier is of the latest design.

The Mineral Jig is not included in the flowsheet, but on many ores of this type it is applicable either alone or with the unit cell. The grade of jig concentrate is usually very high grade and ideal for blending with the flotation concentrate. If native silver or gold values are present, the jig is a very essential addition to the flowsheet and would be used on the rod mill discharge in this case.

The classifier overflow is treated in a conventional manner using Sub-A Flotation Machines of cell-to-cell design which enables double cleaning of the silver-lead and zinc concentrates without the need of pumps. For large tonnage operations the Sub A Free Flow Machine is optional for roughing and scavenging, but the cell to cell type is always used in the cleaner circuits where high selectivity is essential. The two flotation banks are arranged so that the banks face one another and can be conveniently controlled by one operator from a single aisle. Operation of the Conditioner can also be observed from this aisle. A Sampler is used on the zinc tailing to provide an instant means for the operator to evaluate plant results. Some plants find it beneficial to use a visual sampler on the lead tailing ahead of the zinc circuit. The Sampler is also useful for evaluating the lead or zinc concentrate.General view of the flotation section at a modern silver-lead-zincmill. The lead circuit is on the left and the zinc circuit ison the right.

The silver-lead concentrate (including the unit cell concentrate) and the zinc concentrate are separately treated through wet cyclones to remove the coarse sulfides as thick underflow products suitable for direct filtration. The cyclone overflow products are ideally suited for thickening and subsequent filtration with their respective cyclone underflows. This procedure avoids any overload of heavy sulfides in the thickeners and, therefore, simplifies the operation of the thickeners. SRL Pumps are engineered for use with wet cyclones and give trouble-free service.

In addition to the feed sample, which is cut by means of a Type C Automatic Sampler, the final silver-lead and zinc flotation concentrates are sampled using Type B cutters. The final plant tailing is also sampled in the same manner.

This flow-sheet incorporates all features of a modern day mill for optimum efficiency and general simplicity for ease of operations. Instrumentation devices can be included to facilitate automatic control of the plant circuits if desired.

Many factors affect the metallurgical results of every plant. However, in a study of this type it is interesting to note the recoveries and grades that are actually being made at successful mills. The figures of these two plants are included for their value in making economic studies of new deposits.

flotation

flotation

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Compared to other blowers technology, Continental Industrie Multistage Blowers deliveroil freeair without pulsation, whichguaranteea constant flow and pressure along the process. The combination betweenmechanicalrotation of the rotor and the bubbling is creating a very efficient action in catching the mineral particles to obtain the concentrate.

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