silica sand processing & sand washing plant equipment
Silica sand low in iron is much in demand for glass, ceramic and pottery use, and for many of these applications clean, white sand is desired. Impurities such as clay slime, iron stain, and heavy minerals including iron oxides, garnet, chromite, zircon, and other accessory minerals must not be present. Chromium, for example, must not be present, even in extremely small amounts, in order for the sand to be acceptable to certain markets. Feldspars and mica are also objectionable. Generally, iron content must be reduced to 0.030% Fe2O3 or less.
Silica sand for making glass, pottery and ceramics must meet rigid specifications and generally standard washing schemes are inadequate for meeting these requirements. Sand for the glass industry must contain not more than 0.03% Fe2O3. Concentrating tables will remove free iron particles but iron stained and middling particles escape gravity methods. Flotation has been very successfully applied in the industry for making very low iron glass sand suitable even for optical requirements.Sub-A Flotation Machines are extensively used in this industry for they give the selectivity desired and are constructed to withstand the corrosive pulp conditions normally encountered (acid circuits) and also the abrasive action of the coarse, granular, slime free washed sand.
The flowsheet illustrates the more common methods of sand beneficiation. Silica may be obtained from sandstone, dry sand deposits and wet sand deposits. Special materials handling methods are applicable in each case.
The silica bearing sandstone must be mined or quarried much in the manner for handling hard rock. The mined ore is reduced by a Jaw Crusher to about 1 size for the average small tonnage operation. For larger scale operations two-stage crushing is advisable.
The crushed ore is reduced to natural sand grain size by Rod Milling. Generally, one pass treatment through the Rod Mill is sufficient. Grinding is done wet at dilutions in excess of normal grinding practice. A Spiral Screen fitted to the mill discharge removes the plus 20 mesh oversize which either goes to waste or is conveyed back to the mill feed for retreatment.
Sand from such deposits is generally loaded into trucks and transported dry to the mill receiving bin. It is then fed on to a vibrating screen with sufficient water to wash the sand through the 20 mesh stainless screen cloth. Water sprays further wash the oversize which goes to waste or for other use. The minus 20 mesh is the product going to further treatment.
The sand and water slurry for one of the three fore-mentioned methods is classified or dewatered. This may be conveniently done by cyclones or by mechanical dewatering classifiers such as the drag, screw, or rake classifiers.
From classification the sand, at 70 to 75% solids, is introduced into a Attrition Scrubber for removal of surface stain from the sand grains. This is done by actual rubbing of the wet sand grains, one against another, in an intensely agitated high density pulp. Most of the work is done among the sand grains not against the rotating propellers.
For this service rubber covered turbine type propellers of special design and pitch are used. Peripheral speed is relatively low, but it is necessary to introduce sufficient power to keep the entire mass in violent movement without any lost motion or splash. The degree of surface filming and iron oxide stain will determine the retention time required in the Scrubber.
The scrubbed sand from the Attrition Machine is diluted with water to 25-30% solids and pumped to a second set of cyclones for further desliming and removal of slimes released in the scrubber. In some cases the sand at this point is down to the required iron oxide specifications by scrubbing only. In this case, the cyclone or classifier sand product becomes final product.
Deslimed sand containing mica, feldspar, and iron bearing heavy minerals can be successfully cleaned to specifications by Sub-A Flotation. Generally this is done in an acid pulp circuit. Conditioning with H2SO4 and iron promoting reagents is most effective at high density, 70-75% solids. To minimize conditioning and assure proper reagentizing a two-stage Heavy Duty Open Conditioner with Rubber Covered Turbine Propellers is used. This unit has two tanks and mechanisms driven from one motor.
The conditioned pulp is diluted with water to 25-30% solids and fed to a Sub-A Flotation Machine especially designed for handling the abrasive, slime free sand. Acid proof construction in most cases is necessary as the pulps may be corrosive from the presence of sulfuric acid. A pH of 2.5-3.0 is common. Wood construction with molded rubber and 304 or 316 stainless steel are the usual materials of construction. In the flotation step the impurity minerals are floated off in a froth product which is diverted to waste. The clean, contaminent-free silica sand discharges from the end of the machine.
The flotation tailing product at 25 to 30% solids contains the clean silica sand. A SRL Pump delivers it to a Dewatering Classifier for final dewatering. A mechanical classifier is generally preferable for this step as the sand can be dewatered down to 15 to 20% moisture content for belt conveying to stock pile or drainage bins. In some cases the sand is pumped directly to drainage bins but in such cases it would be preferable to place a cyclone in the circuit to eliminate the bulk of the water. Sand filters of top feed or horizontal pan design may also be used for more complete water removal on a continuous basis.
Dry grinding to minus 100 or minus 200 mesh is done in Mills with silica or ceramic lining and using flint pebbles or high density ceramic or porcelain balls. This avoids any iron contamination from the grinding media.
In some cases it may be necessary to place high intensity magnetic separators in the circuit ahead of the grinding mill to remove last traces of iron which may escape removal in the wet treatment scrubbing and flotation steps. Iron scale and foreign iron particles are also removed by the magnetic separator.
In general most silica sands can be beneficiated to acceptable specifications by the flowsheet illustrated. Reagent cost for flotation is low, being in the order of 5 to 10 cents per ton of sand treated. If feldspars and mica must also be removed, reagent costs may approach a maximum of 50 cents per ton.
Laboratory test work is advisable to determine the exact treatment steps necessary. Often, attrition scrubbing and desliming will produce very low iron silica sand suitable for the glass trade. Complete batch and pilot plant test facilities are available to test your sand and determine the exact size of equipment required and the most economical reagent combinations.
Silica sand for making glass, pottery and ceramics must meet rigid specifications and generally standard washing schemes are inadequate for meeting these requirements. Sand for the glass industry must contain not more than 0.03% Fe2O3. Concentrating tables will remove free iron particles but iron stained and middling particles escape gravity methods. Flotation has been very successfully applied in the industry for making very low iron glass sand suitable even for optical requirements.
Sub-A Flotation Machines are extensively used in this industry for they give the selectivity desired and are constructed to withstand the corrosive pulp conditions normally encountered (acid circuits) and also the abrasive action of the coarse, granular, slime free washed sand.
The flowsheet illustrated is typical for production of glasssand by flotation. Generally large tonnages are treated, forexample, 30 to 60 tons per hour. Most sand deposits can be handled by means of a dredge and the sand pumped to the treatment plant. Sandstone deposits are also being treated and may require elaborate mining methods, aerial tramways, crushers, and wet grinding. Rod Mills with grate discharges serve for wet grinding to reduce the crushed sandstone to the particle size before the sand grains were cementedtogether in the deposit. Rod milling is replacing the older conventional grinding systems such as edge runner wet mills or Chilean type mills.
Silica sand pumped from the pit is passed over a screen, either stationary, revolving or vibrating type, to remove tramp oversize. The screen undersize is washed and dewatered generally in a spiral type classifier. Sometimes cone, centrifugal and rake type classifiers may also be used for this service. To clean the sand grains it may be necessary to thoroughly scrub the sand in a heavy-duty sand scrubber similar to the Heavy-duty Agitator used for foundry sand scrubbing. This unit is placed ahead of the washing and dewatering step when required. The overflow from the classifier containing the excess water and slimes is considered a waste product. Thickening of the wastes for water reclamation and tailings disposal in some areas may be necessary.
The washed and dewatered sand from the spiral-type classifier is conveyed to a storage bin ahead of the flotation section. It is very important to provide a steady feed to flotation as dilution, reagents and time control determines the efficiency of the process.
Feeding wet sand out of a storage bin at a uniform rate presents a materials handling problem. In some cases the sand can be uniformly fed by means of a belt or vibrating-type feeder. Vibrators on the storage bin may also be necessary to insure uniform movement of the sand to the feeder. In some cases the wet sand is removed from the bin by hydraulic means and pumped to a spiral-type classifier for further dewatering before being conveyed to the next step in the flowsheet.
Conditioning of the sand with reagents is the most critical step in the process. Generally, for greater efficiency, it is necessary to condition at maximum density. It is for this reason the sand must be delivered to the agitators or conditioners with a minimum amount of moisture. High density conditioning at 70 to 75% solids is usually necessary for efficient reagentizing of the impurity minerals so they will float readily when introduced into the flotation machine.
The Heavy-duty Duplex Open-type Conditioner previously developed for phosphate, feldspar, ilmenite, and other non-metallic mineral flotation is ideal for this application. A duplex unit is necessary to provide the proper contact time. Circular wood tanks are used to withstand the acid pulp conditions and the conditioner shafts and propellers are rubber covered for both the abrasive and corrosive action of the sand and reagents.
Reagents are added to the conditioners, part to the first and the balance to the second tank of the duplex unit, generally for flotation of impurities from silica sand. These reagents are fuel oil, sulphuric acid, pine oil, and a petroleum sulfonate. This is on the basis that the impurities are primarily oxides. If iron is present in sulphide form, then a xanthate reagent is necessary to properly activate and float it. The pulp is usually regulated with sulfuric acid to give a pH of 2.5-3.0 for best results through flotation.
A low reagent cost is necessary because of the low value of the clean sand product. It is also necessary to select a combination of reagents which will float a minimum amount of sand in the impurity product. It is desirable to keep the weight recovery in the clean sand product over 95%. Fatty acid reagents and some of the amines have a tendency to float too much of the sand along with the impurities and are therefore usually avoided.
After proper reagentizing at 70 to 75% solids the pulp is diluted to 25 to 30% solids and introduced into the flotation machine for removal of impurities in the froth product. Thepulp is acid, pH 2 .5 to 3.0 and the sand, being granular and slime free, is rapid settling so a definite handling problem is encountered through flotation.
The Sub-A Flotation Machine has been very successful for silica sand flotation because it will efficiently handle the fast settling sand and move it along from cell to cell positively. Aeration, agitation and selectivity due to the quiet upper zone can be carefully regulated to produce the desired separation. The machine is constructed with a wood tank and molded rubber wearing parts to withstand the corrosive action of the acid pulp. Molded rubber conical-type impellers are preferred for this service when handling a coarse, granular, abrasive sand.
Flotation contact time for removal of impurities is usually short. A 4, and preferably a 6 cell, machine is advisable. Cell to cell pulp level control is also desirable. A 6 cell No. 24 (43 x 43) Sub-A Flotation Machine in most cases is adequate for handling 25 to 30 tons of sand per hour. If the impurities are in sulphide form a standard machine with steel tank and molded rubber parts is adequate provided the pulp is not acid. Otherwise acid proof construction is essential.
The flotation tailing product is the clean sand discharging from the end of the flotation machine at 25 to 30% solids and must be dewatered before further processing. Dewatering can be accomplished in a dewatering classifier and then sent to storage or drying. Top feed or horizontal vacuum filters are often used to remove moisture ahead of the dryer. Dry grinding of the sand to meet market requirements for ceramic and pottery use is also a part of the flowsheet in certain cases.
This particular sand was all minus 20 mesh with only a trace minus 200 mesh and 70% plus 65 mesh. Iron impurity was present as oxide and stained silica grains. The plant which was installed as a result of this test work is consistently making over a 95% weight recovery and a product with not over 0.02% Fe2O3 which at times goes as low as 0.01% Fe2O3.
Si02, minimum..99.8 per cent
Al2O3, maximum..0.1 percent
Fe2O3, maximum..0.02 per cent
CaO + MgO, maximum.0.1 percent
For certain markets, a maximum of 0.030 per cent Fe2O3 is acceptable.
Natural silica-sand deposits generally contain impurityminerals such as clay, mica, and iron oxide and heavy iron minerals which are not sufficiently removed by washing and gravity concentration. Flotation is often used to remove these impurity minerals to meet market specifications.
Anionic-type reagents, such as fatty acids, are used to float some impurities in alkaline pulp. Cationic-type reagents such as amines or amine acetates are also used with inhibitors such as sulphuric or hydrofluoric acids to float certain impurity minerals and depress the silica.
limestone crushing plant layout and price - jxsc machine
How to crush limestone? How much invest for the limestone crushing plant? How to start a stone aggregate making business? machine selection and processing plant layout design. . . . This article to answer these questions as much as possible, from limestone property, crushing circuit layout and rock crusher machine selection, complete production line investment estimation. Join us.
The compact limestone has a compressive strength of 20~120MPa and a density of 2000~2600 kg/m3. When the clay impurities in the limestone exceed 3% to 4%, the frost resistance and water resistance are remarkably lowered. Siliceous limestone has high strength, high hardness and good durability. Most limestones are fine, hard and resistant to weathering, and are mainly used as building materials.
The large piece of limestone is uniform to the jaw crusher for primary crushing by the vibrating feeder; The primary crushed material and the fine material sieved by the vibrating feeder are conveyed to the impact crusher; The circular vibrating screen sieves the limestone after the impact crusher, and the large-grained limestone is returned to the impact crusher to re-crush, the qualified grade materials are graded and transported by the conveyor to different stockpiles.
JXSC supply complete aggregate making machine for various sand & gravel, pebble, limestone, basalt, granite, dolomite, etc. Includes jaw crusher, impact crusher, cone crusher, sand making machine, vibrating screen, vibrating feeder, sand washing machine, convey belt, etc.
The limestone jaw crusher is usually used as the first rock crusher, and it is suited for medium-size crushing of ore and bulk materials with a compressive strength of not more than 320Mpa. Jaw crusher is divided into coarse crushing and fine crushing. The feeding size is 125mm~750mm. It often forms a complete sandstone production line together with cone crusher, impact crusher and sand making machine.
Limestone medium crushing equipment recommended: impact crusher & cone crusher. The impact crusher can granite, limestone, concrete, and the like coarse materials with a side length of less than 500 mm and a compressive strength of less than 350 MPa. Impact crusher VS cone crusher Impact crusher has a lower price, uniform discharge, less needle-like crushed product. The cone crusher is slightly more expensive, but the wearing parts have a long life. In the long run, the cone crusher is more durable. Impact crusher VS hammer crusher The impact crusher has a larger crushing ratio and can more fully utilize the high-speed impact energy of the entire rotor. The impact crusher is easy to wear, which makes it limited in the application of hard material crushing.
Limestone fine crushing machine: VIS sand making machine, HX sand making machine, has a high stone crushing rate, high sanding rate, good finished grain shape. If you need clean sand finish products, use the sand washing machine for cleaning and dewatering.
3. Conveyor belt Responsible for the transportation of materials. The specific configuration of conveyor belts in a limestone crushing line needs to be combined with working conditions and processing requirements.
1. Stationary crushing plant Three-stage crushing process, high capacity Equipment: Vibrating Feeder + Jaw Crusher + Impact Crusher + Sand Making Machine + Round Vibrating Screen + Belt Conveyor 2. Mobile crushing plant Main Equipment: mobile jaw crusher + mobile impact crusher Flexible, small space, lower invest, easy to construct; intelligent design, secure and convenient one-button operation. 3. Semi-mobile crushing plant Capacity: 50-600t/h (the maximal capacity of the mobile and semi-mobile plant are less than that of stationary) Equipment: mobile jaw crusher + mobile impact crusher + sand making machine Movable, less limitation; PLC control system, real-time monitoring of equipment voltage, airflow, temperature, etc., touch screen display production data, operational error voice prompts, more secure. Dust removal.
JXSC is a well-known crusher manufacturer in China. With more than 20 high-tech patents, JXSC is a veritable high-tech enterprise. We produce a full set of limestone crushers, including jaw crusher, impact crusher, cone crusher, VSI impact crusher, vibrating screen, etc. In addition, we design the effective production line according to the actual situation to ensure safety and productivity.