henan seasun heavy industry machinery co., ltd
Copper ore dressing equipment Scope:
Weakly magnetic minerals beneficiation, for example: hematite, limonite, ilmenite, wolframite, tantalum, niobium, etc.. Non-metallic minerals deironing, purification, for example: quartz, feldspar, nepheline, fluorite, sillimanite, spodumene, kaolin.
Two common copper ore flotation process:
1. dye-shaped copper ore flotation process
Generally use relatively simple process, after a period of grinding, fineness -200 mesh occupy about 50% to 70%, once roughing, two or three times selected, one or two times scavenging. Such as disseminated copper minerals has relatively small size, consider to adopt the stage grinding and separation processes. Processing bornite concentrator, mostly coarse concentrate regrinding - a selection of stage grinding and separation processes, and its essence is mixed - flotation process. First by a coarse grinding, roughing, scavenging, and then rough concentrate regrinding recleaner get high-grade copper concentrate and concentrate. Rough grinding -200 mesh about 45% to 50% and then pulverized -200 mesh occupy about 90% to 95%.
2. Dense copper ore flotation process
Dense copper ore chalcopyrite and pyrite as tight symbiosis, pyrite is often secondary copper-activated pyrite content is high, difficult to suppress, sorting difficult. Sorting process requires both get copper concentrate and concentrate. Typically election of copper tailings is pyrite concentrate. If the ore gangue content of more than 20% to 25%, sulfur concentrate needed sorting again. Dense copper ore processing, often using two stages of grinding or grinding, fine grinding fineness requirements. Amount of reagent is also larger, xanthate dosage 100g / (t raw ore) above, lime 8 ~ 10kg (t raw ore) above.
Copper ore beneficiation process:
1. crushing part: basic process of ore crushing process. Its purpose is to crush ore to an appropriate size, suitable for grinding part.
2. Grinding part: Part grind ore processed further to get a smaller size, to match up flotation separation material.
3. flotation sections: the flotation process / upgrade Copper important process. Chemicals are added to the mixer / blender, to make chemical reaction.
Copper ore dressing plant:
Mining ores first by the jaw crusher for preliminary broken, in broken to a reasonable fineness through ascension machine, after to mine machine uniform into ball mill, ball mill by crushing, grinding of ore.
After grinding ball mill of ore materials into the next procedure and: grading. Hierachial machine with different proportion of solid particles in the liquid and the speed of the precipitation different principle of minerals, the mixture to wash, grading. After a wash and classification of the mineral mixture after magnetic separation unit.
Because of various minerals than magnetized coefficient of different magnetic force and, by mechanical force will mixture of magnetic material separated. After magnetic separators preliminary after the separation in mineral grains was sent into the flotation machine, according to different mineral properties of different drugs, make to the minerals and other material separation open.
Desire to minerals is isolated, because its a lot of moisture, must be approved by the initial concentration concentrating machine, then through the dryer drying, you will get dry minerals. Copper fine powder grade reached 45%.
200t/d Copper Ore Beneficiation Equipment:
Motor Power kw
Length according to the site conditions
We can also supply other capacity copper ore beneficiation production line,according to users' needs. Welcome to consult us!
flash flotation of gold
A result of the April meeting FI management decided to install flash flotation in one of the two primary grinding circuits for a plant scale test if Freeports 3 concerns (metallurgy, mechanical reliability, physical fit) could be alleviated.
Laboratory demonstration tests were run with coarsely ground of FI ore samples. A 36% copper concentrate with 7.2 ppm (0.27 oz/t) gold was produced for a 34% copper recovery and 13% gold recovery. Other tests had gold recovery as high as 45%. Concern 1 (metallurgy) was alleviated.
Outokumpu proposed the then new design flash flotation machine the Sk240 for FI. Two Sk 240 machines operating side by side in parallel would have approximately 2 minutes retention time at FI s operating conditions. Two Sk240 machines could be into a FI grinding section by repositioning the cyclones. Concern 3 (physical fit) was alleviated.
2 Sk240 flash flotation machines were installed in the ball mill number 1 circuit. The machines operated parallel with 50% of the feed to each machine. The flash flotation start-up on the ball mill No. 1 circuit was smooth with steady state operating achieved quickly. Initial results were very encouraging. Overall mill gold recovery increased approximately 5%.
FI believes the addition of flash flotation to the grinding circuit has decreased future conventional flotation cell volume requirements for future expansions. Flash flotation will be apart of any future mill expansions with additional grinding capacity.
sequential selective flotation process flowsheet
ORE TREATED: The most common of ores treated in this manner are lead zinc, copper-zinc-iron, copper-nickel, but application may be made to other two or three mineral separations. This flowsheet, without a Unit Flash Flotation Cell or a Mineral Jig, is applicable to ores where the values are in the base metals alone.
ADVANTAGES: The various minerals contained in the ore can be concentrated into products each containing a major portion of one separate metal. In this manner, it is possible to secure the greatest net return for each ofthe metals, shipping each one to the smelter that offers the best schedule for payment on the metal.
PROCESSING COMMENTS: In many cases, where the minerals are freed at a coarse mesh, savings are made in grinding costs through the use of the proven Sub-A Flotation Machine which is the only flotation unit capable of effectively handling coarse feeds.
The sulphide iron minerals contained in practically all base metal ores, may be recovered from the tailings where the product can be marketed for the sulphur or where precious metals are closely associated with these minerals; an additional conditioner and flotation machine make this step feasible. As many as five individual concentrates are being produced from a single ore in actual milling practice.
ORE TREATED: Sulphide ores of lead, copper and zinc are primarily treated. This flowsheet can also be applied to other ores wherein the separation of base metals or nonmetallic minerals may be desired.
ADVANTAGES: The first flotation machine in a copper-lead-zinc separation would produce a copper-lead concentrate. This copper-lead concentrate would go to a second machine wherein the copper would be floated off, leaving a high-grade lead residue. Since the amount of copper-lead concentrate being treated would be small as compared to the original tonnage of the mill, excessive flotation capacity would not be required, as would be in the case of this 3 product flotation process Flowsheet wherein the first machine would produce a lead concentrate, and a second machine would produce a copper concentrate, but both machines treating the large tonnage of the original feed.
PROCESSING COMMENTS: In the case of the lead-copper cited above, the floatability of the lead and copper sulphides are so close together as to make a conventional separation impractical. By recovering these two into a single rougher concentrate, their recovery is accomplished and the preferential floating of one can be brought about through depressing the other. This separation is of particular interest as the copper may be recovered first, leaving a high-grade lead residue; whereas in other cases the lead may be floated first, leaving a high-grade copper residue.
how to operate a flotation circuit
The main ideain collecting the information youll find in the following discussion was to help you, as a flotation machine operator. Regardless of how much or how little you know about it, the ideas youll find here can help you do a better job, if you want them to.
Naturally your company is anxious to have you improve your work, because a lot depends on how well you handle those machines; but dont think that thats the only reason why you ought to do better. The big reason, for you, is that the more skillful you become, the easier it will be for you. The fellows who are always in a jam and working their heads off all shift are also the ones who dont know what its all about. The good operators see trouble coming and prepare for it and for that reason theydont often get into trouble. The jobis easier for them because they know how to do it. We want to try to make it easier for you, too.
Because we dont know how familiar you already are with the flotation process, well have to assume that you are starting about from scratch. Well the first thing you ought to learn is how the process works and what it is that you are trying to do. Well leave the chemistry of flotation out of it though, because it doesnt much matter to you why the thing works so long as it does work, and, frankly, the subject is too deep for us.
The plain facts are that in the pulp as it comes to you from the ball mill circuit is a small quantity, generally a few percent, of a mineral your company expects you to get out. To do this, you will add to the pulp one or more chemical reagents that have the property of combining with the valuable mineral in such a way that these particles of ore can no longer be wetted by water. These reagents do not combine with the waste rock particles, and therefore the latter can still be wetted. Suppose you arc working with a galena ore. After you have put in the proper reagents, if you couldtake a piece of galena out of the pulp and magnify it, you would see that water rolls off the galena as it would off a duck.
Then when the pulp goes to the flotation machines, you add another reagent that creates a froth in the pulp. That is, the reagent helps form millions of air bubbles that are circulated all through the pulp by the action of the machine. Whenever one of these bubbles hits an ore particle that is not wetted by water it sticks to that particle, and before long thereare many such mineral particles sticking to each bubble. None of thebubbles will stick to the waste material. The result is that these air bubbles collect on the surface of the pulp in the machine to form a froth, and all you have to do is see that this froth spills over the side into the proper launder. The valuable mineral is now in the launder, and the waste rock is going down the tailing flame you hope.
All you have to do is to see to it that enough of these reagents is added, but not too much, and that the machines are working properly. That doesnt sound like much of a job, but, believe us, its an art. The thing for you to do if you want to be really good at it, is to ask a lot of questions of people you can count on as knowingthe answer. Dont be afraid of asking fool questions. The mill superintendent and the metallurgist and the shift boss would a lot rather have you ask questions of them and find out how to do the job right, than to have you keep still and do the job wrong.
There are three classes of flotation reagents in general: conditioners, collectors, and frothers. Conditioners are those reagents that are added to the pulp to help the other reagents do a better job. That definition covers a multitude of sins, and we havent space to take up all of them. To list a few conditioners, there are: lime, copper sulphate, soda ash, sodium silicate. Aerosol, and several more. Each of them has a specific job, and it is up to you to learn what it is for the one you are using.
Take lime, for example, which is generally used in flotation to keep pyrite from floating and to adjust the pH of the circuit. Whats pH? Just a flashy term for a convenient way of telling how much acid or alkali there is in the flotation pulp. A pH of 7 means that the pulp is neither acid nor alkaline: above the pulp is alkaline, below 7 it is acid. Lime makes the pulp more alkaline, resulting in apHof 8, 9. 10. or so depending on how much you add. In some mills, this matter of pH is tremendously important and it will pay you big dividends in easy operation if you pay attention and keep the pH where it belongs.
Collectors are the reagents that catch hold of the mineral youre after. The xanthates. thiocarbanilide several of the Aerofloat reagents, thiophosphates, Hydroxamate; all are collectors. If you dont add enough of whichever one of these youre using, the company loses money fast, and youll have words with the shifter tomorrow when the assay sheet comes around. Of course, if you are working in a mill where the metallurgist sets the reagent feed rates, the buck is automatically passed.
Frothers are the reagents that make the bubbles that lift the mineral out of the pulp. Pine oil, fatty acid, MIBC and several other numbered reagents are the most commonly used frothers. Their action is simple. More frothcr, more bubbles. Less frother, fewer bubbles. Dont ever drop a bucketful of pine oil into the flotation machine feed box unless youre tired of working there.
Only three or four of these reagents are being used in your plant. Your job is to find out for sure exactly what each of them is for in your operation. Dont go by what somebody said he heard somebody say the fellow that grinds samples in the assay office said. Buttonhole the metallurgist, if he hasnt already told you, and make him tell you what the reagents are supposed to do. Better still, ask him to put it in writing, or you write it down as he tells you. We know from experience that some flotation operators have ideas about the reagents they are using that would give the mill superintendent the shock of his life if he knew about it. That isnt the operators fault. Nobody had ever told them the facts of life. Dont you be like that.
Now, to get right down to the actual operation, what are the elements with which you have to work? First, of course, are the reagents we mentioned before, and with regard to them we can only repeat our advice to find out as much as you can about how they work. Also, if you are permitted to adjust the reagent feeders yourself, go easy with them. Dont be rushing up every ten minutes to add more xanthate or cut down the pine oil a drop or two. By the time you have made some such small change, the pulp conditions may have changed a little, and you ll simply wear yourself out trying to catch up with conditions that stay one jump ahead of you. Dont over-control.
Aside from the reagents, you have the machine controls to work with. These arc different with different makes of machine, but, in general, they are: the tail gate at the end of each bank of cells; weirs placed in some makes between each cell; weir bars placed along the lip in each cell over which the froth flows: other types of adjustable partitions between cells: and, in some makes, a valve that controls the air admitted to each cell.
In general, you will make up your mind about how to control the machine and the reagents In the appearance of the froth coming out of the machine. We could go on here for several pages describing what a flotation froth ought to look like for all the different kinds of minerals that are now being floated, but youd be interested in only a small part of all that. Here, again, the best thing you can do is get somebody who knows to tell you when the froth in the rougher cells and the cleaner cells looks the way it ought to look. Then you take a good long look at it and try to keep it that way when youre running the machines.
There are, however, certain characteristics that apply to most flotation froths. The bubbles in the froth from a cleaner cell, or from the first couple of cells in a rougher section, should be fairly large, say an inch or so across, and they should be well loaded with mineral and should break down easily when they drop into the launder. If you look at them closely, you will see in the center of each bubble a thin spot that is almost clear, like a little window, and the surface of the bubble will have a slightly watery shine on it as though it were actually wet. These windows and this watery look are, in most cases, a good sign. They mean that the bubble is neither too tough nor too brittle, and that there is a draining action going on along the surface of the bubble that allows waste mineral, shoved up accidentally by the bubble, to drain back into the pulp, where it belongs.
The froth in the rest of the rougher cells should, in most cases, look quite different. The bubbles are smaller, more like the head on a stein of beer, and they dont carry as much mineral. Also, the froth in the roughers spills over faster; in fact, the rougher cells are spoken of as running faster. Here you dont have to worry about waste draining back into the pulp: the main idea is to get the ore mineral out fast.
Watch the froth constantly, then, and learn from it but dont stop with just watching it. You cant be sure of what that froth is carrying unless you really break it down and see. Mill- men who sweep their hands across the froth in a cell and then tell you exactly whats in it may be kidding themselves and you too. There ought to be a white-enameled vanning plaque kept down in the mill at all times, and you ought to learn to use it properly. We cant describe in words how to handle a vanning plaque, because its use requires a peculiar combination of motions that defies description, but with a little , practice and advice from someone who knows, youll get it all right. Then when you take a little froth on the vanning plaque, and break it down, and spread it out, youll see exactly what minerals are being carried by the froth, and, more important, how much of each mineral, if you do that long enough, youll be able eventually to forecast pretty accurately about what the concentrate will run when it is assayed. A vanning plaque is the best single tool you can have in the mill to helpyou decide how the machines should be operated.Another little gadget that is not so important but which is handy, nevertheless, is a froth-depth indicator.
This is simply a wood slab about a foot square and 2-in. thick, in the center of one side of which is fixed a 1 x 1 inch stick and about 18 inches long. The stick must be set perpendicularly to the slab. Set the slab in the classifier or the feed box or some place where the pulp is the same density that it is in the machine, and let it float for a moment. Then measure up from the watermark and mark the stick off in inches and halves. Then to measure the froth depth in the cell, drop the slab into the cell, let it float, and read the depth at the mark nearest the froth surface. This comes in handy because it is sometimes necessary to control the froth depth pretty closely (deeper on cleaners, thinner froth on roughers), and this indicator is the simplest way we can think of to measure froth depth accurately.
One of the best ways of keeping track of whats going on in the machine is to keep a little log of the things you observe and to note down in it the assays of the samples that were taken during that time. Did the froth look dry and tough during most of the last shift? Note it in your book, then see how the assays compare with those corresponding to other froth conditions. You can learn best by experience, and a written record of that experience is a far more reliable guide than your memory, however good your memory may be.
The thing that makes a man a really good flotation operator is his ability to see trouble coming and to avoid it. A good man watches whats going on and runs the machines instead of letting them run him. For example, by noticing little changes in the froth conditions or the pH of the pulp a man can sometimes get a warning of an approaching change in the kind of ore coming into the mill. To treat this different type of ore, he may have to use more lime or more frother or he may have to change the adjustment of the machines. Whatever he has to do, the main point is that by the time the change in ore actually arrives, he is ready for it.
A poor operator, on the other hand, usually gets caught flat-footed by such changes. He catches on only when the froth drops altogether, or begins pouring over, as the case may be, and he has to spend the next hour or so in a sweat trying to straighten things out. Then just about the time hes off rolling a cigarette and telling the shifter, Well, I got that licked, the ore changes again, the froth goes haywire, and our friend is right back in the deep hot grease. By the end of the shift, hes usually run ragged, and the tailing assay for his shift is higher than a kite. He just works too hard.
As we have already noted, the kind of froth you get and the amount of mineral it carries depend pretty much on the reagents you add. The machine controls, however, determine the rate at which the froth comes off the cells. To run a machine faster that is, to make more froth spill overyou raise the pulp level, lower the froth lips, or let in more air. To run the machines slowerthat is, to cut back on the amount of froth you simply reverse these things.
You can also speed up or slow down the amount of froth coming off by changing the amount of frother added, but remember, it is better not to. In general, you should add only just enough frother to get the sort of bubble you want. Therefore, if the machine isnt frothing to suit you, try to make it right with the machine controls first (the weir bars, the pulp level, the air controls). Only when you cant get the right conditions with the machine controls should you begin changing reagents.
One exception to this is a condition when you see quite plainly that you have altogether too much reagent. If the froth is boiling over, for example, and it has an oily look and consists of extremely tiny uniform bubbles, go look at the frother feeder. You are probably using too much. In other words dont hesitate to cut down on reagents if conditions seem to warrant it; but think twice, or three times, before you add more of anything.
There is also an order of preference, you might say, for the machine controls. In general the pulp level in a roughing machine should be carried as high as you can get it and still leave about 2 to 3 in, of froth above it. (Theres where your froth-depth indicator comes in handy.) This is done to help recover more of the mineral you want. The high pulp level holds the mineral in the machine longer, and gives the air bubbles more chances at it. The thin froth, overflowing rapidly, snaps the weakest-floating mineral over into the concentrate launder before it can drain back.
Because this high pulp level in a rougher machine is harder to regulate than the froth depth, it is better to work with the weir bars along the froth lips instead of with the tail gate, or the weirs between cells, if your machine has them. Also, if your machine has an air control (like the Agitair, the Weinig, or the Pan-American) it is better to keep the valve as wide open on the roughers as you can. This is because the more air you add, up to a certain point, the more mineral youre likely to pick up. In addition, the more air added to mechanical machines, the less power they draw and the less wear there is on the impeller. In short, dont cut the air unless you have to and then do it for as short a time as possible.
A flotation machine needs deep froth in order to allow time for unwanted mineral to drain from the froth bubbles back into the pulp. Also, a high pulp level isnt so important in a cleaner cell, because recovery isnt what youre after so much as grade of concentrate. Therefore, in a cleaner cell, a froth depth of at least 8 in. is required in most cases, and you have more leeway in adjusting the pulp level. That is why, in operating a cleaner, you can use the tail gate (or the cell weirs) more than on a rougher.
In cleaning, the rate at which the froth comes over is extremely important, and both the air control and tailing weirs should be used to get the fine adjustment that will give you the best results. Froth scraper adjustment and weir bars, it there are any, may help, but to a lesser extent. Here is where your vanning plaque comes in handy. To run a cleaner properly, you must know what is in the cleaner froth, and the only way you can really find that out is by spreading some of that froth out, not on the palm of your hand, but on a vanning plaque.
All this, remember, is a general statement applied to all operations. In your own mill there may be good reasons why you have to run the machines differently. In that case, find out what pulp level and what froth depth your metallurgist thinks are right, and then keep them that way. But the order of preference still holds, no matter what. On the roughers: weir bars first, then air, then tail gate (or cell weirs), then reagents. On the cleaners: air first, then tail gate (or cell weirs), then weir bars, then reagents. If none of these things works, see if you cant get a job down in the mine.
PNEUMATIC. Nearly everything we have said up to here applies to both air and to mechanical machines. There isnt much to add that applies only to these machines. In fact, in most cases, air machines are rather easier to control than mechanical machines, though the possible adjustment isnt so fine, for example on cleaning operations.
HOG TROUGHS. This term rather loosely describes mechanical machines built on the lines of a long trough in which the impellers are set at regular intervals. There are no pipes or weirs between cells. The type is represented by the Agitair, the Level-Type Fagergren, and the Pan-Americanmachines, the one tail gate controls the pulp level throughout each group of cells. If you want to vary the pulp level between cells somewhere up the line, the only way is to widen or narrow the opening in the partitions between impellers. There is very seldom any real need for this adjustment, and it is better not to try it.
Having the pulp level in the whole machine controllable by the one tail gate may tempt you to whirl the gate up or down every time an adjustment is indicated. Dont do it. Pick a level for the roughers that is about right (good and high, remember), and leave it there. If you have to change the gate, return to the original setting as soon as you can. You can spot this by counting the number of threads exposed above the handwheel when the gate is where you think it ought to be. This gives you the exact location of the gate and saves measuring each time.
Poke a stick into the tail box once in a while to see that it isnt sanding up. If the tail box does get partly sanded up, the pulp level will run higher than you want it and may overflow the machine. Remedy this by opening the sand bleeder gate a little, but dont open it farther than necessary. Make all the tailing come out over the tail gate if you can.
The peculiar virtue of a weir to control the pulp level in each cell is that it permits you to get an extremely nice adjustment of the rate of froth overflow down the length of the machine. One cell fast, the next slow, the next fast, and so on, if you happen to want it that way. This is an extreme example, of course, but it shows what could be done. The practical effect of this flexibility is that you can get an extremely high-grade concentrate with these cells if you handle them right.
But by the same token these individual cell weirs can get you into an awful lot of trouble you dont handle them right, Here again, we say dont over-control, and do try to anticipate trouble. If you do get caught, however, and you find the froth has dropped in all the cells, or that the machines are wildly overflowing, start with the tail-end weir, adjust it properly, and so work back up the line of cells to the head end. But take our word for it, it is better not to find the cells in that condition.
You will of course get into trouble now and again. Pipes will plug up, froth will spill out over the floor, belts will break, bearings get hot, launders leak. We just havent space to list here all the things that could happen to you and suggest remedies for them. Besides, we dont know all the things that could happen to you. The important thing, anyway, is to keep your head, figure out the cause of whatever went wrong, and then think up a way to correct it.
One jam an operator always seems to get into sooner or later, however, is this matter of oil or grease in the pulp. A case is on record where a man cleaned the black grease from under the big gear on a ball mill and tossed the goo into the flotation feed launder to get rid of it. The result was a cross between a bubble bath and the Johnstown flood. Oil and grease are frothers, too, but dont use them as such. If, somehow, oil does get into the circuit and the froth comes pouring out on the floor, all you can do is flush things out as quick as you can, tell the shift boss some miner must have dumped his oil bottle into the muck, and pray hell believe you.
flash flotation with closed circuit grinding
The reason why you need Flash Flotation in a Closed Grinding Circuit relates toRecovering your mineral as soon as free which has long been recognized in ore dressing practice. This not only applies to gravity treatment but also to flotation. For this application the FlashFlotation Cell was developed for use in the grinding circuit and has done a remarkable job in many plants.
A greater amount of granular higher grade concentrates can be produced and, in general, overall plant recovery is improved by reducing slime losses due to overgrinding and colliding of high specific gravity minerals.
Typical flowsheets are shown to indicate a few of the possible applications of FlashCells in grinding circuits. In recent years the successful application of hydraulic cyclones, rubber lined pumps, and two stage grinding circuits have enhanced the feasibility of unit cell applications. Cyclones in particular have increased the flexibility of such applications by permitting positive and continuous gravity flow of unit cell tailings to subsequent treatment steps.
Molded rubber wearing parts are used exclusively in unit cells. If wear is severe due to coarse abrasive solids, a special molded soft rubber compound is available which greatly extends the impeller and wearing plate life. Conical disk impellers and wearing plates are standard for unit cell applications.
Two stage classification is shown in this flowsheet with a Unit Cell between the classifiers. The primary classifier may overflow as coarse as 20 mesh and at densities up to 50% solids. This is ideal feed for the unit cell. Unit cell tailings are classified through a cyclone and the oversize returned to the ball mill for further grinding. The cyclone classifier overflow, 65 mesh or finer, is treated by regular bulk or selective flotation.
With this two stage classification system the unit cell can be conveniently located to deliver a positive gravity discharge of pulp to the pump feeding the cyclone. The pump sump box can be made a part of the unit cell tank if desired.
Two stage grinding and classification is provided in this flowsheet which is generally applicable to larger tonnage installations in which a substantial percentage of the values can be recovered directly from the grinding circuit. The primary Rod Mill in open circuit will reduce crushed ore to approximately minus 10 mesh.A Mineral Jig is recommended if coarse mineral and metallics are present.
The spiral or rake classifier overflow passes to the unit cell and on to classification and regrinding. High grade unit cell concentrates can be produced with this system, and on low ratio of concentration ores a substantial increase in mill capacity is possible. Slime losses are greatly minimized with this combination jig and unit cell circuit.
The trend in many of the large tonnage millingcircuits is to completely eliminate conventional rake or spiral classifiers by going to two stage grinding with a rod and ball mill in series. The rod mill discharge goes direct to the ball mill and then on to a pump and hydraulic cyclone classifier. These modern grinding and classification circuits are ideal for including the unit cell as the primary mineral recovery step.
One large copper operation with two stage grinding and cyclone classification, actually treats cyclone underflow, 20 plus 100 mesh, through Unit Cells. The unit cells recover a substantial percentage of the total copper in final concentrate form. The unit cell tailings at 55% solids return by gravity to the regrind ball mill feed. Since incorporating the unit cells and by careful checking between parallel circuits, it has been established by recovering the mineral as soon as free that final mill tailings were reduced by lb. copper per ton.
Unit Flash Cell flotation tests should be made before planning an installation. This will establish if the ore will respond to such treatment to advantage.A 100 lb. representative sample of the ball mill feed is sufficient for the unit cell flotation tests.
The simplest flotation circuit is a comparatively recent innovation. It consists of the introduction ofa flotation cell into the grinding circuit between ball mill and classifier as shown below.The discharge end of the mill is fitted with a trommel screen with openings about 4 mesh in size to separate out coarse material, which is laundered direct to the classifier ; the remainder of the pulp passes to the flotation cell where most of the mineral which has been released from the gangue is taken off as a concentrate, the necessary reagents having been added at some previous point in the circuit, usually at the mill feed box. Flotation can be carried out in a pulp containing as much as 65% of solids, but water is added in most cases to bring the W/S ratio to about 1/1. In such a thick, heavy pulp it is possibleto float particles as coarse as 10 mesh. At this size, however, only pure mineral will adhere to a bubble, for which reason the concentrate is generally of unusually high grade.
The advantage of this method of flotation is that the valuable minerals are removed from the circuit as soon as they have been released from the gangue, so that their accumulation in the classifier is prevented and the possibility of overgrinding them is reduced. Moreover, the granular nature of the particles floated assists considerably in the subsequent filtration of the combined flotation concentrate. It is a simple matter to instal the cell in the ball mill circuit, since it fits readily intothe space between mill and classifier and occasions no loss of head. The only disadvantage is the heavy wear to which the interior of the cell is subjected by the coarse material passing through it, but the modern method of lining both moving and stationary parts with rubber reduces this difficulty to minor proportions.
Mcintyre Porcupine Mines, Ltd., was one of the first companies to practise flotation in the grinding circuit. Their installation is described later in the paragraph headed Flotation of Gold and Silver Ores . Others soon also adopted the method. In their plant grinding is carried out in a Hardinge Ball Mill in closed circuit with a Dorr Classifier, and a Sub-A Cell is employed as the flotation unit between the two, the pulp being maintained at a density of 65% solids. Under normal operating conditions 60-70% of the copper and 40% of the nickel are recovered in the grinding circuit. Subsequent flotation in Sub-A Machines gives a total recovery of nearly 99% of the copper and over 94% of the nickel. No attempt is made to separate the copper from the nickel minerals.
The process can be adapted to the selective flotation of complex ores. Another mill for instance, where a lead-zinc ore is treated by two-stage selective flotation, the method being very similar to the standard procedure described in the paragraph entitled Flotation of Lead-Zinc Ores , the installation of a cell between ball mill and classifier has resulted in the removal of most of the galena before the pulp passes to the main flotation circuit. The sphalerite in the ore is so finely intermixed with a portion of the galena that, although a large proportion of the latter mineral is actually liberated at a comparatively coarse mesh, it is necessary to reduce the whole tonnage to 87% minus 200 mesh in order to separate the two minerals at all completely. Before flotation in the grinding circuit was tried, three stages of cleaning were required to make a high- grade lead concentrate, and 96% of the finished product would pass through a 325-mesh screen, only a trace remaining on 200 mesh. The introduction of a Sub-A Cell into the grinding circuit enabled over 70% of the lead to be recovered in one operation without cleaning in a concentrate running 65-70% lead. The concentrate contains only 53% of minus 325-mesh material, 25% remaining on 200 mesh, and, being more granular than that obtained in the main flotation circuit, it gives better filtration. The total recovery remains much the same as before. Reagents are added in the ball mill feed box, and the pulp is maintained in the cell at about 58% solids.
There is no necessity to limit the size of the flotation machine between ball mill and classifier to a single cell, through the use of a multi-cell or a long pneumatic machine would involve changing the relative positions of the three units from the present standard arrangement. The trendof progress indicates that the flotation machine may become in some cases as important a factor in the proper classification of the ore during grinding as the classifier itself is at present.
Hydrocyclones are used in many grinding circuits to make a size separation which ideally sends the fine ore fraction to conventional flotation and the coarse fraction back to the mill for further grinding. The separation results not only from particle size but also from particle specific gravity. The result is a cyclone underflow which is higher in grade than the cyclone feed. When comparing sulphides and precious metals to silicates, the floatable size fraction in the cyclone underflow contains higher mineral values than gangue. This results because the lower specific gravity gangue particles tend to follow the water in the cyclone overflow.
Typical grinding mill circulating loads range from 200% to 500% with a large part being particles which should have reported to conventional flotation. These particles, mainly heavy sulphides and precious metals, are being reground sometimes several times before eventually making it to the conventional flotation circuit. With each pass through the mill, the particles are ground finer until they are overground. This produces slimes which are usually lost to tailings. The attempt has been made in the past to recover valuable minerals from grinding circuits by flotation. This method, referred to as a unit cell operation, treated grinding mill discharge with a conventional flotation machine. Until now the success of this method has been limited by the inability of a conventional machine to treat the very coarse, high density slurries associated with grinding mill discharges.
Outokumpu developed a specially designed tank to work in conjunction with its flotation agitation mechanism to recover valuable minerals from grinding and classification circuits before they are overground and lost as slimes. The Outokumpu Skim-air coarse flotation machine has been used successfully to recover values from both grinding mill discharge and hydrocyclone underflow.
The Skim-Air Flash Flotation machine floats only those liberated valuable particles which are quick floating. There is not sufficient residence time in the machine to float the slower floating middlings and gangue particles. Thus, each time a particle with ideal fast floating characteristics reports to the cyclone underflow, it is removed in the Skim-Air.
The feed to the Skim-Air machine is normally in the range of 65% to 85% solids. In most cases optimum results are achieved with little or no dilution water being added to the machine. The concentrate produced in the Skim-Air is normally sent as final concentrate. Because only quick floating mineral particles have time to float in the Skim-Air, the concentrate from the machine is usually higher grade than that produced from the conventional flotation circuit. The higher feed density allows coarser particles to be floated resulting in an overall coarser concentrate being produced in the Skim-Air than in conventional flotation.
The overall recovery of valuable minerals can be increased through reduced overgrinding. This results because the quick floating liberated valuable particles in the cyclone underflow are removed from the circuit by the Skim-Air and sent directly as final concentrate. If left in the circuit as part of the recirculating load, these particles will be further ground and reduced in size until they become part of the slow floating slimes fraction. At this point they can easily be lost to tailings. Overgrinding and slimes losses are particularly a problem when processing heavy sulphides such as copper, lead and zinc or precious metals such as gold and silver.
In operations where coarse fraction losses are a problem, the use of a Skim-Air allows the ore to be ground finer without fear of overgrinding the valuable mineral. This is particularly helpful in lead/zinc concentrators where a finer grind may liberate more zinc but also increase lead slimes losses.
Figure 2 shows the narrowing of the particle size range being sent to conventional flotation. The difference between the two curves corresponds to a decrease in relative losses of both the slimes and oversize fractions.
When being fed from the cyclone underflow, the Skim-Air is able to produce concentrate with a grade equal to or better than that being produced in conventional flotation. Much of the floatable size gangue in the hydrocyclone feed passes with the water to the cyclone overflow and on to conventional flotation. This results in a feed to the Skim-Air which is very low in floatable gangue. Coupling this with a particle residence time in the machine of 1-2 minutes which allows only liberated values to float, enables the Skim-Air to produce a high grade concentrate.