THE MINERALS SEPARATION PROCESS
This process represents the joint efforts of Sulman, Picard, and Ballot, and various improvements in processes and apparatus have been added at different times by Froment, Cattermole, Sulman, Picard, Ballot, Higgins, Chapman. Lavers, Greenway, Nutter, Hoover, and others of a large staff. The owner of all these patents is the Minerals Separation, Ltd., a company, the special province of which was intended to be the development of flotation processes. The company licenses the use of the process. The application of this process to a typical Broken Hill zinkiferous material will be described. This material is the tailing from the lead-concentrating mills after the major part of the lead has been removed by gravity-concentration. Mineralogically, the material has approximately the following composition :
Per cent.
ZnS . . . . . . . . 27.1
ZnSO4 . . . . . . . . 2.4
PbS . . . . . . . . 6.4
PbS04 . . . . . . . . 1.3
FeS2 . . . . . . . . 2.5
MnCO3 . . . . . . . . 4.6
CaCO3 . . . . . . . . 3.2
SiO2 . . . . . . . . 42.4
Total . . . . 89.9
The balance of the 100% is made up mostly of garnet and rhodonite and a complex carbonate containing iron, calcium, zinc, and magnesium. The blende is ' black jack ' of about the following composition :
Per cent.
ZnS . . . . . . . . 81
FeS2 . . . . . . . . 14
MnS . . . . . . . . 3
The average assay of the material to be treated by^flotation is :
Zinc . . . . . . . .14 to 20%
Lead . . . . . . . .6%
Silver . . . . . . 7.5 oz. per long ton.
It is necessary to crush this material to about 40-mesh for three reasons : (i) Larger particles float with reluctance ; (2) the sulphides must be freed from the gangue ; (3) crushing has a brightening effect on the sulphide particles.
In this process wide limits as to the amount of slime produced in crushing are permissible. A certain amount of slimed sulphides is absolutely essential to the best frothing result ; but there seems no upper limit beyond which fine crushing is deleterious. One plant worked successfully on material 95% of which would pass a loo-mesh screen. After the ore is crushed to the requisite fineness it is de-watered to a pulp as near as may be three of water to one of ore, this proportion having been determined by a series of trials extending over several years to be the most likely to produce good results under the other conditions imposed.
After de-watering, the pulp is run into an apparatus designed by the author, and patented for Minerals Separation, Ltd., owners of this process, in British Patent 4911 of 1909. The original form of the apparatus was as in Fig. 36. but several improvements were made later. In order to understand the later form it will be easiest to begin with a description of the original apparatus. This consisted essentially of three mixing and agitating compartments joined to a modified spitzkasten. The three mixing compartments were connected together by apertures Aa at the bottom of the partitions Ai. These apertures can be of almost any shape as long as the area of the aperture is within certain wide limits. The right-hand mixing compartment is connected with the spitzkasten by the aperture A3 similar in all respects to the aperture Aa. At J is a horizontal lip, which maintains a water-level, and at H is an outlet which is of such a size that there will always be an overflow over J. The agitators B are driven by belts or gears and should travel with a peripheral speed of about 1,200 or 1,300 feet per minute. This will cause the liquid pulp in the compartments to line the sides of the compartment about half-way to the top, and at the centre of the compartment the water-level will be considerably lower than it is in the spitzkasten. Fig. 37 is a longitudinal section of the three mixers and spitzkasten, and shows the position assumed by the water during operation. At K is a baffle over which the pulp must flow, the edge of K being a few inches below the water-level J, this distance depending on the size of the plant and other factors, the outside limits being 2 and 8 inches. At D is an apparatus for feeding acid, and at E is an apparatus for feeding oil.
The 3 to i pulp is fed into the compartment to the left of Fig. 36 at C, and along with it are fed in also, say, 2lb. of oil and lolb. of sulphuric acid to the ton of ore. Live steam is also introduced into this compartment through a pipe (not shown) in sufficient quantity to raise the temperature of the pulp to 70 C. Owing to the speed of the agitator these ingredients are thoroughly mixed ; in fact, they are churned violently. Large quantities of air are beaten into the pulp. By running the machine for a few minutes on water alone it will be observed that the quantity of air so beaten into the pulp is enormous, for the clean water will be milk-white. As the inflow of pulp is continuous, the outflow from the left-hand compartment into the middle compartment is also continuous and of equal volume. In the middle compartment the pulp receives a further violent agitation, and then passes continuously into the right-hand compartment to be agitated once more. From the right-hand compartment the froth emerges through A3 into the spitzkasten over the baffle K. The rate at which the pulp passes over the baffle K is exactly the same as that at which it is fed at C. As the pulp emerges from A3 a dense froth, composed of sulphides and bubbles of gas, immediately rises to the surface, where it floats along to J, and passes over into the launder G, and so to the bins. The gangue, on the other hand, does not float, but just manages to get over the baffle K, and then drops to the tip of the spitzkasten, and is removed at H.
A single box of the above description will not give a perfect extraction, and it is necessary to give the pulp a second and third treatment in a similar box with less agitation. This can be done by simply building three sets like that shown in Fig. 36, and placing them one under the other as in Fig. 38. A set of boxes of this design, with mixing compartments 3 by 3 feet and a spitzkasten 4 by 5 ft., will treat 400 tons of this material per day, and will make something over 150 Ib. of clean zinc concentrate per minute.
Instead of placing three sets of this kind one above the other, a much simpler mechanical arrangement can be made which saves head-room, floor-space, and labour in operation ; and as this is the form of apparatus most recently installed by the Zinc Corporation, and represents the latest development in the process, it will be described at the risk of some repetition. These ideas were also patented for the Minerals Separation, Ltd. This arrangement of plant makes use of the centrifugal effect of the agitators, and uses them partly as pumps. Referring to Figs. 39, 40, and 41, which are elevation, plan, and section of the latest arrangement, A, B, C, D, E, and F are mixing compartments, each containing an agitator running at high speed ; X, Y, and Z are spitzkastens. The ore, water, oil, acid, and steam are fed into the compartment A in proper proportions, where the pulp is thoroughly mixed and violently agitated ; A has a hole at the bottom, which allows the pulp to pass into B, where there is more violent agitation ; B has a hole in the bottom, which allows the pulp to pass into C and from C goes over a baffle into the spitzkasten X, where a heavy, dense mineral froth is floated over the lip of X; the gangue, along with some of the sulphides, passes to ' the tip of the spitzkasten X, the tip being connected by a pipe M with the bottom of D. The agitator in compartment D acts as a centrifugal pump, and draws the material from the tip of X up into compartment D, where the pulp receives further agitation and aeration. The lift required of this pump is very slight, for it will be observed that there is one liquid level throughout the whole of this combined arrangement ; the agitator pump in D has to pump against a head which is practically only the friction head of the system. From D the pulp passes to E, where further aeration by agitation is given ; from E the pulp passes over a baffle into the spitzkasten Y, the froth flowing over the lip of Y and the gangue with a little remaining sulphide dropping down to the tip of Y ; the tip of Y is connected by a pipe N with the bottom of the mixing compartment F, and the agitator in F acts as a pump to draw the pulp up into F. Here the head on the pump is only the friction head, and as in the case of M, N is also the suction side of the centrifugal pump. The pulp gets further agitation in the mixing compartment F, and finally emerges over a baffle into the spitzkasten Z, where the last available mineral froth passes over the lip, and the gangue drops down to the tip, from whence it is drawn through a regulated opening and passes to the tailing flume. A perspective drawing of this plant is also shown in Fig. 42, which may help to understand the scheme.
This plant has the merit of extreme compactness. One unit of 400 tons per day capacity would occupy a floor space of less than 30 by ioft., and less than i2ft. of vertical height. The whole operation is in front of one man, and the labour required is so reduced to a minimum. By placing two units front to front, one operator should watch the treatment of 1,000 tons per day. These agitators take 5 h.p. each for a plant of 400 tons per day capacity, and on most ores six agitators would be ample. Some ore would probably require that the agitators be arranged first a set of three followed by a spitzkasten ; then a set of two followed by a spitzkasten ; and lastly, one agitator followed by a spitzkasten. Other forms consist of one agitator for each of eight spitzkastens, and variations of connections in each case depending on the nature of the ore.
In most flotation plants, whether using this process or the others previously described, it will be found of decided advantage to use the water over and over again, as there is some latent acidity always in solution after the flotation is complete, and besides, the salts in solution have a beneficial coagulating effect. If the salts in solution increase to beyond 4,000 grains per gallon, the millmen have acquired the idea that it has a detrimental effect on the flotation, but this does not seem to be based entirely on sound reasoning ; the detrimental effect is probably an indirect result of salts in solution, and could be obviated by proper manipulation.
One of the recent improvements in this process is by way of using as a froth-producing agent a soluble substance to replace the insoluble oil formerly used. The soluble substances which are available for this purpose are : Alcohols, especially amyl alcohol and some of its soluble salts, such as amyl acetatf ; all the phenols and their near derivatives ; the turpentines and many of the products from the destructive distillation of wood ; most of the essential oils, and especially the oil from eucalyptus amygdalena, one of the most common eucalyptus in Australia. This last is probably the best of all, and as the quantity used is less than a pound per ton of ore, the high price of the oil does not hinder its use. One decided advantage of using these soluble frothing agents is that where a subsequent treatment of the concentrate is desired for the separation of lead and zinc sulphides, it can be treated directly on tables. Where an insoluble oil was formerly used it was necessary to burn this insoluble oil, as it made the sulphides gummy, and they could scarcely be separated by gravity.
The following figures give the dimensions of units of various sizes. Part of this information has been derived from actual observation, and part is deduced from the known behaviour of the process under given conditions. No doubt further work with the process will modify the ideas as to size, even if the form is maintained as at present.
A further improvement to this apparatus, that eliminates all pipes, pumps, and valves, and makes the process practically independent of the operator, is illustrated below. The apparatus and its application to flotation processes will be sufficiently clear from the following descriptions, and Figs. 43, 44, and 45, which are elevation, plan, and section of the new machine :
The ore is fed in at A (Figs. 44 and 45), along with water, oil, and acid, and after a period of agitation and mixing, emerges at the opening B into the flotation-box C. A portion of the sulphides floats and is removed at the lip D. The remainder ot the sulphide with the gangue, etc., is drawn through the hole E into the mixing-compartment F, whence, after further agitation, it is discharged from the hole G into the flotation-box H, where more floating sulphides are removed at the lip I, and so on through the whole series, alternately agitating and taking off a froth, until the last frothing-box J, where the gangue-sand fully depleted of sulphides is withdrawn at the valve K. The agitators in the mixing- compartments should run at a peripheral speed of about 1,500 linear feet per minute.
Another form of apparatus which has many advantages of simplicity is shown in Figs. 46, 47, and 48. In this case the pulp moves in a straight line through the whole series, receiving successive agitations at A, A, A, and yielding froths at B, B, B, which froths are drawn off at the lips D, D, D. At C is a valve and pipe which regulate the outflow of the tailing and the height of water in the whole series. The agitators in the mixingcompartments A, A, A should run at a peripheral speed of about 1,500 linear feet per minute. In B, B, B there are slow-moving agitators to keep the sand slowly in motion ; these should run at 10 to 20 r.p.m., but not fast enough to break the surface of the water. On some ores the agitators may not be needed in B, B, B, etc.
The first mention of the Minerals Separation process is in the Annual Report for the Department of Mines of New South Wales for 1904, where it is recorded that the Sulphide Corporation had been experimenting with an oleaginous process, and that a plant would be erected in the following year. In 1905 the process was described as being either one where the mineral was coagulated and sunk, or where a small amount of oil was used to make the mineral float. At this plant the patents of the company had their first practical application. During 1905 the Cattermole idea was abandoned, and the plant was altered to a flotationprocess plant, and operated as successfully as could be expected in a plant which had undergone so many vicissitudes. The work here in 1907 served as a model for the Zinc Corporation in their first trial of the Minerals Separation process, but they were not able to duplicate the results, and as a result abandoned the Minerals Separation, and installed the Elmore process. The plant continued operations during 1907, but was finally closed in 1908. The material treated was typical Broken Hill dump- tailing from the lead-concentrating mills, and the three years' operations are here shown.
This plan at periods gave much better results than the average, and subsequent work elsewhere with the process justified the confidence of the engineers in its merit.
SIMPLE PLANT | ZINC CORPORATION, LTD | SIMPLE PLANT | ZINC CORPORATION, LTD
