SEPARATION OF SULPHIDES
SEPARATION OF SULPHIDES. Up to the present these methods have not with complete success solved the problem of the separation of the sulphides from each other. The Horwood process is a step in this direction, but little has been heard of it recently, and on economic grounds it is doubtful if in the present form the idea is commercially feasible.
The sulphides of the base metal have the quality of oil and gas adhesion in varying magnitudes, as can be easily demonstrated, but the range of this variability is much smaller than between gangue and sulphides. No one dare say, however, that even this minute variability does not have in it the basis of a commercial separation. Horwood accomplishes the result by going to the expense of a preliminary slight roast, and thus turning some of the sulphides as far as is necessary into a form analogous to gangue minerals, thus destroying the strong adhesive quality of some of the sulphides, and he thereby is able to separate them from those sulphides whose quality of adhesion to oils and gases is unaffected by the slight roast. This is another of the important unsolved problems, and its solution lies in the direction of combining all the favourable factors in such a way that they all act at the proper time and proper place. Some oils cause a better frothing of the blende than of the galena ; some temperatures are better for the frothing of certain sulphides than of others ; some pressures cause a froth to form in which there is a greater proportion of certain sulphides than at other pressures ; the amount of air or gas made available for frothing affects the composition of the froth to a certain extent ; the amount of acid used has a decided influence on the constitution of the froth, and the impurities of the water also have similar effects. The above factors and others, which are available for working in conjunction, conceivably contain the secret of a revolutionary process for solving the longstanding problem of separating completely and commercially mixed sulphides of copper, zinc, and lead. I am inclined to think however, that the solution of this vexed problem lies within the realm of the chemical industry.
COMBINATIONS. The limitations of any one process of ore concentration are the reasons why metallurgists have always used combinations of processes and of apparatus. We have combinations of hand sorting, jigs, shaking tables, varmers, and many others, and these combinations are further combined with amalgamation, cyanide, chlorination processes, and others. Flotation processes quite properly take their useful places in combinations for the purposes of concentration only, but it is not likely that they will soon be used in combination with the cyanide process ; at least, they will probably not be so used until a successful flotation process is discovered which does not use any acid. We would not at first glance think that health conditions would be good in a plant where cyanide treatment of the ore is either preceded or followed by one of the present flotation processes. Nor is it likely that a combination of an oil- flotation process followed by amalgamation will soon be seen, although there would appear to be nothing to prevent flotation-concentration following amalgamation provided cyanidation was not desired.
SLIME. This point will be discussed with some reluctance because the author's past relations have been such that there is a fear he may be charged with favouritism or with advertising a proprietary method. Even at the risk of this criticism it is just to the reader as well as the process owner to venture a private opinion, based on extended observation. One of the important processes previously described makes no attempt to treat slime, and numerous statements have been made in line with this fact. A second process described, while making, perhaps with some justice, claims of an ability to treat slime, has signally failed in at least two important instances unnecessary to specify. A third now seems to be in a way to overcome its earlier difficulties. Among the minor processes there does not seem to be any which have advanced far in the treatment of slimy material.
The Minerals Separation process has for some years stood alone in its ability to handle with ease in operation, and with commercial profit, the slimiest of mill by-products. This has been demonstrated by operations extending to millions of tons and over years of time. There are sound physical reasons for this feature and the principles involved to wit, coagulation of the sulphides, followed by frothing of the coagules, are made the most of. It is unnecessary to give details on the subject of this slime treatment other than are found elsewhere in this and previous chapters. Recent developments of the Potter-Delprat process indicate for certain that slimes can now be treated successfully by this method also.
MAGNITUDE OF OPERATIONS. It is a significant fact worth keeping in mind that nearly, if not quite, all the plants where these processes are now being used are very large plants. They are treating large tonnages at a small profit per ton, and if they were operating on the scale of the average sized mine, as will appear later, the overhead charges would probably eat up all this profit. In addition to this, the operations are on materials which have already been mined and which cost very little to deliver to the bin. If IDS or 12s per ton was added as the cost of mining to the working cost, the profit would disappear. The cost given later is mostly for the Broken Hill district, where the cost is much higher than is considered necessary elsewhere in the world. It seems probable that the same operations in the United States would be 25% less, even though the cost of materials is about the same and wages much higher than in Australia ; on the other hand, labour is doubly efficient and the difference in management beyond the power of figures to express.
