SURFACE ARRANGEMENTS AT

REDUCTION WORKS

INTRODUCTION

1. Definitions.-Reduction plants are usually distinguished as wet and dry. In the first instance the plants are supposed to use water and chemicals for reduction purposes, while in the second they use fire to obtain metals from the ore. The dry process would include magnetic concentration and the concentration of minerals by air, were there at this time any other than experimental plants existing for the latter. The wet process is made to include all those plants that reduce the bulk of ores by means of water, whether chemicals enter into the reduction or not. Concentration, from a metallurgical standpoint, is defined as a separation of ore or metal from its containing rock; whether water or heat is the more convenient and suitable agent for concentration will depend on the location of the mill and the character of the ores, for in some cases one method would answer while the other would be entirely unsatisfactory and too costly.

2. Hydrometallurgy. The process of reducing metallic ores by means of liquids is termed hydrometallurgy. Hydrometallurgy includes both concentration by means of water and reduction by means of chemical solutions. It also includes amalgamation and such methods as are termed combination processes. Hydrometallurgy, as it

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is understood today, embraces both chemical and mechanical concentration wherein water enters as a factor.

3. Hydraulicking is a term given to mining, transporting, and concentrating metal mineral by means of water. The term to within a short period referred entirely to the operation of concentrating gold by means of a stream of water, which mined the ground and gravel containing the gold, transported the same, and allowed the gold to become massed at one point and thus made recoverable. This principle has been extended to mining other minerals, such as iron, phosphate, rock, zinc ore, and platinum, and the term should no longer be limited to gold mining, but it should be extended to such operations as use the same stream of water for mining, transporting, and concentrating minerals.

4. Dredging for minerals approaches hydraulicking as far as concentration by water enters into the operation, but differs from it materially in that the excavating is accomplished by other means than water alone, such as centrifugal pumps or dredging buckets. While water in measure assists the dredging apparatus in excavating, nevertheless it would not transport and concentrate the mineral, as is done in hydraulicking, without the use of a water elevator. Hydraulic elevators, such as are used in the West for placer mining, belong to dredging rather than to hydraulicking.

some

5. Hydrometallurgical Apparatus.-Various mechanical devices are used to concentrate minerals by washing them free from dirt or other impurities. Such machines are not classified with hydraulicking, as they are not mining machines; but although they wash and concentrate minerals, they come under the head of hydrometallurgical apparatus. Mechanical devices, such as jigs, trommels, log washers, hydraulic classifiers, and other similar machines, are not to be placed in a separate class, as they may be made adjuncts to several operations that differ completely in their ultimate method of obtaining the desired results. This character of

hydrometallurgical apparatus is described in Ore Dressing and Milling and will not be specifically explained here; but it is well to understand that such apparatus may be used for concentrating secondary products of milling, as well as the primary products of mining.

6. A second class of hydrometallurgical apparatus includes wet crushing as a preliminary operation, followed by sizing and concentration. Water forms the medium through which the decrease in barren mineral becomes possible. This operation is treated in Ore Dressing and Milling and includes such machines as jigs, trommels, spitzkasten, cone classifiers, bumping tables, concentrators, buddles, and vanners.

Concentration by the use of such machines is for the purpose of obtaining mineral matter in small bulk and then subjecting it to some other treatment. The milling ores thus treated are usually sulphuret and lean ores, which must be concentrated to a small bulk and treated at some distant point. Concentrates containing sulphur are more easily and economically reduced when freed from barren vein material, and in some cases if the ore were not concentrated no values could be obtained.

This system is used to separate lead from zinc in the Missouri-Kansas zinc districts of the United States, where zinc and lead are found in the same ore, and as they do not alloy they cannot be concentrated by fire so as to obtain each separately without making the cost of the concentration exceed their value. The only other means left, then, is a system of hydrometallurgy that will separate the two as far as possible, owing to their difference in specific gravity. This process is not practical when pyrite is associated with blende and galena. The same system is also practiced with the native copper ores in Michigan, where, on account of the difference in specific gravity between the rock and the native copper, they are successfully separated. The process was attempted at the Huston Mines, near Nace, Virginia, in order to separate manganese from limonite, but on account of the

nearness of the minerals in their specific gravities, it was a complete failure.

7. A third hydrometallurgical process includes wet crushing with amalgamation, such as is usually practiced in stamp milling. This process may be extended to include pan and barrel amalgamation. In case there is any considerable loss of gold from incomplete amalgamation, the process may be followed by that previously described or the fourth process.

The operation is hydrochemical in some instances, but not in the sense of lixiviation, for chemicals are not added in the pan process to extract the precious metals, but for the purpose of keeping the almalgam quick and preventing its sickening, flouring, or becoming incorporated with copper.

When the mercury becomes sickened it refuses to act upon the gold, and hence the gold is not recovered by this process. If, therefore, it is possible to keep the mercury bright and active, as may be done by adding chemicals, a larger percentage of precious metals can be recovered.

8. It often happens in stamp milling that only about 40 per cent. of the precious metals in the ore is recovered by amalgamation, and it is seldom that the recovery exceeds 75 per cent. In the case, then, of a $12 ore, the value remaining after amalgamation would be $7.20, if the recovery was but 40 per cent. If by grinding the tailings in pans containing mercury a further percentage of the values may be recovered at a cost that will prove profitable, it is generally done, provided this system of recovery is cheaper and more profitable than some other. Again, if the ore will leave a profit after concentration and shipping expenses to the smelters are deducted, that method will prove advisable provided pan amalgamation does not yield as large returns. In some cases lixiviation may prove more remunerative for a secondary operation than the methods set forth; in any