142 TRANSACTIONS OF THE 
HYDROMETALLURGY AS APPLIED TO THE 
MINERAL INDUSTRY. 
BY CLARENCE A. WRIGHT.* 
It is rather difficult to cover the field of hydrometal- 
lurgy as applied to the mineral industry in such a short 
space of time, but I shall try to point out in as brief a 
manner as possible just where hydrometallurgy may be 
applied in the treatment of ores. 
Hydrometallurgy can include, of course, hydro- 
mechanical methods in the treatment of ores, but it is 
generally referred to as a process or method of treatment 
involving the solution of metals by chemical means, such 
as leaching or amalgamation, and the recovery of the 
metals either in metallic form or as a chemical compound. 
The applicability of any solvent process to the 
extraction of metals depends largely on the character of 
the ore, as the solvents such as acids, react more or less 
with the gangue constituents or elements contained in 
the ore. These gangue constituents not only consume 
the solvents, but elements detrimental to the process are 
frequently brought into solution. 
The effectiveness of a solvent is generally improved by 
roasting the ores and the leaching processes have been 
applied principally to oxidized ores. Although the 
application of any chemical process may be more or less 
limited, higher extractions are generally possible than by 
the usual methods of concentration and subsequent 
smelting. It also has the advantage in cutting down the 
cost of haulage and transportation to a minimum in that 
the final product is in the form of metal or chemical 
compound desired. Leaching in comparison with smelt- 
ing requires little fuel, but on the other hand the cost 
of chemicals may prove to be prohibitive so that it comes 
down to a case of dollars and cents as to which is the 
most economical method of treatment. 
*Hydrometallurgist, U. S. Bureau of Mines. 
