Section III, 1917 lii3] Trans. R.S.C. 



The Electrolytic Precipitation of Zinc. 



By D. MclNTOSH, Ph.D., F.R.S.C. 



(Read May Meeting, 1917.) 



The most important contribution to Hydrometallurgy during the 

 last few years has been the development of the electrolytic zinc 

 process. Although the precipitation of zinc from its sulphate solution 

 and the regeneration of the sulphuric acid has been known and prac- 

 tised for many years, it is only within the last year that the process 

 can be described as a commercial one. Plants are now in operation 

 in Canada, the United States and Japan, and are being erected in 

 many other countries, and the electrolytic process in the opinion of 

 many is now assured of success in competition with the distillation 

 process even "after the war." The production of zinc in great quan- 

 tities of 99 • 95 — 99 • 98 per cent, purity is a triumph in metallurgy and 

 places this element in a class with copper and lead. No doubt this 

 will lead to improvements in the quality of brass and to the discovery 

 of new and useful alloys. 



In this paper I shall give the results of some experiments carried 

 out at Trail for the Consolidated Mining and Smelting Company and 

 published with permission. For those who have worked on the pre- 

 cipitation of zinc, there will be nothing new; those unfamiliar with 

 the process may find some points of interest. 



In the extraction of zinc from its ores, the blende is roasted, and 

 then leached with dilute sulphuric acid. In the solution are salts of 

 iron, antimony, cadmium, arsenic, copper, silver, etc.— all of which 

 affect the precipitation of the zinc — and various colloids. The iron, 

 arsenic and antimony are precipitated by neutralising the solution 

 with roasted ore or limestone; the silver, copper and cadmium by treat- 

 ing with metallic zinc. The zinc is then precipitated electrolytically 

 on aluminum electrodes, and the regenerated acid is used in leaching 

 a fresh quantity of calcined ore. The process may be either a "batch" 

 or a continuous one. But while the merits of these two methods, the 

 interesting phenomena met with in the precipitation of the colloids, etc. 

 are worth discussing, I shall mention only the effect of impurities i^ 

 connection with the electrolysis of the zinc sulphate solution. 



