Recovery of Copper from its Solution in Mine Drainage. 315 



agitating tlie liquors, and for the introduction and removal of the 

 solutions are described. 



The following salts, amongst others, have been proposed for 

 the solution of the copper, viz., ammonia and some ammoniacal 

 salts for the solution of oxides and carbonates ; solutions of sul- 

 phite and hyposulphite of soda; chloride of magnesia; and acid 

 solutions of manganous chloride, the latter being a residue of the 

 chlorine manufacturers. 



Ferrous chloride in a strong brine is used in the " Hunt and 

 Douglas " process, cupric oxide being dissolved with the separa- 

 tion of ferric oxide and formation of cuprous and cupric chloride, 

 the former being kept in solution by the brine. 



2 Fe CI, + 3 Cu O = Cu, OL + Cu CI, + Fe, O3 

 if cuprous oxide is present metallic copper separates : — 



2 Fe CI, + 3 Cu, O = 2 Cu, CI, + Fe, O3 + Cu, 

 but is re-dissolved by the cupric chloride present : — 



Cu + Cu CI, = Cu, CI, 

 so that the greater part of the copper exists in the solution iYi the 

 cuprous state, which requires a less consumption of iron for its 

 subsequent precipitation. 



Purification of the lixiviations is sometimes resorted to before 

 proceeding to the precipitation of the copper. This is usually for 

 the purpose of removing ingredients that would retard the preci- 

 pitation, or be injurious to the resultant precipitate (as antimony, 

 arsenic, lead, (fee), but is sometimes for the purpose of saving the 

 precious metals (gold and silver) when present in sufficient 

 quantity. 



At many precipitation works where cementation is carried on, 

 it has been remarked that often the iron is dissolved without 

 any copper being precipitated ; this may sometimes be due to 

 free acid, but in natural solutions (as mine waters) this is not 

 often the case. In the experiments of Napier in 1844, it was 

 shown that no copper is deposited from a solution containing iron 

 salts, till they were all reduced to the ferrous state, and further- 

 more, at Agordo in 1874, M. Zoppi found that in a solution con- 

 taining ferric sulphate, on the precipitation of some of the copper 

 it was immediately re-dissolved, and that a process of alternate 

 precipitation and re-solution went on till all the iron present was 

 converted to the ferrous state. 



Fe^ (S0,)3-|-Cu = 2Fe S0,+ Cu SO4 



