Recovery of Copper from its Solution in Mine Drainage. 317 



Precipitation of the Copper. 



Copper is usually extracted from its solutions in the metallic 

 state by cementation or precipitation on "metallic iron. In some 

 cases it is obtained as sulphide by precipitating with sulphuretted 

 hydrogen, or some soluble sulphide. Milk of lime, carbonate of 

 lime, or some other carbonates have also been proposed for precip- 

 itating it. 



Cementation: — The preference given to metallic iron as a 

 precipitant, seems to be due to the simplicity of its use and the 

 purity of the copper obtained by this method; it being free from 

 such deleterious impurities as lead, bismuth, &c. The chief ob- 

 jection to its use is its expense, especially when there is an 

 excessive consumption, and when it is not recovered subsequently 

 from the solutions. 



The most advantageous conditions under which it could be 

 used, should be when the consumption was the exact equivalent 

 o£ the copper precipitated, and the iron recovered from solution 

 to be again used for precipitating or for some other purpose. 



From what has been stated previously, it is evident that the 



8 OuSO, + 2 Fe^Fe, {SO,), + 3 Cu 

 cannot take place to any great extent, as the copper so precip- 

 itated would be immediately redissolved, and therefore that the 

 maximum result to be expected with cupric salts is : — ■ 



Cu S04 + Fe=Fe SO, + Cu 

 or quantities directly proportional to their atomic equivalents, — 

 of 63'5 parts of copper for 5Q parts iron; — or for each ton of iron 

 dissolved, 22-67 cwt. of copper precipitated. In practice this is 

 seldom attained, chiefly on account of the presence of ferric salts 

 as previously stated. A glance at the annexed table (A) will 

 show what a wide range there is between the maximum and mini- 

 mum results. 



The form of iron most generally used is cast or pig iron, 

 and it has been found that grey pig, particularly when 

 granulated, reacts more efficiently than white. Wrought iron, 

 however, is more advantageously applied where the liquors 

 are much weakened as towards the end of the precipitating 

 process. Scrap-iron and tin clippings may be also used, the 

 latter especially after the removal of the tin from their 



SciEN. Proc. R.D.S., Vol. hi.. Ft. vi- 2 C 



