Recovery of Copper from its Solution in Mine Drainage. 323 



Conclusion. 

 From the account that has been given of copper precipita- 

 tion as practised at the Ovoca Mines, and the short i-hume of the 

 more improved processes that have been tried at other mines, 

 and in the humid treatment of poor copper ores, it seems thai the 

 resources of this method of treatment have not been exhausted 

 at the Ovoca mines, for, not only is the copper precipitate obtained 

 in an impure state with an excessive consumption of iron, but 

 the copper is not completely extracted from the waters, and all 

 the sulphate of iron is allowed to run to waste; besides, no 

 attempt is made to enrich the waters, which, since active opera- 

 tions in the mines have, in a great measure ceased, are gradually 

 becoming weaker, although poor copper ores, ranging up to two 

 or three per cent, of copper are to be found in the mines.* 



Regarding the impure state of the copper precipitate obtained 

 with an excessive consumption of iron, it has been pointed out that 

 both these defects are principally due to the presence of ferric salts 

 in the solution which not only act directly on the cast iron, thus : — 



(a.) Fe^ O3 (S03)3^-Fe2+2H2 0=^e, O3 S03-l-2Fe SO4-I-2H2 

 some of the iron passing into solution, and a basic sulphate of 

 iron (an ochre) depositing : but also the copper that is precipitated 

 according to the reaction 



(/3.) OuSO,+Fe=FeS04^Cu 

 is redissolved by these ferric salt, thus : — 



(y.) Fe, (804)3+ Cu=2Fe SO,+Cu SO^ 

 a fresh quantity of iron being dissolved on its reprecipitation ; 

 these reactions proceeding alternately till all the ferric salts 

 become reduced. Several methods that may be adopted for the 



* In the "backs" of the great pyrites lodes there are immense quantities of poor copper 

 ores (principally the black and grey ores of copper mixed with pyrites and other sulphides), 

 which on the admission of air and moisture undergo rapid decomposition, the copper and 

 some other substances being rendered soluble. At East Cronebane and Counary there is 

 a largce supply of these easily oxidizable ores, giving in some places sections of ore from 

 6 to 8 fathoms wide and averaging If to 2 per cent, of copper. These ores occur iu a 

 soft unctuous clay which prevents the water from percolating through, so that the ores 

 are preserved in an undecomposed condition till opened up. 



Besides these friable ores there are others in the lode more compact, but which also 

 contain much pyrites and undergo decomposition on exposure. There are also some hard 

 and very complex ores such as the " Kilmacooite " or "bluestone." 



Descriptions of these mines and minerals will be found in " Kecords of the School of 

 Mines," Vol. I., Part 3, by Professor Warington W. Smith, M.A., and in " Notes on the 

 Ancient and Recent Mining Operations in the East Ovoca District," by P. Argall, Proc, 

 Pv.D.S., n.8., Vol. II., p. 211. 



