

Mecovery of Copper from its Solution in Mine Drainage. 821 



(about 144)° F.), till the waters become yellow, this occurs in about 

 twelve hours, the bluish colour disappears, and the boiling is 

 limpid, it is then allowed to settle for a day, the clear liquors are 

 drawn off and the turbid run to settling tanks, where the sus- 

 pended material deposits, this consists of basic salts of iron, impuri- 

 ties from the cast-iron, and about ten per cent, of copper in fine 

 p(jwder, and is locally termed " brunini." 



The iron in the precipitating tanks is washed with water, and 

 the adherent copper removed, when it has deposited the waters 

 are drawn off, this portion of the precipitate is termed " grassure," 

 and contains about 59 per cent, of copuer. 



In 1874) the method of procedure was somewhat altered, as it 

 was found that the consumption of iron was excessive, and that 

 the insoluble basic salts of iron that were produced lowered the 

 quality of the cement copper. Both these defects being due to 

 ferric sulphate in solution, steps were taken to reduce the solution. 

 This was effected by saturating the solution with sulphurous 

 anhydride (SOg) in the following manner : — The liquors were 

 passed down a chimney and into a tank, through both of which 

 the gas (derived from the roasting of the ore) was passing in 

 the opposite direction, so that ferrous sulphate and free sul- 

 phuric acid were formed. The reduced liquors were run on to 

 cast-iron in tanks, that could be heated by a peat fire, the tem- 

 perature at first is 34° R. (about 109° F.) ; in the early stages 

 hydrogen is given off till the metals become coated with copper, 

 the temperature is subsequently raised to 38° R. (118° F.}, and 

 finally to 40° R. (122° F.), when more iron is added to complete 

 the precipitation ; when the whole has been allowed to settle 

 for twenty-four hours and the temperature has become reduced 

 to 35° R. (about 111° F), the clear liquors are run to crj'stal- 

 lizers where sulphate of iron is recovered. The precipitated 

 copper is found in two conditions, about 70 per cent, is found 

 in compact scales adherent to the iron, and is almost pure, while 

 about 80 per cent, occurs in a powder containing arsenic and 

 ferric oxide in considerable quantities. (See Table D.) 



