COPPEE 935 



little water, of which a small quantity is also placed in the bottoms of the tanks. 

 The sulphuric acid thus generated attacks the oxide of copper formed during the pre- 

 liminary roasting, giving rise to the production of sulphate of copper, which percolates 

 through the basaltic diaphragm into the reservoir beneath. 



The liquors which thus accumulate are from time to time distributed qver the 

 surface of the ore, and the operation repeated until the greater portion of the copper 

 has been extracted, when, by shifting the damper, the gases are conducted into 

 another tank similarly arranged. The liquors from the first basin are now pumped 

 into the second, and the operation continued until the ores which it contains have 

 ceased to be acted on by the acid. When sufficiently saturated, the liquors are drawn 

 off into convenient troughs, and the copper precipitated by means of scrap iron. The 

 sulphate of iron thus formed is subsequently crystallised out, and packed into casks 

 for sale. 



On removing the attacked ores from the tank, the finer or upper portions are thrown 

 away as entirely exhausted, nearly the whole of the copper having been removed from 

 them, whilst the coarser fragments are crushed and re-roasted, and finally form the 

 upper stratum in a subsequent operation. 



It has been found that, by operating in this way, ores yielding only 1 per cent, of 

 copper may bo treated with considerable advantage, since the sulphate of iron pro- 

 duced, and the increased value of the roasted blende, are alone sufficient to cover the 

 expenses of the operation. 



By this process, 3 cwts. of coal are said to be required to roast one ton of ore, whilst 

 the same quantity of blende is roasted by an expenditure of 4 cwts. of fuel. 



Treatment of Copper Ores by Hydrochloric Acid. At a short distance from the village 

 of Twiste, in the Waldeck, several considerable bands of sandstone, more or less im- 

 pregnated with green carbonate of copper, have been long known to exist. Although 

 varying considerably in its produce, this ore, on the average, yields 2 per cent, of 

 copper, and was formerly raised and smelted in large quantities ; but this method of 

 treatment not having apparently produced satisfactory results, the operations were 

 ultimately abandoned. 



The insoluble nature of the granular quartzitic gangue with which the copper is 

 associated, suggested, some years since, to Mr. Rhodius, of the Linz Metallurgic 

 Works, the possibility of treating these ores by means of hydrochloric acid, and a large 

 establishment for this purpose was ultimately the result The following is a descrip- 

 tion of this process, as witnessed by Mr. J. A. Phillips, in 1856 : 



These works consist of a crushing mill, for the reduction of the cupreous sandstone 

 to a email size, 16 dissolving tubs, and a considerable number of tanks and reservoirs 

 for the reception of the copper-liquors and the precipitation of the metal by means of 

 scrap-iron. Each of the 16 dissolving tubs is 13 feet in diameter, and 4 feet in depth, 

 and furnished with al arge wooden revolving agitator, set in motion by a run of over- 

 head shafting in connection with a powerful water-wheel. This arrangement admits 

 of the daily treatment of 20 tons of ore, and the consequent production of from 7 to 

 8 cwts. of copper. Each operation is completed in 24 hours, the liquor being removed 

 from the tanks to the precipitating trough by the aid of wooden pumps. The ore is 

 sloped and brought into the works at 4s. per ton. . 



The acid employed at Twiste is obtained from the alkali works in the neighbour- 

 hood of Frankfort, contains 16 per cent, of real acid, and costs, delivered at the works, 

 2s. per 100 Ibs. Each ton of sandstone treated requires 400 Ibs. of acid, which is 

 diluted with water down to 10 per cent, before being added to the ore. Every ton of 

 copper precipitated requires 1 ^ ton of scrap iron, at 41. 5s. per ton. 



These works yielded in 1857, 120 tons of metallic copper, and afforded a net profit of 

 nearly 50 per cent. The residues from the washing vats, run off after the operation, 

 contained but ith per cent, of copper. 



The works at Twiste were ultimately abandoned on account of a falling off in the 

 yield of the ores. 



Humid Process of extracting Copper from Burnt Cupreous Pyrites. Very large 

 quantities of cupreous pyrites, amounting in the aggregate to about 400.000 tons per 

 annum, are imported into this country from Spain and Portugal. The sulphur is 

 utilised in the manufacture of sulphuric acid, and from the burnt residue the large 

 quantity of 1,200 tons of copper is annually extracted. 



The burnt pyrites contains on the average 2J- to 3 per cent, of sulphur, and 3 to 3 

 per cent, of copper. The extraction of the latter is effected as follows : The ore is 

 ground between rolls or iinder edge runners, and a sufficient quantity of unburnt 

 sulphur added to it to raise the per-centage of sulphur to an amount slightly in excess 

 of the copper, at the same time a sufficient quantity of salt, to convert the copper into 

 chloride, is introduced. This mixture passes through a sieve of about 36 holes to the 

 square inch, and is then ready for roasting, which is commonly effected in reverbera- 



