More information : By 1860 the Alderley Edge Mining Company had constructed an extensive works for the treatment of copper, lead and cobalt. It is immediately East of, and adjacent to, West Mine, South-West of Wood Mine. The latter did not provide ore for treatment at the works until the early 1860s. Ore was brought out of West Mine up the 1:6 inclined plane. At the top of the tramway the ore was crushed to 1 cm pieces between iron rollers, and passed to either the lead or copper works. The cobalt ores were mixed in with the copper minerals.
The lead minerals were separated from the sandstone host by grinding between burr-stones, and washing the ore to effect a density separation. Certain lead-bearing sandstones yielded 30-40% lead minerals in this process. The concentrate produced was sold to the Patent White Lead Company at Macclesfield. The lead works closed in 1864 following the failure to capture more of the lead in the washing process.
Crushed copper ore was fed into 16 wooden leaching tanks, each 11 feet x 8 feet x 4 feet, and capable of holding 9 tons of ore. The copper was leached by the application of hydrochloric acid. Each leaching tank had a false bottom covered with brushwood and straw. Three quarters of the ore could be dissolved by the acid, the liquor dripping through the false bottom and collecting in the space beneath. Every two hours the acid was recycled through the remaining ore until the liquor ceased to increase in strength. A steam engine provided the motive power for the recycling.
The resulting acidic green 'sap' was run off into one of five wooden precpitation tanks where light scrap iron and tinplate cuttings were added. In the ensuing chemical reaction, the acid sap dissolved the iron at the expense of the copper, which precipitated in a metallic state. The blackish-brown precipitate was removed, dried, and sold as No.1 or No.2 precipitate, the former containing 80% copper:20% iron, the latter 60% copper: 40% iron.
The remaining iron, manganese and cobalt chloride-bearing solutions were at first treated by concentration and evaporation to produce a cobalt concentrate. A cobalt treatment works was constructed, including furnaces and a stone cooling-tower 80 feet high and 8 feet square. The hot solution was sprayed onto the furnace floor, the resulting acid vapour being condensed and recycled to the copper treatment works. The cobalt works and furnaces were stopped in1864. Up to that date, 357 tons of cobalt and nickel precipitae had been produced.
The copper ore contained unwanted arsenic. This was removed by boiling one part of the solution from the precipitation tanks with two parts of the solution from the leaching tanks, to produce a precipitate of arsenic acid and iron peroxide and an acid solution. By adding this to the leaching tanks the acid was recycled while the unwanted arsenic was deposited with the white sand, now leached of its copper. This arsenic impregnated sand was dug out and dumped. The largest sand dump covered 5 acres, was ca 30m high, and was estimated to cotain 1/4 million tons of waste. (1) |