Treatment of Telluride Gold Ores
An old treatment process to recover precious metals from telluride gold ores was developed by the Hungarian Anton Hauch. The gold ores evaluated by the Hauch reported tellurium, gold, silver, calcium carbonate, manganese sulphide and quartz as main gangue mineral. The objective was to produce tellurium by means of a cheap acid solution from which it could be easily separated. In defining this method, the manganese mineralogy was very important. A quantitative determination of the gold was 30 to 40% of quartz, 10 to 20% of calcium carbonate, 15 to 20% of carbonate and sulphide of manganese, 4 to 8% of galena, 1 to 2% of chalcopyrite, 5 to 9% of clay, 1 to 4% of sphalerite; and some cobalt, nickel, antimony, arsenic, and of course, tellurium, gold and silver.
When the ore was roasted, a portion of the tellurium was volatilized, carrying off some of gold and silver. This loss was minimized by condensation. During the oxidizing roasting manganese carbonate and part of the manganese sulphide were converted into manganese oxide. The manganese sulphide was influenced by the presence of lime. Under the addition of hydrochloric acid and its reaction with manganese oxide some chlorine was produced. It was found that during roasting a large portion of the gold became in metallic state in such way that 45 to 50% of the gold was extracted by amalgamation.
In treating the roasted ores with dilute hydrochloric acid in lead-lined wooden tubs provided with a stirring apparatus, a release of chlorine was produce. This condition helped to convert the metals to be obtained into a soluble state with the exception of silver. The excess of chlorine was conducted into tubs filled with water and this chlorine water was used as solvent for the tellurium sponge. After the solution was drawn off from the ore, the sulphuric acid was added and some gypsum and lead sulphate were precipitated. A further decantation of the solution from the precipitate was considered and a solution of iron sulphate was added to precipitate gold. The solution was filtered off and further treated with metallic zinc to precipitate tellurium as black sponge.
The tellurium sponge was washed with water acidulated with hydrochloric acid, filtered rapidly, dried and smelted without any further addition in a platinum crucible giving raw tellurium, which contained some lead, copper, nickel and antimony. If the tellurium sponge was first dissolved in chlorine water, then was treated for a considerable length of time with sulphuric acid, pure tellurium was obtained and was melted and casted. After the separation of the largest proportion of the gold and tellurium, the remainder was composed of silver chloride and part of the gold in a still soluble condition in the solid residue. In treating the damp residues with a solution of iron sulphate, the gold was converted without loss into a metallic state. From the residues, silver and gold were obtained by amalgamation, and when practicable, it was smelted down with lead.