Effect of waters containing complex cyanides and their treatment in Baia de Aries mountains mining area, Romania

摘要

The cyanidation of gold ore concentrates with diluted alkali solutions at E. M. Baia de Aries, in the presence of oxygen, provides the solubilisation of gold, silver as well as of other metals (copper, zinc, iron, nickel, cobalt etc.) forming both soluble cyanide salts (NaCN, Ca(CN)_2, KCN) and complex cyanides (Na_xMe(CN)_y where Me chemical bounds Cu, Zn, Ag, Fe, Au). Some of these cyanides are found in the wastewaters discharged in the tailings dam after the precious metals recovery. These waters are presently treated with sodium hypochlorite and overflows in Aries river, which is top water source of Turda town. The cyanide content of the treated water randomly exceeds the accepted limit from the legislation in force and this is due to the complex cyanides with high stability in aqueous medium. Because of some disadvantages of this method (such as: high consumption of sodium bypochlorite, and chloride and sodium contamination), other methods were tested too: chemical methods (precipitation or oxidation using different chemical reaents: FeSO_4, FeCl_3, H_2SO_4, H_2O_2), physical and chemical methods (activated carbon adsorption, retention on the volcanic tuffs, ion exchange, reversible, electrodialysis).