������� In February 2000, a large amount of cyanide flooded out from a Romanian gold mine.�� Tonnes of fishes were killed and ecological balance of the Tisza River in Romania and Hungary has been devastated.
Cyanide and Gold Refining
������� Cyanide kills organisms by blocking the breathing mechanism in the mitochondria of cells.� As a result, no oxygen can be taken in and the organisms will suffocate.�
������� The cyanide is used to purify gold extracted from the ore.� Gold reacts with an areated solution of potassium cyanide to form a complex salt, potassium gold cyanide, KAu(CN)2.� Pure gold is then obtained by electrolysis of this salt.
������� 4 Au + 8CN- + O2 + 2 H2O � 4 Au(CN)2- + 4OH-
������� One method of removing the toxic cyanide ions from the effluent is by reacting with chlorine.� Concentrated sodium chloride solution can be added to the solution containing the cyanides.� The solution is then electrolyzed, chlorine generated at the anode reacts with cyanide ions to form harmless substances.
������� Aqua Regia is a mixture consisting of
3 parts of concentrated hydrochloric acid (HCl) and
1 part of concentrated nitric acid (HNO3).�
Its name, aqua regia, which is Latin for "royal water".� It was well known to the alchemists for its power to dissolve gold.� When gold is added to aqua regia, yellow crystals of the acid hydrogen tetrachloroaurate(III), HAuCl4, are produced.