Some Aspects of Substoichiometry with Special Reference to Gold

Abstract

The object of this research was to investigate the applicability of "Substoichiometry" to the development of very simple, selective radio-chemical methods for the determination of trace concentrations of gold in matrices that were considered to be of industrial significance, Neutron activation (N.A.A.), and radio-active isotope—dilution analysis (I.D.A.) methods based on the solvent extraction of gold diethyldithiocarbamate from acidic solution using a substoichiometric amount of the copper (II) or zinc (II) salt of diethyldithiocarbamic acid in chloroform have been developed. The procedures have been applied to the determination of gold in high purity lead, the rockWl, and kale (N.A.A.), gold-bearing ores (I.D.A.), and gold—doped semi-conductor grade silicon (N.A.A. and I.D.A.). Amounts of gold down to 2 x 10-10g (N.A.A.), and 5 x 10-7g/20m1 of solution (1.D.A.) were determined. The composition of the gold diethyldithiocarbamate extracted into chloroform was found to be dependent on the experimental conditions of the extraction. From acidic solution with substoichiometric conditions (i.e. an excess of gold), a gold chelate of molar ratio gold to chlorine to diethyldithiocarbamate of 1:2:1 was extracted, and in the presence of a reductant, (ascorbic acid), as used in the I.D.A. method, a univalent gold diethyldithiocarbamate irrespective of whether an excess of gold, or chelating agent was used in the extraction. However in the presence of an excess of chelating agent, but in the absence of a reductant, a series of gold chelates of molar ratio gold to diethyldithiocarbamate of 1:2 was found to be formed; the distribution ratio of the gold between the chloroform and aqueous phase being dependent on the hydrogen, and chloride ion concentrations of the latter phase. Preliminary studies of the reaction of gold with dithizone in chloroform also revealed the existence of a series of gold dithizonates, the composition of which were dependent upon the experimental conditions.