Abstract:
Proton magnetic resonance (1H NMR) was used to study synthetic gold-bearing and gold-free iron sulfides, hydrotroilite and pyrite prepared by reacting iron(III) oxide with hydrogen sulfide in a neutral aqueous solution. Two types of protons were discovered in the sulfide precipitates: (1) structurally localized, chemically bonded protons as OH- or HS- groups (a broad spectral component) and (2) protons involved in electroneutral water molecules that had been captured during the synthesis (a narrow spectral component). The absolute and relative amounts of these types of protons in solid phases produced under various synthetic conditions are estimated. A negative correlation was established between the gold abundance and the total of type 1 hydrogen-containing groups in the precipitates. Based on these data, it was suggested that gold was accommodated in the solid phase in a chemically bonded form. The leading role of hydrotroilite in gold concentration by the iron sulfides in question was demonstrated. Hydrotroilite is formed as an autonomous phase when the synthesis temperatures is less than 100°C or as a surface water-containing layer on pyrite forming from 100 to 300°C.