Morphological Characteristics of Noble Metals in the Combustion Products of Coals from the Arkhara–Boguchan Deposit (Amur River Region)

Abstract

The chemical and physicochemical characteristics of brown coals from the Arkhara–Boguchan deposit were studied. These coals have increased ash content (to 18.7%) and high aluminum and silicon contents (to 30.5 and to 69.5%, respectively) and the main petrographic components—vitrinite (42%) and semivitrinite (46%). Separate combustion products (slag, fly ash, and sludge) were obtained by burning a bulk sample of 270 kg in the Amur Experimental Technological Complex. In the course of this study, the noble metals Au, Ag, and Pt, which were represented by two morphological types, were detected in all of these fractions. The first type of massive lumpy individuals, often with a noticeable treatment in an aqueous medium, was characterized by a high gold content (>80%), sizes from 2.0 × 1.6 to 115.0 × 160.0 μm, and the presence of impurity elements. According to their characteristics (fineness, composition of impurity elements, etc.), they largely reflected the mineral specialization of ore materials in source areas. The second form of the release of noble metals was loose agglomerates consisting of Au and Ag grains with various concentrations in a temperature range of 600–800°C. The ability to concentrate the grains of noble metals of various genetic natures allows one to consider this interval as the initial stage of gold preservation in fly ash from volatilization by a gas stream.