Gold and rare earth elements in enrichment products from the technogenic wastes of the Caspian Mining-Metallurgical Plant (Aktau, Kazakhstan)

The paper presents the outcome of a comprehensive study at macro- to nanoscale levels of enrichment products from technogenic wastes. The products were obtained thanks to the experience of gravity enrichment during the treatment and preparation of the gold and REE sample material with preliminary mechanical and thermal activation. Thermal activation was applied for the first time. Native gold was identified in the form of single, micron-sized grains and, according to technological testing of enrichment products, there is a predominance of "invisible" dispersed gold. The gold content in the initial material was 2.93 g/t, which upon thermal activation of the sample increased to 6.37 g/t. According to the spectral analysis and electron probe microanalysis, the products of all enrichment stages are characterized by an increased content of yttrium and REEs. The REEs occurrence forms were determined. REEs are mainly found in micro- and nano-sized fluorine and fluorine-free phosphates (in apatite, by substitution of calcium), in REE-phosphates (in xenotime), and less often, possibly, in complex sulfo-phosphates and phosphate silicates. In thermal products consisting of inhomogeneous aggregates of nanosized phases, according to X-ray phase analysis, considering the elemental composition, REEs are included in the composition of phosphates: florensite and phases Ce(P5O14), Ca8MgSm(PO4)7.