North Caucasian Mining and Metallurgical Institute (State Technological University), Vladikavkaz, Republic of North Ossetia-Alania:

S. I. Evdokimov, Associate Professor, Chair of mining, Candidate of Technical Sciences, e-mail: eva-ser@mail.ru
T. E. Gerasimenko, Head of the Intellectual Property Chair, Candidate of Technical Sciences, e-mail: gerasimenko_74@mail.ru

Large-scale development of technogenic resources with low recoverable value is constrained by the lack of technologies that ensure their break-even development. Most of the gold from dumps can be extracted using the least costly gravity methods. In the pilot industrial processing of this raw material, screw separators were used in the main metal concentration operation. The finishing of their heavy fractions was carried out on concentration tables. With the light fraction of gravitational apparatus, 28.7% of the gold was lost. The light fraction material (with gold in the form of thin leaves and scales) has a low contrast in density. Gold of hard-to-recover morphotype was isolated from light fractions of gravitational apparatus by flotation. It was found that with an increase in the content of gold in the feedstock, its recovery into concentrate by flotation increases. In the practice of flotation, the required increase in the metal content in the separation operation is achieved through the turnover of middlings. However, in this case, the gold content of the resulting mixture increases and the separability decreases. This result is due to the fact that grains with reduced flotation properties are returned with the middlings. During flotation, the rough concentrate separated from 1/2 part of the initial feed is mixed with another 1/2 part of the initial feed. As a result, in the main flotation operation, the metal content and the ability of the material to be separated by flotation increase. In this case, the pulp is aerated with a mixture of air with hot steam. Condensation of steam in bubbles is the reason for the increase in completeness of gold recovery and selectivity of the flotation process. The technological efficiency of the developed technology has been proven by the results of its pilot tests. The assessment of economic efficiency was carried out by extraction of metal from the waste of alluvial gold mining and by the amount of capital costs and operating costs associated with its production. When processing man-made raw materials with a low gold content and switching from gravity to gravity-flotation technology due to the profit from additionally obtained gold, the payback period for the discounted cash flow decreases by one year, the value of the net discounted income increases by more than an order of magnitude, and the profitability index by 12.5% (rel.), EBITDA margin — from 31.4 to 42.5%.

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