Analysis of conjugate heat and mass transfer during aerosol flotation of gold from placers
Authors:   North Caucasian Institute of Mining and Metallurgy (State Technological University), EVDOKIMOV Sergey , GERASIMENKO Tatyana ,   North Caucasian Institute of Mining and Metallurgy (State Technological University),   North Caucasian Institute of Mining and Metallurgy (State Technological University), MAKSIMOV Ruslan ,   North Caucasian Institute of Mining and Metallurgy (State Technological University)
Published: July 2022

Introduction. The probability of replenishing the SME of placer gold by registering the reserves of new deposits is low, and the involvement of man-made waste in the economic circulation will allow maintaining the achieved level of gold production from placers for 10-15 years. Purpose of research. The aim of the study is to develop a technology for extracting gold from old wastes of alluvial mining based on the identified patterns of conjugate heat and mass transfer during aerosol flotation of metallic gold. Methodology. For the development of technogenic wastes of alluvial gold mining, an enrichment module based on gravity and flotation methods has been developed. The module equipment has passed research tests in industrial conditions. During flotation, the increase in the gold content in the operation of the main flotation is carried out by mixing the crude concentrate isolated from ½ of the original feed with the other ½ of it. A mixture of air and hot steam was used as the gas phase during flotation. Research results and discussion. The temperature difference at the gas-liquid interface is the driving force of the vapor-liquid phase transition with the release of significant condensation heat. The time of particle sticking to the bubble is commensurate with the time of heating the interfacial surface due to the heat of vapor condensation. This allows us to consider temperature as one of the reasons for changing the result of flotation by a mixture of air and water vapor. Due to vapor condensation, the bubble size and the intensity of interfacial heat transfer decrease. When the minimum size is reached, overheating of the vapor in the bubble leads to an increase in the evaporation of the solvent and pressure in the gas phase: the heat transfer between the phases and the size of the bubble begin to increase. Transient processes in steam are non-polytropic and the limiting bubble sizes decrease with time: at the minimum size and maximum temperature, the heat transfer of steam is higher than the heat transfer of water with an increase in the size of the bubble and a drop in temperature in it. The limiting transitions of the bubble size are the cause of high-speed oscillations of the bubble walls, which decay with time. When the bubble surface is stretched in the three-phase contact zone, the gas-liquid surface tension increases due to a decrease in the density of the adsorption layer of surfactant molecules, which causes an increase in the force holding the hydrophobic extractable particle on the bubble surface. Radial tensile-compression deformations lead to shedding from the bubble surface of hydrophilic gangue minerals randomly retained by the bubble surface (for example, in the case of high occupation of the bubble surface by extracted particles). Conclusion. It is substantiated that the combined gravity-flotation technology is economically justified: the added value of marketable products provides an increase in the value of the net present value and the return on investment index, and a reduction in their payback period. It has been proven that the addition of gravity technology with flotation methods for extracting gold provides an increase in annual metal production by ~27% rel. due to the additional extraction of forms of gold that are “resistant” to gravitational methods.