Combined gravitation-flotation technology for technogenic gold placer concentration

Abstract

Gold recovery from placer washing waste was carried out using a flotation method where circulating rough concentrate is used to increase the recovered metal content in the rougher flotation operation. Moreover, flotation is carried out with a mixture of air with hot steam. Pressure in bubbles drops and their sizes decrease as a result of vapor condensation at the first moment of time under conditions of vapor-air flotation. Heat exchange between the phases worsens when the bubble is compressed, and mass transfer stops at the minimum bubble size, while temperature and vapor pressure in the bubble reach their maximum. As the bubble grows in size, superheated steam becomes saturated and pressure in the bubble decreases resulting in resumed condensation. The bubble surface undergoes damped oscillations. When the bubble surface vibrates, the motion of a slowly developing concentration-capillary Marangoni flow to the center of the interphase film cannot compensate for its thinning by the counter thermocapillary flow with a high hydrodynamic stability potential from the film center to its periphery. The vapor-air flotation results obtained can be interpreted in the context of this mechanism of wetting film stability changes during the vapor-liquid phase transition. Pilot tests of gravity and gravity-flotation technologies for gold extraction from a technogenic placer of gold have been carried out. It has been proved that the main effect of using the developed configuration of the scheme and the mode of flotation with a vapor-air mixture is a decrease in the concentrate yield by ~ 25% rel. while maintaining the achieved level of recovery and concentrate quality. When using the combined technology, the added value of marketable products provides an increase in the value of net discounted income and the return on investment index, and a decrease in their payback period.