Flotation of a Low-Grade Zinc Oxide Ore After Surface Modification at High Temperature

There are abundant low-grade zinc oxide ores in Yunnan Province, China, but it is extremely difficult to recover Zn and Pb from them using traditional technology. They are often stockpiled during the exploitation of sulfide ores and high-grade zinc oxide ores and become a kind of solid waste. In this study, a novel methodology using surface modification by sulfidation and reduction at high temperature followed by flotation is proposed. Several factors, such as the sulfur dosage, roasting temperature, coal powder dosage and holding time, that affect the flotation performance of the Zn concentrate were examined in detail, and the optimum process parameters were determined. A flotation concentrate containing 32.1% Zn and 8.0% Pb was obtained with zinc and lead recoveries of 91.3% and 92.3%, respectively. To further interpret the surface modification mechanism of smithsonite, the surface morphology and constituents of the sample before and after reaction were investigated by electron probe microanalysis and thermodynamic calculations. The results showed that zinc sulfide was generated at the outer layer of the zinc oxide mineral after thermal modification, resulting in an improvement of the flotation performance. The purpose of the present study is to apply the surface modification technology previously applied to pure smithsonite to low-grade zinc oxide ore or solid waste to convert them into valuable resources.