Slag Cleaning Processes: A Growing Concern

In the last two decades copper metallurgy has faced tough challenges to comply with environmental regulations and falling copper prices. Although in the last months copper price has increased, still the environmental issue and operation related costs remain and as long as foreseen they will continue to do so. To reduce emissions to the atmosphere and to shorten the converting cycle, most industrial processes, as well as emerging ones, are aiming at production of high matte grade. However, the increase in oxygen potential required by these processes results in highly oxidised slags with significant copper contents, which require their treatment for copper recovery. Despite the fact that long established slag cleaning processes perform reasonaby well for slags in the range 1.5% - 2.5% in copper, i.e. coexisting matte in the order 60% in copper content, they must be reconsidered when applying to slags equilibrating with high matte grades and/or white metal. The present study concentrates on the mechanism of copper losses into slags, its association to sulfur and oxygen, mainly, and methods for its recovery. Based on these considerations, high temperature liquid-liquid phase separation, i.e. Teniente type reactor, slag flotation and slag leaching methods technologies are discussed as specially applied in Chilean smelters. Also, a new approach based on material characteristics of both matte and slag, i.e. magnetic separation, is presented.