Environmental leaching behaviour of copper-nickel bearing Duluth gabbro and flotation tailings

Abstract

The leaching characteristics of copper-nickel bearing Duluth gabbro and flotation tailings in contact with water were studied in the laboratory through agitation leaching in shake flasks (up to 8 months) and percolation leaching in columns (up to 96 months). The influence of sulphur content and bacterial activity on acid generation and heavy metal ion release from the above materials was assessed and the acid buffering characteristics of typical flotation tailings were evaluated, along with those of constituent minerals such as olivine, plagioclase and biotite separated from the tailings. Duluth gabbro copper-nickel ores and flotation tailings exhibit good acid-neutralizing capacity and equilibrate with water at neutral or mildly alkaline pH levels. The presence of bacterial activity significantly increases acid production and metal ion release and there is a direct relationship between percent sulphur and the acid generation trend. External additions of calcite or mottled taconite tails to the gabbro and tailings reduce heavy metal ion release substantially and arrest acid generation efficiently.