Extraction of Copper from a Low-Grade Ore by Rhamnolipids

Abstract

Mining residues, in general and metal ores, in particular, contain heavy metals within the rock. These heavy metals, including copper (Cu) for which there is an increasing demand around the world, are very harmful to humans and, as such, are a serious problem for the environment. In this study, a rhamnolipid biosurfactant was used to extract copper from an oxide residue with 8,950 mg copper per kg ore. To optimize the conditions for maximum extraction, several batch tests were performed on washed ore samples at 25°C. The best ore particle size for optimal extraction was determined to be between 0.15 and 0.3 mm while the optimal pH of the washing solution was 6. A minimum volume of 10 mL rhamnolipid of 2% concentration for 1 g of ore was required to extract about 28% of copper from the ore. Adding 1% NaOH to the biosurfactant solution dramatically improved the copper extraction from the residue up to 42% in 6 days. Unwashed samples of mixed size particles were tested under the optimized conditions and 24% of copper was extracted. A sequential extraction procedure on the residues was performed to determine the forms of copper in the ore. Although the oxide and hydroxide, residual, and carbonates are the main forms, copper was extracted mainly by the biosurfactant from the oxide and hydroxide portions.