Formation of copper matte from copper slag using gypsum from hydrometallurgical plants

As primary resources become more and more complex in their chemical composition and some places poor in their valuable metals in the ore secondary sources like slag phases from the production processes get in the focus of the metal industry. Currently about 70 % of copper slag remains is ineffectively utilized. Hence the need of their treatment and attend to ecological environment problems that they might cause. The current study focuses on the recovery of copper from copper slag by using gypsum formed during impurities removal in hydrometallurgical plants. The fayalitic slag was provided by Gecamines in the DR Congo and the gypsum from the small scale hydrometallurgical plant in Lubumbashi in the Democratic Republic of Congo. The gypsum played a double role of sulphur provider and flux. The aimed basicity of the slag through the addition of gypsum was 1. XRF, XRD were used to characterize gypsum whereas the slag and the subsequent products analysed with XRD, XRF and SEM. The working temperature was set at 1400 °C for two hours with CO blown at 0.2 l/min in the furnace to allow copper to be freed from other oxides and form a sulfide. Graphite crucible was used in an alumina tube furnace. Coke was added to limit crucible reaction. The heating rate was 7 °C/ min. Results confirmed the presence of covellite and FeS stating matte effectively formed while anorthite was present in the slag confirming the influence of the CaO added through gypsum on the final slag produced.