Using of reactant obtained from mill scale in hydrometallurgical copper exraction

The production process in the foundry and rolling mills, which have an important place in the metallurgical industry, have a high temperature. During this process, mill scale occurs on the hot slab and billet surface because of high temperature and oxidized media. The mill scale that occuring on the slab and billets is seen as important metallurgical waste, however, it can not be evaluated economically with regard metal content. The evaluation of mill scale in the iron and steel sector is a common problem and for similar sectors in the world, so that it has become a topic of frequent focus on researchers. Copper production from sulphide ores and concentrates, to a large extent, have been accomplished by using pyrometallurgical techniques that consists thesmelting processes at high temperatures. Production of copper from chalcopyrite concentrate by pyrometallurgical methods occurs the basic steps which obtained matte exposes the converting process to get blister copper. As environmental sensitivity, the leaching of chalcopyrite concentrates has been considered for many years, alternatively. Nevertheless, chalcopyrite requires strong oxidants because it is an insoluble, covalent compound, like most sulphide minerals. During the pyrometallurgical processing, various types of slags are generated containing significant amounts valuable metal (average copper content 5 %). Slag containing valuable metals is generated during smelting and converting. After cooling-solidification, these two slags are crushed, ground and treated by flotation, and then feed to smelting furnace In this study, it was investigated that the mill scale containing iron was treatment with HCl as ferric chloride and this oxidizing solution was used for copper extraction from chalcopyrite concentrate and slag. The study was carried out in three stages. In the first stage studies, air and mechanical stirrer were used to iron dissolution from mill scale. In optimal conditions for first stage (leaching time=60 min, leaching temperature=105 °C, HCl cocentration= 7 M, solid-liquid ratio=1/10, mechanicallt stirring speed= 400 rpm, particle size of mill scale= -74 µm), 100 % Fe, Fe3+ concentration 55.05 and Fe3+/Fe2+ ratio 5.04 determined. In the second stage of the study, the solution obtained in the first stage was used as leach reagent in the extraction of chalcopyrite concentrate and copper from slag. Under optimum conditions (leaching time= 120 min, leaching temperature= 105 °C, solid-liquid ratio=1/25, stirring speed in magnetic stirrer= 400 rpm, and particle size of concantrate and slag= -74 µm), copper dissolution from chalcpyrite concentrate and slag was obtained as 95.04 % and 97.22 %, respectiely. In the third stage of the study, copper extraction was investigated from chalcopyirite concentrate and slag in presence of commercially available FeCl3 and HCl, and the results obtained were compared. When using solutions prepared taking into account the optimum conditions obtained in the first stage studies, copper dissolution from chalcopyrite and slag in presence of 7 M HCl was obtianed as 14 % and 84 %, respectively. However, in the leaching experiments with commercial FeCl3, it was found that the copper extraction from the concentrate and slag was 96.75 % and 96.13 %, respectively. In addition, chalcopyrite concentrate and slag severally were subjected to leaching process together with HCl + mill scale. In the experiments performed for the chalcopyrite concentrate, it was determined that 95.73 % of the copper was taken to the solution at optimum conditions and the total iron concentration was 83.41 g/l. On the other hand, copper recovery was determined as 78.66 % at optimum conditions obtained in experimental studies with copper production slag. In these conditions, the iron concentration in the solution is 66.18 g/l. As a result, it was revealed that the oxidation potential of the iron chloride solution that obtained from mill scale as using of leaching reactant in the extraction of copper from chalcopyrite concentrate and slag could be used sufficiently in the leaching process. Keywords: Chalcopyrite, Copper, Hydrometallurgy, Mill scale, Hydrochloric acid, Leaching, Metallurgical waste, Iron.