Abstract
Copper slags produced in vast quantities in smelting operations could be considered as secondary material sources instead of stockpiling them in landfills. This study investigates the recovery of valuable metals from copper slag and the valorisation of the leach residue as construction material in line with the principles of a circular economy. By taking into account that the environmental characterization of the as-received copper slag did not allow its disposal in landfills without prior treatment, chemical and biological leaching were tested for the recovery of metals. Pre-treatment with acids, namely HNO3 and H2SO4, resulted in the extraction of several target metals and the production of an almost inert waste. Despite the clearly better oxidative conditions prevailing in the bioleaching reactors, chemical leaching resulted in the higher dissolution of Cu (71% vs. 51%), Co (70% vs. 36%), and Zn (65% vs. 44%). The acid consumption was much lower during the bioleaching experiments compared to the chemical leaching. The bioleach residue was suitable for its use as supplementary cementitious material, showing a better performance than the reference sample without causing any detrimental effects to the calcium aluminate cement (CAC) quality. The complete valorisation of copper slags is expected to improve the economics of the process, by avoiding landfill costs and producing saleable products with high added value.
Highlights
In smelting, copper-rich matte containing sulphides and copper slag as by-product are formed [1].For every ton of copper produced during smelting and refining operations, approximately 2.2–3 tons of fayalite slag is produced and the management of these significant quantities is difficult [2,3].Copper slags contain high amounts of iron, silicon, and aluminium oxides, while the main mineralogical phases are fayalite and magnetite [4]
The aim of this study is to evaluate the environmental characteristics of a copper slag, define the degree of dissolution of metals during chemical and biological leaching, and investigate the potential use of the bioleach residue as Supplementary cementitious materials (SCMs) in order to valorise the whole material value chain following the principles of a circular economy
The detailed environmental characterization of the as-received copper slag indicated that the slag (a) cannot be characterized as toxic according to the TCLP test; (b) based on the EN 12457-3 results, the slag cannot be disposed of in landfills unless prior treatment is carried out; and (c) based on the NEN test results, only three elements, namely Cu, Zn, and Pb, showed noticeable solubilisation
Summary
Copper-rich matte containing sulphides and copper slag as by-product are formed [1].For every ton of copper produced during smelting and refining operations, approximately 2.2–3 tons of fayalite slag is produced and the management of these significant quantities is difficult [2,3].Copper slags contain high amounts of iron, silicon, and aluminium oxides, while the main mineralogical phases are fayalite and magnetite [4]. Copper-rich matte containing sulphides and copper slag as by-product are formed [1]. For every ton of copper produced during smelting and refining operations, approximately 2.2–3 tons of fayalite slag is produced and the management of these significant quantities is difficult [2,3]. Copper slags contain high amounts of iron, silicon, and aluminium oxides, while the main mineralogical phases are fayalite and magnetite [4]. Copper and zinc occur as impurities in silicates, while sulphides and the intermetallic phases occur as minor components containing metals in high concentrations [5]. A significant portion of the produced slag is stockpiled [1], an option that may result in environmental and space challenges [2]. It is necessary to carry out a complete environmental
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