667 Korean J. Chem. Eng., 32(4), 667-676 (2015) DOI: 10.1007/s11814-014-0298-6 INVITED REVIEW PAPER pISSN: 0256-1115 eISSN: 1975-7220 INVITED REVIEW PAPER † To whom correspondence should be addressed. E-mail: panda.sandeep84@gmail.com Copyright by The Korean Institute of Chemical Engineers. Extraction of copper from copper slag: Mineralogical insights, physical beneficiation and bioleaching studies Sandeep Panda * , *** ,† , Srabani Mishra * , Danda Srinivas Rao ** , Nilotpala Pradhan * , Umaballava Mohapatra *** , Shivakumar Angadi ** , and Barada Kanta Mishra * *Department of Bioresources Engineering, CSIR-Institute of Minerals and Materials Technology (IMMT), Bhubaneswar-751013, Odisha, India **Department of Mineral Processing, CSIR-Institute of Minerals and Materials Technology (IMMT), Bhubaneswar-751013, Odisha, India ***North Orissa University (NOU), Baripada-757003, Odisha, India (Received 28 March 2014 • accepted 5 October 2014) Abstract-Copper slag was subjected to in-depth mineralogical characterization by integrated instrumental tech- niques and evaluated for the efficacy of physical beneficiation and mixed meso-acidophilic bioleaching tests towards recovery of copper. Point-to-point mineral chemistry of the copper slag is discussed in detail to give better insight into the association of copper in slag. Characterization studies of the representative sample revealed the presence of fayalite and magnetite along with metallic copper disseminated within the iron and silicate phases. Physical beneficiation of the feed slag (~0.6% Cu) in a 2 L working volume flotation cell using sodium isopropyl xanthate resulted in Cu beneficia- tion up to 2-4% and final recovery within 42-46%. On the other hand, a mixed meso-acidophilic bacterial consortium comprised of a group of iron and/or sulfur oxidizing bacteria resulted in enhanced recovery of Cu (~92-96%) from the slag sample. SEM characterization of the bioleached slag residue also showed massive coagulated texture with severe weathered structures. FE-SEM elemental mapping with EDS analysis indicated that the bioleached residues were devoid of copper. Keywords: Copper Slag, Characterization, Microscope, Physical Beneficiation, Bioleaching INTRODUCTION Metallurgical and mineral processing industries generate a huge amount of wastes in the form of fines, slimes, slag, sludge etc., thereby creating environmental problems with ecological imbalances. Over decades, the primary aim has been directed towards the develop- ment of a zero waste technology by the utilization of such by-prod- ucts or other industrial wastes. Simultaneous extraction of valuable metals by means of an ecofriendly technology is highly empha- sized to bring in additional revenues to the producing industries [1,2]. Industrial wastes such as blast furnace slag from steel plants and fly ash from thermal power plant have earned huge applicabil- ity as an additive in cement making [3]. Still, several other wastes from the steel industries like LD (Linz - Donawitz) slag, LD dust, flue dust, sludge, iron ore slimes and red mud from aluminum industries have gained a reputation for their numerous applications as a value-added product [4]. Transformation of such solid wastes from one form to another in view of its valorization either by the same production unit or by a different industrial installation has thus become very essential not only for conserving metal and min- eral resources but also for protecting the environment. Copper ore globally at an average contains ~1% copper and the rest being silica, alumina, calcium, iron and magnesium. The cost of production of copper is very high due to the involvement of com- plicated steps right from ore processing to metal production. Al- though, the entire crush-grind-float treatment process to recover metal value is cost effective, recovery of any additional metal val- ues from the generated wastes by a cost effective technique is highly desirable to earn additional revenue for the copper industry. One such material to be considered is the copper slag which is being produced during smelting and converting steps of copper matte production. It has been roughly estimated that for every ton of cop- per metal produced, about 2.2 tons of slag is generated causing sev- eral environmental and space/land (dumping) problems. The com- mon management options for copper slag are recycling, recover- ing of metal, production of value added products such as abrasive tools, roofing granules, cutting tools, abrasive, tiles, glass, road-base construction, railroad ballast, asphalt pavements [5] etc. One of the greatest potential applications for reusing copper slag is in cement and concrete production [3]. Some investigation on slag has indicated that an appreciable amount of Cu, Co, Ni can be recovered by hydrometallurgical and flota- tion techniques [6-9]. However, hydrometallurgical applications for recovery of metal values from slags are not encouraging. For example, high concentration acid leaching has shown problems of the formation of silica gel, which induces an increase of leach liquor viscosity, difficult pulp filtration and crud formation during solvent extraction [7]. Therefore, from an environmental and economical