Solvent extraction recovery and separation of cadmium and copper from sulphate solution Ehsan Bidari a, *, Mehdi Irannejad a , Mahdi Gharabaghi b a Department of Mining & Metallurgical Engineering, Amirkabir University of Technology, Tehran, Iran b School of Mining Engineering, College of Engineering, University of Tehran, Iran Introduction Elimination of heavy metals from industrial wastes at the point of environmental aspects was always important. Furthermore there is an attitude toward the recovery of precious metals from low-grade or complex ores, secondary resources and industrial wastes because of the reduction of world’s high grade resources and metals high prices. Generally, hydrometallurgical route (leaching–solvent extrac- tion–electro winning) is found suitable to process lower grade ores, wastes such as slag, tailings and recycled solutions [1]. Solvent extraction is now a very well-established process in hydrometal- lurgy. It is used for the hydrometallurgical processing of copper, nickel, cobalt, zinc, uranium, molybdenum, tungsten, vanadium, rare earths, zirconium, hafnium, niobium, tantalum, indium, gallium, germanium, the platinum group metals, boron, reproces- sing nuclear fuels, purification of wet process phosphoric acid, nitric acid recovery, etc. [2]. In this study recovery and separation of cadmium and copper were considered. Cadmium and its compounds are toxic and poisoning occurs through inhalation and ingestion. In spite of its toxicity, it is used in different industries such as electroplating, pigments, synthetic chemicals, ceramics, metallurgical and photo- graphic products, electronics and other industries [3]. Cadmium is extracted from the by-products of zinc metallurgy among which copper–cadmium slag, cadmium–rich dust and also from the spent Ni-Cd batteries. Pure cadmium can be recovered through solvent extraction, electrolysis refining or vacuum distillation [4]. Among the available processing alternatives, solvent extraction is a technique that not only meets the strict environmental regulations but also high purity value added products could be produced. Acidic extractants, including carboxylic acids, dialkyl phosphoric and dialkyl phosphinic acids, can be used to extract cadmium (II). The extraction of cadmium (II) is selective in the presence of Zn(II), Ni(II), Co(II), Mn(II), Fe(II), Ca(II) and Mg(II) with DpH 0.5 (Me/Cd) = 1.5 where Me = Zn (II), and not less than 2.5 for the remainder of these cations. However, copper (II) and lead (II) can be co-extracted [5]. Different kinds of extractant were used to extract cadmium from aqueous solution and a comprehensive literature about them are available [3,6]. Among phosphoric acids, (Di(2-ethylhexyl)) phosphoric acids (D2EHPA) which is successfully used as cadmium extractant in several industrial and experimental works, is used in this study and the extraction mechanism of the metal ion (in this case cadmium) with D2EHPA which is diluted in kerosene may be expressed as follows [7]: M nþ þ n þ p 2 ðH 2 A 2 Þ org @ ðMA n ðHAÞ p Þ org þ nH þ (1) where (H 2 A 2 ) is extractant in dimeric form, M is metal, n is valence of the metal or metal complex ion and (n + p) number of molecules of extractant engaged in reaction. Working with concentrations Journal of Environmental Chemical Engineering 1 (2013) 1269–1274 ARTICLE INFO Article history: Received 12 July 2013 Accepted 19 September 2013 Keywords: Solvent extraction Copper Cadmium Phosphoric acid Oxime ABSTRACT In this study solvent extraction process has been used for separation of cadmium and copper from sulphate solution. A phosphoric acid extractant (D2EHPA) and an oxime extractant (MEX) in kerosene diluent were used as cadmium and copper extractants, respectively. The results showed that 1 g/L cadmium could be extracted by 30–35% (v/v) D2EHPA at the pH of 3.5–4. Cadmium separation factor over copper with D2EHPA was calculated 4.04 in best condition of pH (=2). On the other hand 3% MEX separated 1 g/L copper over cadmium optimally at the pH of 3.5 and under this condition of pH, copper separation factor is calculated 4495.5. Loading capacity studies showed that copper existence in cadmium aqueous solution reduces cadmium extraction with D2EHPA up to 10% whilst copper extraction percentage with MEX does not vary considerably in the presence of cadmium. ß 2013 Elsevier Ltd. All rights reserved. * Corresponding author. Tel.: +98 914 8224306. E-mail address: e.bidari@aut.ac.ir (E. Bidari). Contents lists available at ScienceDirect Journal of Environmental Chemical Engineering journal homepage: www.elsevier.com/locate/jece 2213-3437/$ – see front matter ß 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jece.2013.09.016