Separation of Ni and Co by D2EHPA in the Presence of Citrate Ion
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TRODUCTION
DUE to the ceaseless exploitation of Ni/Co primary resources, the recycling of secondary resources for extraction of their metallic contents is undoubtedly environmentally friendly and can be economical. Ni and Co have special properties and important applications.[1–3] One of the most important secondary resources of Ni/ Co is electronic wastes (E-wastes), which has been widely produced as the discarded electrical/electronic devices. The perfunctory processing of E-wastes not only results in an increase in human health risks and environmental pollution but also results in the loss of their valuable metallic contents. Apart from the large amounts of lead and copper, small amounts of nickel, cadmium, cobalt, and manganese can be found in such wastes.[4–8] The first step of a hydrometallurgical process for the pre-treated E-wastes (mechanical pretreatments such as shredding/grinding[9,10] and thermal pretreatments[10]) is the implementation of the leaching process. The pregnant leaching liquors (PLS) contain a variety of metallic ions depending on the type of E-waste.
HAMED NADIMI, DAVOUD HAGHSHENAS FATMEHSARI, and SADEGH FIROOZI are with the Department of Mining and Metallurgical Engineering, Amirkabir University of Technology, P.O. Box 15875-4413, Tehran, Iran. Contact e-mail: s.fi[email protected] Manuscript submitted January 1, 2017.
METALLURGICAL AND MATERIALS TRANSACTIONS B
The next step of the hydrometallurgical metal production process is the solution purification/concentration. Among different solution purification/concentration methods—including chemical precipitation, cementation and ion exchange—solvent extraction is the most effective techniques especially when other methods are not able to separate the elements. D2EHPA, a cheap and stable phosphoric acid extractant, can extract many metallic cations from various chloride,[11–14] nitric,[15,16] and sulfate[17–19] solutions. Haghshenas et al.[20]showed that Zn, Cd, and Cu can be effectively separated by D2EHPA from sulfate solutions; however, D2EHPA is an inefficient organic extractant for the separation of Co and Ni. An effective method for a successful separation of Co and Ni is the use of a synergistic solvent extraction system; i.e., a mixture of extractants can effectively improve the separation of Co and Ni; this strategy has been employed by many researchers.[21–24] A subtle approach for the effective separation of Co and Ni is the ‘‘conditioning of the aqueous phase’’ which results in different affinity of Co and Ni towards an extractant. A survey of the literature indicates that carboxylate groups affects metal absorption mechanisms in a solvent extraction system.[25–27] For instance, Nadimi et al.[28] showed that the difference between pH0.5 (the pH value that corresponds to 50 pct extraction of metallic ion) of Co and Ni reaches a value of 0.9 by the addition of 0.3 M tartrate ion. Considering the inexpensiveness and availability of D2EHPA together with its poor Co–Ni separation efficiency, this paper reports recent results obtained
from an extensive
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