Extraction of Ni (II) from Spent Hydrodesulfurization HDS Catalyst Through Leaching and Electroless Precipitation of Ni(
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TRODUCTION
NICKEL is a valuable metal for mankind. The worldwide growing demand for nickel is increasing due to an increase in consumption of steel, which led to the dependence upon extraction of this metal from lowgrade ores. To manage the resources, metals from different wastes and residues should also be recycled back. In recent years, the literature on nickel extraction has explored the extraction of nickel from low-grade laterite ores,[1–3] spent catalysts,[1,4] spent batteries,[5,6] and slags.[7] There are various modes of extractions such as leaching through sulfuric acid,[8] hydrochloric acid,[4] oxidative leaching, boleaching,[3,9–11] selective leaching,[12,13] influence of additives on leaching[14] (including heat treatment prior to leaching),[15,16] and some of them involve sulfonation roasting.[17–19] New concepts on extractions may include overall green technology[20] and microwave techniques.[21] The leach liquor can go for metal production, production of salts of nickel as oxide, or hydroxide. Nickel hydroxide is in high demand due to its application as an electrode material for batteries. The use of NiMH batteries is century old process. NiMH batteries are very robust kind of batteries, i.e., resistant of misuses like overcharging, overdischarging, short circuiting, etc. It can be precipitated either electrochemically[22,23] or chemically.[24,25] Studies on the effect of additives on the preparation of electrochemical[26] and chemical SANGITA R. PRADHAN, Ph.D. Student, BARSHA DASH, Scientist, KALI SANJAY, Principal Scientist, and T.SUBBAIAH, Chief Scientist, are with the CSIR-Institute of Minerals and Materials Technology, Bhubaneswar 751 013, India. Contact e-mail: barsha. [email protected] Manuscript submitted July 12, 2012. Article published online January 12, 2013. METALLURGICAL AND MATERIALS TRANSACTIONS B
Ni(OH)2[27,28] show the improvement in the discharge capacities. Many studies were reported on precipitation of the impurities of the liquor and subsequent precipitation of pure nickel hydroxide[29] or selective precipitation from mixed Ni and Co solutions.[30] In this process, efforts were made to extract Ni from a spent hydrodesulfurization catalyst through sulfuric acid leaching and precipitate nickel hydroxide suitable for battery industries in conventional hydrometallurgical route. The reason for preferring sulfuric acid over other acids is that sulfuric acid is the most common acid for leaching due to the following advantages: (1) high solubility of metals, (2) low price, (3) down processes like solvent extraction/electrotwinning are established in sulfate media, (4) regeneration of acid after leaching, and (5) negligible fuming problem. Nickel hydroxide was precipitated in three different precipitation methods to get maximum discharge capacity. First one is neutralization precipitation. Second one is the neutralization followed by aging as aging promotes the process of agglomeration. The third one is the use of surfactant in the neutralization precipitation system. Surfactants when used inhibi
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