Recovery and Characterization of Nickel Oxalate and Oxide Obtained from Spent Methanation Catalysts
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INTRODUCTION
METHANATION catalysts are used in ammonia production plants for the conversion of carbon oxides (CO and CO2) and H2 to CH4 in the methanation reactor. Most of these commercial catalysts consist of 20-35 pct NiO, dispersed in refractory support materials like Al2O3/SiO2 and promoted with Fe2O3/TiO2. During the process, large quantities (in tons) of catalysts are discharged as waste and accumulated after periodical use due to increase in pressure drop/sintering and decrease in activity with time.[1] The accumulation of spent catalysts causes severe pollution problems and it is estimated that more than 150000-170000 t/year of spent catalyst discharged as waste worldwide.[2,3] From the literature, it may be seen that spent catalysts are an alternative secondary source for nickel extraction. Many researchers have reported hydrometallurgical extraction of nickel from spent catalysts employing different leaching/precipitating methods. As the method of extraction varies with the composition of the materials, therefore, it gives further scope for investigation in this field.
NAGA RAJU BATTI is with the Department of QC & SSP Audit, Projects & Development India Limited, PDIL Bhawan, A-14, Sector-1, Gautam Buddh Nagar, Noida, UP, 201301, India. Contact e-mail: [email protected] N.R. MANDRE is with the Department of Fuel, Minerals and Metallurgical Engineering, Indian Institute of Technology (Indian School of Mines), Dhanbad, Jharkhand, 826004, India. Manuscript submitted December 4, 2019.
METALLURGICAL AND MATERIALS TRANSACTIONS B
Abdel-Aal and Rashad studied nickel leaching kinetics on spent nickel catalysts (Al2O3-NiO) with 50 pct H2SO4 at 358 K extracted 94 pct NiO.[4] Lee et al. recovered 98 pct NiO with 100 pct purity by the precipitation and separation of Al with Na2CO3 solution at pH ~ 5.4 from a sulphuric acid-leached solution of spent nickel catalysts (NiO-Al2O3).[5] Sheik et al. investigated leaching kinetics on spent nickel catalysts (Al2O3-NiO) and indicated the extraction of 97.5 pct of NiO with HNO3 (5.0 mol/L) at 353 K.[6] Valverde et al. studied on the isolation of elements through precipitation and solvent extraction from H2SO4 leached solution of spent catalysts (CoMo and Al2O3/NiMo) at 363 K.[7] Nazemi and Rashchi reported 99.5 pct of Ni recovery from H2SO4 leached solution of spent catalysts (Al2O3/ NiO); in this process, Ni was precipitated directly with NH3.[8] Patnaik et al. recovered Ni as nickel hydroxide from H2SO4 leached solution of spent nickel catalysts (Al2O3-NiO-SiO2); in this method, the precipitation and separation of Al were achieved with NaOH solution at different pH values.[9] In a study carried by Vuyyuru et al., Chauhan et al., Goel et al., and Oza et al. shown that more than 95 pct nickel recovery as nickel salt (NiSO4 or NiNO3) from spent nickel catalysts by leaching with EDTA.[2,10–12] Sahu et al. reported 88.2 pct and 90.1 pct Ni by selective precipitation with Na2S and (NH4)2(C2O4) and separation of iron at pH > 3.5 from the H2SO4 leached solution of spent nickel c
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