COMPARATIVE STUDY OF PERFORMANCE OF DIFFERENT CHELATING AGENTS FOR EXTRACTION OF NI FROM SPENT CATALYST

摘要

The mobilization of heavy metals from spent catalyst is of the essence due to increasing demand of complex metallic composites in industries and to reduce the metallic waste. Present study involves the development of environmental friendly methodology for extraction of nickel from spent catalyst of fertilizer industry by adopting the chelating agents. The concept of chelation explored here to bind metal from spent catalyst and subsequently to be de-chelated by acid addition to extract metal. All chelation experiments were conducted in atmospheric reflux conditions and process parameters (reaction time, molar concentration of solvent, solid-liquid ratio of reacting mixture, pH, reaction temperature, particle size) were optimized in order to maximize the metal extraction. Three different chelating agents (EDTA, DTPA, and NTA) were employed for extraction of Ni. EDTA has been used earlier in the literature for Ni extraction with solid to liquid ratio 1:50. To reduce the S:L ratio, experiments were conducted with S/L 1:20 and very less increment were seen with increasing S/L. It was also observed that at optimized reaction conditions, DTPA showed the highest (84%) Ni extraction among all three chelating agents. Recovery of DTPA was not more than 40% at atmospheric condition, while at refrigeration condition, DTPA recovery was improved and reached upto 80-86%. Recovery of EDTA solid (93%-97%) was highest among these chelating agents. Comparative evaluation of various chelating agents on the basis of extraction efficiencies concluded that complexing ability of DTPA is slightly higher than EDTA but poor biodegradability and less recovery of DTPA makes this chelating agent less feasible to use. NTA showed its maximum 65% Ni extraction. Less extraction of Ni using NTA is due to its quadridentate structure which causes lesser stability of Ni-NTA complex. Characterization of spent catalyst and chelating agents was performed to understand the structural and phyisco-chemical properties.