Effect of chelating agents on mobilization of metal from waste catalyst

DTPA and EDTA are synthetic chelating agents used in many industrial applications, because of their low biodegradability and strong complexing capacities. These chelating agents can transfer toxic heavy metals from solid to liquid phase. The mobilization of Ni from waste catalyst in the presence of two synthetic organic ligands (polycarboxylate, EDTA and DTPA) was investigated as a function of complexing agent concentration and reaction time to determine necessary equilibrium time and catalyst to liquid ratio. The concentration of chelate ranged from 0.2 M to 1 M and extraction of Ni increased dramatically with increasing chelate concentration. The precipitation of Ni was obtained as NiSO4. The recovery of Ni with EDTA and DTPA was 87% and 95%, respectively. This mobilization is the result of a competition between association with the solid phase and dissolved complexes. Coordination capacity with nickel and recovery in recycling of EDTA was observed slightly less compared to DTPA with same conditions. Extraction efficiency and reusability of both chelating agents are compared in the present study.