Extraction of nickel from spent catalyst using fresh and recovered EDTA

This study investigates the possibility of recovering nickel from spent catalyst (NiO/Al2O3) used in the fertilizer industry. EDTA (ethylenediaminetetraaceticacid) di sodium salt was used as a chelating to extract the Ni after which sulfuric acid was added to obtain NiSO4. The dechelation process takes 5-6 h to break the complex and EDTA which was recovered as H4EDTA acid in the solid form and solution contains NiSO4. The objective was to evaluate the nickel removal efficiency of EDTA and reusability of recovered EDTA. The parameters affecting nickel recovery were EDTA concentration, time of chelation, catalyst to liquid ratio (s:l), mixing speed, pH and catalyst particle size. The extraction was up to 95% under the following conditions: 0.8 M concentration of EDTA, solid to liquid ratio 1:50 (g/ml), particle size 100 μm, pH 10, 10 h of chelation time, 700 rpm and 100 °C. Up to 95% of the EDTA could be recovered without losing significant activity.