Description:
The ever-increasing demand for ferrochrome alloys has resulted in a substantial accumulation of ferrochrome slag by-products in respective mining areas. On the other hand, the ferrochrome slag has been identified as one waste material that is rich in magnesium (Mg) and has not been effectively exploited. Beneficiating of ferrochrome slag waste material is envisaged as a means of achieving sustainable recovery of magnesium (Mg). Previous studies have used sulphuric acid as a lixiviant for leaching at low temperatures to recover Mg from ferrochrome slag. In this study, the recovery of Mg from ferrochrome slag was investigated using hydrochloric acid (HCl) as the lixiviant at low temperatures as various metal oxides have been proven to be more amenable to leaching using hydrochloric acid. The effects of acid concentration, leaching temperature, and reaction time on the recovery of Mg was investigated. Kinetic and thermodynamic analysis of the leaching process were also investigated as these are critical factors for maximum extraction of the Mg. The results showed that a significant amount of 88.2wt% Mg can be successfully recovered using 5 M HCl with a solid to liquid ratio of 1:10, mixing intensity of 250 rpm, reaction time and temperature of 150 minutes and 70 oC respectively. This is a substantial amount of Mg recovered that can be used directly as a magnesium source for struvite precipitation with out any further purification similar to utilizing raw sea water which has shown to improve the overall economics of the process. Kinetic analysis using the shrinking core model (SCM) was applied to determine the best fit of the experimental data. A linear relationship was obtained with the (correlation coefficients for the chemical reaction model (kc) > 0.9, indicating a good fit). The activation energy obtained for the diffusion and chemical reaction models were 10.44 and 41.45 kJ/mol, respectively, indicating that the chemical reaction step is the rate-limiting step