Recovery of chromium from ferronickel slag: A comparison of microwave roasting and conventional roasting strategies

A novel strategy for selective recovery of chromium from ferronickel slag via microwave assisted sodium peroxide roasting followed by water leaching was proposed in this study. The experimental results showed that 94.21% of chromium was leached with 64.43% of sodium and 6.13% of silicon, while only 0.06 wt% chromium remained in the leaching residue when the mixture of ferronickel slag and sodium peroxide with the mass ratio of 1 was roasted at 600 °C for 20 min before leaching at 50 °C for 1 h with the liquid-to-solid ratio of 10 mL/g. In comparison with conventional roasting, the microwave roasting showed a much higher efficiency for recovering chromium from ferronickel slag with the recovery of chromium increased by 12.92%, resulting from the enhanced conversion of Cr2O3 in the slag to NaCrO2 and from the looser and more porous structure during the roasting process which was beneficial for subsequent water leaching.