Kinetics of chromium extraction as sodium chromate from stainless steel dust

Abstract

Stainless steel dust contains chromium is hazardous in nature. It is not suitable to throw in the environment without processing. Chromium recovery from this waste is not only beneficial than mined ore but also to reduce unwanted chromium in the environment. Chromium at high temperature is attacked by sodium carbonate by forming sodium chromate. With this in view soda ash roasting followed by water leaching of stainless steel dust is an important step to recover chromium. The roasting of the stainless steel dust with soda has been carried out in the temperature range of 600–900°C. It was found that at 800°C in 90 minute, maximum 95% of chromium can be recovered as sodium chromate. The mode of conversion was investigated by studying the kinetics of the process. Based on experimental data the kinetics model gave the best fit showed the applicability of topochemical reaction. Kinetic data also indicated that the sodium chromate formation occurred on the surface of the Cr2O3 particles and proceeded through reactant and product phase boundary. Activation energy of 39 kJ/mole was acquired to proceed the reaction under the temperature range studied. XRD phase identification and SEM-EDS studies confirmed the experimental observation and mode of conversion from chromium oxide to sodium chromate formation.