Abstract:
The alkali-fusion method was carried out by reacting chromite concentrate with molten sodium hydroxide under oxidizing conditions to form sodium chromate. The fusion product was leached with methanol to remove the unreacted NaOH and then leached with water to obtain chromate solution. The effect of parameters such as fusion temperature (550, 600 and 650degreesC), fusion time (20, 40, 60 and 90 min) and the weight ratio of NaOH to Cr2O3 in the chromite on alkali fusion was investigated. In both methanol and water leaching steps, the parameters were solid/liquid (s/l) ratio (1/2, 1/3, 1/4 and 1/5), leaching time (10, 20 and 30 min) and temperature (25, 35 and 50degreesC for methanol leaching, 25 and 50degreesC for water leaching). The highest extraction efficiency (96.2%) of chromium in the chromite was obtained at 650degreesC and a fusion time of 60 min. The weight ratio of NaOH to Cr2O3 in chromite was 6/1. In methanol leaching, 82.6% of the unreacted NaOH was recovered at 50degreesC, a leaching time of 60 min and 1/4 of s/l ratio. The kinetics of alkali fusion was also studied and the resuits showed that the reaction was chemically controlled and activation energy was 94.6 kJ/mol.
