The ferrous oxalate from iron removal process of ferrochrome acid leaching solution was treated by oxygen oxidation and ammonia leaching for recovery of oxalate and preparation of iron oxide black pigment. The effects of ammonia amount, reaction temperature, ratio of liquid to solid, reaction time, oxygen flow rate, solution pH value and crystallization temperature on the leaching rate of C2O42- and the performance of iron oxide black were studied. The optimal conditions were obtained as follows: crystallization temperature 60℃, reaction temperature 80℃, 3 times theoretical amount of ammonia, ratio of liquid to solid 5 mL/g, oxygen flow rate 0.1 L/min, pH value 6.9~7.4, and reaction time 3 h. Under the optimal conditions, the leaching rate of C2O42- was almost 100%, and the iron oxide black had excellent pigment performance compared with 722 iron oxide black product.