Phase diagram analysis of the carbonation process of sodium chromate and ammonia solution

Abstract

The solubility and phase diagram of Na+, NH4+/ /CrO42-, HCO3--H 2O system are determined in this paper. According to the solubility and phase diagram, the solid phases in carbonation process of sodium chromate in ammonia solution are discussed. The results show that a crystalline zone of NaNH4CrO4·2H2O exists, NaHCO 3, NaNH4CrO4·2H2O and (NH4)2CrO4 crystallize out in turn during carbonation process as the concentration of sodium chromate in ammonia water exceeds the concentration corresponding to P2(P2′) in phase diagram. Proper concentration is 0.8633-1.1377 g/g H2O for sodium chromate, 0.0611-0.0986 g/g H2O for ammonia, lower than the concentration corresponding to P2(P2′) plot. The NaHCO3 and NaNH4CrO4·2H2O crystals can be separated by hydrocyclone.