Solubility of Sodium Oxalate in Kraft Black Liquors Above 100 °C

Abstract

The solubility of sodium oxalate was measured in kraft black liquors at temperatures of 115 °C to 140 °C with dry solid contents of 45% to 70%. The composition of black liquors studied were varied with respect to sodium concentration by addition of sodium salts. The solubility of sodium oxalate increased with increasing temperature and decreased with increasing liquor dry solid contents. The solubility data showed no dependence on the liquor composition at a constant concentration of sodium. A mathematical expression was derived and validated from the experimental data at the conditions investigated to predict the solubility of sodium oxalate as a function of temperature and sodium concentration. An application to assess the solubility and precipitation risk of sodium oxalate is demonstrated in seven evaporator bodies using the newly derived models.