Effect of Calcium and Magnesium Ions on Calcium Oxalate Formation in Sugar Solutions

Abstract

During the concentration of sugarcane juice, there is continuous deposition of nonsugar impurities on the surface of evaporator units. Because the scale deposit has a low thermal conductivity, its accumulation impairs heat transfer and eventually renders the process uneconomical owing to reduced throughput. Calcium oxalate is the main intractable scale formed in factories that process sugarcane. It is not removed by conventional chemical cleaning methods. This paper describes studies on the apparent solubility product of calcium oxalate in the presence of sugar and calcium and magnesium ions at different temperatures and pH's. A solubility product model was obtained that states that the apparent solubility product of calcium oxalate decreases with increasing temperature and sugar concentration, but increases with increasing pH. The model was able to predict calcium oxalate solubility changes in raw sugarcane factory processes, indicating that the apparent solubility product of calcium oxalate declines rapidly through the evaporator set. The results also indicated that calcium oxalate solubility is increased in the presence of calcium and, in particular, magnesium ions.