Crystallization Behavior Of Sodium Oxalate In The Evaporation Process Of Sodium Aluminate Solution

Sodium oxalate, originated from the oxygenolysis of organic substances in Bayer process, is concentrated continuously with the circulation of the solution until exceeds its equilibrium concentration, and then it will precipitates from the solution, which has an adverse effect on the stable operation of production and the quality of the product. Removal of sodium oxalate from sodium aluminate solution by precipitation process after evaporation has many advantages, such as simple process, low energy consumption and low cost. However, there are also some shortcomings in this method, such as low precipitation rate and bad settlement property of sodium oxalate due to the complexity of the solution system. And then, crystallization behavior of sodium oxalate in the evaporation process of sodium aluminate solution is studied. The main progresses are listed as follows:1) Sodium oxalate solubility models was established by Bromley equation, which can provide a thermodynamic basis for predicting the solubility of sodium oxalate in the evaporation process;2) Composition of sodium aluminate solution on the crystallization of sodium oxalate were researched, which proves that the existence of sodium humate in the solution is the main reason leading to low precipitation rate and bad settlement property of sodium oxalate in the evaporation process.3) Influence of evaporation conditions on the crystal grain size of sodium oxalate were studied, and the results show that the crystal growth rate of sodium oxalate can be promoted by increasing the evaporation temperature, prolonging the evaporation time and adding crystallization additives. The methods to control the growth of crystal particles were proposed and crystals of sodium oxalate can grow up to10μm under optimum conditions;4) Effects of sodium carbonate(sulfate) on the sedimentation and separation of the co-precipitated slag is researched, and the results show that increasing the content of sodium carbonate(sulfate) in the co-precipitated slag of sodium oxalate-sodium carbonate(sulfate) can improve the sedimentation separation performance of the co-precipitation slag. These studies can provide theoretical guidance and technical reference for the solving of sodium oxalate problems in Bayer process. There are36figures,27tables and81references in this paper.