Study On Oxidation Of Organic Matters In Bayer Liquor By Sodium Persulfate

In the production of alumina by the Bayer process,organic matters in the Bayer liquor come mainly from bauxite and additives.These organics accumulate and undergo complex reactions under the cyclic nature of the Bayer process,resulting in high organic content and complex composition in the system,which affects the production process.To address this problem,domestic and foreign scholars have studied different methods to reduce organic matter content in sodium aluminate solution,among which the oxidation method has a good prospect of application.In this study,the solid oxidant sodium persulfate was selected for the oxidation of organic matter in sodium aluminate solution.The main research objects were synthetic sodium aluminate solutions containing different organic matter and industrial sodium aluminate solutions from different sources,and the changes of TOC（total organic carbon）removal rate and concentration of organic matter such as oxalate under different conditions of temperature,time and sodium persulfate concentration were studied,focusing on the changes of organic oxidation products.The aim was to provide guidance for the application of sodium persulfate in the plant to reduce the concentration of organic matter in the system,and the main results of the study were as follows.（1）The TOC removal rates of humic acid-containing solutions were43.26%and 22.73%,and the oxalate concentrations were 0.234 g/L and0.027 g/L,respectively,during the holding process at 280°C and 90°C.The TOC removal rates and oxalate concentrations increased after oxidation.（2）Extending the oxidation time and increasing the amount of sodium persulfate addition were beneficial to improve the TOC removal rate.Oxalate concentration increased firstly and then remained unchanged with the increase of oxidation time,and increased continuously with the increase of sodium persulfate concentration.（3）The increase in the concentration of caustic soda containing humic acid solution will weaken the oxidation effect of sodium persulfate,making the TOC removal rate and oxalate concentration decrease.（4）Oxalate,acetate and benzoate in sodium aluminate solution can be oxidized.Acetate will generate oxalate when the oxidation temperature is higher than 70℃;benzoate will generate oxalate when oxidized at the experimental temperature;acetate and benzoate will generate succinate when oxidized.（5）During the oxidation of sodium aluminate solutions containing humic acid,the presence of Cl^-has a small effect on the TOC removal rate,while the presence of CO₃^2-significantly reduces TOC removal rate.The presence of both Cl^-and CO₃^2-decreases the oxalate concentration.At260°C,the increasing concentration of Cl^-in the synthesis solution causes the concentration of acetate to increase continuously.（6）The use of catalysts such as Cu O can significantly improve the TOC removal rate after sodium persulfate oxidation.For sodium aluminate solution containing humic acid,the catalysts with better oxidation effect at80°C and 260°C were 5 g/L Ni₂O₃ and 3 g/L Ni₂O₃,respectively.For the Zunyi,Tiandong and Pingguo solution,the catalysts with better oxidation were 1 g/L Fe₂O₃,1 g/L Cu O and 3 g/L Fe₂O₃,respectively.（7）In synthetic or industrial solutions,the concentrations of formic acid and acetic acid after oxidation with sodium sulfate under different conditions vary less.