Control of Sodium Oxalate Precipitation by Ammonium/Quaternary Ammonium Compounds in the Gibbsite Precipitation Stage of Bayer Liquor

A series of problems are caused by the presence of sodium oxalate in Bayer liquor in alumina plants. For instance, sodium oxalate reduces the production of alumina and increases the density, viscosity, specific heat and boiling point of the sodium aluminate solution. Meanwhile, it also increases production of fine-seed alumina and impurities in alumina. To reduce the precipitation of sodium oxalate in the gibbsite precipitation stage, the effects of surfactants, including lauryl dimethyl amine oxide, dodecyl trimethyl ammonium bromide (DTAB), hexadecyl trimethyl ammonium bromide, and trime thyloctadecyl ammonium bromide, on sodium oxalate in Bayer liquor were investigated and characterized by ICS, FTIR, LPS, and SEM. In addition, the effects of the surfactant amounts and the quantities of seeds on the inhibition of sodium oxalate precipitation were also investigated. The ICS results showed that sodium oxalate precipitation can be inhibited by the surfactants mentioned. DTAB had the worst inhibition efficiency on sodium oxalate compared with the other three surfactants. Under the optimal conditions, that is, the amount of DTAB added was 20 mg/L, the quantity of seeds was 40 g/L, and the action time was 2 h, the precipitation of sodium oxalate was significantly inhibited with an inhibition efficiency of 61.5%. An increase in the quantities of seeds was not conducive to the function of the surfactants. The FTIR results revealed that the surfactants functioned as sodium oxalate via physical adsorption. The results of LPS and SEM analyses indicated that the addition of surfactant resulted in a significant reduction in fine-grained gibbsite, sodium oxalate agglomerated into clusters and the number of needle-like sodium oxalate decreased. This study provides new insights into the regulation of sodium oxalate in Bayer liquor.