Search

The economical removal of organics from sodium aluminate solutions has been required for decades. Based on security filtration using tricalcium aluminate hexahydrate (TCA) as a filter aid, a novel short process to eliminate impurity particles and remove organics simultaneously was presented. Ultrafine TCA samples with poor crystallization, high TCA content, high surface free energy, and large lattice distortion were prepared in the concentrated sodium aluminate solution. The zeta potential of the TCA binary mixture in alkaline solutions was linearly depended on the TCA content, suggesting the additivity of the zeta potential in the binary mixture. The variation in the electrical double layer of the TCA binary mixture was demonstrated in the alkaline solution. Furthermore, the ultrafine TCA exhibited a high adsorption capacity for organics with long alkyl chains and high relative-molecular-mass. The adsorption capacity of 69.69 mg/g organic carbon for sodium humate was achieved, whereas the digestion at a high temperature remarkably reduced the adsorption capacity of TCA.

The synthesis of sodium ferrite and its desulfurization performance in S2−-bearing sodium aluminate solutions were investigated. The thermodynamic analysis shows that the lowest temperature is about 810 K for synthesizing sodium ferrite by roasting the mixture of ferric oxide and sodium carbonate. The results indicate that the formation process of sodium ferrite can be completed at 1173 K for 60 min, meanwhile raising temperature and reducing Na2CO3particle size are beneficial to accelerating the formation of sodium ferrite. Sodium ferrite is an efficient desulfurizer to remove the S2−in aluminate solution, and the desulfurization rate can reach approximately 70% at 373 K for 60 min with the molar ratio of iron to sulfur of 1:1–1.5:1. Furthermore, the desulfurization is achieved by NaFeS2·2H2O precipitation through the reaction of and S2−in aluminate solution, and the desulfurization efficiency relies on the generated by dissolving sodium ferrite.

Pure compounds and kaolin were employed to investigate the reaction behavior of ferric oxide in the trinary system Fe2O3–SiO2–Al2O3during reductive sintering process. The thermodynamic analyses and reductive sintering experimental results show that ferrous oxide generated from the reduction of ferric oxide by carbon can react with silicon dioxide and aluminum oxide to form ferrous silicate and hercynite at 1173 K, respectively. In the trinary system Fe2O3–SiO2–Al2O3, ferrous oxide obtained from ferric oxide reduction preferentially reacts with aluminum oxide to form hercynite, and the reaction of ferrous oxide with silicon dioxide occurs only when there is surplus ferrous oxide after the exhaustion of aluminum oxide. When sintering temperature rises to 1473 K, hercynite further reacts with silicon dioxide to form mullite and ferrous oxide. Results presented in this work may throw a new light upon the separation of alumina and silica present in Al/Fe-bearing materials with low mass ratio of alumina to silica in alumina production.

Surface tension of sodium aluminate solution and the contact angle between Al(OH)3particles and aluminate solution were measured, then the dependence of Al(OH)3solubility on its particle size was calculated and thus the variation of the critical nucleus sizes was determined based on the Ostwald ripening formula. The results show that the Al(OH)3solubility in sodium aluminate solution decreases with the increment of particle size, and the critical nucleus sizes increase with the rise of alkali concentration, caustic ratio and precipitation temperature. The results also imply that the presence of small particles in seeded precipitation system is an important factor to limit the depth of precipitation.