Crown Ether Aluminate Solution By The Process

To promote decomposition of sodium aluminate liquors is a very important topic in alumina production industry. Seed precipitation of sodium aluminate solution enhanced with additives has good advantages such as simple operation condition and low cost, and thus has good application foreground. 15-crown-5-ether and 18-crown-6-ether which have unique caged structure were adopted as additives in the seeded precipitation process. The effect of crown ether was investigated in the paper by analyzing the precipitation ratio, particle size distribution, morphology and crystal characteristics of Al(OH)₃ product on different experimental conditions of temperature, caustic concentration of liquor and the concentration of additives. the interaction between the crown ether with different Molecular ring diameter and the alkali metal ions in aluminate solution was suggested. In addition, the influence of crown other on homogeneous nucleation of Al(OH)₃ was discussed. Which cofrimed the mechanism: crown ether combinated with alkali metal ions selectivity and do favor to the combination of aluminate ions, and the crystallization is enhanced subsequently. Conclusions were made as follows.1. 15-crown-5-ether can enhance the decomposition of sodium aluminate liquors, the effect is More obvious at higher concentration of additives and higher caustic concentration of liquor. 18-crown-6-either has no effect on the precipitation ratio and the particle size.2. The seed precipitation of sodium aluminate solution was enhanced slightly by 18-crown-6-either. 15 - crown -5 -ether has no significant promotion of the decomposition of potassium aluminate solution.3. The enhancement mechanism is visualized as follow: crown ether combinated with alkali metal ions selectivity which favors the combination of aluminate ions and the formation of network and the crystallization is enhanced subsequently.4. 15 - crown -5-ether and 18 - crown -6-ether can reduce the homogeneous nucleation induction period of sodium aluminate and potassium aluminate solution respectively. The peak width of ²⁷Al NMR of sodium aluminate liquor broadens as the 15-crown-5-ether is introduced but narrows as the 18-crown-6-ether is introduced. The peak width of ²⁷Al NMR of sodium aluminate liquor broadens as the 18-crown-6-ether is introduced but narrow as the 15-crown-5-ether is introduced.