Comparison of Chemical Reactivity of Bauxite-tailings Pre-and Post-calcinations and Whitening Bauxite-tailing

Bauxite-tailings is aluminosilicate wastes and is used in polymer as fillers. But its intrinsic low-whiteness has limited its large-scale application in polymeric materials. Conventional methods for whitening bauxite-tailings were ineffective. A new method, which involved reactions with phosphoric acid and calcinations, was proposed to whiten bauxite-railings. Two process routes were employed to whiten bauxite- tailings, which were pre- and post-reaction calcination. While the process of pre-reaction calcination was able to achieve a whiteness of 87% from bauxite-railings, it required high-energy post-treatment processes such as washing, milling and drying. The process of post-reaction calcination, on the other hand, resulted in an increase in whiteness of bauxite-tailings from 19% to 73%. This was achieved using 4.5% of added phosphorous, 40% acid concentration, reaction time of 2.5 hours and a calcination temperature of 600 ℃ The resultant did not require any further processing, and was therefore industrially feasible. The whitened tailings consisted of corundum, anatase, and quartz. When compared to calcined tailings, whitened tailings possessed a higher content of amorphous material, the disappearance of red iron minerals, and the emergence of a new phase of A1PO4.

An improved implementable process for the synthesis of zeolite 4A from bauxite tailings and its Cr^(3+) removal capacity

A simple and practical method for the synthesis of zeolite 4A from bauxite tailings is presented in this paper. Systematic investigations were carried out regarding the capacity of zeolite 4A to remove Cr（III） from aqueous solutions with relatively low initial concentrations of Cr（III）（5–100 mg·L^（-1））. It is found that the new method is extremely cost-effective and can significantly contribute in decreasing environmental pollution caused by the dumping of bauxite tailings. The Cr（III） removal capacity highly depends on the initial p H value and concentration of Cr（III） in the solution. The maximum removal capacity of Cr（III） was evaluated to be 85.1 mg×g^（-1） for zeolite 4A, measured at an initial p H value of 4 and an initial Cr（III） concentration of 5 mg·L^（-1）. This approach enables a higher removal capacity at lower concentrations of Cr（III）, which is a clear advantage over the chemical precipitation method. The removal mechanism of Cr（III） by zeolite 4A was examined. The results suggest that both ion exchange and the surface adsorption-crystallization reaction are critical steps. These two steps collectively resulted in the high removal capacity of zeolite 4A to remove Cr（III）.

Utilization of Bauxite Tailing

The characteristics of bauxite tailing in China were reviewed,and the current utilization methods and the actuality were discussed.It is found that the bauxite tailing is mainly used for production of building materials and chemical products,and extraction of useful component,etc.Meanwhile,the shortages of these utilization methods were analyzed.In order to enlarge the bauxite tailing application,some new utilization paths were proposed,such as preparing zeolite 4A and corundum-mullite composite materials,which are high value added materials.The utilization ways of bauxite tailing were widened,the utilization ratio of resources and the economic benefit were improved.