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-tailings. Two process routes were employed to whiten bauxitetailings, which were pre- and post-reaction calcination. While the process of pre-reaction calcination was able to achieve a whiteness of 87% from bauxite-tailings, 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 °C. 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 AlPO4.