A Study On Selective Coagulation Separation Of Diasporic-bauxite By Inorganic Coagulating Agent

Alumina is mainly produced by Bayer process in China. This process, however, requires a high ratio of aluminium to silicate of bauxite, which is mostly achieved by mineral beneficiation, due to the poor bauxite quality in China. Tests on the selective coagulation separation of diaspore and kaolinite have been carried out by adopting diversified inorganic coagulants in this paper, based on the summarizing and consulting relative literatures at home and abroad.Natural sedimentation behaviours of pure minerals of diaspore and kaolinite at various pH conditions were investigated. Deconcentration behaviours of these minerals were also investigated by using sodium carbonate, sodium hexametaphosphate and sodium fluosilicate, which are the common dispersants in the beneficiation technology of bauxite. Study on the latter behaviours is imperative, because the process of selective coagulating can only be conducted on a good dispersing condition of minerals. Tests show that the optimum dosage of sodium carbonate is12mg/L, and it’s2.5mg/L for sodium hexametaphosphate.Effects of agglomeration of these minerals by using aluminum sulfate, ferric chloride, polymeric aluminum sulfate, polymeric ferric chloride and polymeric ferric sulfate were investigated next, on the dispersing conditions created by sodium carbonate and sodium hexametaphosphate. Tests result indicates that selective coagulation can be achieved to some extent, using polymeric aluminum sulfate, polymeric ferric chloride and polymeric ferric sulfate. In the dispersing system of sodium carbonate, the differences of sedimentation productivity between diaspore and kaolinite were39%,44%and63%, as the dosages of three abovementioned coagulants were40mg/L,40mg/L and20mg/L respectively. While in the system of sodium hexametaphosphate, the differences of sedimentation productivity were38%,40%and58%, when the dosages of the coagulants were all100mg/L.Tests of selective coagulation separation on artificial mixed minerals with respective A/S of3,5,7have been carried out by adopting polymeric ferric sulfate. On the condition of20mg/L of sodium carbonate and20mg/L of polymeric ferric sulfate, A/S of the artificial mixed minerals can increase to4.46,7.20and9.40; and the concentrate productivities were50.25%,68.35%and74.39%respectively. On the condition of4mg/L of sodium hexametaphosphate and100mg/L of polymeric ferric sulfate, A/S were increased to4.29,6.67and8.79; and productivities were47.00%,61.44%and64.69%respectively.According to the optimal reagent system of artificial mixed minerals tests,3000g/t of sodium carbonate and30g/t of polymeric ferric sulfate were employed for raw diaspore with a A/S of4.39. Concentrate with a A/S of6.43and Al2O3recovery of87.28%have been achieved, after sedimentation and separation for three times.It can be concluded that selective coagulation separation between diaspore and kaolinite can be achieved in some extent by using polymeric ferric sulfate. Study on the minerals structure, Zeta potential determinations and the function mechanism between minerals and reagents verifies this conclusion as well.