Chemical Pre-Desilication Of The Low-Grade Bauxite And The Resource Utilization Of Silicon

China is pretty rich in bauxite resources but large amounts of these bauxites are consumed each year.With the increasing demand for bauxite and the depletion of high-grade bauxite resources in our country,the key to solve the significant strategic demand of bauxite is to improve the mass ratio of alumina and silica of low-grade bauxite through pre-desilication so that it can be used in Bayer process.In this paper,targeting at a typical diaspore bauxite in Henan Province(A/S=2-3),the method of roasting and alkali leaching was adopted to effectively improve the mass ratio of alumina and silica of the minerals.The A/S of bauxite after treatment was up to 7.55.In addition,due to the high alkali concentration and complex impurities in desilication solution,the utilization of silicon in the solution is still difficult to be solved.This goal could also be achieved by seed induction and circulating alkali solution induction put forward in this paper.And a kind of calcium silicate with concentrated particle size distribution(PSD)was successfully prepared,which could be used as paper filler.The alkali solution after silicon removal can be reused in the pre-desilication process,thus realizing the green and sustainable circulation of the whole process.The achievements and innovative results are exhibited as follows:(1)For the low-grade bauxite(A/S=2.26),it was firstly roasted at 1000? for 1 h,and then leached in 200 g/L alkali solution at 95? for 40 min with liquid-solid ratio of 8.And the highest A/S of the product was increased to 7.55.And the kinetics of the leaching process was carried out by shrinking model.The results showed that the reactions with alkali concentration of 100 g/L and 200 g/L were both controlled by chemical reaction rate.And the activation energy was 59.49 kJ/mol and 51.61 kJ/mol,respectively.(2)It was found that the foil-shaped calcium silicate with narrow PSD centered at 10,um could be synthesized from desilication solution,by the introduction of tiny amounts of calcium silicate seed(0.4 g/L)and pre-hydration of calcium oxide in 100 g/L alkali solution.Further experiments showed that different seeds had different effects on the PSD of products.Compared with seed-2 or seed-3,seed-1 had the best induction effect at 90?.(3)It was found that the pre-hydration of calcium silicate in 100 g/L alkali solution with tiny amounts of silicate(CSiO2 0.59 g/L)could also result in the calcium silicate product with controllable PSD centered at 10 ?m.The online focused beam reflectance measurement(FBRM)and other measurements showed that the calcium silicate with narrow PSD could be obtained by the combined approaches of the slow hydration of CaO and the induced reaction crystallization of silicate.Compared with larger calcium silicate and PCC,the obtained product used as paper filler could greatly improve the bulk of paper while maintaining similar tensile strength.And compared with GCC,the wear rate of this filler is lower,which shows great potential in industrial application.