Preparation And Application Of Amorphous Silica From Microsilica

Microsilica is a by-product in the production of silicon and ferrosilicon alloys. It is obtained by deoxidization of high-purity quartz with coke in electric arc furnaces. Currently, microsilica can be partially used as concrete admixture and refractory castable. However, its use is limited and the use value is low. The disposal of microsilica is mainly stacking in China.This method not only takes up a large area of land, but also causes a threat to environment and human health. Therefore, it is meaningful to improve resource utilization range and level of microsilica for reducing solid waste and environmental pollution.In this paper, microsilica was researched as raw material. The amorphous silica was prepared by using chemical precipitation. The chemical and physical properties of the product, mainly amorphous silica, were tested. The applications of the amorphous silica in complexion with titanium dioxide and preparing silica sol were discussed.The dyeing reason and elimination measures of the sodium silicate solution and the amorphous silica, obtained from microsilica, were researched. Because microsilica was stacked for a long time which producing organic matter. The organic matter can be eliminated by using the measure of roasting. With the evaluation index of the whiteness after roasting, the optimum roasting conditions were got: roasting temperature 700 ℃, roasting time 3h. The whiteness of the microsilica was increased from 47.77 to 72.86.The sodium silicate solution was prepared from the roasted microsilica(700℃) after the process of alkali-soluble by sodium hydroxide. The sodium silicate solution is colorless and transparent, which obtained Si O218.16g/L and Na2O10.84g/L. The modulus is 2.41. The optimal parameters of the process of alkali-soluble were: the reaction temperature 90℃, the dosage of Na OH 3.5g / 10 g roasting materials, liquid to solid ratio 8: 1 and the reaction time 40 min.The preparing technology and characterization of amorphous silica by the reaction of sodium silicate and sulfuric acid(acid precipitation) were studied. The optimal parameters in the process of acid precipitation were: the reaction temperature70℃, the aging time was 2h, the value of p H of titration endpoint 8 and the concentration of sulfuric acid 2mol/L. The Si O2 content in the product prepared under this condition was 96.06%. Its whiteness was 90.2 and the size of particles ranged from 2μm to 20μm. The specific surface area of the amorphous silica was 417.2m2/g, and its pore volume and diameter were 0.405cm3/g and 3.801 nm, respectively. The recovery rate of Si O2 is 99.79%. The formation mechanism of the amorphous silica in the process of acid precipitation was analyzed.The exploration experimental research which contained the complex of the amorphous silica and titanium dioxide particle and the preparation of silica sol were made. The Si O2-Ti O2 composite particles had similar pigment properties compared with titanium dioxide. The Si O2 particles were covered by Ti O2 particles. The silica sol was milky suspension and has stable nature.