Study On Preparing Conditions Of Highly Dispersed Nano-silica By Straw Ash

In this dissertation,highly dispersed nano-silica was prepared using straw ash as raw material,and the preparation conditions,including the acid leaching of the straw ash,alkali leaching of the acid leaching residue and the preparation of highly dispersed nano-silica from sodium silicate solution,were investigated and optimized.The main conclusions obtained were as follows:(1)The conditions for the acid leaching of straw ash by sulfuric acid were optimized as:the concentration of the sulfuric acid 15%,the mass ratio of straw ash to sulfuric acid 1:4,the reaction temperature 80℃,the reaction time 2.5h.The repeated experiments under the optimized condition showed that the average leaching rate of potassium oxide in straw ash could reach 97.4%.(2)The conditions for the alkali leaching of the acid leaching residue process were optimized as:the mass ratio of acid leaching residue to alkali lye 1:5,the concentration of the alkali lye 2mol·L-1,the reaction time 7h,the reaction temperature 120℃.The repeated experiments under the optimized condition showed that the average leaching rate silica in acid leaching residue could reach 88.44%.(3)D-sodium gluconate was screened as the optimized dispersant and the optimized preparation condition of nano-silica were obtained as follows:the reaction temperature 90℃,the dispersant addition 2%,the concentration of sodium silicate 11%,the CO2 flow rate 110mL· min-1.The repeated experiments under the optimized condition showed that the average yield of silica could reach 96.65%and the as-prepared nano-silica performed good dispersion with the particle size of about 20～40 nm and the average macroscopic size(d100)less than 315 nm by DLS analysis.(4)Compared with silica samples prepared without dispersant,the particle size of silica particles prepared by adding D-sodium gluconate reduced significantly and had less hydroxyl groups on the surface of silica.The probable mechanism of action might be:Dispersant D-sodium gluconate could join with silicon hydroxyl group on the surface of the particles and form the coating film,destroying the hydrogen bond and reducing the surface energy of the particles,thus reducing the agglomeration of the particle and particle size,while increasing the dispersion of the particles.