Study On Preparation And Modification Of Silica From Rice Husk Ash

Rice husk resources are plentiful in our country. Rice husk ash that was obtained by power generation or combustion has become one of important factors of environmental pollution. In order to take full advantage of resource, raise the economic benefit, and protect the ecological environment, the experimental conditions of preparation of high quality silica from rice husk ash were studied in this paper. Silica was dissolved out in the form of sodium silicate through rice husk ash reacting with sodium hydroxide. The factors include the concentration of sodium hydroxide, reaction time, reaction temperature and stirring speed were investigated. The optimal reaction conditions for the preparation of sodium silicate by single-factor and orthogonal experiments were determined: reaction concentration 2mol/L(40m L), reaction time 3h, reaction temperature 100℃, stirring speed 175r/min. The modulus of sodium silicate was 0.706 and the impregnation ratio of silica was 95.85%. The silica was prepared by using ethanol as the activating agent and dispersant, sodium bicarbonate as precipitant. In the simulation experiment, the optimal reaction conditions for the preparation of silica were obtained by single-factor and orthogonal experiments: the concentration of sodium silicate 0.6mol/L, the concentration of sodium hydroxide 0.5mol/L, temperature 50℃, alcohol-liquid volume ratio 0.15, reaction time 1h, aging time 2h. The purity of silica was 99.50% under these conditions. These conditions played an important role in guiding the process of preparation of silica. Experimental conditions were derived as follows: temperature 50℃, alcohol-liquid volume ratio 0.15, reaction time 1h, aging time 3h when silica was prepared from rice husk ash. The purity of silica was 99.40%. The effects of drying-way, the form of precipitating agent and the difference of surfactant on the particle size of silica were investigated on the base of above experiments. Under the conditions of 1% polyethylene glycol(6000) as surfactant, saturated sodium bicarbonate solution reacting with sodium silicate and freeze drying, a kind of good-dispersion and high-purity silica which of particle size was 50 nm was derived. The improving performance of silica through adding KH-602 was researched. The best modified conditions were obtained: modified time 2.5h, the concentration of modifier 30%, modified temperature 70℃. Under the experimental conditions, the grafting rate reached to 13.45%. The crystal structure of silica had no obvious changes after modifing. The modified silica had better adsorption on Cu2+. The amount of adsorption of it reached to 12.37, much higher than 6.63.