Preparation Of Calcium Silicate Hydrate By Dealkalization Of Sodium Calcium Silicon Residue

With the application of high alumina fly ash instead of bauxite to extract alumina in the industrial practice,a large amount of high alumina fly ash was used to extract aluminum slag,of which the sodium calcium silica slag was extracted from high alumina fly ash and low calcium sintering method.It would pollute the environment and waste resources,if these sodium calcium silica slag cannot be processed in time.There was high content of CaO and SiO₂ in the sodium calcium silica slag.And the high alkali content became the key factor restricting its comprehensive utilization.Therefore,the research on the sodium calcium silicon de-alkali process would play a very positive role in the development of the alumina industry.It contains the preparation of hydrated calcium silicate that not only can improve the comprehensive utilization rate of aluminum extraction slag and reduce environmental hazards,but also the recovered alkali can be used to reduce the cost of alumina production.In this article,it attempted to use soda lime low calcium sintered high alumina fly ash to extract aluminum slag as a raw material,and silicon calcium slag as a reference to carry out research on sodium calcium silicon de-alkali process.Through single factor test and orthogonal test,the sodium calcium silicon was determined.And the optimum process parameters of silicon dealkaliization were analyzed for the mechanism of dealkaliization to provide a basis for industrialized production.Based on this,the adsorption characteristics of dehydrated products,hydrated calcium silicate,de-alkali product-tobermorite,and phosphorus were discussed.The specific research content was as follows:?1?Exploration of sodium calcium silicon de-alkali process parameters.Employing the dynamic hydrothermal method,it studied the effects of de-alkali temperature,de-alkali time,liquid-solid ratio and dosage of de-alkali agent on the dealkalization rate of sodium calcium silicon.The result showed that the de-alkali time had the most significant effect on the sodium calcium silicon dealkaliation,followed by the de-alkali temperature.Within the range of the amount of de-alkali agent set in the experiment,the addition of lime milk de-alkali agent was not conducive to the decomposition reaction due to the encapsulation effect,which reduced the rate of alkali removal,and also the effect of decalcification of sodium calcium silicon slag.By verifying the optimal scheme of the orthogonal test,the optimal process parameters for the soda lime silica dealkaliization were obtained as follows:de-alkali temperature T=170?,de-alkali time t=120 min,liquid-solid ratio L/S=5,and dosage of de-alkali agent C=0%.Under this condition,the sodium calcium silica dealkaliization rate can reach more than 95%,and the Na₂O content was reduced from 24.19%to about 1%.?2?The adsorption characteristics of hydrated calcium silicate,de-alkali product-tobermorite on phosphorus.It took the amount of adsorbent,the initial phosphorus concentration,and the p H value of the initial solution as the influencing factors for phosphorus adsorption.The results showed that the phosphorus removal performance was the best and the phosphorus removal rate can reach 99%,when the dosage of the de-alkali product-tobermorite was 4 g/L,and the initial phosphorus concentration was less than 50mg/L,pH value was about 5.Through the comprehensive comparison of phosphorus adsorption properties of different adsorbent materials,it was found that in a phosphorus solution with a dosage of 0.3 g,adsorption of 100mL 100 mg/L,and pH=5,the de-alkali product-tobermorite was superior to other phosphorus adsorption properties.Phosphorus removal rate reached above 78%.The adsorption characteristics test showed that the adsorption of phosphate ions on the surface of the de-alkali product-tobermorite conformed to the pseudo-second-order kinetic equation,the isothermal adsorption process accorded with the Langmuir-type adsorption model,and the equilibrium adsorption capacity at 25?was up to 35.37 mg/g.