Study On The Characteristics Of Removing And Reusing Phosphorus By Calcium Silicate Hydrate

Phosphorus is one important factor leading eutrophication， which is alsononrenewable and irreplaceable resource. Developing and researching sewage treatmentprocess that matches the phosphorus recycled materials demanded prompt solution.Existing studies had showed that hydrated calcium silicate material with a porousstructure released calcium ions and hydroxide ions, and could adsorbe phosphate in thesolution and then generated microenvironment which was productive for the formationof hydroxyapatite and recovery of high-quality phosphorus. Based on the abovebackground, this experiment selected calcium carbide slag calcareous material and silicasiliceous materials as raw materials, and studied the preparation methods of hydratedcalcium silicate with porous structure and release properties, which were suitable forphosphorus recovery. Phosphorus removal and phosphorus recovery properties of thecalcium silicate hydrate were also investigated. The experimental results showed that:①When calcium silicon molar ratio was1.8, reaction time was4.5h, the reactiontemperature was170℃, and stirring rate was90r/min, calcium silicate hydrate was crispwith more pore surface distribution; the pore structure, average pore diameter andspecific surface area were the largest;the specific surface area was121.03m²g^-1, thetotal pore volume was0.65cm³g^-1and the average pore size was21.49nm; dissolvedcalcium capacity was the best and the concentration of dissoluted calcium ion was12.87mg/L. Under this condition, phosphorus removal efficiency of calcium silicatehydrate was the best. The residual phosphorus concentration was only1.16mg/L, andthe phosphorus removal efficiency was98.84%. Four factors and four levels orthogonaltest showed that the optimal synthesis conditions consistent with the single-factor test,and the range analysis indicated that the molar ratio of calcium silicon was the maininfluencing factors.②Calcium silicate hydrate prepared under the optimum conditions was used forphosphorus removal, and reaction time, stirring intensity, pH of the solution, initialphosphorus concentration and material dosage was selected as impact factors. Theresults showed that when the reaction time was60min, stirring intensity was40r/min,pH value was8.5, the initial phosphorus concentration was100mg/L and dosage of4g/Lhydration calcium silicate hads the best performance for phosphorus removal, andphosphorus removal efficiency reached98.84%. ③Comparison results of the phosphorus removal performance of various calciummaterials showed that the order of phosphorus removal capacity was: hydrated calciumsilicate> tobermorite> dolomite, whose phosphorus removal efficiency were98.84%,86.14%and51.68%. The phosphorus recycling performance of various calciummaterials were also studied, the results showed that after10-times’ phosphorusremoval the sediment phosphorus in tobermorite was11.46%; after3-times’ phosphorusremoval the sediment phosphorus in dolomite was2.59%; after15-times’ phosphorusremoval the sediment phosphorus in hydrated calcium silicate was17.59%. Therefore,hydrated calcium silicate had better phosphorus recovery performance. Further XRDpatterns and FTIR analysis showed that phosphorus in the solution was mainlytransformed into hydroxyapatite and embedded into hydrated calcium silicate. The BETanalysis and SEM analysis showed that the specific surface area,total pore volume andaverage pore size of hydrated calcium silicate were the largest, which were121.03m²g^-1,0.65cm³g^-1and21.49nm. This crisp structure made the material havehigh dissolved calcium and alkali characteristics, but also made the material havecertain strength and would not collapse. Therefore, hydrated calcium silicate could beenrichment carrier for phosphorus.