Preparation And Application In Wastewater Treatment Of Silicate Filter Medias

With the continuous development of industrialization and urbanization in China,the amount of wastewater discharge increases year by year,resulting in a large number of water pollution.In recent years,China has issued many environmental protection policies to strengthen environmental protection.Although the water body is gradually improving,the eutrophication and heavy metal pollution of the water body are still a problem.In this project,the silicate filter material with C-S-Hgel and tobermorite as the main mineral phase was prepared by hydrothermal synthesis technology,and its physicochemical properties and hydrolysis properties were studied.The filter material was applied in the field of wastewater treatment to remove ammonia nitrogen,phosphorus and nickel ions in water.This paper uses fly ash with pozzolanic activity as silica raw materials,cement and lime as calcium raw materials,and uses hydrothermal synthesis technology to prepare hydrated silicate ceramsite with C-S-Hgel and tobermorite as the main mineral phases.The results show that the filter media has excellent performance,not only the strength is high,the maximum single ball strength is 10.52 MPa;the rough porous,its bet is 8.53-14.147m²/g,and the maximum pore volume is 0.085 m³/g.The filter media will hydrolyze slowly in aqueous solution to release calcium ion and maintain alkaline atmosphere in water.The p H of the solution was maintained at 10.0-10.5 and the concentration of calcium ion was about 22.53mg/L when L-Series hydrated silicate filter material contacted with water for 720 min.It is found that the trend of hydroxyl ion and calcium release is to increase rapidly at first,then slow down,and finally reach hydrolysis equilibrium.The release mechanism is that there is a concentration difference between the calcium ions in the pore solution and the aqueous solution,which leads to the diffusion of calcium ions,thus destroying the internal solid-liquid equilibrium,resulting in the hydrolysis of C-S-Hgel and tobermorite produced by the hydration of the material,and releasing calcium ions.The silicate filter madia was used as the filler of biological aerated filter（BAF）to carry out the experiment of ammonia nitrogen wastewater treatment,and the quartz sand filter material sold in the market was selected to operate under the same conditions as the control group.The results showed that the hydroxyl ions released by silicate filter media neutralized the hydrogen ions produced by microbial nitrification reaction continuously,which avoided the accumulation of acidity in the system.The p H value of the system remained above 7 after30 days of operation,which maintained the continuous nitrification reaction,and the removal rate of ammonia nitrogen remained at about 100%.However,due to the lack of buffer solution in quartz sand filter system,a large amount of hydrogen ions produced by nitrification reaction accumulated,which made the p H of the system drop to 5.38 after 30 days of operation,inhibited the nitrification reaction,and the removal rate of ammonia nitrogen reduced to below 10%.This paper continued to carry out the static and dynamic adsorption experiments of silicate filter material for phosphorus in water.It is found that the filter material has good adsorption performance for phosphorus in water,and its static saturated adsorption capacity reaches 2.10mg/g.It was found that the adsorption process was most consistent with the Langmuir isotherm model and pseudo-second-order reaction kinetic model,indicating that the process was a monolayer adsorption process controlled by chemical adsorption.The adsorption process is completed by the reaction of calcium ions released from the filter material with phosphate and the physical adsorption of the pores of the filter material itself.Combined with the good removal ability of phosphorus in water,BAF was used to carry out the experiment of simultaneous treatment of ammonia nitrogen and phosphorus in water.It was found that the removal rate of 4-6mg/L phosphorus in the water by the filter material was more than 80%,while the removal rate of ammonia nitrogen by microorganisms was not affected,and the removal rate of 70-90mg/L ammonia nitrogen was still more than 99%.Moreover,the mineral phase of the water treated by the filter material was stable,and there were abundant microorganisms attached on the surface and inside,with good biocompatibility.Using fly ash,quartz tailing,diatomite and natural zeolite as different siliceous materials,silicate filter madias with good adsorption performance for heavy metal Ni²⁺were prepared by hydrothermal synthesis technology.It was found that zeolite filter media（Z100）had the best adsorption performance for Ni²⁺in water.The removal rate of 100-500mg/L Ni²⁺reached99%,and its saturated adsorption capacity reached 11.67mg/g.The adsorption process of Ni²⁺on Z100 is in accordance with Langmuir isothermal adsorption model and the pseudo-second-order reaction kinetic model,which indicates that the process is a monolayer adsorption process controlled by chemical adsorption.The adsorption process is formed by the reaction of OH^-released from filter media with Ni²⁺,ion exchange between zeolite and Al-tobermorite,and p Hysical adsorption by pores of filter media.