Research On The Preparation And Application Of Ceramsites From Calcium-rich Solid Waste

A research has been made on the recycle of calcium-rich solid waste,namely lime mud and propylene oxide sludge in this dissertation.In order to find a low-cost and harmless way to reuse them,the theory of mineral synthesis of anorthite and gehlenite was adopted to produce ceramsites.Ceramsites were applied as filter materials in biological aerated filter to explore their application in wastewater treatment.Modification of ceramsites was also carried out to obtain products with better properties.The experiments and results are as follows:Ceramsites were prepared from lime mud and propylene oxide sludge respectively with some other raw materials by wet molding process.After the curing process of room temperature and dried at 105?for 24 hours,raw ceramsites were sintered at 1050?for 2hours and finally contained anorthite and gehlenite as main mineral phases.Anorthite and gehlenite can decompose partly in water to release Ca²⁺and OH^-,adjusting the pH of the water.Ceramsites made from lime mud is light-weighted and the water absorption rate can reach 47.24%within 24 hours and the cylinder compression strength is 2.43MPa.The hydration of 4g ceramsites could make the pH of 200mL pure water reach 10.55 and the concentration of Ca²⁺could reach 92.20mg/L within 12 hours.The cylinder compression strength of ceramsites prepared by propylene oxide sludge was generally higher,ranging from4.47MPa to 17.68MPa.The hydration could make the pH of pure water reach 8.99 and the concentration of Ca²⁺could reach 129.48mg/L within 12 hours at most.When using pure reagents such as calcium carbonate and calcium hydroxide to synthesize anorthite and gehlenite samples,it was found that calcium hydroxide could reduce the temperature of solid phase reaction and promote the sintering and crystallization of samples.Ceramsites with anorthite and gehlenite were used as filter materials combined with microorganisms in the reactor of biological aerated filter to treat wastewater with ammonia nitrogen utilizing the nitration reaction,compared with commercial quartz sand ceramsites.Results show that the adsorption of ceramsites on ammonia nitrogen is relatively limited.When combined with microorganisms for the treatment of wastewater containing 100mg/L ammonia nitrogen,the hydration of ceramsites made from lime mud could adjust the pH value of the reactor to 8.74-7.08 while that of ceramsites made from propylene oxide sludge was 8.33-5.88.The reacters both started in 13 days successfully and the average removal rate of ammonia nitrogen was 94-98%.Ammonia nitrogen could be completely wiped out.The reactor using quartz sand ceramsites could started with the help of phosphate buffer to adjust pH value but gradually failed in lack of the phosphate buffer as the nitrification was suppressed by the high concentrations of H⁺.The mineral phases of ceramsites did not change before and after water treatment and the biocompatibility was good.Ceramsites could be reused for water treatment again.The residual organic carbon on the surface of ceramsites reused could make microorganisms grow and reproduce rapidly in a very short time,which shortened the start-up time of the reactor to 3 days.The reused ceramsites could adjust the pH value of the reactor to 8.03-5.90 and the average removal rate of ammonia nitrogen was87.53%,whose maximum could be 100%.Long-term water treatment experiments require high strength,stable structure and excellent hydration performance of ceramsites,so the modification of ceramsites is studied by means of raw material optimization,parameter improvement and structure design.The results show that using dry and finer raw materials could obtain ceramsites with higher strength.When reducing pore-forming agents,calcium raw materials and increasing silicon and aluminum raw materials,ceramsites full of anorthite could be made,whose cylinder compression strength could reach 6.46MPa.Increasing calcination temperature could increase the proportion of anorthite phase in ceramsites and improve the strength of products.Cylinder compression strength of ceramsites calcined at 1150?could reach 27.98MPa.When reducing silicon and aluminum raw materials,increasing calcium raw materials and pore-forming agents,ceramsites full of gehlenite could be made,whose hydration properties promomted as the final pH value of pure water with ceramsites changed from 8.34 to 9.17within 12 hours.The composite ceramsites could be obtained by physical combination of the two kinds of ceramsites.The inner ceramsites were made from lime mud with a good efficiency of calcium release and alkalinity leach.The outer ceramsites were made from propylene oxide sludge with high strength.Cylinder compression strength of composite ceramsites could reach 5.17MPa and the pH value could reach 9.28 after 12 hours of hydration,showing excellent comprehensive performance.After being applied to biological aerated filter with microorganisms to treat wastewater with ammonia nitrogen,reactor could started successfully within 16 days and the average removal rate of ammonia nitrogen was89.17%.Meanwhile,complete nitrification could also be achieved.The pH value of the water in the reactor was in the range of 8.80-5.20.