Palygorskite Modified And The Research Of Its N&P Adsorption Performances And Mechanism

Palygorskite is a nature clay mineral having large surface and high cation exchange capacities,often used as adsorption mineral.At present, there are so many reportes about palygorskite as a adsorption of low concentration of ammonium or phosphate, but having few reports about high concentration of ammonium and phosphorus in wastewater.In this paper, aim at high concentration of ammonium and phosphate wastewater, modification was performed by thermal and alkali of palygorskite and reaction parameters optimization was carried on to investigate the effect of the removal of ammonium and phosphate by modified palygorskite,get the optimum parameters and screen the best modification condition. Thermogravimetric(TG), X-ray diffraction spectrum (XRD), scanning electron microscopy and energy spectrum analysis(SEM-EDS),Fourier infrared spectrum (FTIR), Zeta potential (ZP) and specific surface area were used to characterize the resulted of samples to explore the mechanism of the removal of ammonium and phosphate.The main conclusions of this paper are showed as follow:(1) TG and SEM results of thermal modified palygorskites shown that the surface adsorbed water and the channel water in palygorskite lost, but the crystal structure do not change when the temperature below 142?. The half crystal water in palygorskite got out of the cryatal so that the crystal in slight fold when the temperature rang of 142? to 308?. The rest crystal water lost when the temperature rang of 308? to 501?,part of structure water lost at the same time,also the structure of the palygorskite was destroyed.All of the water lost when the temperature rose to 501? to 710?, however the crystal framework of silicon-oxygen tetrahedron was still retained. SEM results furtherly proved the conclusion that the structure of palygorskite was destroyed gradually with the increase of temperature; With in a certain range, the keeping time had a little effect on the structure of the palygorskite.(2) XRD and SEM results of alkali modified palygorskites shown that alkali destroyed the original structure of palygorskite to generate Na2Si2O5. At 700?, silicate crystals were uniform and arraged regularly. Many close channel was formed between crystals. Alkali could cleavage fully with a long time and react more thoroughly with palygorskite.The optimal modification time was 4 hours. Within a certain range, the ratio of alkali to palygorskite was larger, the alkali and palygorskite mixed more evenly, and the silicate crystals were more uniform and arranged more orderly. Sodium hydroxide could only react with local palygorskite when the ratio of alkali to palygorskite was smaller. The generated Na2Si2Os embedded in the channel which haven't collapsed completely in palygorskite to block the channels and decrease the surface area of palygorskite. The ZP result shows that the alkalic modified products were negatively charged which were advantageous to the cation adsorption.(3) The optimum reaction parameters of the removal of ammonium and phosphate by modified palygorskite were that optimal initial concentration of NH4+-N and PO43--P were 100mg/L and 90mg/L respectively.The optimum pH of thermal and alkali modified palygorskite were 9.5 and 8.5 respectively. The two modified palygorskite had the same optimal dosrge, reaction time and speed which were 0.8 g, 4 h and 200 r/min.(4) The study of the removal of ammonium and phosphate shown that best samples were R-6002 and J-7004-1:1. The effect of the removal of ammonium and phosphate by R-6002 and J-7004-1:1 were higher than original palygorskite.The removal rate of N and P were 30.89% and 80.77% respectively by R-6002,which was 2.8 times and 15.9 times as much as that in original palygorskite.The result of J-7004-1:1 were 41.97% and 60.22% respectively,which was 3.8 times and 12.2 times as much as that in original palygorskite.J-7004-1:1 was higher than R-6002 with the removal rate of N,about higher 11.08%.But R-6002 was 16.68% higher than J-7004-1:1 about the removal ratr of P. Overall, the effect of the removal of N and P thermal modified palygorskite is better than alkali modified samples. According to the results of adsorption kinetic, Pseudo-second order model and Langmuir model could better fit the adsorption process for NH4+-N and PO43--P by palygorskite. Adsorption isotherms results shown that the R-6002 maximum adsorption capacity of NH4+-N and PO43--P were 5.433mg/g and 15.633mg/g respectively. And the J-7004-1:1 maximum adsorption capacity of NH4+-N and PO43--P were 4.859mg/g and 13.936mg/g respectively. The fitting correlation coefficient of Langmuir were 0.71-0.92 which were not very high.It shown that the adsorption process for NH4+-N and PO43--P by R-6002 and J-7004-1:1 were not completely belong to the Langmuir model. Maybe the mechanism of removal of N and P was not just a monolayer adsorption. According to the characterization results and the effect of the removal of N and P, the mechanism of removal of N and P has physical adsorption,chemical adsorption and chemical precipitation reaction.