Dissertation
Dissertation > Environmental science, safety science > Processing and comprehensive utilization of waste > General issues > Wastewater treatment and utilization

Adsorption Effects of Phosphate and Chromium from Aqueous Solution by Adsorption Using LDH and Mg/Fe/Al Modified Montmorillonites

Author ZhangWenHao
Tutor WangDaiChang
School Henan Agricultural University
Course Soil
Keywords modified montmorillonite Layered double hydroxides isothermal adsorption kinetics thermodynamics
CLC X703
Type Master's thesis
Year 2011
Downloads 18
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The Mg-Al Layered double hydroxides was synthesized by the coprecipitation method. Characteristics of phosphate adsorption on Mg-Al layer double hydroxide (Mg-Al LDH) and Na-montmorillonite (Na-Mt) and Mg/Fe/Al modifiedmontmorillonite (Mg-Al-Mt and Fe-Mt and Fe-Al-Mt) were studied by isotherm adsorption and kinetic experiments at different pH values.The results were drawn as follows:1. The percentage of phosphate adsorption on Na-Mt and Fe-Mt and Fe-Al-Mt decreased,and that on Mg-Al LDH increased with solution pH increase. The adsorptin effects of phosphate adsorption on Mg-Al LDH、Fe-Mt and Fe-Al-Mt were about 95%, higher 40% and 80% than that of Mg-Al-Mt and Na-Mt, respectively. The percentage of chromium adsorption on Na-Mt were about 2~8%,and were not obvious;The percentage of chromium adsorption on Fe-Mt and Fe-Al-Mt decreased with solution pH increase. The impact of solution pH for Mg-Al and Mg-Al-Mt were not obvious.2. The order of maximum adsorption capacity (Q_m) from Langmuir equation was Fe-Al-Mt > Fe- Mt > Mg-Al LDH > Mg-Al-Mt> Na-Mt; K_F vaules of relatively adsorption capacity form Freundlich equation was the order of Mg-Al>Fe-Mt >Fe-Al-Mt >Mg-Al-Mt>Na-Mt.The Langmuir and Freundlich equations were used to describe chromium equilibrium sorption on LDH and modified montmorillonite. The values of Q_m for Mg-Al and Mg-Al-Mt are larger than Fe-Mt and Fe-Al-Mt, and that value for Na-Mt is smallest of all. The values of Q_m for Mg-Al were the order of 1Mg-1Al> 4Mg-1Al> 2Mg-1Al > 1Mg-2Al.3. The thermodynamics of the adsorption process indicates endothermic with phosphate. The positive values of△H decreased with the percentage of phosphate adsorption increased. The negative values of△G decreased with the temperature increased indicate the spontaneous nature of phosphate adsorption. The positive values of△S indicated a increased randomness during the adsorption of phosphate onto LDH and modified montmorillonite.4. The pseudo-second order kinetics provide the best correlation of the experimental data of various modified Mt and Mg-Al-LDH, and the determination coefficients(R~2)were 0.999. There also was correlation coefficient R~2(0.89~0.94)on various minerals fitted by Elovich equation. Parabolic diffusion equation was most suitable to descrirbe the phosphate adsorption on Na-Mt, and because phosphate adsorption is a diffusion process by inlaid in mineral layers and don’t involve chemical adsorption processes. The chromium adsorption kinetic date were fitted with pseudo-first, pseudo-second kinetic models, Elovich epuation and Parabolic diffusion equation. Parabolic diffusion equation was most suitable to descrirbe the chromium adsorption on Na-Mt,The pseudo-second order kinetics provide the best correlation of the experimental data of LDH and modified montmorillonite. The adsorptin effects of chromium adsorption on 2Mg-1Al and 1Mg-1Al were about 95%, higher than that of 4Mg-1Al and 1Mg-2Al, 70% and 81%,respectively.5. The concomitant anions have different extent adverse effect on adsorbent, but the differences were less than 10%, so the effect of concomitant anions for phosphate adsorption on LDH and modified montmorillonite were not abvious.

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