Adsorption Of Phosphate, Ammonium And Dye From Aqueous Solution By Modified Zeolites

Since reform and opening-up, rapid economic development makes large quantities of untreated pollutants such as phosphate, ammonium and dye being discharged into surface water bodies directly. The presence of nitrogen(N) and phosphorus(P) in water is an important factor responsible for causing eutrophication, and most of dyes have three induced effects(carcinogenic, teratogenic, and mutagenic). Therefore, it is necessary to remove N, P and dyes from wastewater before their discharge into surface water bodies. Natural zeolite can effectively remove cations contaminants and the modified zeolite has a good effect on anion contaminants. In this study, lanthanum/magnetite/zeolite(La/Fe3O4/Zeo) composite, cetylpyridinium bromide(CPB) modified zeolites, HAP-Fe3O4-zeolite(HAP/Fe3O4/Zeo) composites were prepared and characterized. The La/Fe3O4/Zeo composite was used as an adsorbent to remove phosphate and ammonium from aqueous solution. The CPB-modified zeolites and HAP-Fe3O4-zeolite(HAP/Fe3O4/Zeo) composites were used as adsorbents to remove anionic dyes from aquous solution. Results of this work will be helpful for the application of modified zeolites to remove nutrients(phosphate and ammonium) or anionic dyes from wastewater.La/Fe3O4/Zeo composite was used as an adsorbent to remove phosphate and ammonium from aqueous solution. The adsorption of phosphate and ammonium on La/Fe3O4/Zeo composite was investigated in batch mode. Results showed that the La/Fe3O4/Zeo composite was effective for the removal of phosphate and ammonium from aqueous solution. The phosphate and ammonium adsorption capacity for La/Fe3O4/Zeo composite decreased with increasing solution p H from 6 to 11. The equilibrium adsorption data of phosphate and ammonium on La/Fe3O4/Zeo composite could be described by the Langmuir and Freundlich isotherm models. The maximum phosphate and ammonium monolayer adsorption capacities for La/Fe3O4/Zeo composite derived from the Langmuir isotherm were determined to be 12.9 mg P/g and 6.99 mg NH4+/g, respectively(p H 7 and 298 K). The adsorption kinetic data of phosphate and ammonium on La/Fe3O4/Zeo composite can be better described by the pseudo-second-order kinetic equation. The presence of chloride, sulfate or bicarbonate in solution had no negative effect on the adsorption of phosphate on La/Fe3O4/Zeo composite. The presence of potassium or sodium ion in solution had a great negative effect on the adsorption of ammonium on La/Fe3O4/Zeo composite, while the presence of calcium ion had a slight negative effect on the adsorption of ammonium. The main mechanism for phosphate adsorption onto La/Fe3O4/Zeo composite at p H 7 was ligand exchange interaction, and the main mechanism for ammonium adsorption onto La/Fe3O4/Zeo was cation exchange.Cetylpyridinium bromide(CPB)-modified zeolites with different coverage types were prepared by loading different amounts of CPB on natural zeolites, and they were used as adsorbents to remove methyl orange(MO) from aqueous solution. The effect of various parameters such as CPB loading amounts, adsorbent dosage, solution p H, reaction temperature, initial adsorbate concentration, and contact time on MO adsorption onto CPB-modified zeolites was investigated using batch method. Results showed that the natural zeolite had negligible affinity for MO in aqueous solution, while the CPB-modified zeolites exhibited much higher MO removal efficiency than the natural zeolite. The MO adsorption capacity for CPB-modified zeolite increased with increasing CPB loading amount. The MO removal efficiency of bilayer CPB-modified zeolite increased with increasing adsorbent dosage, while the amount of MO adsorbed decreased with increasing adsorbent dosage. The equilibrium adsorption data of MO on bilayer CPB-modified zeolite could be described by the Langmuir isotherm model. Based on the Langmuir isotherm model, the predicted maximum MO adsorption capacity for bilayer CPB-modified zeolite with CPB loading amount of 341 mmol/(kg zeolite) was found to be 63.7 mg/g at 303 K and p H 7. The adsorption kinetic data of MO on bilayer CPB-modified zeolite followed a pseudo-second-order kinetic model. Solution p H and reaction temperature had little influence on MO adsorption onto bilayer CPB-modified zeolite.A novel hydroxyapatite/magnetite/zeolite(HAP/Fe3O4/Zeo) composite was prepared, characterized and used as an adsorbent to remove Congo red(CR) from aqueous solution. The adsorption characteristics of CR from aqueous solution on the HAP/Fe3O4/Zeo composite were investigated using batch experiments. Results showed that the CR removal efficiency of the HAP/Fe3O4/Zeo composite increased with increasing adsorbent dosage, while the amount of CR adsorbed on the HAP/Fe3O4/Zeo composite decreased with increasing adsorbent dosage. The adsorption kinetic data of CR on the HAP/Fe3O4/Zeo composite well followed a pseudo-second-order model. The equilibrium adsorption data of CR on the HAP/Fe3O4/Zeo composite could be described by the Langmuir and Freundlich isotherm models. The maximum monolayer adsorption capacity for CR derived from the Langmuir isotherm model was determined to be 117 mg/g at p H 7 and 303 K. The main mechanisms for the adsorption of CR on the HAP/Fe3O4/Zeo composite at p H 7 include surface complexation, hydrogen bonding and Lewis acid-base reaction. Thermal regeneration showed that the HAP/Fe3O4/Zeo composite could be used for desorption-adsorption cycles with high removal efficiency for CR in each cycle. X-ray diffraction(XRD) analysis revealed that the HAP/Fe3O4/Zeo composite contained Fe3O4, and this composite has relatively high saturation magnetization. The HAP/Fe3O4/Zeo composite adsorbed with CR could be collected from aqueous solution under an external magnetic field quickly.Based on the results above, the La/Fe3O4/Zeo composite is a promising adsorbent for the simultaneous removal of phosphate and ammonium from wastewater. The bilayer CPB-modified zeolite is a promising adsorbent for the removal of MO from wastewater. The HAP/Fe3O4/Zeo composite is a promising adsorbent for the removal of CR from wastewater.