The Adsorption And Mechanism Of Xpanded Rice Husk For Heavy Metals

The research was supported by the Key Technology R&D Program of China. The project is the preparation and study of bioadsorbent for mining wastewater (No.2007BAB18B08). From the view of waste resource recycle and the view of reducing chemical pollution, expanded rice husk was researched on the adsorption of heavy metal wastewater indetail. As a new kind of biosorbents, its adsorption characteristics of removing Cu2+, Ag+, Pb2+and mixture aqueous solutions of Cu2+-Ag+and Cu2+-Pb2+were studied in batch experiments comparing with properties of raw rice husk(RRH), nature diatomite (ND), nature bentonite (NB), commercial coconut-shell activated carbon (C-AC) from nature resources and cation exchange resin(CER) in the same conditions. Meanwhile, the investigation was carried out on the mechanism of heavy metal ions adsorbed by expanded rice husk. The results were concluded as follows:(1) The FTIR of ERH show that its surface contained-NH2,-COOH. The ERH have more-CH2-and-CH3than RRH. The ERH was slight lower than RRH about the BET surface area, but the pore volume was increased from0.00780to0.0105cm3/g; the point of zero charge is increased from2.2to2.6. The surface has negatively charge when the pH value was greater than the point of zero charge. The powder resistance of ERH was reduced from4.83GΩ to577MΩ. The data of XRF indicated ERH have SiO2approximately21.8%, the data of XRD show that SiO2have amorphous structure. The data of TG show that ERH’s decomposition temperature was294.39℃. The analysis of SEM images, ERH have rougher surface than RRH. The data of EDS show that SiO2was gathered in package-like structure at the surface.(2) The adsorption isotherms of ERH can be fitted best with the Langmuir model, the maximum adsorption capacities of ERH was11.8mg/g. The data was fit in kinetics pseudo-first/second order kinetics models, respectively, ERH have to reach kinetic equilibrium in90min, E%was83%.The ERH in Cu2+solution have well removal between pH4to6, The thermody nami c analysis revealed that the adsorption process was spontaneous at low temperature, it’s an exothermic reaction process. At the room temperature, ERH have better adsorption capacity than RRH, from4.71mg/g, and3.60mg/g.(3) The adsorption isotherms of ERH can be fitted best with the Langmuir model in Ag+solution, the maximum adsorption capacities of ERH was18.6mg/g. The data was fit in kinetics p seudo-second order kinetics model. At600min, ERH have to reach kinetic equilibrium, E%was60.3%. The ERH in Ag+solution have well removal between pH3to5. The thermody nami c analysis revealed that the adsorption process was spontaneous at low temperature, it’s an endothermic reaction process. At the room temperature, ERH have better adsorption capacity than other sorbents.(RRH3.69mg/g, ND10.3mg/g, NB17.0mg/g)(4) The adsorption isotherms of ERH can be fitted best with the Langmuir model in Pb2+solution, the maximum adsorption capacities of ERH was40.2mg/g. The data was fit in kinetics p seudo-sec ond order kinetics model. At260min, ERH have to reach kinetic equilibrium, E%was95.2%. The ERH in Pb2+solution have well removal at pH6. The thermodynamic analysis revealed that the adsorption process was spontaneous,it’s against the adsorption raction at high temperature. ERH have better adsorption capacity than other sorbents.(RRH11.2mg/g,C-AC31.0mg/g,ND23.4mg/g,NB31.0mg/g,CER32.6mg/g).(5) In heavy metal mixture wastewater Cu2+-Ag+, the results showed that the adsorption capacities of ERH removal Cu2+was11.7mg/g and Ag+was4.46mg/g. The adsorption isotherms of ERH can be best-fit with the Langmuir model for Cu2+in Cu2+-Ag+. In the Cu2+-Pb2+, the results showed that the adsorption capacities about Cu2+was7.13mg/g and Pb2+was10.6mg/g.(6) The data of fitting Dubinin-Radushkevich (DR) isotherm model suggested that the adsorption mechanism were ion exchange and physical sorption for ERH in single-ion system. However,single-ion system or double-ion system the adsorption mechanism was ion exchange for Cu2+. Cu2+and Pb2+were against each adsorption,the adsorption capacity have a large reduced.The adsorption of Pb2+from physical adsorption mechanism in the single-ion system changed into ion exchange.In a wo rd,the data of experimental and theoretical analysis show that the ERH have good adsorption capacities and selectivity,ERH has potential in the field of heavy metal waste water. The adsorption mech nism of single-ions was changed when added other heavy metals.