Preparation And Characterization Of Anion Adsorbent Derived From Rice Straw

Rice straws (RS) are regarded as abundant and available biological resources.But most of them are abandoned or combusted without proper utilization leading toenvironmental pollution and safety incidents. The problem of eutrophication is one ofthe serious water pollution problems. It mainly because of excessive nutrients inwater containing nitrogen and phosphorus available for algae, in which phosphorus isthe limiting factor of the algae proliferation is caused by water eutrophication keynutrients. In this paper, the original method based on rice straw anionic sorbentsynthesized and applied to water, phosphate adsorption studies.Modified rice straw (MRS) was prepared from rice residue after reaction withepichlorohydrin and triethylamine in the presence of N,N-dimethylformamide andethylenediamine. An optimal synthesis condition of MRS Was determined after thesingle influential factor experiments. Data of phosphate removal and yield were usedas performance indicators of the products prepared. The physical and chemicalcharacteristics of RS and MRS were examined by lots of instruments, such asscanning electronic microscope, elemental analysis instrument, infrared spectroscopyinstrument and a variety of chemical methods, and were compared with the originalrice straw.The results indicated that the dosages of reactants, experimental time andexperimental temperatures all influenced the preparation of MRS, so the conditionsshould be strictly controlled in the modification process. The best adsorptionconditions: pH4to10; adsorbent dosage of5g/L; temperature on the adsorptioneffect is not significantly affected, so the actual application is not subject to thelimitations of seasonal temperature. The rate of phosphorus removal was more than90%.The physical and chemical characteristics of MRS had significant difference withthose of RS. The surface of MRS were as clearer and smoother in comparison withRS,and lots of holes were observed in the lengthways residues；IR spectrums of MRSand RS demonstrated an increase of amino groups in the structure of MRS, and it wasvalidated by the elemental analysis which indicated a significant increase of nitrogencontent in MRS. The electric charge of the MRS was positive, rather than negative asRS. The adsorption performances of MRS were tested by batch adsorptionExperiments. MRS had large dose range to guarantee high removal rate of phosphatefrom aqueous solution. The maximum adsorption capacities reached1.96mmol/g. Theadsorption of phosphate by MRS could reach equilibrium in15min, and thepseudo-second-order equation generated the best agreement will experimental data foradsorption systems. Intra-particle diffusion is not the only rate-limiting step; otherkinetic processes ale simultaneously occurring and contribute to the adsorptionmechanism．For regeneration, the desorption rate of the0.2g saturated adsorption of anionsrice straw after modification can be achieved by more than90%by using20ml,0.1mol/L NaOH solution.10cycles of adsorption an desorption tests showed that theadsorption capacity of rice straw is not changed significantly, indicating that themodification of rice straw can apply to the eutrophication treatment.