The Preparation Of Anion Adsorbent With Spent Grains And Its Application In Low Concentration Arsenic Adsorption From Water

In recent years, the surface water and ground water of China have been suffered from arsenic contamination. The safety of drinking water is on the line. The traditional treatment methods can’t meet the increasingly stringent environmental protection requirements. However, it has lots of advantages such as efficient, economical and reproducible for arsenic removal using biological adsorbent. Nowaday, the output of agricultural waste is giant in China, which is onlybe burnt and/or poultry feed.Using agricultural waste as high efficiency adsorbent, and applying to the treatment of arsenic-containing water can not only utilize the agricultural waste, but also governe the arsenic pollution from water.In this paper spent grains from brewery was chosen as the absorbent to remove arsenite from water. The preparation anion adsorbent with spent grains(hereinafter referred to as SG-AA) was alkaline pretreated by Na OH, which followed by reacting with epichlorohydrin and quaternized with trimethylamine solution. The optimum preparation conditions were obtained. First of all, the solid-liquid ratio of original spent grains and 2 mol/L Na OH was 1g to 10 m L, which the suspension being 2 h. Then the ratio of alkalization spent grains, epichlorohydrin, Na OH, ethanol was 1 g:5 m L:8 m L:2 m L, which the suspension placing in a water bath and stirring 4 h at 65℃. The thirdly, the ratio of cross-linking spent grains and 30% trimethylamine solution was 1g:5 m L, which the suspension placing in a water bath and stirring 2 h at 65℃. At last, the modified spent grains was rinsed with copious deionized water to neutral, which followed by placing in the oven to dry at 80 ℃.Scanning Electron Microscope, Energy Dispersive Spectrometer, Fourier Transform Infrared Spectroscopy, X-ray Diffraction were used to test the structure and physico-chemical properties of the original spent grains and SG-AA. Spent grains appear wood fiber characteristics, and stays with the non-crystalline or amorphous. The weight loss of spent grains includes two procedures. One is the removal of adsorbed water, the other is the thermal decomposition of spent grains. The surface of SG-AA has some changes for many folds, grooves and pits. The activities of hydroxyl(-OH), alkyl and carbonyl(C=O) groups with modified spent grains has been enhanced.The quaternary amine groups has been introduced. The p HPZC of SG-AA appeared in the range of p H-7~8, p H<p HPZC, the surface of SG-AA is positive charge, which benefits to the adsorption of anion.The physichemical factors and adsorption mechanism for arsenic by SG-AA have been investigated. Compared with the original spent grains, the removal efficiency for As(III) by SG-AA can be improved 61.11%. The initial concentrations of 0.5 mg/L As(III) can be reduced to 0.01 mg/L, which can meet the requirement of “The Health Standards for Drinking Water”(GB5479-2006). The optimum adsorption conditions for arsenic-containing water by SG-AA were p H 3~7, dosage 8 g/L, reaction time 30 min. The adsorption behavior for arsenic by SG-AA conformed to the pseudo-first order kinetics equation and the Langmuir adsorption model, which illustrated that the adsorption reaction is mainly controlled by diffusion process and belongs to the monolayer adsorption. With the increase of concentration of As(III) or reaction temperature, the saturated adsorption capacity for As(III) by SG-AA also be increased. When the temperature was 328 K, the saturated adsorption capacity can be reached 0.302 mg/g. Through a variety of modern instrumental analysis, it was confirmed that the SG-AA adsorpted arsenic selectively, in which the hydroxyl and amino group of the surface of SG-AA combining with arsenic.The adsorption column was filled by SG-AA to investigate the dynamic adsorption for arsenic. The breakthrough curve of adsorption column was related to the flow velocity of solution, initial concentration of arsenite and column height. Increasing the flow velocity of solution, raising the initial concentration of arsenite, reducing the column height can make the breakthrough of adsorption column accelerate. The relationship between the running time of adsorption column and the column height can be described by BDST model, in which the correlation coefficient R2 reaches 0.9992. Yoon-Nelson model can predict the theoretical time of Ct/Co=50%, which is very close to the experimental data. The breakthrough time of actual arsenic-containing water with SG-AA has been advanced, but it still has a good adsorption capability for arsenite. After three times of adsorption-desorption-regeneration, the adsorption capacity of breakthrough declined only 12.19%, which showed a high stability for the arsenite adsorption by SG-AA.