| In recent years, there are some researches on using biological activated carbon as a new adsorption material to remove heavy metals from contaminated soil and water, but few researches are found for removal arsenic (As) from wastewater. In this paper, 5 kinds of carbonized rice husk were prepared with rice husk as raw material through anoxic pyrolysis at different temperature. The 5 materials were modified with acids and alkalis, and As adsorption test was conducted to screen the material with high adsorption effect of As from wastewater, which was marked as CRHCaO600. Magnetic nano Fe3O4 was loaded on the surface of CRHCaO600 and a new material, modifed carbonized rice husk loaded nano Fe3O4, marked as CRH-I, was prepared. In this study, the effects of adsorption time, solution pH, and addition amount of CRH-I on adsorption of As containing solution were investigated. The characteristics of As adsorption was discussed through experiments of kinetics and isothermal adsorption. Meanwhile, the adsorption and desorption capacity of As in solutions and the removal capacity of As in real As containing wastewater were researed for CRH-I. Finally, the BET surface area, pore structure analysis, SEM, XRD and FTIR were analized to study the adsorption characteristics and mechanisms of CRH-I for As. The main results of this paper were summarized as follows:(1) Screening through the As adsorption test indicated that carbonized rice husk were activated after CaO modification which removed more As(V) from solution than the other materials. The best removal effects were found for CRHCaO600, and the removeal ratio reached 82%. Therefore, CRHCaO600 was selected for further modification with magnetic nano Fe3O4 loading to prepare CRH-I, a new material.(2) The adsorption experiments showed tha at the beginning of adsorption, the rate was fast; with increasing the adsorption time, the rate decreased gradually. The adsorption equilibrium of CRH-I for As(V) in solution was reached at about 8 h. Compared with CRHCaO600, the removal raios of CRH-I for As(V) in wastewater increased significantly. With decreasing pH values of solution, the removal raios of CRH-I for As(V) in wastewater increased gradually, which reached 98.3% at pH 2. However, this ratio was only 63.7% at pH 11. The adsorption reaction of As(V) on CRH-I was satisfied with the dynamics equation of quasi two-level and the correlation coefficient R2 was 0.999. The experimental data of As(V) adsorption on CRH-I conformed better to the Langmuir isotherm equation than the Freundlich isotherm equation at different temperatures, and the correlation coefficient R2 was 0.985 at 25℃. Calculation results of adsorption thermodynamics demonstrated that the process of CRH-I adsorbing As(V) in solution was spontaneous, and the low temperature was more conducive to the adsorption.(3) The experiments of adsorption and desorption of As(V) on CRH-I indicated that the removal ratios of As(V) in solution after 5 times of adsorption and desorption processes by reusing CRH-I were 83.2% 66.4%,65.6%,67.2%,64.0%, respectively. This showed that the removal ratio of As(V) on CRH-I was still quite high after the first adsorption and desorption; and from then on, the removal ratio began to decrease after the second time and kept at a relatively stable level of about 65%. This experiment implied that CRH-I was of a good adsorption capacity for As(V) in solution and of a stable regenerating capacity for adsorption.(4) BET observation indicated that compared with CRH600, the specific surface area of CRH-I increased by about 30%, reaching to 182.03 m2·g-1. The micro surface area and microspore volume of CRH-I expanded about 6 times. XRD test results showed that no new crystal was found in the adsorption process of As(V) on CRH-I and implied that this was a surface adsorption. FTIR analysis showed that compared with CRH600, more intermolecular carboxyl and phenolic hydroxyl groups were found inside CRH-I, and aromatization effects and aliphatic ether substances were produced in preparation of CRH-I.(5) Pre-treatment combined CRH-I addition was used for real As containing wastewater. The concentrations of As(III) and As(V) in yielding water were 0.034 mg·L-1 and 0.245 mg·L-1, respectively, reaching to the requirements of the National Integrated Wastewater Discharge Standard (GB8978-1996) (The maximum allowable concentration of arsenic emissions is 0.5 mg·L-1), when addition of CRH-I was 2 g and solid-liquid ratio was 1:200. The removal ratios of heavy metals in this wastewater on CRH-I increased with increasing CRH-I addition gradually, and reached to 9.8%-30.7% for Pb,34.1%-55.1% for Cd,10.9%-22.8% for Zn, and 57.1%-66.7% for Mn, respectively. Among the 4 heavy metals, the concentrations of Pb and Cd in yielding water satisfied the emission standards. |
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