Removal Of As(Ⅲ) And As(Ⅴ) From Aqueous Solutions Using Nanoscale Zero Valent Iron-reduced Graphite Oxide Modified Composites

Arsenic has long been controlled as one of the most priority control elements because ofits toxicity and carcinogenicity. Nanoscale zero valent iron (NZVI) has high adsorptioncapacity of As(III) and As(V), but it is limited in practical use due to its small particle sizeand aggregation effect. Now it is need to find a good carrier to load NZVI to develop theirstrengths and avoid its disadvantage. Reduce graphite oxide (RGO) has been used as asupporter because of its high surface area and good electron transport properties.In our study, we loaded NZVI to graphene for the removal of arsenic in the water. Thecharacteristics of RGO-NZVI were determined with X-ray diffraction, X-ray photoelectronspectroscopy, Zeta potential, BET and transmission electron microscopy characterization forcharacterization. We also studied the effects of reaction time, pH, temperature and othervariables. In order to compare the difference of NZVI, RGO and RGO-NZVI, we do thecomparative experiment under the same conditions.The results show that NZVI had been loaded into the RGO successfully. According tothe data inferred from Langmuir model, the adsorption capacity of As(III) and As(V) was35.83mg/g and29.04mg/g, respectively. The residual concentration was found to meet thestandard of WHO after the samples were treated with0.4g/L NZVI-RGO when the initialconcentration of As(III) and As(V) were below8mg/L and3mg/L. Especially, when theinitial concentration of As(III) was below3mg/L, the residual concentration was within1μg/L; whereas, the residual concentration was undetected when the initial concentration ofAs(III) was1mg/L. The initial concentration range can reach WHO standard more widely.The initial pH of the solution has important effect for the adsorption capacity, and the effectis different for As(III) and As(V). For the As(V), it is the role of electrostatic attraction. Themechanisms of adsorption with As(V) and As(III) are different, the adsorption of As(III) isdivided into two processes, surface complexation (pH <9.1) and electrostatic interactions(pH>9.1).The study also compared the difference of the adsorption of NZVI, RGO and RGO-NZVI with As (III) and As (V). The adsorption effect of NZVI is well, but RGO absorption is bad,both adsorption isotherms are met Langmuir isotherm model, the maximum adsorptioncapacity of As (III) and As (V) are calculated to25.04and22.4366,5.5405and4.1973mg/grespectively. The maximum adsorption capacity of the mechanisms of adsorption with As(V)and As(III) are different, the adsorption of As(III) is divided into two processes, surfacecomplexation(pH <9.1) and electrostatic interaction (pH>9.1).The study also did the adsorption of NZVI, RGO with As (III) and As (V) to compare thedifference with RGO-NZVI. The results indicated NZVI have an obvious effect, but RGO haslittle effect. Their adsorption isotherms met the Langmuir isotherm model, their adsorptioncapacity of As(III) and As(V) were25.04and22.4366,5.5405and4.1973mg/g. And themaximum adsorption capacity of RGO-NZVI also greater than the sum of the NZVI and RGO,thus provided that RGO-NZVI is a better material to remove arsenic.