Study On As (Ⅲ) Purification From Aqueous Solution By Nano Iron Composites

Aqueous solution which contains Arsenic (As(Ⅲ)) remediation by nano-iron (NI) has received increasing interest in recent years, the NI has presented good performance in Arsenic removal due to its high reactivity and selectivity. However, NI particles are apt to aggregate in result of their high surface energy and magnetism, which greatly limited the application of NI in practical remediation. To solve the above problems, batch experiments were run in this study, and Oyster shell(OS) was chosen as supported material and Carboxymethyl Cellulose(CMC) was chosen as coated material to prepare stable and highly reactive composites.The primary objective of the experiment was to optimize the synthesis conditions for preparing the NI, OS/NI and CMC/NI. Meanwhile NI, OS/NI and CMC/NI were evaluated to remove As(Ⅲ) pollutants in aqueous solution, moreover, the effects of the preparation parameters as well as the treatment conditions on the As(Ⅲ) removal were also investigated. Including the influence of iron source, reductant, initial concentration of As(Ⅲ), initial pH as well as temperature on arsenic removal by OS/NI, CMC/NI and NI. The micromorphologies and composition of the composites were characterized by using field emission scanning electron microscopy(FESEM) and fourier transform infrared spectroscopy(FTIR). The impact of OS and CMC on NI surface structure and properties were discussed, and also the As(Ⅲ) removal mechanism of the OS/NI was investigated. Finally, X-ray photoelectron spectroscopy(XPS) and FTIR analysis on surface of OS/NI before and after reacting with As(Ⅲ) were operated in order to study the As(Ⅲ) removal mechanism.The main conclusions of the experiment are constituted of four parts as follows:1. The condition for preparation of OS/NI composite was optimized:Under the room temperature, the OS average particle size of< 425 μm, and FeSO4 as iron resource, KBH4 as reductant, the As(Ⅲ) in aqueous solution were almost removed.Under the optimal CMC/NI synthesized conditions with the coating ratio of 37wt%, and FeSO4 as iron source, KBH4 as reductant at room temperature. The As(Ⅲ) in aqueous solution were removed about 90%.2. Characterization of FESEM and FTIR results showed that OS/NI was dispersedly in the pore or the pore opening of OS, with a mean particle size of about 60 μm respectively, the peak weakened in the spectrum of Fe-O, hinting the decrease of Fe-O and the increase of the oxidation resistance of NI particles in NI/OS composite.Characterization of FESEM and FTIR results showed that the carboxy group of CMC was coordinated to the NI in monodentate ligand method. The peak weakened in the spectrum of Fe-O was hinting the decrease of Fe-O and the increase of the oxidation resistance of NI particles in CMC/NI composite.3. Batch experiments indicated that the physicochemical properties of the iron nanoparticles, such as diameter and aggregation, were influenced by the iron source more than the choice of reductant and temperature in the synthesis process, and these properties were closely related to the treatment performance of the composite. With higher temperature, the lower As(Ⅲ) removal. The variation of the pH value had no important impact on the removal performance of the NI/OS and CMC/NI composites. Indicated that the OS/NI and CMC/NI composites have good acid/alkali resistance.4. The removal of As(Ⅲ) by OS/NI was fitted by pseudo-second-order kinetics and Langmuir formula. Indicated that the removal process was monolayer adsorption, and the process are all ruled by chemical adsorption. The initial As(Ⅲ) concentration caused greater effects on the removal of As(Ⅲ) compared to the other factors. According to the XPS and FTIR, the As(Ⅴ), As(Ⅲ) and As(0) all could be detected on the surface of OS/NI after reacted with As(Ⅲ), which demonstrated that the removal of As(Ⅲ) was the result of adsorption, reduction and oxidation.