Synthesis And Characterization Of Dispersed Zero-valent Iron Nanoparticles And The Removal Of As(Ⅲ)

Recently, due to their high reactivity and the rapid removal of pollutants included variousorganic contaminants, heavy metal ions as well as notorious inorganic anions, nanoscalezerovalent iron（nZVI） has drawn extensive research focus in groundwater remediation.However, nZVI particles tend to aggregate due to their magnetism and high surface energy,which greatly limited the application of nZVI in groundwater remediation.To solve the above problems, a series of screening tests were run in this study, andpoly（styrenesulfonate）（PSS） was chosen as dispersant to prepare stable and highly reactivenZVI/PSS slurry. Nitrogen adsorption and desorption method, transmission electronmicroscopy（TEM）, X-ray photoelectron spectroscopy（XPS）, X-ray diffraction（XRD）, andZeta（ζ）-potential analyses were applied to characterize nZVI/PSS. The impact of PSS onnZVI surface structure and properties were discussed. Moreover, the influence of nZVIloading, initial concentration of As（III）, initial pH as well as cation(Na⁺and Ca²⁺ on arsenicremoval by nZVI and nZVI/PSS were investigated. Finally, XPS analysis on surface of nZVIand nZVI/PSS before and after reacting with As（III） were run in order to investigate the As（III）removal mechanism.The main conclusions of this work are made of four parts as follows:1. The condition for preparation of nZVI/PSS slurry was optimized:100mL nZVI slurry(nZVI concentration:10g·L^-1) were added to2mL5%（w/v） PSS aqueous solution. Themixture was purged with nitrogen gas and stirred at300rpm for3h. The nZVI/PSS slurry asprepared could be stable for2weeks.2. Characterization results showed that nZVI and nZVI/PSS are largely spherical, with amean particle size of50-60nm and BET of29.60m²·g^-1and38.44m²·g^-1respectively. TheXPS studies indicated that percentage of C, OH^-, and O₂-of nZVI/PSS increased, while theadsorbed H₂O decreased compared to that of nZVI. The XRD studies indicated that Fe（0）exists as α-Fe0at nZVI/PSS surface instead of amorphous Fe（0） at nZVI surface.3. Batch experiments showed that the removal rate of As（III） by both nZVI andnZVI/PSS increased with increasing of dosage of nZVI or nZVI/PSS, and decreased with increasing of pH, initial concentration of As（III） and concentration of Na⁺and Ca²⁺. Overall,the reactivity of nZVI/PSS with As（III） is excellent and comparible with that of nZVI.4. The removal of As（III） by nZVI and nZVI/PSS fit in pseudo-first-order kinetics. Theinitial pH and cation(Na⁺and Ca²⁺ concentration caused greater effects on the removal ofAs（III） compared to other factors. As（V）, As（III） and As（0） could be detected on the surface ofnZVI as well as nZVI/PSS after reacted with As（III）, which indicated that the removal ofAs（III） was the result of oxidation, reduction and adsorption.