Fate of As(V)-treated nano zero-valent iron: determination of arsenic desorption potential under varying environmental conditions by phosphate extraction.
Nano zero-valent iron (NZVI) offers a promising approach for arsenic remediation, but the spent NZVI with elevated arsenic content could arouse safety concerns. This study investigated the fate of As(V)-treated NZVI (As-NZVI), by examining the desorption potential of As under varying conditions. The desorption kinetics of As from As-NZVI as induced by phosphate was well described by a biphasic rate model. The effects of As(V)/NZVI mass ratio, pH, and aging time on arsenic desorption from As-NZVI by phosphate were investigated. Less arsenic desorption was observed at lower pH or higher As(V)/NZVI mass ratio, where stronger complexes (bidentate) formed between As(V) and NZVI corrosion products as indicated by FTIR analysis. Compared with the fresh As-NZVI, the amount of phosphate-extractable As significantly decreased in As-NZVI aged for 30 or 60 days. The results of the sequential extraction experiments demonstrated that a larger fraction of As was sorbed in the crystalline phases after aging, making it less susceptible to phosphate displacement. However, at pH 9, a slightly higher proportion of phosphate-extractable As was observed in the 60-day sample than in the 30-day sample. XPS results revealed the transformation of As(V) to more easily desorbed As(III) during aging and a higher As(III)/As(V) ratio in the 60-day sample at pH 9, which might have resulted in the higher desorption.
Department of Civil and Environmental Engineering, The Hong Kong University of Science and Technology, Clear Water Bay, Sai Kung, Hong Kong, PR China.
Haoran
H
Dong
Xiaohong
X
Guan
Irene M C
IM
Lo
D000327:Adsorption; D001151:Arsenic / Q000737:chemistry* / Q000493:pharmacokinetics; D006863:Hydrogen-Ion Concentration; D007501:Iron / Q000737:chemistry*; D007700:Kinetics; D008956:Models, Chemical; D049329:Nanostructures / Q000737:chemistry*; D010710:Phosphates / Q000737:chemistry*; D056951:Photoelectron Spectroscopy; D017550:Spectroscopy, Fourier Transform Infrared; D013997:Time Factors; D014874:Water Pollutants, Chemical / Q000737:chemistry* / Q000493:pharmacokinetics; D018508:Water Purification / Q000379:methods; D014961:X-Ray Diffraction
D010710:Phosphates; D014874:Water Pollutants, Chemical; D007501:Iron; D001151:Arsenic