Transport of the arsenic (As)-loaded nano zero-valent iron in groundwater-saturated sand columns: Roles of surface modification and As loading.

In this study, the effects of surface modification of nZVI and arsenic (As) loading on the mobility of the three types of As-loaded nZVI (As-loaded pristine, chitosan-modified and polyaniline-modified nZVI) in quartz sand-packed columns were investigated. Breakthrough curves and retention profiles for the three types of As-loaded nZVI were analyzed by the Tufenkji-Elimelech equations and the HYDRUS-1D model. The mobility of both types of As-loaded modified nZVI was higher than the As-loaded pristine nZVI at both low and high As loadings. Compared to low As loading, the mobility of the three types of As-loaded nZVI was higher at high As loading. The values of the calculated and the fitted retention parameters of the three As-loaded nZVI were lower when As loading was higher or nZVI was modified, which were in line with the experimental column findings. The mechanisms of As-loaded nZVI transport were probably due to ripening and sedimentation. The As in the effluent was mainly from the As-loaded nZVI particles when nZVI was detected and was from the As release when no nZVI was detectable. It was evident that the mobility of the three types of As-loaded nZVI particles were severely limited (the maximum transport distance was less than 60 cm), regardless of surface modification and As loading. Therefore, the As release from the As-loaded nZVI could cause potentially wide pollution and should be paid more attention regarding to the application of nZVI in As remediation.