Novel slow release ammonium persulfate capsules for in situ remediation of high arsenic groundwater

Abstract Slow-release materials (SRMs) are a promising oxidant delivery technology for in situ chemical oxidation (ISCO) to remove arsenic (As) from groundwater on site. Microcapsules capable of slowly releasing ammonium persulfate (APS) have been developed and applied to aquifer Fe-coating technology. APS microcapsules and dissolved Fe(II) can be injected into an As-contaminated aquifer to boost the formation of hydrous ferric oxide or hydroxide, thus immobilizing aqueous arsenic via adsorption. This study reports on the use of microcapsules with extended release time to control the redox environment in the in situ remediation of As-contaminated groundwater and prevent the reductive dissolution of hydrous ferric oxide or hydroxide. The experimental results demonstrate that microcapsules capable of slowly releasing the APS oxidant were successfully prepared. The core–shell structure of the microcapsules in which APS was enclosed with poly(methyl methacrylate) (PMMA) was confirmed with X-ray diffraction (XRD) and X-ray photo-electron spectroscopic (XPS) analyses, and the uniform morphology of the 1-µm microcapsules was revealed by scanning electron microscopy (SEM). The life span of the APS microcapsules was estimated to be 9 days. Zero-order release kinetics could qualitatively explain the experimental curve and predict the release mechanism. The small microcapsules had satisfactory transport performance in porous media and could represent a more efficient, long-term strategy for in situ remediation of high arsenic groundwater.