Long-lasting and efficient peroxydisulfate-based groundwater remediation driven by the slowly released Fe(II) from natural chlorite

The rapid depletion of peroxydisulfate (PDS) and the competitive inactivation of reactive species by excessive Fe restrict the oxidation duration and performance of iron (Fe)-based catalysts activated PDS for in situ chemical oxidation (ISCO). Here, natural chlorite, one of the Fe-rich clay minerals, is used as activator to enhance the performance and efficiency of PDS-based ISCO. It was found that acidification of contaminated groundwater drives the slowly release of aqueous Fe(II) from chlorite and serving as the source of multiple reactive species including hydroxyl radical (^•OH), sulfate radical (SO₄^•−), and Fe(IV). Benefitting from the controlled release of Fe(II), the scavenging of oxidative species by Fe(II) is notably alleviated, leading to the oxidant utilization efficiency of chlorite/PDS improved by 24–95 % compared to the Fe(II)/PDS and ZVI/PDS, and the costs of oxidants reduced by over 50 %. Long-term experiments indicate that PDS is relatively persistent and slowly consumed by chlorite, hence the oxidative ability for pollution control remains for over one month. This work not only proposes an effective, low-cost and promising alternative process for groundwater remediation, but also demonstrates the significance of slowly released Fe(II) in breaking the trade-off between peroxide activation rate and peroxide utilization efficiency in ISCO.