Capability and mechanism of Cr(VI) removal by phthalic acid modified sulfidated microscale zero valent iron

Mechanochemically sulfidated microscale zero valent iron (S-mZVI^bm) exhibits promising Cr(VI) removal performance but is prone to be passivated by Cr(VI), how to mitigate the passivation is still a challenge. In this study, we successfully synthesized phthalic acid (PA, carboxyl-rich organic acid) modified S-mZVI^bm particles (PA-S-mZVI^bm (4:1)) through ball milling. The pre-corrosion of the ZVI surface by PA effectively increased the specific surface area of ZVI. Additionally, the carboxyl groups complexed with Cr(VI), thereby enhancing its Cr(VI) removal capacity and alleviating the passivation. The Cr(VI) removal by PA-S-mZVI^bm (4:1) was mainly a chemisorption process on the surface and its Cr(VI) removal capacity (55.47 mg/g) was 1.26 and 9.94 – 14.83 times that of PA-mZVI^bm and S-mZVI^bm, respectively. The electron efficiency of Cr(VI) removal by both PA-S-mZVI^bm (4:1) and S-mZVI^bm was ∼100 %, however, the Fe(0) utilization efficiency of PA-S-mZVI^bm (4:1) was at least 15 times higher than that of S-mZVI^bm, explaining the superior performance of PA-S-mZVI^bm (4:1). This study confirmed that PA modification could effectively mitigate the passivation and improve the Fe(0) utilization efficiency of S-mZVI^bm.