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 .