Abstract: We studied reaction mechanism and efficiency of in situ remediation of Cr(Ⅵ) contaminated aquifer by Fe(Ⅲ)  enhanced tannic acid (TA). The results show that Fe(Ⅲ) can effectively improve the remediation efficiency of tannic acid to Cr(Ⅵ) contaminated aquifer by complexing with tannic acid. The two adjacent phenolic hydroxyl groups of pyrogallol structure in tannic acid molecule combine with Fe(Ⅲ) to prvide electrons,  so at least 9 mol tannic acid is needed to repair 1 mol Cr(Ⅵ). For the best strengthening effect of Fe(Ⅲ),  n（TA）∶n（Fe(Ⅲ)）=3∶5. At this time,  the tannic acid/Fe(Ⅲ) structure is the most stable and the storage capacity reaches the maximum.  After Cr(Ⅵ) pollution is repaired,  Fe(Ⅲ)  forms stable FeOOH under the action of tannic acid to adsorb Cr(Ⅲ) and form coprecipitation,  so as to achieve the purpose of remving total chromium. 

Key words: tannic acid/Fe(Ⅲ) system； Cr(Ⅵ) reduction; ,  in situ remediation; , iron-chromium coprecipitation