Experimental study on the removal of Cr(Ⅵ) from water by biochar-based sulfide modification loaded with nano-zero valent iron

In order to treat Cr(Ⅵ) pollution in groundwater, biochar-supported nano-zero valent iron (BC-nZVI) was prepared by the carbothermal method, and the modified material (M-BC-nZVI) was prepared by vulcanization modification of BC-nZVI. The chromium removal capacity, Cr to Fe ratio (Cr/Fe) and the reactivity of M-BC-nZVI were used to analyze the superiority of M-BC-nZVI for chromium removal. A failure rate model was established through the simulated column test to calculate the chromium removal capacity of M-BC-nZVI that completely failed. Finally, the application feasibility of M-BC-nZVI in removing Cr(Ⅵ) was analyzed by comparing it with the relevant studies. The results showed that the removal capacity, Cr/Fe and pseudo-first-order reaction rate constant (k_obs) of M-BC-nZVI were 1.86, 1.95 and 3.00 times higher than those of BC-nZVI, respectively. Therefore, compared with BC-nZVI, M-BC-nZVI had certain advantages in various aspects. Each simulated column had no obvious blockage during operation, and the failure rate constant of M-BC-nZVI increased with the increase of influent concentration. The highest chromium removal capacity (12.70 mg/g) reached when the failure chromium removal rate was 1.0% of the initial chromium removal rate and the influent Cr(Ⅵ) concentration was 5 mg/L. By comparing Cr/Fe of M-BC-nZVI with iron-based materials and iron-based modified materials reported in other studies, Cr/Fe of M-BC-nZVI was 1.06 to 42.06 times that of other studies. Therefore, based on the chromic removal performance of the material, it was feasible to apply M-BC-nZVI to permeable reactive barrier to treat Cr(Ⅵ) pollution in groundwater.