Enhanced removal of hexavalent chromium by lignosulfonate modified zero valent iron: Reaction kinetic, performance and mechanism

The application of lignin derivative as modifier is an economical and efficient approach to improve the reactivity of raw material towards pollutant removal. In this study, lignosulfonate modified zero valent iron (LS-ZVI) was firstly prepared by ball-milling method and utilized for Cr(VI) removal under different conditions. The comparative experiments showed that lignosulfonate modification could significantly enhance the Cr(VI) removal by ZVI from <10 % to 100 % within 90 min reaction. Compared to ZVI, the specific surface area of LS-ZVI increased 3.4 times and surface Fe(0) content increased from 3.4 % to 10.5 % due to the surface erosion, resulting in the high-efficient Cr(VI) removal. Solution and solid-phase analyses indicated that Fe(0) played dominated role and generated Fe(II) involved in Cr(VI) removal process, which mainly included rapid adsorption, reduction and co-precipitation. Batch experiments revealed that lower pH conditions were beneficial for Cr(VI) removal and the effect of co-existing ions (Ca2+, Mg2+, NO3-, Cl-, and SO42-) was negligible except the inhibitory effect of NO3-. Moreover, LS-ZVI also exhibited excellent removal performance for Ni(II), Zn(II), and Cd(II) with removal efficiency beyond 96.6 %. Overall, this work provides a feasible approach for enhancing the reactivity of commercial ZVI in the treatment of heavy metal pollution.