Cr(VI) removal from groundwater using double surfactant-modified nanoscale zero-valent iron (nZVI): Effects of materials in different status.

The excellent potential of nanoscale zero-valent iron (nZVI) makes it a promising remedy for contaminated aquifers. More efficient remediation modes with nZVI have been investigated recently to overcome the inherent drawbacks of materials. In this study, a double surfactant-modified synthesis method is established to make the removal of Cr(VI) more efficiency. A specific focus of the materials status (suspension or powder) is devoted to explore the best application condition, especially for groundwater remediation. A non-ionic surfactant, polyvinylpyrrolidone (PVP), and an anionic surfactant, sodium oleate (NaOA), were selected to modify nZVI simultaneously. The kinetics and isotherm experiments, reactions at different pHs, initial concentrations, gas conditions, and coexisting ion conditions were conducted to analyse the removal mechanism. The characterizations before and after the reaction were used to further explain the results. From the batch experiments, a synergistic effect could be recognized in Cr(VI) elimination when PVP and NaOA were both used for nZVI modification. The materials in suspension (without drying process) exhibited higher removal efficiency in comparison with powder ones. These reactions happened in acidic condition demonstrated higher reactivity. The anaerobic condition facilitated the reaction, which showed prospect application in groundwater. Equilibrium could be reached within 2 min using the suspension sample with a removal efficiency above 99.5% and a maximum removal amount of 231.75 mg g-1. The reaction process was well-fitted with pseudo-second-order kinetics and the Langmuir model. Cr(VI) was fully transformed into Cr(III), a safer status. These results show this is a promising in-situ method to eliminate Cr(VI) pollution in groundwater.