Effects and mechanism of humic acid on chromium(VI) removal by zero-valent iron (Fe0) nanoparticles

The present study dealt with the performance evaluation of the nanoscale Fe0 systems for the remediation of chromium contaminated groundwater in the ambient environment. The role of humic acid (HA) in the Cr(VI) removal and the reduction mechanism were investigated. HA was found to exert an obvious inhibitory effect on Cr(VI) removal by Fe0 nanoparticles, and the Cr(VI) removal efficiencies decreased from 71.6%, 58.4%, 57.8% to 38.5% with the increasing HA concentrations (0, 5, 10, 20 to 40 mg L−1). A dual effect of humic acid on chromium(VI) reduction by Fe0 nanoparticles was observed. HA adsorbed on the surface of Fe0 nanoparticles and occupied the active surface sites, leading to the decrease in Cr(VI) reduction rates. Greater was the adsorbed HA, the more obvious was the inhibitory effect. However, the HA adsorption on iron surface areas was one of the factors leading to the decreased reduction rate. The appropriate starch dosage (0.5 g per 0.3 g nanoscale Fe0 particles) could definitely eliminate the inhibitory effect of humic acid.