Adsorption kinetics of hexavalent chromium on to natural red-earth: a laboratory simulated study

Heavy metal contamination of water is a significant threat to organisms and to public health. Among them, chromium is one of the important heavy metals in the environment that originates mainly from anthropogenic activities. Natural red earth (NRE), a ferrous-coated natural sand, is one of the materials that could be used to remove heavy metals from contaminated water. Laboratory-scale simulated experiments were carried out to identify the retention behavior of Cr(VI) on NRE. The effects of solution pH, initial Cr(VI) concentration, the amount of NRE used and the contact time were examined. Almost 63% Cr(VI) was adsorbed within 20 minutes. When particle size ranged from 125 to 180 μm, the Cr adsorption data followed the Langmuir isotherm model, providing a higher R² value of 0.9523, suggesting monolayer coverage on the homogeneous surface with a uniform distribution of energetic adsorption sites. The monolayer coverage of Cr on NRE is estimated as 11.35 mg/g. The data showed that NRE can be used to remove Cr(VI) from aqueous solutions effectively, and this method is found to be simple, effective, economical and environmentally friendly.