Removal of Chromium from Water using Manganese Oxide Based Adsorbents: Adsorption of Cr(III) and Cr(VI)

The removal of chromium from water down to environmentally acceptable levels is required because of the toxicity of this contaminant species. The removal of chromium from water should be achieved in an effective manner using relatively simple and inexpensive technology. Various technologies such as ion exchange, membrane filtration, adsorption and reduction-filtration-precipitation have been employed for removal of chromium from water. Adsorption is considered as a relatively simple and effective technology with low operational cost. Metal oxides such as manganese oxides have commonly been used as potential adsorbents for the removal of heavy metals. However, the application of pure manganese oxides as viable adsorbents or filter media in a flow-through (adsorber) column system is limited due to the low hydraulic conductivity and extant colloidal form of the pure manganese oxides. Manganese-coated sand (MCS) has exhibited a considerably appreciable adsorption capacity toward several heavy metal species which are present in water as cations or as oxyanions. In this study, we focused on synthesizing and evaluating a novel MCS sorbent with a high hydraulic conductivity as a potential sorbent for removal of two chromium species [Cr(III) and Cr(VI)] from water. In order to investigate the adsorption mechanism and interactions between the two chromium species with the MCS sorbent, we employed several surface characterization techniques to analyze the crystallinity and surface oxides on the surface of the MCS sorbent, surface charge, surface elemental composition and oxidation states of manganese and chromium before and after adsorption. A surface complexation model was developed for the adsorption process based on the experimental adsorption data and surface characterization results. A sustainability assessment was performed to compare the sustainability of the MCS adsorber system with two other technologies used for the removal of chromium from water.