| Vanadium is an emerging contaminant that is known to be toxic and can cause digestive and respiratory problems in humans. Regulations for vanadium concentrations in drinking water are currently lacking in most states in the United States, except for California (15microg/L). As a part of a water quality testing project with the United Nations High Commissioner for Refugees (UNHCR), the drinking water in refugee camps in Djibouti was evaluated, and vanadium levels as high as 100microg/L were measured. Little work has been done on finding economical vanadium remediation techniques. This study focuses on the optimization of vanadium removal by iron oxides, which are ubiquitous in the natural environment and are known to be effective at removing and stabilizing heavy metals from solution. Two forms of nano-sized iron oxides, hematite and goethite, have been selected for this study because of their large surface area and thermodynamic stability. Bench-scale batch experiments have been performed to determine the efficacy of vanadium removal from solution by hematite and goethite while varying the (i)pH, (ii)conductivity, and (iii)initial vanadium concentration.;Results show that both hematite and goethite will remove vanadium from solution to non-detect levels at various initial vanadium concentrations and pH ranges. Adsorption maximum is observed at around 40 mg/L vanadium concentration for both hematite and goethite. The edge curves show that vanadium adsorption on both iron oxides is strongly pH dependent. Lower pH favors adsorption despite the electrostatic repulsion between the vanadate cation and the positively charged oxide surface. Higher conductivity favors vanadium adsorption at pH 7 and 8 for both types of iron oxides. The Freundlich isotherm model closely matched the data from this study. A plot of the isotherm equilibrium constants with respect to conductivity suggests a linear trend. The two-step extraction procedure shows that the majority of the sorbed vanadium was strongly adsorbed to the goethite surface. |
