Pb(II) adsorption on Tata chromite mine overburden

Low chromite containing overburden is usually dumped as a waste material during mining of chromite ore. A large quantity of such waste is generated in TISCO chromite mines, India. Since this overburden material contains 20–46% iron, it can be a potential adsorbent for toxic metal ions present in wastewaters and industrial effluents. A typical sample of overburden from TISCO chromite mines containing 43.75% iron was used for Pb(II) adsorption from aqueous solutions. The specific surface area was estimated to be 50.8 m2/g. The XRD pattern showed the presence of goethite, hematite and silica (quartz) as the major crystalline phases. The experimental parameters varied during adsorption were time, pH, temperature, Pb(II) and sample concentration. The maximum loading capacity was estimated to be 24.28 mg g−1 of sample under the following conditions: initial Pb(II) concentration 250 mg L−1, temperature 35°C, pH 5.23, 2 g L−1 of chromite overburden sample and time 30 min. The adsorption data at pH 5.23 fitted well to Langmuir and Freundlich isotherms. The data at lower pH values of 2 and 4 fitted only to Langmuir model. The thermodynamic parameters ΔG°, ΔH° and ΔS° were determined at various pH values. From the results it was observed that the adsorption at pH of 2 and 4 was endothermic while at pH 5.23, it was independent of temperature. The XRD pattern of Pb(II) overburden sample revealed that relative intensity of (110) plane of goethite and (012) plane of SiO2 decreased during adsorption. The good loading capacity of this material suggests that it can be effectively used for Pb(II) removal from aqueous solutions.