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 LÀ1, temperature 358C, pH 5.23, 2 g LÀ1 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 DG8, DH8 and DS8 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.

In the present study results obtained from batch experiments for Pb(II) adsorption from aqueous solution on a typical overburden sample of TISCO chromite mines have been discussed. The XRD pattern revealed that the major crystalline phases present were goethite, hematite and silica. The adsorption kinetics followed pseudo second-order model indicating chemical adsorption. Maximum Pb(II) adsorption at pH 5.23, temperature 358C, initial Pb(II) concentration of 250 mg LÀ1 was 24.28 mg Pb(II) per gram of sample. The adsorption process was endothermic in nature at low pH of 2 and 4 and was accompanied by positive entropy and positive Gibbs free energy. At pH 5.23, the adsorption process was independent of temperature indicating different mechanism of adsorption at different pH values. The adsorption data fitted well to Langmuir and Freundlich isotherms at pH of 5.23. Data fitted only to Langmuir isotherm model at pH values of 2 and 4. The Pb(II) adsorption affected the specific planes of goethite and silica thereby reducing their percentage of relative intensities. The short contact time of 30 min DES4295.3d 6/24/2009 13:33:10 a.u α−FeOOH SiO2 α−Fe2O3 Fig. 10. XRD Pattern of Pb(II) loaded TISCO overburden sample.