Effect of Ni2+ ion doping on the physical characteristics and chromate adsorption behavior of goethite

Pure and 0.25% Ni(2+) ion doped goethite samples, prepared by the coprecipitation method, were characterized for pH of Point of Zero Charge (pH(pzc)), Surface area, XRD, TG-DTA, FTIR and TEM. Effect of Ni(2+) ions doping on the adsorption of chromate on goethite was investigated at pH-3, -5 and -7 in the temperature range 303-323K. It was found that adsorption of chromate increases with decreasing pH and increasing temperature on both pure and Ni(2+)-doped goethite. Adsorption of chromate was found to increase from 61.4% to 82.92% with Ni(2+) ion doping in goethite matrix at the lowest pH (pH-3) and highest temperature (323K), using 1.02 mmol L(-1) chromate solution. Langmuir isotherm was found applicable to the experimental data. The values of Delta H (isosteric heat of adsorption) calculated for both the samples of goethite were positive, showing endothermic nature of the adsorption process.