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

Pure and 0.25% Ni2+ ion doped goethite samples, prepared by the coprecipitation method, were characterized for pH of Point of Zero Charge (pHpzc), Surface area, XRD, TG-DTA, FTIR and TEM. Effect of Ni2+ ions doping on the adsorption of chromate on goethite was investigated at pH-3, -5 and -7 in the temperature range 303–323 K. It was found that adsorption of chromate increases with decreasing pH and increasing temperature on both pure and Ni2+-doped goethite. Adsorption of chromate was found to increase from 61.4% to 82.92% with Ni2+ ion doping in goethite matrix at the lowest pH (pH-3) and highest temperature (323 K), using 1.02 mmol L−1 chromate solution. Langmuir isotherm was found applicable to the experimental data. The values of ΔH¯ (isosteric heat of adsorption) calculated for both the samples of goethite were positive, showing endothermic nature of the adsorption process.