Removal of Cr(III) from tannery wastewater by adsorption onto bentonite clay

In this study adsorption technique was applied for the successful removal of Cr(III) from tannery wastewater. For this purpose wastewater samples were collected from 18 tanneries to know the actual concentration of Cr(III) present in the influent (chrome tanning stage) and the combined wastewater. Maximum of 93% adsorption has been achieved on pre-treated (with sludge) wastewater samples with a shaking time of 15 min, while 76% is achieved in case of untreated samples with a shaking time of 45 min at a pH of 2.4–2.5. The process of uptake follows both the Langmuir and Freundlich isotherm models. Thermodynamic parameters such as ΔH°, ΔS° and ΔG° were calculated from the slope and intercept of the linear plot of ln KD against 1/T. Column studies have also been carried out using a certain concentration of wastewater. More than 99% recovery has been achieved by using 5 g of the bentonite with 3 M sulfuric acid solutions. Atomic absorption spectrophotometer was applied to determine the concentration of Cr(III) before and after adsorption.