Adsorption of Cr( Ⅵ ) onto landfill liner-soil materials

The adsorption capacity of landfill liners containing granular activated carbon(GAC),or bentonite activated by acid,for Cr(Ⅵ) is investigated by the batch tests.The results show that the Cr(Ⅵ) sorption to all soil samples is nonlinear and characterized by a Langmuir isotherm model.Both the GAC and activated bentonite can be used as sorptive amendments for trapping Cr(Ⅵ) in landfill liners.The adsorption capacity of Cr(Ⅵ) onto all the soils increases with increasing temperature,and decreases with an increase of soil-solid concentration.As the soil-solid concentration increases,the Langmuir isotherm parameters(qm,b) first decreases logarithmically,but then stabilizes when the soil-solid concentration exceeds a critical value(e.g.,200 g/L).The isotherm parameters also increase linearly with increasing temperature.It is concluded that the values of the isotherm parameters measured under low soil-solid concentration may not properly simulate the real engineering situation.The isotherm parameters obtained with low soil-solid concentration can result in an overestimation of the retardation factor of landfill liner.Consequently,the batch tests should be conducted using a sufficiently high soil-solid concentration in order to obtain isotherm parameters close to the field situation.