Adsorption of Cu(II) and Pb(II) onto a grafted silica: isotherms and kinetic models.
The isotherms and kinetics of adsorption of lead(II) and copper(II) onto a grafted silica are studied at 20 degrees C. A commercial silica is grafted with an ethylediamine derivative, N-[3-(trimethoxysilyl)propyl]-ethylenediamine. From the Langmuir isotherms, maximum adsorption capacities of the grafted silica towards Pb(II) and Cu(II) are determined (0.184 mmol Pb(II)g-1 and 0.261 mmol Cu(II)g-1) and compared to those of non-modified silica (respectively, 0.019 and 0.036 mmol g-1). Four kinetic models, i.e., pseudo-first order, pseudo-second order, Langmuir and double-exponential are applied to fit the experimental kinetic data. The kinetic parameters are determined which allow to calculate the theoretical metal uptake as a function of time. The results are discussed and indicate the best fit is obtained with the double-exponential model. A discussion on the adsorption mechanism with respect to the double-exponential model leads to two possible interpretations: the metal uptake may follow a diffusion-controlled mechanism or a two-site adsorption process.
D000327:Adsorption; D003300:Copper / Q000737:chemistry*; D004058:Diffusion; D007700:Kinetics; D007854:Lead / Q000737:chemistry*; D008962:Models, Theoretical; D012822:Silicon Dioxide / Q000737:chemistry*; D013696:Temperature; D018508:Water Purification / Q000379:methods
D007854:Lead; D012822:Silicon Dioxide; D003300:Copper