Prediction of adsorption from aqueous phase of organic molecules as a function of some physicochemical characteristics of activated carbons

Filtration onto activated carbon is often use in order to eliminate organic micropollutants from drinking water. However, plant operators generally do not have appropriate tools to assess the lifespan of such filters and cann ot prejudge the effectiveness of the treatment units. To develop an adequat e predictive model of this lifespan, it is needed to quantify the physicoch emical characteristics of activated carbon which influence the adsorption p henomena. In this study, several physicochemical characteristics of nine ac tivated carbons were determined (specific surface, pore distribution, miner al elements, surface functions, electrokinetic potential, interfacial tensi on, thermodynamic constants). From these characteristics, correlations were carried out in order to indicate general trends for the use of activated c arbons having various origins and activation processes. Sorption kinetics a nd isotherms for two molecules with very different physicochemical properti es (atrazine and phenol) were carried out in order to determine their respe ctive adsorption capacity. The comparison between the physicochemical chara cteristics of the carbons and these adsorption capacities allowed to discus s on the influence of the nature and the structure of the carbons on adsorp tion of organic compound. The sorption kinetics can help to better understa nd the role of the physicochemical characteristics of the activated carbon in the mechanisms of adsorption. This study pointed out the following resul ts: (i) the number of polar primary sites of adsorption increases as the nu mber of add functions increases and as the number of basic functions decrea ses; (ii) the maximum capacity of adsorbed water increases as a function of the specific area and decreases with the number of add functions of the ac tivated carbon; (iii) the adsorption of atrazine (molecule with low polar) is controlled in part by physical parameters such as specific area, (iv) th e polar groups facilitate the adsorption of phenol (very polar molecule); ( v) the values of the zeta potential are difficult to interpret: the presenc e of undetermined functional groups probably play a role on the sorption me chanisms. These results may be considered in the perspective of the develop ment of a predictive model of the lifespan of activated carbon filters.