Sorption capacities of various activated carbons towards nitrates: effects of nitrate concentration, pH, time and co-existing ions

With the increase in agriculture intensity, associated with the use of nitrogen-based fertilizers, nitrate pollution is starting to be an issue in soils and waters. Therefore, there is a need to find a way to prevent nitrate from leaching from the soils by retaining it into the soil. One of the solutions is to use carbon-based amendments such as activated carbon, which has a good sorption capacity. This study aimed at evaluating the sorption capacities of several activated carbons towards nitrate, and study the effects of different parameters, i.e. initial nitrate concentration, initial solution pH, contact time and co-existing anions, on their sorption capacities. Results showed that among eight tested activated carbons, from different feedstocks, four (L27, 2 K, 5 K, CS) presented a high sorption capacity, between 5.91 and 14.55 mg.g −1 , which was affected ( p < 0.001) by contact time (maximum sorption occurred within 60 min), solution pH (maximum sorption at pH 2) and the presence of co-existing anions. Moreover, the construction of sorption isotherms showed that sorption occurred mainly through monolayer, while the kinetic model showed a chemical sorption mechanism. Finally, infra-red analysis of the activated carbons revealed that various functional groups were involved in the sorption but also that electrostatic interaction was not the only sorption mechanism. This study demonstrates the importance of feedstock and activation type, as well as particular properties of activated carbon for the sorption of nitrate. It also shows the potential of four materials (L27,2 K, 5 K, CS) for the retention of nitrate in water-soil systems.