Retention capacity of natural sands for the treatment of waters containing arsenic trace levels
Résumé
The aim of this work is to study the As retention capacity of two natural sand, a quartz sand and a volcanic red sand. Sorption experiments were performed in batch reactors at a constant ionic strength (0.010 M NaNO3). pH was controlled by acid or base microadditions. As, Fe, Al and Si were analysed in the aqueous phase to control their fate. Kinetic experiments of arsenic sorption showed that a fast step followed by a slow one could be observed depending on the sand. In the most rapid step, the formation of monodentate complexes could be the main phenomenon while in the slowest one bidendate and binuclear complexes could predominate. During As(V) sorption, the analyses of Al, Fe and Si showed that the dissolution of the different minerals present in the sands as Al, Si and Fe (hydr)oxides was not affected by As(V) sorption. From the point of view of the surface reactivity, the quartz sand has more available sites for arsenic sorption than the volcanic sand. However, the red soil shows a better retention capacity as expressed in amount of As per solid mass unit: 666 nmol g-1 and 9.4 nmol g-1 for the red soil and the quartz sand, respectively, for a contact time of 288 h.