Results are shown in Figs. 5a and 5b (size of symbols was
chosen to correspond to uncertainty). After 4 h, the adsorbed
quantity was stable for all the solids and for both arsenite and arsenate,
except for Alx(OH)y-Montm. Therefore, an equilibrium
time of 4 h was chosen for the following experiments concerning
all matrices but Alx(OH)y-Montm. This equilibrium time
is in agreement with Raven et al. (31) and Pierce and Moore
(32) who observed that 99% of the maximum observed arsenite
and arsenate adsorption on ferrihydrite was complete within
4 h of reaction initiation. Alx(OH)y-Montm presented a lower
adsorption capacity than the other matrices. The removal is not
proportionally related to the surface area, so SSA is not the primary
factor controlling the interaction of arsenite and arsenate
with the different matrices.