I do not know the relative affinity with high accuracy. Both are bound to a significant extent. I think that phosphate is more strongly bound, based on related data such as that below where phosphate is better able to prevent binding of a third ion (arsenate) than is silicate. hence I think sufficient phosphate will displace silicate on the GFO.
Removal of arsenic (As) from water by co-precipitation with Fe(III) (oxyhydr)oxides is a widely used technique in water treatment. Nevertheless, As re…
www.sciencedirect.com
From these results it can be concluded that the removal of As(V) in the presence of Si and P was affected mainly because of the reduced adsorption of As(V), whereas in the presence of NOM a reduced adsorption and a reduced Fe(III) removal both were responsible.
Phosphate reduced As(V) adsorption the most, mainly because of its similar affinity for adsorption sites and higher concentration than As(V). But, the overall As(V) removal efficiency was reduced the most with the variations in NOM concentrations, mainly because NOM rendered a large portion of Fe(III) mobile in the solution.
