How much silicates do diatoms need to grow.

[Miami Reef]

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.

Impact of phosphate, silicate and natural organic matter on the size of Fe(III) precipitates and arsenate co-precipitation efficiency in calcium containing water

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…

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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.

Can silica unbind from GFO to reach equilibrium when concentrations in the bulk water drop from consumption?

 

[Randy Holmes-Farley]

Can silica unbind from GFO to reach equilibrium when concentrations in the bulk water drop from consumption?

I would expect that to happen, but I’m not sure where the equilibrium lies. Displacement of the silicate (knocking it off) by something that binds more strongly (possibly phosphate) may also be a significant process.