I can't speak to nano silicate as a Se removal mechanism, but there has been some Japanese work with the use of lanthanum, probably as the chloride, for this purpose.
There are reports that nano-silicates will lower the water ORP to -550 mV to -860 mV, and oxidize and precipitate all selenate and selenite. I have also recieved reports that this is also achieved using nano-titania. I'm looking for a published paper or other written confirmation.
I have seen consistent removal results of >95% removal of Se with iron co-precipitation in FGD wastewater. This is operating full scale at ~500gpm blowdown from FGD using ferric chloride and polymer as coagulant.
that sounds almost too good to be true- I thnk it depends on the particular form of Se that is present in the FGD purge.
Other means being studied, besides bioreactors, is a trickle filter ( packed bed) of AC activated carbon or , better yet, sawdust or powdered torrefied wood dust.