Vinegar is a good weed killer and general disinfectant. For a really good disinfectant that's stronger then bleach, spray your equipment with vinegar then wait 30 seconds and spray again using hydrogen peroxide. Never pre-mix. Always spay in two passes, the order doesn't really matter.
That's the only thing that I could think of for your extra hydrogen peroxide. I've heard of people spraying their plants and seeds with H2O2, but it seems to me like it would do more harm then good. I know a lot of gardeners that are cheap and use creative methods to grow organically on the cheap, but I don't know of anyone who really uses hydrogen peroxide other then on small cuts and scrapes.
If the silica you have is anything like the AN Rhino Skin or Bonticare Silica Blast, I'd say use it until it's empty just so it doesn't go to waste. Personally I really don't have a lot of faith that it will do anything, so I wouldn't recommend buying more of it, but if you already have it go ahead and use it.