Good luck, tough row to hoe! First I suggest that if you suspect that a surface that is intended to be painted has been exposed to silicone compounds, first wash it down with strong detergents BEFORE any attempt to sand or grind. These actions will only spread or imbed the nasty stuff. What ever stage you are in now, about the only thing that you can do is repeated wash downs with a professional remover as was suggested.
Silicone is very persistent, microscopic amounts will cause "fish eyes" in paint. Just a tiny amount in the system will shut down an entire multi-million dollar industrial paint shop. (don’t ask how I know!) Be cautious of using hand lotions, body anti-perspiration cosmetics around any high quality painting operation.
Joe B