Sulfur (or brimstone, as it is sometimes also called) is one of few minerals that can burn. In burning it produces an acrid and toxic smoke that can serve as a fumigant. It played a devastating role in the Lord's destruction of Sodom and Gomorrah (Genesis 19:24; Luke 17:29) and featured in God’s judgment warnings to Israel (Deuteronomy 29:23; Psalm 11:6; Isaiah 30:33). Mentioning “sulfur” in the present context enhances the picture of judgment as the Lord radically fumigates the Deceiver.
10 and the devil who had deceived them was thrown into the lake of fire and sulfur where the beast and the false prophet were, and they will be tormented day and night forever and ever.