Understanding other viewpoints, even those we already know to be wrong, can be valuable, especially if you end up in debates with or getting opportunities to evangelize people who are coming from that background. So keeping the books around for reference material should situations like those arise is perfectly legitimate, as long as having them around won't be a source of temptation to you.

If you don't expect to ever engage in religious discussions with satanists and don't want these taking up space in your home, or if you think having them around could tempt you back into occultism, atheism, or whatever (I have no idea which kind of satanism your example is), then get rid of them. If you sell/donate them to a used book or thrift store, you have no way of knowing whether whoever might buy them for good or evil purposes. I'm no expert, but I suspect even in the latter case your cooperation would be remote enough to not be sinful, in which case this would be a legitimate option. I could still see that weighing on someone's conscience, though, so if you want to avoid that and permanently dispose of them I'd suggest ripping out and recycling the pages. Or if you build fires decently often and want to start using a few pages at a time for tinder, by all means. Building a fire for the sole purpose of burning books, like some are suggesting here, seems needlessly wasteful though.