NO! Satanists cannot use Wiccan spells ... Create your own spells first and second learn that you have to choose left or right handed path... There is a coven that is left handed path... And btw you say you are a mix of everything so ... -.-
A spell is simply a way of directing energy and will to accomplish a particular purpose. It is a magical practice, not necessarily a religious one. So there is no reason that someone could not use a spell crafted by a practitioner of another path. You might need to modify it a bit to make it more personal and appropriate for your purpose, but other than that there are no limits.