I had to quit my job do to workplace harrment?

i had to recently quit my job because my boss and hr would not do anything about my complaint on harrment from a co-worker. she has called a nurse a white b**** and threated to beat her a** and nothing was done. she is very racial to white people and works with the elderly and not pleasant to them either . she threatened to slap me to a nurse and the nurse choose to come and tell me which is very unprofessional. and the supervisor did nothing so i wrote a letter to the d.o. n. and she did nothing but take me off the unit where we worked togeter. hmmmm i told the d.o.n. that i can not work for a company that allows this behavior anylonger so i quit but what can i do legally to stop this company from this type of behavior and someone else ending up the same way i was or and elderly person being abused from this lady. i loved my job and got along with everyone . is it because she is black she can do this crap to other people its not fair ...... help me stop her