Special Needs student with disruptive behavior (racial slurs towards teacher)
A professor in this situation should consult with the university office that is responsible for students with disabilities, let them handle the situation, and follow their recommendations regarding what to do if it happens again. Anything else is beyond the scope of the professor's role. 

Professors are not qualified to "counsel" students with disabilities, and shouldn't try to (amateur psychology can be very harmful to the "patient.") 

In some parts of the world, there are legal issues related to disciplining students with disabilities.1 Again, the office that deals with students with disabilities should be aware of these legal issues and are best placed to advise the professor.



1 For example, in the US:


  IDEA requires that a student’s disability be taken into account when considering disciplinary action resulting from a violation   of the school code of conduct [in high school]. This is not the case in higher education


(Source). Other jurisdictions will have varying legal protections for students with disabilities.