See the very long thread
How to eliminate Sulfates from waste water effluents
thread127-37319
and the FAQ
Sulphate removal
How do I remove sulphates from effluent?
faq164-544
You will need to give a more thorough description and analyses for the water, as suspended organic solids interfere with some treatment options. Cations, pH, etc.
What is the sulfate source? Any chance to modify, or if this is coming from a sulfite treatment, maybe isolate that wastewater stream.