CESR Process for Sulfate Removal
Cost-Effective Sulfate Removal (CESR) is a chemical treatment process that can reduce sulfate concentrations to very low levels. Originally developed in Europe, the CESR process is used in full-scale installations there but has only been evaluated at the bench-scale and pilot-scale levels in the U.S. The process combines addition of lime and a chemical called Lumnite MG-4 to precipitate a calcium aluminum sulfate hydrated compound called ettringite.
Here's a paper on the process: