By-product materials are processed to mitigate undesirable effects. In some embodiments, industrial waste by-products are recycled using calcium polysulfide and used in building materials. In certain implementations, toxins are rendered non-viable as human pathogens by reaction with calcium polysulfide to create non-soluble sulfide crystals locked in the material as hydration is completed. The sulfides are not soluble in water and are locked into position within the resulting hydrate material, which mitigates escape of or changes of state in the toxins.