Methods and systems for utilizing carbide lime or slag

A method comprising:

• a) treating a slag solid or carbide lime suspension with an ammonium salt in water to produce an aqueous solution comprising calcium salt, ammonium salt, and solids;
• b) contacting the aqueous solution with carbon dioxide from an industrial process under one or more precipitation conditions to produce a precipitation material comprising calcium carbonate and a supernatant aqueous solution wherein the precipitation material and the supernatant aqueous solution comprise residual ammonium salt;
• and
• c) removing and optionally recovering ammonia and/or ammonium salt using one or more steps of (i) recovering a gas exhaust stream comprising ammonia during the treating and/or the contacting step;
• (ii) recovering the residual ammonium salt from the supernatant aqueous solution;
• and (iii) removing and optionally recovering the residual ammonium salt from the precipitation material;
• wherein the method further comprises separating the solids from the aqueous solution before the contacting step and adding the separated solids to the precipitation material as a filler.