Abstract: The present invention is a process to react limestone with sulfate and/or sulfuric acid solutions and/or other solutions containing sulfates, in order to neutralize the solutions and precipitate the sulfates, in such a way that the limestone is used with an efficiency that makes the use of limestone economic. This reaction is most often used in the environmental cleanup of mine and industrial wastes, however it may be used in other industrial applications. In previously existing technology, the reaction is typically done in agitated tanks containing a slurry of the solution mixed with lime or limestone, or in percolating beds of crushed limestone. Typically the reaction of limestone in such systems is very slow and inefficient, so that normally the use of limestone is precluded—it is instead necessary to utilize lime (calcium oxide or hydroxide).