Ash containing considerable amounts of free little as the most active component requires stabilization to assure safe landfilling. Using CO2 front,flue gases as a neutralizing agent, also the emission of CO2 is diminished. The most extensive effect could be achieved by treating ash-water suspensions with CO2-containing gas. As even minute amounts of extraneous substances present in water influence the extent and rate of lime solubility in water, the behavior of lithe as the key component of ash in various conditions was studied and the mechanisms of process deceleration was proposed. As the next step, a laboratory-scale continuous-flow reactor system for aqueous carbonation of oil shale ash and main considerations for industrial pilot-scale plant design were developed.