About 95% of electricity production in the Republic of Estonia is based on the firing of pulverised local solid fuel - oil shale. This process is accompanied by high CO2 emission and followed by the formation of waste alkali ash in huge quantities. Ash is removed by hydrotransport and deposited in wet dumps. A complex of laboratory and field experiments with different ashes and their transport water samples from operating power plant (1610 MW) was carried out. Low activity and low carbonation rate of dry ash were determined as well as a much higher activity of previously hydrated ash, which in favourable conditions could be completely carbonated. An up to 50-60% degree of carbonation of transport waters by binding CO2 from the air in the production cycle was established. The total amount of CO2 bound from the air and calculated basing on the results of laboratory model experiments reached 37 kg per 1 ton of oil shale burnt in the electricity production. The relative part of bound CO2 formed 20.5% and 4.2% from the carbonate and total emission of CO2, respectively. The recommendations to increase the amount of CO2 bound at natural field conditions have been worked out. By implementing them, the amount of bound CO2 could be essentially increased - up to 35-36 and 6-7%, respectively.