A new wet system to treat carbon dioxide in hue gas using water as an absorbent and soil as a cation-exchanger is proposed. The system consists of the following four processes. (i) Dissolution occurs of CO2 from the flue gas into soil-containing water and is accompanied by formation of carbonate ions and an increase in the pH of the solution. Soil functions as a cation-exchanger because it is rich in alkaline-earth-metal ions. (ii) The CO2 increase results in enhancement of hyrogen-ion and alkaline-earth-metal ion exchanges. (iii) Separation of the soil and aeration of the solution takes place. (iv) Carbonate-ion and alkaline-earth-metal ion reactions form carbonate salts, which are insoluble in water. The remaining solution is not toxic and does not damage the environment. It can be reused in the system or released into a river or the ocean. Our wet system is expected to be applied in developing countries because (a) inexpensive soil can be used as the cation-exchanger, (b) the discharged solution is harmless to nature and (c) insoluble carbonates may be used commercially.