Carbonation of aqueous suspension containing red mud

Carbonation experiments were carried out on an aqueous suspension containing red mud, a by-product of Al2O3 manufacture by the Bayer process.(1) In the course of carbonation, the components of the red mud cease practically from dissolution after about 120min.(2) The quantities of Na, Si, Ca and Mg dissolved by carbonation, which give the highest value at 10°C, decrease with rising the temperature at which the carbonation is made, respectively.(3) With increase in the concentration of CO2 gas, they increase, on the contrary, the quantity of Fe dissolved by carbonation decrease.(4) With increasing a ratio of red mud to H2O, the quantities of Na, Ca, Mg and Fe dissolved by carbonation increase, however, that of Si attains the maximum at the ratio of 1 to 20.(5) The course of carbonation depends upon the variety of red mud to be leached.(6) It is found from the rate of dissolution of Na amounting to 33% at maximum that a partial decomposition of the sodium aluminosilicate in the red mud may be taken place during carbonation. Generally, the quantities of Si, Ca, Mg and Fe dissolved by carbonation are small.(7) From the results obtained, some discussions are made for the chemical reactions during the carbonation and an optimum condition is determined to recover Na as NaHCO3 solution from red mud.