PRODUCTION OF SODIUM CARBONATE AND ALUMINA FROM DAWSONITES

The Berezovoyarskoe deposit is the largest dawsonite Na2AlCO3(OH)2 deposit in Russia. It is located in the Kemerovo Region (Kuznetsk basin, Kuzbass). The inferred resources of this deposit amount to ≈ 400 mln. tonnes, including ≥ 140 mln. tonnes of Al2O3 and ≥ 145 mln. tonnes of sodium carbonate (Na2CO3). Dawsonite-containing rocks are mainly represented by argillites, which are fine gravely, hard and have low permeability. The dawsonite surface is passivated by a zeolite crust, therefore, underground leaching of the ores from this deposit is not viable even by using hydraulic fracturing technology or any other activation method. The thickness of any of the five dawsonite horizons ranges from 17.5 to 27 m. The shallow depth of the overburden (~ 50 m) represented by friable grounds and level spacing allow open-cut mining and in-situ processing of the dawsonite ores. A full cycle of producing smelter grade alumina and sodium carbonate requires significant capital expenses that makes it less cost-effective. Geological features of the deposit and available infrastructure (limestone quarries, coal pits, etc.) provide for another solution. In-situ chemical dawsonite processing was developed to obtain a concentrate containing secondary dawsonite, pseudoboehmite, thermonatrite (Na2CO3×H2O) and other forms of sodium bicarbonate with an impurity of sodium hydroalumosilicate (DSP). Control of concentrations during the carbonation decomposition of the solutions enables to obtain the required composition of the concentrate. The Achinsk alumina refinery, which is located not far from the deposit, produces alumina and sodium carbonate from nephelines (Na,K)AlSiO4, therefore, it can use the dawsonite concentrate to produce smelter grade alumina and sodium carbonate. Adding the dawsonite concentrate to pressure desilication of the aluminate liquor allows improving alumina and sodium carbonate production with minimal alterations of the Achinsk production process. The technology reduces the carbon footprint without generating any additional solid wastes (e.g. belite mud) and has a number of other benefits. Moreover, the dawsonite concentrate can be used to balance the alkali losses at the two Urals alumina refineries.