Thermal Processing of Sodium sulphate to Sodium carbonate

Abstract

 Abstract — Mine water is environmentally toxic due to high metal concentrations. Strict legislation is enforced. Water of drinking quality needs to be produced and zero waste should be left at the mine site. The ROC (Reverse osmosis/Cooling) process can meet these requirements. In the ROC process, Na 2 CO 3 is used in the pre-treatment stage for selective recovery of metal compounds, such as Fe(OH) 3 at pH3.5, followed by reverse osmosis for recovery of drinking water and brine containing 90 g/L Na 2 SO 4 . In the sub-sequent cooling stage, Na 2 SO 4 .10H 2 O is removed through cooling, due to its low solubility of 45 g/L at 0°C. The purpose of this investigation was to investigate the thermal conversion of the product, Na 2 SO 4 .10H 2 O, to the raw material, Na 2 CO 3 . It was found that (i) Na 2 SO 4 .10H 2 O can be converted to Na 2 SO 4 though heating between 60°C and 100°C, (ii) Na 2 SO 4 cannot be converted directly to Na 2 S, as the raw material, Na 2 SO 4 , melts in the same temperature region where the reduction takes place, namely above 860°C, (iii) Na 2 S can be produced via CaS (indirect method) (Pyrusim simulation studies) and (iv) Na 2 S can be converted to NaHS, NaHCO 3 and Na 2 CO 3 (OLI simulation