Upcycling of waste sodium sulfate to sodium carbonate and sulfur

Abstract

Abstract Waste sodium sulfate (Na 2 SO 4 ) is a common industrial byproduct that poses environmental risks and resource loss if improperly managed. Here, we report a thermochemical upcycling method to convert waste Na 2 SO 4 into value-added sodium carbonate (Na 2 CO 3 ) and sulfur (S x ). In this process, Na 2 SO 4 is first reduced to sodium sulfide (Na 2 S) at 750 °C using charcoal. Subsequently, the generated Na 2 S is oxidized by CO 2 via carbonation at 300 °C to produce Na 2 CO 3 and S x . Temperature modulation shifts thermodynamic equilibrium to drive the conversion of SO 4 2− to S x , achieving a carbonate yield of 95.35% with purity exceeding 99.53%. Life cycle assessment (LCA) indicates that this anhydrous route reduces the global warming potential by > 0.43 kg CO 2 -eq per kg Na 2 CO 3 compared with the conventional sodium sulfate-based ammonia-soda process (SSA-Process). By eliminating water-intensive steps and ammonia (NH 3 ) usage, our method lowers the end-point environmental impact to 34.69 mPt per kg Na 2 CO 3 (vs. 48.81 mPt for conventional routes). Overall, this work provides a sustainable strategy for reclaiming waste salts and closing the sodium and sulfur cycles.