Upcycling of waste sodium sulfate to sodium carbonate and sulfur

Waste sodium sulfate (Na₂SO₄) 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 Na₂SO₄ into value-added sodium carbonate (Na₂CO₃) and sulfur (S_x). In this process, Na₂SO₄ is first reduced to sodium sulfide (Na₂S) at 750 °C using charcoal. Subsequently, the generated Na₂S is oxidized by CO₂ via carbonation at 300 °C to produce Na₂CO₃ and S_x. Temperature modulation shifts thermodynamic equilibrium to drive the conversion of SO₄^2- 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 CO₂-eq per kg Na₂CO₃ compared with the conventional sodium sulfate-based ammonia-soda process (SSA-Process). By eliminating water-intensive steps and ammonia (NH₃) usage, our method lowers the end-point environmental impact to 34.69 mPt per kg Na₂CO₃ (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.