A new strategy for the comprehensive utilization of wastewater from the production of soda ash by sodium sulfate-based ammonia-soda process

The production of soda ash by the ammonia-soda process using carbon dioxide and ammonia for sodium sulfate is an effective method to realize the comprehensive utilization of waste resources of sodium sulfate, but this method produces a large amount of wastewater whose main substances are sodium bicarbonate and ammonium sulfate, which limits the modular industrial application of the production of soda ash by sodium sulfate-based ammonia-soda process(SSA-Process). At present, the main utilization method for the wastewater from the production of soda ash by SSA-Process is evaporation crystallization method to deal with the by-products of sodium sulfate and ammonium sulfate, which is a low-value, complex and energy-consuming process, so is an urgent need for a low-cost, high-value, short-process method to comprehensively utilize wastewater from the production of soda ash by SSA-Process. Based on the application theory of calcium hydroxide (Ca(OH)₂) in the traditional ammonia-soda process, this present study systematically investigated the causticization law and mechanism of Ca(OH)₂ in a simulated wastewater from the production of soda ash by SSA-Process. On this basis, a new process of Ca(OH)₂ segmented causticization was developed to realize the comprehensive utilization of wastewater from production of soda ash by SSA-Process. The results showed that this process enabled a highly efficient ammonia cycle for cost reduction and the production of high purity ultrafine calcium carbonate products and sodium sulfate solids, as well as calcium-based raw material for building materials.