Phosphogypsum–a byproduct of phosphoric acid production–piled near eco-sensitive regions, poses both environmental and health risks. By reacting phosphogypsum with NaOH, Ca(OH)₂ is produced, which can be utilized for CO₂ sequestration. The cost of NaOH, however, and the low market value of the byproduct, a concentrated Na₂SO₄ stream, hinder the economic viability of this approach. Here, we propose to increase the cost-efficiency of phosphogypsum processing by converting the Na₂SO₄ to NaOH and H₂SO₄ using bipolar membrane electrodialysis (BMED). The result is a cleaner and more circular process, as NaOH can be recycled for dissolving phosphogypsum, while H₂SO₄ can be reintroduced into the industrial phosphoric acid production or used to leach valuable metals out of the phosphogypsum. To assess the feasibility of BMED integration, we used a bench-scale system to probe the trade-off between obtaining high base-product concentration and obtaining high specific energy consumption. This was done for synthetic Na₂SO₄ solutions at various concentrations, applied voltages, and types of anion-exchange membranes. Economic analysis based on the results showed that a two-step batch BMED process is able to reduce the chemical cost by 50%, as compared to purchasing NaOH. Integrating BMED with existing approaches can, therefore, improve the sustainability and cost-efficiency of phosphogypsum valorization.

中文翻译：

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通过将电渗析与双极膜结合来增强磷石膏回收的可持续性

磷酸生产过程中产生的副产品磷酸石膏堆积在生态敏感地区附近，对环境和健康均构成威胁。通过使磷石膏与NaOH反应，可生成Ca（OH）₂，可将其用于CO ₂隔离。然而，NaOH的成本以及副产物的低市场价值，即浓缩的Na ₂ SO ₄物流，阻碍了该方法的经济可行性。在这里，我们建议通过将Na ₂ SO ₄转化为NaOH和H ₂ SO ₄来提高磷石膏加工的成本效率。使用双极膜电渗析（BMED）。结果是更清洁，更循环的过程，因为可以将NaOH再循环以溶解磷石膏，而H ₂ SO ₄可以重新引入工业磷酸生产中或用于从磷石膏中浸出有价值的金属。为了评估BMED整合的可行性，我们使用了台式规模的系统来探索获得高基本产物浓度和获得高单位能耗之间的权衡。这是针对合成Na ₂ SO _4进行的不同浓度，施加电压和阴离子交换膜类型的溶液。根据结果​​进行的经济分析表明，与购买NaOH相比，两步间歇BMED工艺能够将化学成本降低50％。因此，将BMED与现有方法集成可以提高磷石膏增值的可持续性和成本效率。