The purpose of this paper is twofold. The first is to convert phosphogypsum (PG) waste, mainly composed by gypsum (CaSO4·2H2O), into potassium sulfate (K2SO4) compound, which help to reduce the environmental impact and open new ways and valuable chain for the industrial manufacturing of phosphoric acid. The second is to recover MgSO4·7H2O from desalination reject brine water (RBW), thereby minimizing its associated environmental impact. The novelty of the current study is to simultaneously use the recovered salts K2SO4 and MgSO4·7H2O to produce K2Mg(SO4)2.6H2O (K2MgS6), considered as a double fertilizer. Additionally, Solid–Liquid Equilibria (SLE) are frequently applied to several industry domains. SLE are an interesting outline to visualize the precipitation, separation, and purification of a solid phase and the pathways by which crystallization can occur. The SLE of the ternary phase diagrams K2SO4-MgSO4-H2O at 25 °C and 0 °C were especially used to successfully determine the operating conditions and the design of a crystallization process during the PG/RBW conversion into K2MgS6. Several characterization techniques (i.e., XRD, DTA/DTG, SEM/EDS, FTIR) were employed to identify the solids formed during this process. An analysis on the distribution of natural radionuclides and heavy metals was carried out to confirm the effectiveness of the developed process. The main conclusion of this study was that K2MgS6 fertilizer can be manufactured by combining PG and RBW from desalination plants. Furthermore, the formed fertilizer, K2MgS6, is highly recommended for many applications in the agriculture sector.

中文翻译：

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在制造 K2Mg（SO4）2·6H2O 肥料的过程中同时回收海水淡化废盐水和磷石膏废料


本文的目的有两个。首先是将主要由石膏 （CaSO4·2H2O） 组成的磷石膏 （PG） 废物转化为硫酸钾 （K2SO4） 化合物，这有助于减少对环境的影响，并为磷酸的工业制造开辟新的途径和有价值的链条。第二种是从海水淡化废盐水 （RBW） 中回收 MgSO4·7H2O，从而最大限度地减少其对环境的影响。本研究的新颖之处在于同时使用回收盐 K2SO4 和 MgSO4·7H2O 生产 K2Mg（SO4）26H2O （K2MgS6），被认为是双重肥料。此外，固液平衡 （SLE） 经常应用于多个行业领域。SLE 是一个有趣的轮廓，用于可视化固相的沉淀、分离和纯化以及结晶的途径。特别使用 25 °C 和 0 °C 时三元相图 K2SO4-MgSO4-H2O 的 SLE 成功确定了 PG/RBW 转化为 K2MgS6 过程中的操作条件和结晶过程的设计。采用了几种表征技术（即 XRD、DTA/DTG、SEM/EDS、FTIR）来识别在此过程中形成的固体。对天然放射性核素和重金属的分布进行了分析，以确认所开发工艺的有效性。本研究的主要结论是 K2MgS6 肥料可以通过结合海水淡化厂的 PG 和 RBW 来制造。此外，形成的肥料 K2MgS6 被强烈推荐用于农业领域的许多应用。