Wu Zhengyang, Feng Zongyu, Zhao Longsheng, Li Zheng, Wang Meng, Xia Chao
National Engineering Research Center for Rare Earth, Grirem Advanced Materials Co., Ltd., Beijing 100088, China.
Rare Earth Functional Materials (Xiong'an) Innovation Center Co., Ltd., Xiongan 071700, China.
Materials (Basel). 2025 Jun 16;18(12):2824. doi: 10.3390/ma18122824.
The precipitation process of rare earth from a rare earth chloride solution using magnesium bicarbonate yields a dilute magnesium chloride (MgCl) solution. The dilute MgCl solution can only be concentrated to a maximum concentration of about 70 g/L by conventional reverse osmosis (RO), which is insufficient for recycling. Low-salt-rejection reverse osmosis (LSRRO) allows for a higher concentration of brine while operating at moderate pressures. However, research on LSRRO for the concentration of MgCl solution is still at an initial stage. In this study, polyamide RO membranes were treated with sodium hypochlorite (NaClO) to prepare low-salt-rejection membranes. The effects of NaClO concentration, pH, and chlorination time on the membrane properties were investigated. Under alkaline chlorination conditions, the membrane's salt rejection decreased, and water flux increased with increasing NaClO concentration and chlorination time. This can be explained by the hydrolysis of polyamide in the alkaline solution to form carboxylic acids and amines, resulting in a decrease in the crosslinking degree of polyamide. The low-salt-rejection membrane was prepared by exposing it to a NaClO solution at a concentration of 15 g/L and a pH of 11 for 3 h, and the salt rejection of MgCl was 50.7%. The MgCl solution with a concentration of 20 g/L was concentrated using multi-stage LSRRO at the pressure of 5 MPa. The concentration of the concentrated brine reached 120 g/L, which is 87% higher than the theoretical maximum concentration of 64 g/L for conventional RO at the pressure of 5 MPa. The specific energy consumption (SEC) was 4.17 kWh/m, which decreased by about 80% compared to that of mechanical vapor recompression (MVR). This provides an alternative route for the efficient concentration of a diluted MgCl solution with lower energy consumption.
利用碳酸氢镁从稀土氯化物溶液中沉淀稀土的过程会产生稀氯化镁（MgCl）溶液。通过传统的反渗透（RO），稀MgCl溶液只能浓缩到最大浓度约70 g/L，这对于循环利用来说是不够的。低盐截留反渗透（LSRRO）在中等压力下运行时能够实现更高的盐水浓度。然而，关于用于浓缩MgCl溶液的LSRRO的研究仍处于初始阶段。在本研究中，用次氯酸钠（NaClO）处理聚酰胺RO膜以制备低盐截留膜。研究了NaClO浓度、pH值和氯化时间对膜性能的影响。在碱性氯化条件下，随着NaClO浓度和氯化时间的增加，膜的盐截留率降低，水通量增加。这可以通过聚酰胺在碱性溶液中水解形成羧酸和胺来解释，导致聚酰胺的交联度降低。通过将其暴露于浓度为15 g/L、pH值为11的NaClO溶液中3小时制备低盐截留膜，MgCl的盐截留率为50.7%。在5 MPa的压力下，使用多级LSRRO对浓度为20 g/L的MgCl溶液进行浓缩。浓缩盐水的浓度达到120 g/L，比在5 MPa压力下传统RO的理论最大浓度64 g/L高出87%。比能耗（SEC）为4.17 kWh/m，与机械蒸汽再压缩（MVR）相比降低了约80%。这为以较低能耗高效浓缩稀释的MgCl溶液提供了一条替代途径。
