美国里海大学陈豪和Arup SenGupta Nature Water：室温超高盐水再浓缩技术

成果简介

近日，美国里海大学陈豪和Arup SenGupta在Nature 子刊Nature Water上发表了题为“Accelerated low-temperature, low-fouling brine concentration through evaporative ion exchange mediated by the effect of functional groups”的研究论文。文中报道了一种由高容量离子交换树脂独特的渗透和蒸发特性介导的盐水浓缩工艺：Evaporative Ion Exchange (EIX)。该工艺可于室温下快速浓缩高盐废水，以缩小储存体积。对于Marcellus气页岩的高盐采出水（TDS>150,000mg/L），这种蒸发离子交换工艺使高盐废水于常温下浓缩至TDS > 400000 mg/L，从而导致钡和氯化钠在室温下自然沉淀/结晶，且不会导致离子交换树脂的堵塞及污染。该工艺对内陆地区高盐废水脱盐，减小储存体积有积极意义。

在远离海洋的内陆地区，处理总溶解固体(TDS)大于60,000 mg/L的盐水溶液，例如：垃圾填埋场的渗滤液、膜废弃物、气井的产出水和各种其他工业过程的浓缩溶液（高盐盐水），存在尚未解决的技术、环境，政策和经济障碍。现有的相关技术，如深井注入（Deep-Well Injection），自然蒸发（Lagoon，Land Evaporation），多级热蒸馏（MSF），膜蒸馏 (MD)以及其他渗透膜技术（FO，RO）受限于政策法规，占地面积，高能耗产出比以及盐离子沉淀、结垢和以及对膜不可逆污染等问题。因此开发新型常温下快速浓缩结晶工艺以实现零液体排放（zero-liquid-discharge）降低盐水处理成本至关重要。

本研究发现以复合型离子交换树脂为载体，利用其高离子交换渗透性和快速蒸发特性, 可以通过循环运行实现高盐水的快速浓缩。与现有的在沸点或沸点附近运行的高温工艺不同，EIX工艺在可接近室温下运行不需要额外的热能输入，其主要驱动力为其高容量离子交换官能团的存在导致的树脂高吸水性及空气的相对湿度的敏感性。同时由于吉布斯-道南效应（Gibbs–Donnan effect）这种循环EIX工艺不会产生结垢或结垢问题，并且浓缩后的盐水可以在室温下进行自然沉淀/结晶。泻湖或陆地蒸发也有类似的特点即不需要额外的热量输入，但由于单位体积传质面积以及对环境相对湿度的敏感度的差异，其蒸发浓缩速度远不及EIX工艺。

图文导读

EIX 工艺简介

聚合离子交换树脂中存在大量的带有电荷的功能团，其内部存在极高的渗透压，干燥的离子交换树脂与浓盐水接触时，官能团无法扩散到水中，而水分子可以高效快速的渗透进树脂内部，同时由于吉布斯-唐南效应，水中的电解质尤其是高价态离子将被拒绝在外。这一现象类似于正渗透（Forward Osmosis），离子交换树脂及水的接触界面相当于半透膜。吸水的过程导致树脂的弹性膨胀最终于树脂交联结构的压缩力达到平衡。这一过程，水分扩散到树脂内部，导致盐水中电解质浓度相对升高，进而实现常温下能够快速浓缩浓盐水，在热力学上是有利的。当膨胀后的饱和树脂与不饱和湿度的空气接触时，渗透吸水效应不复存在，由于其对相对湿度的高敏感性，因此，树脂将显著收缩同时蒸发内部水分，其蒸发潜热完全由不饱和的周围空气提供，因此可在室温不需要额外提供热源的情况下进行。相对干燥后的树脂，再次与盐水接触以达到循环浓缩的效果。该EIX工艺的科学原理在于，在与相对低湿度的环境空气接触时，在水饱和条件下和不饱和条件下的离子交换树脂的平衡吸水量存在很大差异。。

Fig. 1 | Underlying scientific concept of the EIX process.

a,b, Schematic of the EIX cycle showing osmotic water uptake by an ion exchanger in contact with brine solution (a) and water loss/evaporation on contact with air (b). c, Water uptake for different levels of salinity, from 0 (deionized water) to 300,000 mg l/L NaCl solution (n = 3). The units g water g dry material −1 represents g water per gram dry material. d, Microphotographs of a single resin bead in equilibrium with solutions of different salinity. e, Evidence of a significant increase in the TDS in solution for both SAC (C100) and SBA (A400) resins (n = 3). BV, bed volume. f, No change in the TDS in solution (n = 4) can be observed for polystyrene (PAD900) and polyacrylic (PAD900) matrices, silica gel, and activated carbon (AC; Supplementary Table 1). The error bars represent the standard deviation (s.d.); the data are presented as mean ± s.d.

常温下合成盐水EIX工艺效果验证

Fig. 2 | EIX process validation with synthetic hypersaline at ambient temperature.

a, Comparison of the water uptake isotherms for an ion exchanger (IX; Purolite A502P) and a polymer matrix (PAD900) at different RHs. b, Comparison of the water uptake and latent heat of evaporation (ΔH) for the ion exchanger and polymer matrix under 10% RH and saturated conditions. d, Enhancement of the specific gravity of the parent ion exchanger by doping with ZrO 2 nanoparticles. e, Laboratory set-up used for the EIX process.c, Water uptake isotherms for different types of ion exchanger at different RHs.f, Comparison of TDS (NaCl) values for three consecutive cycles of the EIX process for the ion exchanger and polymer matrix. The dashed line shows the TDS concentration in the initial solution. g,h, Effluent histories of the inlet and outlet temperatures (g) and RH (h) during three consecutive cycles.

常温下Marcellus超高浓盐水EIX工艺效果验证

Fig. 3 | EIX process validation with Marcellus hypersaline brine at ambient temperature.

a, Concentration of Marcellus hypersaline brine (NaCl) after four successive EIX cycles and a waiting period of 24 h. The dashed line shows the TDS concentration in the initial solution. b, Photographs of the water samples after each cycle and the precipitate after the fourth cycle. c, Concentrations of individual cations and chloride in the samples collected after each cycle. d,e, SEM-EDX mapping images (BSE, backscattered electron image) (d) and linear intensity profiles (e) of the precipitate, demonstrating the predominance of Cl, Na and Ba atoms. f,g, Effluent histories of the outlet air temperature (f) and RH (g) during four consecutive cycles.