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新疆地处内陆干旱区,降雨少、蒸发大,淡水资源匮乏,严重制约了新疆地区社会经济发展[1-3]。南疆地区拥有丰富的咸水资源[4-5],但并未被有效利用,反而对灌区排水载体造成严重污染[6]。因此,南疆地区咸水的开发利用刻不容缓。
咸水淡化作为减轻水体污染、缓解淡水资源紧张的有效途径,被众多学者所关注[7-11]。咸水淡化技术通常有反渗透法、电渗析法、冷冻法。段作山等[12]以地下水为淡化原水,采用了反渗透除氟除氨氮技术对水质进行提标改造,结果表明,反渗透工艺对氟化物与氨氮的去除率分别为97%和88%。且反渗透膜对
$ \mathrm{SO}_{4}^{2-}$ 、$\mathrm{PO}_{4}^{3-} $ 均有很高的截留性能,达到99.20%以上[13]。潘俊杰等[14]采用高效低耗的频繁倒极电渗析(EDR)技术去除地下水源中的硝酸盐,结果显示产水中硝酸盐含量完全符合国家饮用水标准,整套工艺设备运行稳定、能耗低、对原水含盐量变化适应性强等优点。因此在咸水淡化过程中,掌握其盐分及离子运移规律具有重要意义。冷冻法具有能耗低、预处理简单、腐蚀轻等优点[15],是一种高效的咸水淡化技术,在淡化效率[16]、经济效应[17]、能量损耗[18]等方面做出了深入研究,但冷冻法在不同冷冻温度条件下,结冰与融冰过程中盐分及离子迁移规律尚不明晰。因此,基于目前所取得的研究成果,需要开展以南疆咸水为淡化原水的冷冻法室内模拟试验,探索咸水结冰与融化过程中盐分与离子的迁移规律。基于此,本文分析了不同冷冻温度下,南疆农田排水结冰与融化过程中,矿化度及离子浓度的分布规律;探讨了基于多级冷冻与重力脱盐条件下,盐分及Cl−、
$ \mathrm{SO}_{4}^{2-}$ 、K+、Na+的迁移规律成因,以期为南疆咸水冷冻法淡化技术的推广应用提供依据。
南疆咸水结冰与融化过程中盐分及离子的变化
Changes of salt and ions in the process of salt water freezing and melting in Southern Xinjiang
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摘要: 咸水淡化是缓解淡水资源紧张,减轻水体污染的有效途径。本试验分析了南疆农田排水不同冷冻温度下,结冰与融化过程中矿化度及离子浓度的分布规律;探讨了基于多级冷冻与重力脱盐条件下,盐分及Cl−、
$\mathrm{SO}_{4}^{2-} $ 、K+、Na+的迁移规律成因。试验结果表明,冰融水矿化度与离子浓度随冷冻温度的降低而上升;不同温度处理下,各级冰融水矿化度与离子浓度相较于初始水样(F0)均显著降低(P<0.05),冰晶逐级冷冻过程中,冰融水矿化度与离子浓度逐渐升高;各离子进入冰晶的迁移速率存在差异,离子结冰比率拟合线斜率呈K+> Cl−>Na+>$\mathrm{SO}_{4}^{2-} $ 的分布规律。冰晶逐级融化过程中,冰融水矿化度、Cl−、K+、Na+浓度呈现先快速下降、后缓慢下降、最终趋于平稳的变化趋势;$\mathrm{SO}_{4}^{2-} $ 浓度下降趋势平稳。冰融水由最初的Na−Cl型咸水,逐渐转变成SO4·Cl−Na型的微咸水。本文结论可为南疆咸水冷冻法淡化技术应用提供依据Abstract: Salt water desalination is an effective way to relieve the shortage of fresh water resources and water pollution. This article analyses the distribution of salinity and ion concentration during freezing and melting of farmland drainage in Southern Xinjiang under different freezing temperatures; which explains the migration reason of salt, Cl−,$\mathrm{SO}_{4}^{2-} $ , K+, and Na+ under the condition of multistage freezing and gravity desalting. The results show that the salinity and ion concentration of ice melt water increase with the decrease of freezing temperature. Under the various temperatures, compared with the initial water sample (F0), the salinity and ion concentration of ice melt water significantly decreased (P < 0.05), during the gradual freezing of ice crystals, the salinity and ion concentration of ice melt water gradually increased. The migration rate of different ions getting into ice crystals is different, and the slope of fitting line of ion freezing ratio is K+>Cl−>Na+>$\mathrm{SO}_{4}^{2-} $ . In the process of melting ice crystals step by step the salinity of ice melt water, concentrations of Cl−, K+ and Na+ decrease rapidly first, then decrease slowly, and finally get stabilized. The concentration of$\mathrm{SO}_{4}^{2-} $ declines steadily. The ice melt water gradually changes from Na−Cl salt water to SO4·Cl−Na brackish water. The conclusions of this article can provide a basis for the application of salt water freezing desalination technology in Southern Xinjiang.-
Key words:
- desalination of salt water /
- salinity /
- ion migration /
- icing process /
- melting process
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表 1 供试原水水质指标(mg·L−1)
Table 1. Test raw water quality index(mg·L−1)
矿化度
SalinitypH Cl− $ \mathrm{SO}_{4}^{2-}$ Na+ K+ 4906.77 8.36 1291.10 282.59 1789.58 104.91 表 2 咸水冰M1—M5离子变化
Table 2. Salt water ice M1—M5 ion change
冷冻温度/℃
Freezing temperature融水
Melt waterCl−/
(mg·L−1) /$\mathrm{SO}_{4}^{2-} $
(mg·L−1)K+/
(mg·L−)Na+/
(mg·L−1)−6 M1 1029.23±83.11a 211.67±18.21a 78.68±7.24a 1229.14±71.61a M2 313.03±19.85b 180.26±13.76b 27.00±2.75b 480.56±45.71b M3 216.47±15.37b 127.92±11.51c 17.88±1.40c 332.54±23.54c M4 95.83±10.40c 82.25±6.83d 8.73±1.16d 164.95±13.13d M5 54.17 ±6.90c 54.40±3.74d 5.53±0.64d 98.78±6.90d −12 M1 1118.23±96.94a 231.91±16.76a 82.38±11.60a 1483.32±108.14a M2 381.34±19.29b 196.03±20.07b 32.54±4.35b 625.83±56.64b M3 274.50±22.23b 144.01±11.47c 23.17±4.56bc 436.95±42.77c M4 120.97±18.95c 90.92±11.32d 11.24±1.70cd 209.69±15.30d M5 65.73±6.99c 63.69±6.79d 6.68±1.02d 125.60±9.80d −18 M1 1257.73±94.81a 270.04±17.52a 94.26±6.51a 1671.67±100.56a M2 633.77±57.89b 219.30±10.66b 45.61±5.72b 896.18±52.69b M3 381.10±40.01c 182.42±16.46c 28.97±2.29c 587.65±45.48c M4 214.27±15.64d 131.83±8.68d 16.72±1.85d 356.21±44.61cd M5 123.10±9.21d 89.07±8.15e 10.05±1.44d 214.86±18.66d 注:表中数据为平均值±标准差;同列不同小写字母表示差异性显著(P<0.05).
Note: The data in the table are the mean ± standard deviation; different lowercase letters in the same column indicate significant differences(P<0.05). -
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