反渗透对含硼放射性废水中硼酸脱除性能与机理研究

发布时间：2018-05-17 03:40

本文选题：反渗透 + 放射性废水　；参考：《武汉大学》2014年博士论文

【摘要】：核设施在运行、维修和退役阶段会产生大量含硼放射性废水,此类废水必须经除放射性并分离硼酸后才能向环境排放。目前采用的蒸发处理方法存在系统工艺复杂、能耗高的缺点。本文在在深入调研含硼放射性废水处理方法的基础上,对苦咸水反渗透膜分离硼酸的特性进行全面研究,并提出采用多羟基化合物络合强化的方法改善反渗透膜分离硼酸的性能。采用人工配制的模拟废水和实际放射性废水进行了含硼废水的处理实验,并基于不可逆热力学模型对反渗透分离硼酸的机理及性能进行了分析,为反渗透方法用于处理含硼放射性废水打下了技术基础。不同条件下反渗透膜对硼酸分离特性实验结果表明,影响反渗透除硼率最重要的因素是进水pH,随着进水pH的上升反渗透除硼率不断提高,pH为10.31时CPA2膜和BW30膜对硼酸的截留率分别达到了91%和92.1%。反渗透除硼率随着操作压力的增大和水温的降低而提高,膜元件的回收率和进水含盐量对反渗透除硼率也有一定影响,而进水硼浓度对除硼率几乎没有影响。硼酸络合实验结果表明,多羟基化合物对硼酸络合作用由强到弱的排列顺序为：山梨醇甘露醇果糖≈木糖醇葡萄糖。通过多羟基化合物的络合强化,可以明显提高反渗透过程的除硼效果。在pH为8.5以上时,经过甘露醇按2：1的络合比进行络合强化后,两种反渗透膜的除硼率均分别提高7～10个百分点；按5：1的络合比进行络合强化后,除硼率提高12～18个百分点。山梨醇和甘露醇络合强化反渗透正交实验结果表明,pH对络合强化反渗透除硼效率的影响最大,水温次之,回收率和压力相对来说影响程度较小。络合强化反渗透可以在相对低的pH条件下实现较高的硼酸去除率,反渗透膜在相对低的pH下运行可以降低膜结垢风险,延长使用寿命,这对于含硼废水的处理具有实际意义。模拟含硼放射性废水反渗透处理实验结果显示,在pH为9.13时,经山梨醇按5：1的摩尔比络合后,CPA2和BW30两种膜对硼酸的去除率分别处于96.60%～98.49%和97.32%～99.21%的范围内,比直接反渗透的除硼率有显著提高。在模拟含硼废水处理过程中,脱盐率随着操作压力的提高、回收率的下降而上升。在同样的进水压力和回收率下,脱盐率随着进水pH的提高明显上升。另外,经反渗透膜处理后,透过水中钴浓度降低到检测限以下。对铯的去除效果与pH、操作压力和回收率有关,在pH为9.13时,铯的去除率可达到95%以上。实际含硼放射性废水反渗透处理实验结果表明,在进水压力1.0MPa、回收率约为25%的条件下,直接反渗透对硼酸的去除率仅为51.12%,山梨醇络合强化反渗透(络合摩尔比5：1)对硼酸的去除率为89.68%,比直接反渗透下的去除率提高了约75%。络合强化反渗透对实际含硼废水中硼酸有非常好的截留效果。实际含硼放射性废水的络合强化反渗透浓缩处理实验结果显示,反渗透膜在除硼的同时,还对废水中的盐分和放射性核素保持了比较好的去除效果,对硼酸的去除率保持在86.78%～89.21%之间,脱盐率则在94.0%-94.8%之间变化,对废水中54Mn、60Co和137Cs的去污因子最高可达934。将反渗透过程中硼酸的传质过程分解成H3B03和H2BO3-两种组分进行讨论,并根据实验数据,运用不可逆热力学模型,计算出了CPA2膜和BW30膜对两种组分的反射系数以及两种组分在反渗透膜中的透过系数。并由组分的反射系数和透过系数,计算出了反渗透过程中的硼反射系数和硼透过系数。并根据反射系数和透过系数的变化,合理解释了反渗透过程中除硼率的变化机理。采用不可逆热力学模型,计算预测了25℃时CPA2和BW30两种反渗透膜在不同进水压力和pH条件下的除硼率,预测结果与实验数据相吻合。
[Abstract]:A large amount of radioactive waste water containing boron is produced in the stage of operation, maintenance and decommissioning. This kind of waste water must be discharged to the environment after radioactive removal and separation of boric acid. The current evaporation treatment method has the disadvantages of complex system technology and high energy consumption. This paper is based on the deep study of the treatment of boron containing radioactive waste water. The characteristics of boric acid separation by the reverse osmosis membrane of bitter salt water are studied comprehensively, and the method of complex strengthening of polyhydroxy compounds is proposed to improve the performance of boric acid separation by the reverse osmosis membrane. The experiment of treating boron containing wastewater with artificial wastewater and actual radioactive waste water is carried out, and the reverse osmosis is based on the irreversible thermodynamic model. The mechanism and properties of boric acid separation were analyzed, which laid a technical foundation for RO treatment of boron containing radioactive waste water.
The experimental results of boric acid separation under different conditions show that the most important factor affecting the rate of boron removal is influent pH. With the increasing of the influent pH, the rate of boron removal is increasing. When the pH is 10.31, the retention of boric acid to the CPA2 film and the BW30 film is up to 91%, and the rate of the reverse osmosis removal is increased with the increase of the operating pressure. With the increase of water temperature, the recovery rate of the membrane elements and the salt content of the influent also have some influence on the rate of boron removal, while the concentration of influent boron has little effect on the boron removal rate.
The results of boric acid complexation showed that the arrangement sequence of polyhydroxy compounds for boric acid collaterals from strong to weak is: sorbitol mannitol fructose and xylitol glucose. Through the complexation of polyhydroxy compounds, the effect of boron removal in the reverse osmosis process can be obviously improved. When pH is more than 8.5, the complexation ratio of mannitol to 2:1 is obtained. The boron removal rate of the two kinds of reverse osmosis membranes increased by 7~10 percentage points, respectively, and the boron removal rate increased by 12~18 percentage points after complexing with the complexing ratio of 5:1. The orthogonal experimental results of sorbitol and mannitol complexation enhanced reverse osmosis showed that pH had the greatest influence on the efficiency of boronide removal by complexing enhanced reverse osmosis. The ratio of yield and pressure is relatively small. Complex enhanced reverse osmosis can achieve high removal rate of boric acid at relatively low pH conditions. The operation of reverse osmosis film under relatively low pH can reduce the risk of fouling and prolong the service life, which is of practical significance for the treatment of boron containing wastewater.
The experimental results of reverse osmosis treatment of simulated boron containing radioactive waste water show that the removal rate of two kinds of CPA2 and BW30 membranes to boric acid is in the range of 96.60% to 98.49% and 97.32% to 99.21%, respectively, after the pH is 9.13, and the rate of boron removal is significantly higher than that of direct reverse osmosis. The desalination rate increases with the increase of operating pressure and the decrease of recovery rate. Under the same influent pressure and recovery rate, the desalination rate increases obviously with the increase of the influent pH. In addition, the cobalt concentration in the water is reduced to below the detection limit after the reverse osmosis membrane treatment. The removal effect of cesium is related to the pH, operating pressure and recovery rate, at pH 9 At.13, the removal rate of cesium can reach more than 95%.
The experimental results of reverse osmosis treatment of actual boron containing radioactive waste water show that the removal rate of boric acid by direct reverse osmosis is only 51.12% under the condition of inlet pressure 1.0MPa and the recovery rate is about 25%, and the removal rate of boric acid by sorbitol complexing enhanced reverse osmosis (complex molar ratio 5:1) is 89.68%, which is about 75%. collaterals higher than that of direct reverse osmosis. The experimental results show that the reverse osmosis membrane has a good removal effect on the salt and radioactive nuclides in the wastewater, and the removal rate of boric acid remains at 86.7. Between 8% and 89.21%, the desalination rate changes between 94.0%-94.8%, and the decontamination factor for 54Mn, 60Co and 137Cs in wastewater is up to 934..
The mass transfer process of boric acid in the process of reverse osmosis is decomposed into two components of H3B03 and H2BO3-. According to the experimental data, the reflection coefficient of the two components and the transmittance coefficient of the two components in the reverse osmosis membrane are calculated by using the irreversible thermodynamic model, and the reflection coefficient and the transmission coefficient of the components are obtained. The boron reflection coefficient and boron transmission coefficient in the process of reverse osmosis are calculated. According to the change of reflection coefficient and transmission coefficient, the mechanism of the change of boron removal rate in the process of reverse osmosis is reasonably explained. Using an irreversible thermodynamic model, the prediction of the removal of two kinds of CPA2 and two kinds of reverse osmosis membranes at 25 degrees C under the conditions of different influent pressure and pH is calculated. The results are in good agreement with the experimental data.
【学位授予单位】：武汉大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：X771

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