我们开发了双极膜电渗析(BPED)技术,用于同时去除和回收废水中的硼。BPED使用两池电渗析装置进行,该装置由夹在两个双极性膜(BPM)之间的阴离子交换膜(AEM)组成。通过使溶液循环通过细胞,即去除池和浓缩池,进行半间歇式操作。将进料流与小室的储备罐的体积比设置为4:1(去除:浓缩)。四羟基硼酸根离子通过AEM从去除池传输到浓缩池。在理想情况下,当将相同初始浓度的溶液同时供给浓缩和去除池时,浓缩物中的硼浓度应浓缩至初始浓度的5倍。然后将浓缩的溶液用于第二步骤以进一步浓缩溶液。然后将该浓缩溶液用于第三步骤,依此类推。逐步进行该操作,直到硼浓度足够高以易于回收硼酸为止。硼酸钠溶液(初始浓度:100 mg / L)的五个单元的堆叠实验结果表明,精矿中的硼浓度约为4,而稀释液中的硼浓度小于10 mg / L,这是低于日本废水的法规价值。经过四个步骤,精矿中的硼浓度接近于硼酸的溶解度(约10,000 mg / L),在此浓度下,硼可以回收再利用。然后将该浓缩溶液用于第三步骤,依此类推。逐步进行该操作,直到硼浓度足够高以易于回收硼酸为止。硼酸钠溶液(初始浓度:100 mg / L)的五个单元的堆叠实验结果表明,精矿中的硼浓度约为4,而稀释液中的硼浓度小于10 mg / L,这是低于日本废水的法规价值。经过四个步骤,精矿中的硼浓度接近于硼酸的溶解度(约10,000 mg / L),此时可以回收硼以进行再循环。然后将该浓缩溶液用于第三步骤,依此类推。逐步进行该操作,直到硼浓度足够高以易于回收硼酸为止。硼酸钠溶液(初始浓度:100 mg / L)的五个单元的堆叠实验结果表明,精矿中的硼浓度约为4,而稀释液中的硼浓度小于10 mg / L,这是低于日本废水的法规价值。经过四个步骤,精矿中的硼浓度接近于硼酸的溶解度(约10,000 mg / L),在该浓度下,硼可以回收再利用。硼酸钠溶液(初始浓度:100 mg / L)的五个单元的堆叠实验结果表明,精矿中的硼浓度约为4,而稀释液中的硼浓度小于10 mg / L,这是低于日本废水的法规价值。经过四个步骤,精矿中的硼浓度接近于硼酸的溶解度(约10,000 mg / L),在该浓度下,硼可以回收再利用。硼酸钠溶液(初始浓度:100 mg / L)的五个单元的堆叠实验结果表明,精矿中的硼浓度约为4,而稀释液中的硼浓度小于10 mg / L,这是低于日本废水的法规价值。经过四个步骤,精矿中的硼浓度接近于硼酸的溶解度(约10,000 mg / L),在该浓度下,硼可以回收再利用。
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Simultaneous removal and recovery of boron from waste water by multi-step bipolar membrane electrodialysis
We have developed bipolar membrane electrodialysis (BPED) for simultaneous removal and recovery of boron from waste water. BPED is performed with a two-cell electrodialysis unit composed of an anion exchange membrane (AEM) sandwiched between two bipolar membranes (BPM). A semi-batch type operation was performed by circulating solutions through the cells, namely, the removal and concentration cells. The volume ratio of the reserve tanks for the feed stream to the cells was set to 4:1 (removal: concentratation). Tetrahydroxyborate ions were transported from the removal cell to the concentration cell through the AEM. In the ideal case, the boron concentration in the concentrate should be concentrated to 5 times the initial concentration, when the solutions of the same initial concentration were supplied to both cells of concentration and removal. The concentrated solution was then used for second step to further concentrate the solution. This concentrated solution was then used for third step, and so forth. The operation was continued step-by-step until the boron concentration was sufficiently high to easily recover boric acid. The experimental results with a stack of five cells for the sodium borate solutions (initial concentration: 100 mg/L) showed that the boron concentration in the concentrate was about 4, while that in the diluate was less than 10 mg/L, which is below the regulatory value for waste water in Japan. After four steps, the boron concentration in the concentrate reached close to the solubility of boric acid (ca 10,000 mg/L), at which boron can be recovered for recycling.