【作者】 冯霄；

【导师】 吴祖成；

【作者基本信息】 浙江大学 ， 环境工程， 2008， 博士

【摘要】 重金属和营养盐是当前最受关注的水体污染物之一，同时也是宝贵的资源。重金属废水和营养盐废水的大量排放，不仅造成严重的环境污染，也导致了资源的极大浪费。传统的重金属废水处理方法和脱氮除磷工艺各有优势，但仍不同程度地存在投资大、产水水质偏低、易产生二次污染等缺点。特别是当废水浓度较低时，传统处理工艺在技术、经济等方面受到很多限制而很难做到净化和回收兼顾，难以满足废水资源化的要求。电去离子（Electrodeionization，EDI）是一种清洁高效的新型分离技术，可深度去除并回收废水中的离子态物质。现有的研究虽然证明了EDI处理低浓度重金属废水的可行性，但无法彻底避免过程中普遍存在的重金属氢氧化物沉淀，装置运行的长期稳定性有待提高，关于EDI处理含多种重金属离子废水和营养盐废水的研究更少有报道。由此，本论文对EDI技术处理低浓度重金属废水和营养盐废水进行了较为系统的研究。以Ni²⁺离子为模型离子与树脂进行静态吸附交换，考察了EDI装置对失效树脂的电再生特性。结果表明，增大电极液导电性、升高电压及提高树脂预载离子量可显著提高树脂再生效果。电极液中加入的少量Na₂SO₄电解质是电极反应的引发剂，可促使电极反应快速进行，产生大量的H⁺对树脂进行再生。离子交换树脂的持续再生由电极反应产生的H⁺和OH^-离子来实现。阴、阳离子交换树脂的分别填充及电性相同的离子交换膜靠近排列使得树脂电再生过程中EDI装置的浓室溶液始终呈酸性，pH值低至3左右，抑制了Ni（OH）₂沉淀在阴膜表面产生，树脂表面亦未有Ni（OH）₂沉淀附着，避免了传统EDI过程容易出现的金属氢氧化物沉淀现象，有望实现长期运行和重金属废水的连续处理。考察了不同实验条件下EDI过程对Ni²⁺离子的脱除和浓缩性能。过程的主要影响因素包括离子交换树脂、离子交换膜、膜堆电压和原水Ni²⁺离子浓度等。在优化的操作条件下，对含Ni²⁺离子浓度50 mg/L的原水进行EDI处理，Ni²⁺离子浓缩倍数8．5～14．7，脱除率大于98％，出水Ni²⁺离子浓度低于1．0mg/L，电流效率23．6～37．9％，长时间运行稳定性能良好。表明EDI能够在不需要化学再生树脂的情况下，实现对重金属离子的深度脱除和浓缩。探讨了水中共存Ni²⁺、Cu²⁺、Zn²⁺离子在EDI膜堆中的行为差异及选择分离性，结合Nernst-Planck方程对EDI过程的离子传递机理进行的分析表明，树脂对离子的亲合力和选择性顺序为Ni²⁺＞Cu²⁺＞Zn²⁺，离子在EDI膜堆中的迁移能力顺序和浓缩倍数顺序为Zn²⁺＞Cu²⁺＞Ni²⁺。说明树脂对不同离子的亲合力有差别，树脂将优先选择混合液中亲合力大的离子进行吸附交换，但是亲合力越大，离子从树脂解吸即树脂电再生的阻力也越大，树脂对离子选择性的提高必然导致离子在树脂内迁移能力的降低及浓缩倍数的下降。离子传递机理描述表明，分离系数β实质上是混合离子在树脂中的电迁移率或者扩散系数之比，β值越大，离子之间的电迁移率差别越大，从而可分离性越高。混合离子的分离系数大小顺序为β_{（Zn2+-Ni2+）}＞β_{（Zn2+-Cu2+）}＞β_{（Cu2+-Ni2+）}，说明在定向迁移过程中共存离子之间产生竞争。Zn²⁺的竞争力最强，因此其电迁移率最大，由于Zn²⁺的竞争，Cu²⁺和Ni²⁺的迁移速率下降，与Cu²⁺相比，Ni²⁺受Zn²⁺竞争的影响较大，因此Cu²⁺的电迁移率次之，Ni²⁺的最小。探索了营养盐阴离子在EDI膜堆中的迁移与浓缩的基本特性。装置运行4h后NO₃^-、PO₄^3-的浓缩倍数即分别达到4．8～6．8和2．7～4．0，出水离子浓度均低于0．1mg/L，去除率大于97％。表明EDI能够对水中营养盐离子进行浓缩和深度去除。不同实验条件下树脂对PO₄^3-的亲合力均大于对NO₃^-的亲合力，NO₃^-通过阴树脂床层的电迁移率是PO₄^3-的3．6倍左右，这直接导致了PO₄^3-浓缩倍数的降低。上述结果表明，采用改进的EDI装置，不仅能浓缩和脱除低浓度重金属阳离子，而且对低浓度营养盐阴离子亦能进行浓缩和深度去除，这对资源回收利用及环境保护意义重大。更多还原

【Abstract】 As two kinds of the most primary pollutants in the water, Heavy metals and nutritivesalts are also valuable and useful resources. Discharge of wastewater containing heavy metalions or nutritive salts leads to not only serious environmental pollution, but prodigiousresource waste. Traditional technologies for the correlative wastewater treatment have theirown advantages, however, their disadvantages, such as high cost, low efficiency andsecondary pollution, are outstanding. There are many technological and economic limitationsand it is difficult for them to realize both wastewater purify and resource recycle, especiallyfor dilute solutions.Electrodeionization （EDI） is a clean, efficient and neotype separative technology. It canrealize deep desalination and ions recycle. Though current studies on the treatment ofwastewater containing low concentration of heavy metal ions by EDI prove the processfeasibility, they cannot avoid the precipitation of bivalent metal hydroxide commonlyhappened in the EDI membrane stack, and the long-time stability of EDI has been greatlylimited by this drawback. As for treatment of wastewater containing multiple heavy metalions and wastewater containing nutritive salts, the reports are rare. Therefore, treatment ofdilute wastewater containing heavy metal ions and wastewater containing nutritive salts werestudied respectively in this paper.The electro-regeneration effect of cation exchange resins loaded with nickel ions wasinvestigated in the EDI stack. It was found that Electrode solution, applied voltage and initialmetal ion concentration had remarkable influence on the electro-regeneration of cationexchange resin. Addition of a small amount of Na₂SO₄ into the electrode solution, moderateincrease of applied voltage and initial metal ion concentration could get better regenerationeffect. Na₂SO₄ introduced into the electrode compartments was an initiating reagent of theelectrode reactions, and it could accelerate the anode reaction to generate H⁺ ions. Continuouselectro-regeneration of ion exchange resin were achieved by H⁺ ions produced from the anodereaction and OH^- ions generated form the cathode reaction. Separative fill of anion exchange resins and cation exchange resins and closer arrangement of ion exchange membrane with thesame electric property kept the solution in the concentrate compartment of EDI acid enoughduring the process of electro-regeneration, and the pH value was as low as about 3. Thisacidic environment was very favorable for avoiding Ni（OH）₂ precipitation in the concentratecompartment. It was accordingly hopeful to realize long-time EDI running and continuouswastewater treatment.Effects of different operating conditions on the removal and concentration performanceof nickel ions by the EDI process were investigated. It was found that type of the resin, typeof the membrane, applied voltage and concentration of nickel ion in the wastewater werecrucial to the process. Under the optimized operational condition, simulated wastewatercontaining 50mg/L Ni²⁺ was treated.A steady and continuous process of wastewater treatmentcould be achieved with enrichment factor of 8.5～14.7, removal efficiency of at least 98% andcurrent efficiency of 23.6～37.9%, and concentration of nicked ion in purified water wasbelow 1.0 mg/L. This demonstrated the applicability of deep removal and concentration ofheavy metal ions by EDI without additional chemical regeneration of resins.Behavior difference and selective separation of co-exist nickel, copper and zinc ions inthe EDI membrane stack were discussed, and the ion transport mechanism was analysedcombining Nernat-Planck equation. It showed that the affinity and selectivity sequence wasNi²⁺＞CU²⁺＞Zn²⁺, while transport ability and enrichment factor was Zn²⁺＞Cu²⁺＞Ni²⁺.When the affinity of the ions to resin was different, resins would select and adsorb the ionwith strong affinity. However, the stronger the affinity was, the stronger the desorptionresistance. Improve of selectivity of resins to ions must lead to reduction of transport abilityand drop of enrichment factor.It showed from the description of ion transport mechanism that, the separative coefficientβwas virtually the ratio of ion electromigration rate or ion diffusion coefficient. The larger thevalue ofβwas, the larger the difference of electromigration rate between ions, accordingly thebetter the separative performance. The sequence ofβwasβ_{（Zn2+-Ni2+）}＞β_{（Zn2+-Cu2+）}＞β_{（Cu2+-Ni2+）}·It could be seen that ions were competitive with each other in mixed solutions. Zinc ion wasthe most competitive, thus its electromigration rate was the highest, and due to thecompetition of zinc, electromigration rates of nickel and copper decreased. Nickel ion was influenced by zinc ion more than copper ion, therefore, electromigration rates of copper ionwas lower and that of nickel was the lowest.Emigration and concentration characteristics of nutritive salt anions were explored.Enrichment factor of NO₃^- and PO₄^3- achieved 4.8～6.8 and 2.7～4.0, respectively, after theEDI running of 4 hours. Concentrations of both ions in purified water were below 0. 1mg/L,and the removal rate was more than 97%. This demonstrated the applicability of deep removaland concentration of nutritive salt anions by EDI without additional chemical regeneration ofresins. It was found that the affinity of resin to PO₄^3- ion was larger than that to NO₃^- ion, andthe electromigration rate of NO₃^- ion was about 3.6 times that of PO₄^3- ion. This causeddirectly the decrease of PO₄^3- ion enrichment factor.All the results showed that, it was feasible and applicable to remove deeply andconcentrate both heavy metal cations and nutritive salt anions by the improved EDI process.This was important and significant to to resource recycle and environmental protection.更多还原