RCEES OpenIR  > 环境水质学国家重点实验室
电化学方法去除及回收水中五价锑研究
Alternative TitleRemoval and reclamation of Pentavalent Antimony from Water Using Electrochemical Methods
曹迪
Subtype博士
Thesis Advisor赵旭
2019-06
Degree Grantor中国科学院生态环境研究中心
Place of Conferral北京
Degree Name工学博士
Degree Discipline环境工程
Keyword五价锑,电混凝,电沉积,绿锈,水合电子 Pentavalent Antimony, Electrocoagulation, Electrodeposition, Green Rust, Hydrated Electrons
Abstract

      锑,化学符号Sb,是一种有毒金属。含锑化学品的主要用途为制造阻燃剂,聚酯合成催化剂,以及制备铅锑合金等。我国是世界上锑的最主要产区,由此带来的含锑重金属废水的治理问题十分严重。锑具有多种价态,在水体中主要以正三价以及正五价两种存在形式。在常规的水处理方法如混凝沉淀等过程中,五价锑较三价锑更难得到去除。因此,如何在水处理过程中实现五价锑的高效去除,是含锑废水处理的难点问题之一。此外,能否在水处理过程中实现锑的资源化,也是值得研究的重点问题。在废水净化处理技术中,电混凝是一种有效处理重金属污水的手段。但传统电混凝技术对于五价锑的去除效率仍然较低,且电混凝技术只能将重金属从水相中转移到污泥中,无法实现重金属的彻底去除。本文针对上述问题,从如何提高电混凝中锑的去除效率和从水中回收五价锑及其相关机理方面进行了相关研究,首次阐明了电混凝除锑过程中絮体的关键组分,提出二价金属离子强化电混凝去除五价锑的方式。此外,首次提出了采用水合电子使五价锑还原为三价锑,并进一步实现了金属锑的电化学回收。本工作主要研究内容及结论如下:

(1)在电混凝过程中对影响五价锑的去除因素、絮体形态和五价锑去除率之间的关系进行了研究。对于五价锑在电混凝的去除过程及相关影响因素的研究发现,在低溶解氧含量、弱酸性至中性的pH 条件下五价锑的去除效率显著高于高溶解氧含量、强碱性pH 值下五价锑的去除效率。分析发现,这是因为溶液中的溶解氧和酸碱性可以影响电混凝过程中絮体的形成。进一步对絮体进行解析后发现,在较低溶解氧、较低pH 条件下,电混凝过程中生成絮凝体的主要成分为具有层状结构的绿锈。在电流密度为5 mA cm-2 条件下,处理30min,即可实现五价锑(50 mg L-1)去除率达到96%以上。而在高溶解氧含量、强碱性环境下,五价锑在30 min 的去除率仅有70%左右。针对绿锈稳定性较低,容易转化为其他物质的特点,我们进一步通过向体系中加入适量亚硫酸钠的方式来提高电混凝过程中五价锑的去除效率,并发现亚硫酸钠的投加可以使得绿锈稳定存在,进一步提高了五价锑的去除效率。
(2)提出了进一步提高电混凝过程中五价锑去除效率的方式:向含锑废水中投加微量的二价金属离子,使得电混凝过程中选择性地生成具有更强污染物去除能力的絮体——绿锈,进而提高五价锑在电混凝过程中的去除效率。研究发现,向水体中投加0.2 mM 锰离子,即可使体系中选择性地稳定生成绿锈。此时,将五价锑废水(50 mg L-1)中锑的浓度降低到1.0 mg L-1 以下的时间可缩短一半以上。同时,投加锰离子后,产生的絮体具有更强的吸附能力和更好的沉降性能,有利于水处理中污染物的去除。进一步,针对某些废水中五价锑和二价钴共存的特点,研究了电混凝过程中五价锑和钴离子在去除过程中的相互影响以及原因。研究发现,钴离子的存在也可以促进污水中五价锑的去除。经过对絮体的一系列表征分析和对于两种金属的去除过程比较,发现在电混凝过程中,钴离子主要通过与反应过程中产生的铁离子共同与氢氧根结合生成更为稳定的绿锈,使得生成的絮体具有较强的五价锑去除能力。进一步证实某些二价离子存在可使生成的絮体具有更强的五价锑吸附能力,提高五价锑的去除效率。

(3)针对电混凝去除五价锑过程中会产生污泥,且无法实现五价锑的回收的问题,提出了一种将水体中的五价锑资源化的方法。利用水合电子的强还原性以及三价锑可在阴极还原回收这两种特性,我们提出,利用紫外光激发亚硫酸钠产生水合电子来还原五价锑,并通过外加电场作用将锑回收到阴极,实现了锑的资源化。在这部分工作中,我们设计了紫外/亚硫酸盐/电沉积体系用于实现水中五价锑的回收。研究发现,水合电子可高效将五价锑选择性还原为三价锑。在紫外/亚硫酸盐/电沉积体系中,外加-1.2 V 电压,可以实现五价锑(约50mg L-1)在6 小时内几乎完全回收到阴极,有效地实现了五价锑的污水处理问题及锑的资源化。然而只有在溶液为中性及碱性条件下,水合电子才能高效产生。在本研究中,电化学体系中由于阴极析氢同时生成氢氧根会引起溶液的pH值升高,促进溶液初始pH 为酸性条件下水合电子的产生,实现酸性条件下五价锑的还原和电沉积回收。

Other Abstract

      Antimony (Sb) is a toxic metal. The main applications of Sb in the industry include the fabrication of flame retardants, catalysts for plastic industry and antimonylead alloys, etc. China is the largest antimony producer in the world, and the problem of antimony pollution accompanied the producing of antimony is severe. Among various oxidation states of antimony, Sb(V) and Sb(III) are the two main forms, and Sb(V) is generally more difficult to be removed than Sb(III) through regular water treatment processes such as coagulation. Therefore, the development of an effective method for Sb(V) removal from water is necessary. Besides, the reclamation of antimony as a valuable resource is also worth investigating. Electrocoagulation has been used for the treatment of wastewater containing heavy metals, but it is not very
effective for the removal of Sb(V). In addition, the heavy metals are transported into the sludge and cannot be recovered by electrocoagulation. To solve the above mentioned problems, in this work, for the first time, the key species for Sb(V) removal in the flocs generated in EC were identified, and an enhanced electrocoagulation method by the addition of bivalent ions was proposed. In addition, the reduction of Sb(V) by hydrated electrons were proposed for the first time and the successful recovery of Sb(V) in an electrochemical process was achieved. The
reclamation of Sb from wastewater and the relating mechanisms were also investigated. The main conclusions obtained from this study are listed below:
(1) First, we investigated the influencing factors of Sb(V) removal by
electrocoagulation, and a possible relationship between the reaction conditions and Sb(V) removal efficiency was established. Results indicated that under the condition of low dissolved oxygen concentration, weak acidic to neutral pH, the removal of Sb(V) is more effective. Through the analyses of the formed flocs, it was found that green rusts instead of magnetite or ferrihydrite were formed with lower oxygen concentration and lower pH values. The generated green rusts has a layered structure,
which gave the flocs higher surface area and higher ion exchange capacity, and this is beneficial for the removal of Sb(V). After 30 min of treatment, the removal efficiency of Sb(V) (initial concentration: 50 mg L-1) can be up to 96% under low DO and low pH conditions, while the removal efficiency is only about 70% under high DO concentration and high pH values. Because green rusts are unstable and easily transforms into other forms, we tried to slow down the transformation of green rust by adding sulfite into the electrocoagulation process, and found that the addition of sulfite can stabilize the generated green rust and increase the removal efficiency of Sb(V) in electrocoagulation.

      (2) The stable generation of green rust could be a key factor for effective Sb(V) removal in Fe electrocoagulation, and the existence of some bivalent ions can stabilize green rusts. In this part, we proposed a new method to improve Sb(V) removal efficiency by adding Mn(II) into the electrocoagulation process. Results indicated that the added Mn(II) can promote the generation of green rust, and the removal of Sb(V) is benefited. In the Mn(II) enhanced EC process, the added Mn(II) (0-0.5 mM) was also simultaneously removed. The addition of only 0.2 mM Mn(II) can allow the EC system to steadily generate green rust with higher stability, and the time for the reducing the concentration of Sb(V) from 50.0 mg L-1 to below 1.0 mg L-1 can be reduced by 50%. In the eanwhile, pollution caused by other metal can coexist with antimony pollution in antimony mining area. In this part, we also investigated the influence of Sb(V) and Co(II) on the removal of each other in the electrocoagulation process. Results indicated that the presence of Co(II) can promote the removal of Sb(V), while the influence of Sb(V) on the removal of Co(II) was insignificant. After analyzing the formed precipitates, it was concluded that with the presence of Co(II), green rusts can be more stably generated, which facilitated the removal of Sb(V) in electrocoagulation process. These results further proved that the existance of some bivalent anions can improve the stable generation of green rusts and the removal of Sb(V) in electrocoagulation.
      (3) To realize the reclamation of Sb(V) as a useful resource, we developed a hydrated electron assisted electrodeposition process. Because Sb(V) cannot be directly recovered onto the cathode by electrodeposition, UV/sulfite process were introduced to generate hydrated electrons to reduce Sb(V) to Sb(III). In the UV/sulfite/electrodeposition process, Sb(V) can be effectively reduced to Sb(III) and then be recovered onto the cathode by the electrodepositon process. Results indicated that hydrated electrons can effectively reduce Sb(V) to Sb(III), and applying -1.2 V (vs. SCE) potential can achieve a Sb recovery rate of 90% within 6 h, indicating the hydrated electrons assisted electrodeposition process is very effective for the treatment of Sb(V) pollution and the reclamation of Sb(V) from wastewater. Besides,
it was also found that the increase of pH induced by the generation of hydroxide ions from the cathode in the electrochemical system can promote the generation of hydrated electrons at low pH values, which can further promote the recovery of Sb(V) under acidic conditions.

Pages136
Language中文
Document Type学位论文
Identifierhttp://ir.rcees.ac.cn/handle/311016/42181
Collection环境水质学国家重点实验室
Corresponding Author曹迪
Recommended Citation
GB/T 7714
曹迪. 电化学方法去除及回收水中五价锑研究[D]. 北京. 中国科学院生态环境研究中心,2019.
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