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高酸度的含砷废水也被称为污酸,是难以处理的废水之一。在重金属冶炼工艺中,冶炼过程配有的烟气制酸设备等附属的生产系统均会产生污酸[1]。国内外对含砷废水的处理方法很多,其中,石灰铁盐法由于其处理流程简单、成本低廉等优点被广泛应用[2-4]。石灰法工艺主要采用活性炭作为催化剂,通入空气进行氧化,将污酸中的三价砷氧化为五价砷[5],当废水的pH为3左右时,FeAsO4会开始沉淀,用石灰乳调pH到7左右时,砷的脱除率可达到99.3%。但是这种方法也存在问题:需要先加入大量的碱中和硫酸,再调整pH,使溶液中的砷可形成砷酸盐或亚砷酸盐后脱除,产生的这些难溶物一般在堆放的过程中会不稳定,容易形成砷的二次污染; 此外,这些含砷渣中的砷都呈毒性极强的氧化态[6]。Cu+的配合物因其结构丰富,在诸多领域中表现出良好的应用前景[7-10],Cu+通常不稳定,易歧化,故需要与配体形成配合物才能稳定存在。根据分子轨道理论,卤族元素能与Cu+形成稳定的配合物[11],其中溴化亚铜具有还原性[12],能将三价或五价砷还原为单质砷。本研究提出了一种在高酸高砷的污酸溶液中直接还原高效去除砷的新方法,该方法不需要消耗碱,脱砷渣中的砷以单质形态存在,基本无毒[13],为砷的合理化利用提供有益的参考。
溴与铜协同还原法脱除污酸中的砷
Arsenic removal from waste acid via synergistic reduction of copper and bromide
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摘要: 针对高酸度的含砷废水处理难度大的问题,通过溴与铜的协同作用将高价态的砷还原为单质来实现脱砷,采用ICP测定、阴离子电极分析、XRF检测对反应前后的溶液滤渣进行了表征;研究了还原反应中各因素对反应的影响。结果表明:反应温度、反应时间、氢离子浓度、铜粉目数及搅拌速率的升高均有利于砷还原反应的发生;增加铜粉及溴化钠用量,有助于反应进行,铜粉与溴化钠过量则引起反应后溶液中铜、溴离子浓度升高。在最优条件下,反应后砷的去除率可达到99.5%以上,溶液中的铜离子为60 mg·L-1以下,通过XRF分析反应后所得的滤渣发现,溶液中的砷均沉淀进入固体。通过溴与铜协同还原的方法,溶液中的高价砷还原为单质,实现了高酸度环境下砷的脱除。Abstract: Waste acid is a complex industrial wastewater containing high acidity and arsenic contents and difficult to treat. In this study, a new method was developed to remove arsenic from waste acid based on the synergistic reduction of As(Ⅲ) to elemental As by bromine and copper. The elemental compositions in solution and filtration residue were characterized by ICP measurement, anion electrode analysis and XRF detection, respectively. In addition, the impacts of various factors on the reduction reaction were studied. The results show that the increase of reaction temperature, time, hydrogen ion concentration, the mesh of copper powder and stirring rate facilitated the arsenic reduction reaction. Moreover, increase of copper powder and sodium bromide dosages could conduce to the proceeding of the reduction reaction, while excessive dosage of copper powder and sodium bromide led to an increase in copper and bromide ion concentrations in the solution. Under the optimal conditions, the arsenic removal rate could reach over 99.5%, and the copper ion concentration in the solution was below 60 mg·L-1. XRF analysis on the filtration residue after reduction reaction indicated that the arsenics in the solution precipitated into the solid residual. Through the synergistic reduction by copper and bromide, the high valent arsenic in the solution was reduced to elemental As, then arsenic removal from waste acid containing high acidity could be accomplished.
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Key words:
- waste acid /
- synergistic reduction /
- wastewater treatment /
- arsenic removal /
- resource recovery
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表 1 污酸主要离子含量
Table 1. Main ion contents of waste acid
mg·L-1 Cu2+ As3+/As5+ Pb2+ Zn2+ Cd2+ 22.11 7 893 17.0 732.4 70.4 表 2 滤渣中主要元素所占百分比
Table 2. Percentage of main elements of filtration residue
% Cu As Br O S 61.56 6.43 29.36 2.53 0.05 表 3 滤液中主要离子含量
Table 3. Main ion content in the filtrate
mg·L-1 Cu2+ As3+/As5+ Pb2+ Zn2+ Cd2+ Br- 59.5 37.4 11.1 470.8 46.2 8 950 -
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