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目前,氰化法是最普遍的提金工艺[1],但过程中会产生大量的氰化废水,该类废水具有成分复杂、含盐量高、处理难度大等特点,因其含有大量的氰化物,直接排放会造成严重的污染问题[2-3]。在国内已经得到工业实践的方法有酸化法、碱性氯化法和SO2-空气法,但存在环境二次污染,处理成本高、过程难以控制、处理不达标等问题。其他的化学氧化法[4]、离子交换法[5]、化学沉淀法[6]等仍处于实验室阶段。因此,寻找一种短流程、高效低耗的处理方法,实现节能减排得到黄金冶炼企业的普遍关注。
电絮凝法常用处理城市污水与工业废水,此外,该方法还可用于重金属离子和无机离子的去除[7]。DAS等[8]采用集成臭氧辅助电絮凝法去除钢铁工业废水中的氰化物,在臭氧生成率1.33 mg·L−1、臭氧氧化时间40 min、电流密度100 A·m−2的和电解时间30 min的条件下,总氰质量浓度由150 mg·L−1降为0.1 mg·L−1,但电解过程中阳极易形成包裹极板表面的氧化膜,使极板与溶液接触面积减少,阻止阳极溶解,造成极板钝化[9],牺牲阳极在电解体系中不断被损耗,需要定期更换极板以确保反应正常进行[10]。电解氧化法是指利用直流电进行氧化还原反应,达到污染物分解的方法,常用于氰化废水[11-12]、电镀废水[13]的处理,研究表明,电解氧化法可以有效降解氰化废水中的金属氰络合物。LEI等[14]采用三维电化学体系处理氰化物废水,以煤基电极为主电极的三维电极体系,施加电压4 V,处理时间5 h,极板间距10 mm,活性炭颗粒用量2 g,CNT、Cu、Zn、CN−和SCN−的去除率分别为94.14%、94.53%、98.14%、98.55%和93.13%。曾鑫辉等[15]采用电解氧化法处理金矿废水,在电压6 V、pH=9、电解时间3 h、极板间距1.5 cm、NaCl添加量10 g·L−1的条件下,CNT、COD和铜氰络合物的去除率达到97.2%、96%和97.7%。Cl−的添加虽然有利于污染物的去除,但是处理后余氯浓度高,增加了环境风险。絮凝是指添加适当的絮凝剂使水或液体中悬浮微粒集聚变大,或形成絮团,从而加快粒子的聚沉,达到固-液分离的目的。常用于处理染料/纺织废水、农业废水、食品加工工业废水、纸浆和造纸废水、制革废水、垃圾渗滤液、废水中的重金属离子等[16]。聚硅酸铝铁是一种新型无机高分子絮凝剂,是在聚硅酸及传统铝盐、铁盐基础上发展起来的聚硅酸与金属盐的复合产物。该絮凝剂的大分子链上所带正电荷密度高,因絮凝剂溶解性、电中和及吸附架桥能力强、易制备、价格低廉等特点,成为无机高分子絮凝剂研究的热点[17]。许小洁等[18]研究了联合硅藻土与聚合氯化铝强化混凝对原水中重金属离子的去除,聚合氯化铝添加量为30 mg·L−1,硅藻土添加量为1.5 g·L−1时,重金属Cu、Pb和Cd的去除率分别达到57.5%、83.7%和22.2%。
针对电絮凝法存在阳极钝化,电化学氧化法存在电解质添加量大,处理后余氯浓度高,处理成本高等问题,制备绿色无氯絮凝剂,本研究采用絮凝-电解氧化联合工艺,研究了氰化废水处理过程中重金属离子和氰化物的去除规律及过程机理,以期为氰化提金废水的治理提供参考。
絮凝-电解氧化联合处理氰化提金废水
Cyanidation gold extraction wastewater treatment by combined flocculation-electrolysis oxidation
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摘要: 采用絮凝-电解氧化联合技术处理氰化废水,主要研究了聚硅酸铝铁 (PSAF) 添加量、絮凝时间、pH、电压、电解时间、极板间距对总氰(CNT)、游离氰(CN−)、Cu、Zn离子去除率的影响,并对其反应机制做了分析。研究表明,当PSAF添加量为2 g·L−1,絮凝时间为30 min,pH为9条件下,CNT、CN−、Zn、Cu离子的去除率分别可达42.97%、100%、84.40%、34.88%。Zn(CN)42−、Cu(CN)32−、CN−的吸附量分别为567.88、89.76、439.74 mg·L−1。以钛板为阴极,石墨板为阳极,采用一阴两阳体系对絮凝后液进行电解氧化实验,在电压为3 V、电解时间为2 h、极板间距为10 mm条件下,CNT、CN−、Zn、Cu离子的去除率可达91.70%、100%、99.15%、94.49%。絮凝过程中Zn(CN)42−、Cu(CN)32−、CN−的去除是由电荷中和和化学吸附共同作用的,其中电荷中和起主要作用。Zn(CN)42−、Cu(CN)32−、CN-的化学吸附主要归因于其与PSAF水解产生的羟基阳离子发生交换反应。XRD分析表明,加入酸性絮凝剂PSAF的瞬间,部分Zn(CN)42-反应为Zn(CN)2沉淀。电解氧化过程中Zn(CN)42−、Cu(CN)32−破络释放的氰根会被阳极表面产生的O2、·OH完全氧化为N2和CO2,Zn、Cu离子在阴极板电沉积而被去除。Abstract: In this study, the flocculation-electrolysis technology was used to treat the high-concentration cyanidation gold extraction wastewater. The effects of polyaluminum ferric silicate (PSAF) addition, flocculation time, pH, voltage, electrolysis time and electrode distance on the removal rates of total cyanide (CNT), free cyanide (CN−), Cu ions and Zn ions were mainly studied, and the reaction mechanism was also identified. The results showed that when PSAF dosage was 2 g·L−1, the flocculation time was 30 min and pH was 9, the removal rates of CNT, CN−, Zn, and Cu ions in wastewater could reach 42.97%, 100%, 84.40% and 34.88%, respectively. The adsorption capacities of Zn(CN)42−, Cu(CN)32−, and CN− were 567.88 mg·L−1、89.76 mg·L−1、439.74 mg·L−1, respectively. The electrolytic oxidation experiments of the flocculated liquid were conducted by using a graphite plate-cathode and two titanium plate-anode system. At the voltage of 3 V, electrolysis time of 2 h and electrode distance of 10 mm, the removal rates of CNT, CN−, Zn and Cu ions in the wastewater were 91.70%、100%、99.15% and 94.49%, respectively. Zeta potential and FTIR analysis showed that the removal of Zn(CN)42−, Cu(CN)32−, CN− during the flocculation process was a combination of charge neutralization and chemisorption, of which charge neutralization played a major role. The chemisorption of Zn(CN)42−, Cu(CN)32−, and CN− was mainly attributed to the exchange reaction with the positively charged hydroxyl cations produced by PSAF hydrolysis. XRD analysis showed that a part of Zn(CN)42− reacted as Zn(CN)2 precipitate at the moment of acidic flocculant PSAF dosing. During the electrolytic oxidation process, the cyanogen released by Zn(CN)42− and Cu(CN)32− breaking could be completely oxidized to N2 and CO2 by O2, ·OH generated on the anode surface, and Zn and Cu ions were removed by the electrodeposition on the cathode plate.
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Key words:
- cyanide wastewater /
- flocculant /
- polyaluminum ferric silicate /
- electrolytic oxidation
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表 1 平行实验结果
Table 1. Parallel experiment results
组分 序号 沉淀后液/
(mg·L−1)电解后液/
(mg·L−1)去除率/
%平均
去除率/%CNT A 921.56 138.10 91.37 91.70 B 909.71 134.10 91.62 C 906.35 126.26 92.11 CN- A 0 0 100 100 B 0 0 100 C 0 0 100 Zn A 121.75 7.44 98.89 99.15 B 109.55 5.1 99.24 C 83.47 4.63 99.31 Cu A 173.02 17.87 93.06 94.49 B 166.15 13.41 94.79 C 163.60 11.3 95.61 -
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