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氰化提金过程中会产生大量的氰化废水,并且为了保证后续浸出效果,在碱浸过程中需要脱药。经脱药后,原精矿粉中的黄药、乙硫氮、浮选油等药剂被脱出,使水中COD升高。这类废水中氰化物主要以金属氰络合物以及SCN−的形式存在,溶液中的有机物的含量大,且难处理。现有的酸化法[1]、化学沉淀法[2]、生物氧化法[3-4]、溶剂萃取法[5-6]等由于普遍存在环境污染大、成本高、过程难控制、处理不达标等问题,难以大规模推广应用。因此,探索一条对环境污染较小、成本低、过程控制简单、高效的处理工艺对我国黄金产业发展有着至关重要的意义。
电解氧化法具有处理效果好、环境污染小等特点,常被用于处理电镀废水[7]、焦化废水[8-9]以及印染废水[10]等。电解过程中阳极反应产生的过氧化氢[11]、羟基自由基[12]、活性氯(Cl2、ClO−、HClO)[13-14]等的氧化作用是污染物去除的主要原因。NIDHEESH等[14]采用石墨作阳极对工业废水进行电化学氧化法处理,额外添加氯化钠可显著提高COD和色度的去除率,强调了Cl−在间接氧化过程中的重要性。GAO等[15]以不锈钢圆柱为阴极,多孔石墨为阳极电解处理氰化废水,发现NaCl的加入可以促进氰化物在阳极表面的氧化及Ag+的阴极回收,相比未加入NaCl之前,当添加2.9 g·L−1 NaCl,电解3.0 h下氰化物的去除率从57.5%提升至大于99%,Ag+去除率达到≥ 95.0%的时间从2.5 h降至1.0 h,实现了氰化物的去除的同时回收废水中的有价元素。LI[16]等采用电解氧化法对垃圾渗滤液中难降解污染物进行去除,以Ti/RuO2-IrO2为阳极,Al为阴极,在电流密度为0.1 A·cm−2,pH为6.37,Cl−质量浓度为6.5 g·L−1的条件下电解150 min,COD和NH3-N去除率分别为83.7%和100%,通过GC-MS分析表明,在电解过程中有机物的种类和质量百分比明显下降,有机物的去除主要依靠溶液中的Cl−在阳极生成氯化物衍生物种(HClO、ClO−等)对其进行氧化去除。FAJARDO [17]等采用Ti/RuO2阳极电化学氧化工艺处理含酚废水,总酚和COD的初始质量浓度为323 m g·L−1和1 118 mg·L−1,当NaCl质量浓度为10 g·L−1,电流密度为119 mA·cm2,初始pH为3.4,电解3.0 h后总酚和COD的去除率可以达到100%,但处理后的废水中仍剩有大量Cl−。电解氧化法对氰化物与有机物的处理效果显著,其中Cl−的引入对污染物的降解起着至关重要的作用,但额外的电解质如氯盐的加入会提升废水的处理成本,还会引入Cl−等新的成分,同时现有研究基本都停留在对低浓度、成分单一以及模拟溶液的研究阶段,而实际工业混合废水中成分复杂、污染物浓度高,需要综合考量其废水特性,以选择最优的处理方案。
本文以某黄金冶炼厂选冶混合废水为研究对象,废水中含大量Cl−,可为直接电解氧化处理奠定基础,无需加入其他电解质,大大节约处理成本。因此,本研究利用电解氧化法对该金矿废水中高浓度氰化物及有机物处理效果的影响以及过程机理进行了研究,重点考察了电压、电解时间等对氰化物与有机物的去除影响,分析了可能的降解机理,以期为此类金矿废水中氰化物与有机物的综合治理提供新的途径。
电解氧化法处理黄金冶炼厂选冶废水
Treatment of selection and smelting wastewater from gold smelter by electrolytic oxidation
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摘要: 采用电解氧化法处理同时含有高浓度氰化物与COD的黄金冶炼厂选冶废水,主要考查了外加电压、溶液pH、电解时间及极板间距等因素对氰化物和COD去除率的影响,充分利用原水中Cl-的阳极氧化效应,深入探讨了电化学氧化过程及污染物氧化去除机理。结果表明,随着外加电压和电解时间的增大,氰化物和COD去除率逐渐增大。以石墨为阳极,钛合金为阴极,采用一阴两阳电解体系对废水进行氧化,当电压为4.5 V、初始pH为7、电解时间为3 h、极板间距为1.5 cm的条件下,总氰化物 (CNT) 、COD、SCN-及Cu的去除率最高可达99.6%、96%、99.9%与99.2%。电解过程中体系pH逐渐降低,电场作用下定向迁移至阳极附近的污染物去除主要归因于HClO及ClO-的间接氧化作用,当pH大于5.0时以HClO的氧化为主,ClO-的氧化为辅,而pH小于5.0时则主要是HClO的氧化。电解氧化过程中约有36.17%的Cu与SCN-形成CuSCN沉淀而被除去,剩余的铜则扩散至阴极沉积析出。GC-MS分析表明,烷烃类、酯类、酮类等大分子的C=C键、酯基、羰基等化学键和官能团被氧化断链成小分子物质,随后继续被氧化为H2O、CO2和N2。Abstract: The electrolytic oxidation method was used to treat the selection and smelting wastewater from gold smelter containing both high concentrations of cyanide and COD, the effects of applied voltage, solution pH, electrolysis time and plate spacing on the removal rate of cyanide and COD were studied. The anodic oxidation effect of Cl- in raw water were fully used to deeply explore the electrochemical oxidation process and pollutant oxidation removal mechanism. The results showed that with the increase of applied voltage and electrolysis time, the removal rates of cyanide and COD gradually increased. With graphite as the anode and titanium alloy as the cathode, the one-cathode and two-anode electrolysis system was taken to oxidize the wastewater, and the maximum removal rates of the total cyanide (CNT), COD, SCN- and Cu could reach 99.6%, 96%, 99.9% and 99.2%, respectively, when the voltage was 4.5 V, the initial pH was 7, the electrolysis time was 3 h, and the plate spacing was 1.5 cm. During the electrolysis process, the pH value of the system gradually decreased, and the removal of pollutants that directionally migrated to the anode under the action of the electric field was mainly attributed to the indirect oxidation of HClO and ClO-, at pHs higher than 5.0, HClO oxidation was the main pathway, while ClO- oxidation was an auxiliary one, at pHs lower than 5.0, only HClO dominated the oxidation. During the electrolysis and oxidation process, the CuSCN precipitate was formed through the reaction of 36.17% Cu with SCN-, which could be removed accordingly. The surplus of Cu diffused to anode and the electrodeposition occurred. GC-MS test indicated that the chemical bonds and function groups such as C=C bond, ester group, carbonyl group in large molecular organics such as paraffins, ester and ketones were oxidized and degraded into small molecular organics, then were continuously oxidized to H2O、CO2 and N2.
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表 1 处理前后选冶废水中有机物列表
Table 1. List of organic compounds in selection and smelting wastewater before and after treatment
编号 有机物名称 原水 处理后水样 峰面积 百分比/% 峰面积 百分比/% 1 氨基甲酸乙酯 1.23×108 0.21 8.53×107 1.63 2 N,N-二乙基甲酰胺 3.69×108 0.62 8.58×107 1.64 3 氨基甲酸丙酯 1.28×109 2.14 1.46×108 2.78 4 氨基甲酸丁酯 1.42×109 2.37 1.48×108 2.83 5 1-辛醇 9.38×108 1.57 — — 6 2,2,4-三甲基-1,3-戊二醇 — — 5.50×108 10.48 7 异丁酸己酯 — — 5.04×108 9.62 8 2,4-二甲基-2,3-戊二醇 1.04×1010 17.30 — — 9 5-乙基-1,3-二恶烷-5-甲醇 3.36×109 5.61 3.94×108 7.51 10 2-乙基-1,3-己二醇 — — 1.63×109 31.05 11 2-甲基丁酸戊酯 1.55×1010 25.80 — — 12 3-异硫代氰酰丙酸乙酯 2.63×109 4.39 1.02×108 1.94 13 2,4-二叔丁基苯酚 2.59×108 0.43 2.59×108 5.02 14 4,4-二甲基-2-环己烯-1-醇 7.99×109 13.35 — — 15 2,7-二甲基-1-辛醇 6.73×109 11.24 7.21×107 1.37 16 3-十五烷酮 1.43×109 2.38 — — 17 2-甲基-2-丙烯-1-基(2E)-2-丁烯二酸异丁酯 2.47×109 4.13 — — 18 2,3-二丁基环氧乙烷 1.81×109 3.01 — — 19 双 (2-丙基戊基) 邻苯二甲酸酯 3.94×108 0.66 1.79×108 3.41 注:“—”表示未检出。 表 2 处理前后选冶废水中有机组分变化
Table 2. Changes of organic components in selection and smelting wastewater before and after treatment
有机物类别 处理前溶液产物分布 处理后溶液产物分布 峰面积 峰面积占比/% 峰面积 峰面积占比/% 醇类 2.94×109 51.54 2.64×108 63.58 酯类 2.38×109 41.70 1.16×108 28.01 酚类 2.59×107 0.45 2.59×107 6.33 酰胺类 3.70×107 0.65 8.58×106 2.07 烷烃类 1.80×108 3.16 0 0 酮类 1.43×108 2.50 0 0 -
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