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自然界中砷经常与贵金属(如Au)或有色金属(如Cu和Pb)矿物伴生,因此在选矿、金属冶炼及硫酸制备的过程中会产生大量酸性高浓度的含砷废水[1-3],根据我国各类工业水污染排放标准的相关规定,这些废水必须进行有效处理,达到排放标准后才能排放,否则会对环境及人类的健康带来很大的危害,其中,硫化物沉淀法是常用的方法之一,但该方法会产生大量的硫化砷渣[4],砷渣中的砷大多以三价的形式存在,而且As(Ⅲ)的毒性是As(Ⅴ)的20—60倍[5],另外,这些硫化砷渣在自然环境中易受温度、pH值、微生物和共存离子等环境因素的影响[6],从而导致硫化砷渣中的砷重新释放到环境中,引起严重的环境砷污染。因此,硫化砷渣的有效处理对于降低其环境风险具有重要的意义。
将砷渣进行有效的固定是降低其潜在风险的方法之一,常用的固定方法是将砷渣利用惰性材料包裹然后进行卫生填埋[7],然而这种方法对于稳定性差的砷渣来讲,不能从根本上解决其二次溶出砷元素的风险,且由于在处理过程加入大量的惰性材料,导致处理后的砷渣体积成倍增加,从而存在占用大量土地的缺点;从另一方面来讲,如果将砷渣中的砷转化成一种结构和化学性能稳定的物质,那么就会大大降低其溶出的二次风险,这种思路常用于废水中As(Ⅲ)和As(Ⅴ)的去除,如Sunyer等[8-10]将水中的As(Ⅴ)有效地固定在钾明矾石的晶格里,从而达到将As(Ⅴ)稳定化的目的,然而此类明矾石的稳定性虽然较好,但其固砷的效率较低,有研究表明类明矾石中只有15%的硫酸根能被As(Ⅴ)替代[10],而臭葱石作为一种砷酸盐矿物,具有溶解度低、稳定性高和固砷率高等优点[11],因此被认为是一种安全的储砷材料,如Fujita等[12-13]将硫酸亚铁与As(Ⅴ)溶液在50—95℃下反应生成臭葱石,且生成的臭葱石在酸性条件下性能稳定;Gonzalez-Contreras等[14]利用生物反应器将溶液中的五价砷转化成大颗粒的臭葱石;Gomez等[15]利用水热法将Fe2(SO4)3-As2O5-H2SO4体系转化成臭葱石晶体;门玉等[16]通过形成臭葱石和铁素体来去除水中的As(Ⅴ);由此可见,通过生成臭葱石去除As(Ⅴ)和As(Ⅲ)的研究主要集中于含砷废水的研究,较少地应用于砷渣的研究;目前,砷渣的研究依然是借鉴含砷废水的处理思路,即首先将砷渣中的砷通过酸或者碱液浸渍,然后再将浸液中的As(Ⅲ)氧化并转换成臭葱石,如Min等[17]利用NaOH浸出阳极泥中的砷,然后再加入Fe2(SO4)3在80—95℃下氧化生成臭葱石;Ma等[11]将硫化砷渣碱浸后加双氧水氧化成As(Ⅴ),然后再引入Fe2(SO4)3和H2SO4,常压下加热到95 ℃形成臭葱石,由此可见将生成臭葱石的方法借鉴到含砷固废的处理中,通常涉及浸出-氧化-固定等一系列的化学过程,实验操作流程较为复杂;因此寻找一种简便、高效的稳定化处理砷渣的方法具有重要的实际意义。
在本工作中提出了一种简便、高效的硫化砷渣稳定化处理的方法,通过添加适量的Fe2(SO4)3和H2O2,在水热条件下通过一步反应直接将硫化砷渣转化成大颗粒的臭葱石,同时硫化砷渣中的硫离子被氧化成硫单质。本文主要优化了反应温度、时间、pH值以及Fe/As摩尔比等实验条件对臭葱石的形成过程的影响,分析了臭葱石的相组成和形貌,最后对臭葱石的短期稳定性及长期稳定性进行了评价,并将该处理方法用于实际砷渣的稳定化处理,结果表明该方法是一种简单可行的硫化砷渣稳定化方法,为砷渣的稳定化处理提供了一种新思路。
硫化砷渣一步水热矿化成臭葱石和单质硫的研究
One-step hydrothermal transformation of arsenic sulfide residues to scorodite and sulfur
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摘要: 硫化物沉淀法是最常用的处理含砷废水的方法之一,但该方法会产生大量的无定形硫化砷渣,砷渣中的砷元素在微生物和pH值等环境因素的影响下,容易重新释放到环境中引起二次污染。因此本文选取硫化砷作为研究对象,借鉴含砷废水的处理思路,将硫化砷在氧化性条件下转化成化学性质和结构稳定的臭葱石,同时回收单质硫,单质硫的回收率为90%左右,最终实现无定形硫化砷的稳定化处理。实验结果表明,最优的实验条件是水热温度和时间分别为120 ℃和10 h,最佳pH值为3,最佳的Fe/As摩尔比为1.2:1;在上述实验条件下,硫化砷能够一步直接转化成臭葱石,转化率达90%以上。该方法有效地减化了常见的硫化砷渣处理所涉及的溶解-调节-再处理的分步处理过程,且生成的臭葱石浸渍90 d后砷的浸出浓度为2.2 mg·L-1,小于国家的《危险废物鉴别标准浸出毒性鉴别》中规定的限值(5 mg·L-1);最终,将该方法应用于实际砷渣的处理,砷渣处理后砷的浸出浓度小于1 mg·L-1,由此说明该方法是一种简单高效地稳定硫化砷渣和回收硫资源的方法。Abstract: Sulfide precipitation is one of methods used to dispose arsenic-containing wastewater. Notably, the above process can produce many amorphous arsenic sulfide residues. The arsenic sulfide residues are highly toxic and might cause secondary pollution because of the leaching of arsenic element. In this work, the synthesized arsenic sulfide was adopted to study its stabilization based on the protocol of treatment of arsenic-containing wastewater. Under the oxidizing conditions, the arsenic sulfide can be transformed to scorodite and elemental sulfur. The recovery rate of elemental sulfur is about 90%. The optimal conditions are shown as following, hydrothermal temperature is 120 ℃, hydrothermal time is 10 h, pH value is 2 and Fe/As=1.2:1. Under the optimal condition, the conversion rate of arsenic sulfide can reach more than 90%. This method greatly simplifies the conventional treatment of arsenic sulfide residues, which means the process of dissolving-reprecipitation can be accomplished by one step in this work. In addition, the leaching concentration of arsenics is 2.2 mg·L-1 for the treated arsenic sulfide after impregnating 90 days, which is lower than the limiting value (5 mg·L-1 originated from identification standards for hazardous wastes-identification for extraction toxicity). For actual arsenic sulfide, the leaching concentration of arsenics decreased from 425 mg·L-1 to 0.98 mg·L-1 by above transformation treatment. Therefore, this transformation protocol is a promising method for the stabilization of arsenic sulfide residues.
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Key words:
- arsenic sulfide residues /
- stabilization /
- scorodite /
- sulfur
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表 1 实际砷渣性质及水热处理前后的砷浸出浓度
Table 1. The properties of actual arsenic sulfide residues and the leaching concentration of As before and after treatment
砷渣类型
Arsenic sulfide residues来源
Place元素组成/%
Composition of element砷的浸出浓度(TCLP)/(mg·L-1)
The leaching concentration of AsAs S O Cu Al 处理前
Before treatment处理后
After treatment硫化砷渣 河南某铜矿 21.4 37.9 36.1 3.5 1.1 425 0.98 -
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