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锑(Sb)是一种天然存在于自然界中的有毒准金属元素[1],因其与化合物有着良好的阻燃特性,在人类的生产和生活中有着广泛的用途[2]。中国作为世界上最大的锑储量和产量大国,其中产量约占世界的71%,锑污染已成为中国的典型环境污染问题[3]。锑在天然水体中通常以Sb(OH)3和
${\rm{Sb}}\left( {{\rm{OH}}} \right)_6^ - $ 等无机形式存在[4],在大多数氧化水体中锑主要以${\rm{Sb}}\left( {{\rm{OH}}} \right)_6^ - $ 的阴离子形式存在,因此,Sb(Ⅴ)在矿山水环境中最为常见[5],其风险程度远高于其他价态。湖南锡矿山的锑矿开采地区,附近的河流因受到锑矿石堆场渗透水的影响,锑浓度为0.33~11.4 mg·L−1[5],远远高于国家地表水环境质量标准的5 μg·L−1[6]。随着大量锑资源的开采,锑矿废水成为环境中最主要的锑污染来源[7-9],因此,对锑矿废水中Sb(Ⅴ)的去除显得尤为紧迫。高效去除、成本低廉、运行简易是科研技术人员对锑废水治理的追求目标[10]。目前,去除水溶液中锑的技术主要有混凝/絮凝[11]、离子交换[12]、电化学处理[13]、生物修复[14]、吸附[15]等。吸附是一种简单易行的废水处理技术,一般适合于处理量大、浓度范围广的水处理体系,该方法性能优良、成本低廉,因此,与其他方法相比,其具有更强的实用性[16]。已有研究[6, 17]表明,Sb(Ⅴ)吸附剂主要分为3大类:无机吸附剂,其主要是铁、锰、铝等金属氧化物或黏土矿物,通过物理或化学吸附将Sb(Ⅴ)固定在其表面;有机吸附剂,其主要包括炭材料和生物吸附剂,前者主要是活性炭、石墨烯和碳纳米材料,但活性炭对Sb(Ⅴ)的吸附效果并不突出,而石墨烯和碳纳米材料成本又过高,后者主要是植物或生物吸附剂,通过生物质表面的羟基、羧基和氨基以静电吸附或表面络合来吸附Sb(Ⅴ);复合吸附剂,其主要利用无机溶剂对生物质改性或有机溶剂对无机吸附剂进行改性处理后的一种复合吸附剂,其吸附能力远高于单一的吸附剂。
近年来,生物炭作为一种新型的环境功能吸附材料,以其来源广泛、价格低廉、比表面积大、表面有着丰富的官能团等优点而倍受科学家关注[18-19]。传统生物炭表面通常带负电荷[20],对金属阳离子(Zn2+、Pd2+等)有着较好吸附效果[21],然而对以(氧)阴离子形式存在的污染元素而言,其吸附效果并不理想[22]。现有方法通过在生物炭表面负载金属离子,利用化学试剂等对原始生物炭进行改性处理[23-24],可有效增强生物炭吸附阴离子的效果。但这些改性方法的成本较高,且表面负载的金属离子、化学试剂易解吸造成二次污染等特点,在具体的工程应用中会显得不切实际。
笔者所在的课题组前期已使用工业废弃物磷石膏对酒糟生物炭进行了改性处理,并通过设置不同热解温度烧制生物炭样品,发现经磷石膏改性的生物炭能有效吸附以阴离子形式存在的磷酸根离子[25]和Cr(Ⅵ)[18]。本着以废治废的目的,本研究尝试使用上述改性的生物炭去除高浓度锑废水中以(氧)阴离子形式存在的Sb(Ⅴ),并研究其作为含锑废水中Sb(Ⅴ)吸附剂的潜在应用价值,分别考察了不同改性温度、投加量和溶液pH对吸附效果的影响,以确定生物炭对Sb(Ⅴ)的最佳吸附条件,并探讨了改性生物炭对Sb(Ⅴ)的吸附行为,并与其他吸附剂对水中Sb(Ⅴ)的吸附性能进行了对比,同时考察了改性生物炭的吸附稳定性,以期为有关锑矿废水中Sb(Ⅴ)的去除提供科学依据与理论指导。
改性生物炭对高浓度锑废水中Sb(Ⅴ)的去除效果
Removal of Sb(Ⅴ) from antimony-rich wastewater by modified biochar
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摘要: 锑(Sb)污染是我国的典型环境问题之一,高浓度的Sb废水是Sb矿区一个重要的Sb污染来源,治理Sb矿废水的重点是高效去除水中的Sb(Ⅴ)。因此本研究采用经典吸附实验方法,用改性生物炭去除水溶液中的Sb(Ⅴ),旨在评价该改性生物炭在含Sb废水中的应用效果和潜力;结果显示,生物炭经过改性处理后吸附Sb(Ⅴ)能力显著增大,热解温度为600 ℃得到的改性生物炭(MC600),在投加比为2.5 g·L−1、pH=7.5条件下,对Sb(Ⅴ)的吸附能力最强,Langmuir模型拟合的最大饱和吸附量为8 089 mg·kg−1。吸附动力学实验发现Elovich方程对MC600吸附Sb(Ⅴ)的拟合效果最好(R2=0.993),吸附过程主要为非均匀表面吸附;吸附等温实验中MC600对Sb(Ⅴ)的吸附行为适用于Langmuir和Langmuir-Freundlich模型拟合(R2=0.981、0.980),表明MC600对Sb(Ⅴ)的吸附主要以单分子层吸附为主,并伴有部分多分子层吸附。通过对MC600吸附高浓度Sb(Ⅴ)后的样品进行解吸,2种样品3次总解吸率均低于30%,表明MC600吸附Sb(Ⅴ)的效果稳定。以上结果表明,改性的MC600对高浓度Sb废水中Sb(Ⅴ) 的去除具有潜在的应用前景。Abstract: Antimony (Sb) pollution is one of the typical environmental issues in China. High concentration of Sb in wastewater is an important source of Sb pollution in Sb mining area. The key point of treating Sb mine wastewater lies in high efficient removal of Sb(Ⅴ) in wastewater. To evaluate the removal efficiency and capacity of Sb(Ⅴ) from Sb-containing wastewater by modified biochar, batch experiments were conducted in this study. The results showed that Sb(Ⅴ) adsorption performance increased for the biochar after modification. The adsorption kinetics experiment indicated that the Sb(Ⅴ) adsorption by MC600 conforms to the Elovich model (R2=0.993), and the adsorption process was mainly non-uniform surface adsorption. In the adsorption isotherm experiment, the Sb(Ⅴ) adsorption behavior of MC600 was suitable for Langmuir and Langmuir-Freundlich models with respective R2 value of 0.981 and 0.980, which showed that the Sb(Ⅴ) adsorption on MC600 was mainly single molecular layer adsorption with partial multi-molecular layer one. The modified biochar (MC600) pyrolyzed at 600 ℃ presented the maximum adsorption amount for Sb(Ⅴ) at the dosage of 2.5 g·L−1 and pH=7.5. The maximum adsorption capacity determined by the Langmuir model was 8 089 mg·kg−1. According to the desorption experiment, the total desorption ratios of Sb(Ⅴ) from two MC600 samples were less than 30%, which showed that Sb(Ⅴ) adsorption on MC600 was stable. This study provided an alternative way for Sb(Ⅴ) removal from Sb-rich wastewater.
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Key words:
- antimony pollution /
- antimony-containing wastewater /
- modified biochar /
- adsorption /
- desorption
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表 1 Sb(Ⅴ)的吸附动力学拟合参数
Table 1. Fitting parameters of Sb (Ⅴ) adsorption kinetics
吸附剂 拟一级动力学方程 拟二级动力学方程 Elovich方程 双常数方程 qe k1 R2 qe k2 R2 α β R2 k n R2 BC600 970 0.772 0.882 1 029 0.001 0.950 4 600 0.007 0.972 488 0.220 0.925 MC600 2 672 3.376 0.817 2 765 0.002 0.908 61 118 0.003 0.993 1 057 0.174 0.985 注:R2为拟合优度(0<R2<1),下同。 表 2 Sb(Ⅴ)的吸附等温线拟合参数
Table 2. Fitting parameters of Sb(Ⅴ) adsorption isotherm
吸附剂 Freundlich Langmuir Langmuir-Freundlich k n R2 Q b R2 Q b n R2 BC600 117.8 1.454 0.964 2 657 0.041 0.930 6 660 0.018 0.781 0.974 MC600 270.9 1.455 0.942 8 089 0.030 0.981 9 102 0.029 0.927 0.980 表 3 MC600吸附Sb(Ⅴ)后的解吸效果
Table 3. Desorption effect of Sb(Ⅴ) adsorbed MC600
初始浓度/(mg·L−1) 解吸次数 解吸率/% 总解吸率/% 60.9 1 16.8 27.5 60.9 2 7.9 60.9 3 2.8 121.8 1 20.0 29.3 121.8 2 7.2 121.8 3 2.1 -
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