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当前全球人口不断增长,但土壤质量却不断下降,现代文明再次面临粮食危机[1]。过去几十年,污水灌溉、采矿、冶炼、废弃物处理、以及农药、化肥大量使用等人类活动导致土壤重金属积累与超标[2-3],继而影响着农产品安全,威胁着人类健康。土壤治理方法中原位稳定化技术因其具有成本低、见效快、操作简便、对污染点位扰动较小等优势而得到了广泛应用 [4]。但该技术使用的常见修复剂大多存在一定的缺陷,如石灰类材料碱性太强,易造成土壤板结;含磷矿物材料使用不当会间接造成水体污染;黏土矿物成分单一、有效活性组分较低,存在施用量过大等问题 [5]。因此合理选择或开发高效、经济、环境友好的修复剂是原位稳定化技术的关键[6]。
近年来,水铁矿-腐殖酸(Fh-HA)复合材料的制备及应用受到了广大学者的研究[7-9]。相较于单一修复剂而言,复合材料更能满足各种不同要求[10]。多种材料在性能上相互取长补短, 产生协同效应,使复合材料的综合性能往往优于原组成材料[11]。腐殖酸的引入,增加了水铁矿的官能团种类,改变了比表面积,并增大了孔径尺寸;此外,水铁矿在此过程中晶格结构不变,没有向其他铁氧化物转变[12]。腐殖酸仅存在于水铁矿的晶格夹缝间,阻碍水铁矿结晶转化,同时也减缓自身在土壤中的矿化降解[13],因此Fh-HA在稳定土壤重金属方面具有优越的性能。但是腐殖酸在一定条件下,具有较高的溶解性 [14-15],重金属离子在Fh-HA复合物表面的吸附也受到腐殖酸溶解性的影响[16]。自然环境下的酸雨、水淹等现象都可能导致腐殖酸溶解,引起复合材料结构破坏,吸附的重金属再次活化。溶解性腐殖酸与水铁矿的相互作用也会明显增强水铁矿中重金属的释放[17]。若对腐殖酸进行高温改性可使其羟基和羧基等官能团发生脱水反应,增强疏水性,达到不溶的目的[18],从而提高复合材料的稳定性。虽然改性过程减少了腐殖酸可用于吸附重金属的酸性基团,但对于酸性基团的金属络合常数并没有影响[19]。马明广[20]、陈荣平[21]等制备热改性腐殖酸吸附水中重金属,均展现出了高吸附效率,并且不易损失、可以重复利用。由此本文提出一种将腐殖酸高温改性形成不溶性腐殖酸,再与水铁矿结合成更稳定的Fh-IHA复合材料的思路。
目前Fh-IHA对自然环境下碱性土壤重金属的吸附性能以及土壤基本理化性质的影响鲜有研究。然而评价修复材料稳定污染土壤重金属的效果时,不仅要关注重金属有效性,还要关注其本身对土壤基本理化性质的影响。因此本研究以甘肃白银某Cd、Pb污染农田为试验区,进行田间稳定化试验,旨在为重金属污染防控提供一种环境友好的修复材料。主要内容如下:(1)采用高温改性腐殖酸与水铁矿制备成Fh-IHA复合材料,并通过扫描电子显微镜、X射线衍射、傅里叶红外光谱、比表面积与Fh-HA进行表面性能对比分析;(2)经田间稳定化试验,分析Fh-IHA对土壤pH值,有机质,铵态氮、速效磷、有效钾的影响;(3)根据改进BCR法,探讨处理后污染土壤中Cd、Pb的形态变化特征,掌握Fh-IHA对重金属Cd、Pb的稳定规律。
优化水铁矿-腐殖酸复合材料对镉、铅污染土壤的稳定化
Study on stabilization of soil contaminated with cadmium and lead by optimization of carbon and iron composites
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摘要: 为解决土壤重金属污染问题,用高温改性腐殖酸制备出水铁矿-不溶性腐殖酸(Fh-IHA)复合材料,通过扫描电镜(SEM)、比表面积(BET)、X射线衍射(XRD)、傅里叶红外光谱(FTIR)分析Fh-IHA的表面特性,结合田间稳定试验研究施加Fh-IHA对土壤pH,有机质(OM),铵态氮(A-N)、有效磷(A-P)、速效钾(A-K)和镉、铅形态的影响。结果表明,Fh-IHA表面粗糙、比表面积大、含有多种官能团,可通过表面络合、静电吸附结合镉、铅离子;稳定化修复后土壤pH轻微降低,有机质升高,铵态氮、有效磷、速效钾转变为缓效养分;稳定态镉、铅百分比含量分别升高22.1%—34.0%、15.6%—21.4%,且经90 d监测未出现活化现象。研究表明,Fh-IHA对土壤中重金属镉、铅稳定效果显著,可作为一种环境友好的土壤重金属污染修复材料。Abstract: To solve contaminated soil by heavy metals, A synthesis of ferrihydrite-insoluble humic acid composite was prepared using high temperature modified humic acid and ferrihydrite. The composite was characterized by scanning electron microscope (SEM), specific surface area (BET), X-ray diffraction (XRD) and fourier transform infrared spectrometry (FTIR) to explore surface characteristics. The effects of introduced Fh-IHA to soil on soil pH, organic matter(OM), ammonium nitrogen(A-N), available phosphorus(A-P), available potassium(A-K), and speciation of cadmium and lead were researched combined with field plot test. The results discovered that Fh-IHA is featured with rough surface, large specific area and abundant functional groups, can complex with cadmium ions and lead ions by surface complexation and electrostatic absorption. After immobilization remediation, soil pH lowered, the content of organic matter increased, and A-N, A-P, A-K were transformed to slow release fertilizers. The percentage of stable cadimium and stable lead in soil increased 22.1%—34.0% and 15.6%—21.4% respectively. Furtherly, the reactivation of cadmium and lead was not detected after 90 days of monitoring. The paper showed that Fh-IHA delivered superior results in immobilizing heavy metal ions, it can be used as an environment-friendly materials for remediation for contaminated soil by heavy metals.
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Key words:
- ferrihydrite /
- insoluble humic acid /
- cadmium, lead pollution /
- soil remediation
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表 1 土壤基本理化性质
Table 1. Basic physical and chemical properties of soil
pH 阳离子交换量/
(cmol·kg-1)
CEC有机质/
(g·kg−1)
OM铵态氮/
(mg·kg−1)
A-N有效磷/
(mg·kg−1)
A-P速效钾/
(mg·kg−1)
A-K镉/
(mg·kg-1)
Cd铅/
(mg·kg-1)
Pb8.15 8.83 7.55 29.57 42.70 129.42 10.93 95.47 -
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