金属硫化物矿区稻田土壤中硫素的迁移转化及次生硫酸盐矿物中重金属的溶出机制

发布时间：2017-12-28 21:31

本文关键词：金属硫化物矿区稻田土壤中硫素的迁移转化及次生硫酸盐矿物中重金属的溶出机制　出处：《华南理工大学》2016年博士论文　论文类型：学位论文

【摘要】：酸性矿山废水(acid mining drainage,AMD)具有低p H、高硫酸盐、高铁及富含重金属等特征。AMD通过地表径流、下渗及农业灌溉等途径污染下游农田,导致土壤严重酸化、重金属污染以及富含重金属次生矿物的生成。一直以来,学者们对于AMD污染土壤中重金属的分布、迁移以及毒性进行了大量的研究工作,但是对重金属主要伴生元素硫的种类、分布、迁移转化以及富含重金属次生矿物的稳定性研究尚不多见。虽然硫无毒性,但是硫的迁移转化对于土壤酸化以及重金属的释放等具有重要影响。本论文以广东省大宝山多金属硫化物矿区受AMD污染的稻田为研究对象,从稻田土壤中硫的种类、形态分布特征、硫酸根的迁移转化、硫同位素的分馏特征以及不同酸度对次生矿物中重金属释放行为等方面研究金属硫化物矿区稻田土壤中硫素的迁移转化及次生铁硫酸盐矿物中重金属的溶出机制。论文取得主要研究成果如下:(1)AMD灌溉污染稻田土壤中硫的时空及形态分布特征:从上游到下游受AMD污染的横石河水中总硫呈现逐渐递减的趋势,但是沿河两岸稻田土壤中从上游凉桥(S1)至下游徐屋(S5)交换性硫和全硫未呈现规律性的分布。虽然S1~S5已经不采用横石河水灌溉,但是土壤中交换性硫和全硫是未受AMD灌溉的双石村(S6)土壤的2~20倍和1.5~2.8倍,因此交换性硫和全硫可以作为AMD灌溉的标记。另外在上坝村(S3)土壤剖面20~30cm深度存在交换性硫的峰值(934 mg/kg)。2012-2014年的研究发现S3土壤剖面交换性硫的周期性变化不显著,2014年20~30cm深度交换性硫含量最高为1207mg/kg。分析土壤的理化性质发现土壤的p H低、比表面积大、无定形铁氧化含量高和粉粒含量高是硫酸根被赋存的主要原因。在S3土壤剖面中,还原态无机硫(铬还原态硫化物为主)主要分布在表层(0~20 cm),原因是表层丰富的全碳和全氮为硫酸盐的还原提供了能量和电子。不同形态硫在土壤剖面的赋存差异显著:还原态无机硫硫和碳键硫主要分布在表层土壤,吸附态硫主要在20~30cm深度,酯键硫在每一层都有较高含量630~1065 mg/kg,AMD灌溉进入的硫在土壤剖面主要形成了交换性硫和酯键硫。(2)AMD污染土壤中SO_4~(2-)的迁移转化途径:SO_4~(2-)(0~1000 mg/kg)吸附实验,发现上坝村AMD灌溉土壤(0~80 cm深度的5层土壤剖面)都未发生SO_4~(2-)的吸附,反而有大量SO_4~(2-)被解吸,表层土壤(0~20cm)解吸量比率最高达52%~86%。这主要是因为SO_4~(2-)在土壤剖面的赋存形态不同,在表层土壤中高浓度的有机质和磷酸根(450 mg/kg)通过竞争吸附占据了SO_4~(2-)吸附位点,SO_4~(2-)赋存形态主要为水溶态(88%);在中间层土壤(20~40 cm)羟基(νH-O-H)和无定形铁氧化物内层络合吸附了大量的SO_4~(2-),赋存形态主要是吸附态。另外每一层土壤SO_4~(2-)的吸附已经达到饱和且含未被吸附的水溶态硫,其主要来源为有机硫(酯键硫)的矿化作用。同位素分析结果表明:表层土壤中水溶态硫和吸附态硫的δ34S值为-4.60‰和-5.67‰,低于横石河水的最低值-1.03‰,由于植物的吸收和微生物的还原都只会提高土壤中SO_4~(2-)-δ34S,而有机硫的矿化释放出大量的SO_4~(2-)-δ32S,从而降低土壤中水溶态硫和吸附态硫的δ34S值。因此当前的清水灌溉,硫酸根主要的迁移转化途径主要为:吸附态和水溶态解吸进入土壤溶液,前期赋存的酯键硫在矿化作用下也会释放SO_4~(2-)到土壤溶液。(3)矿区河流及农田硫素的分馏特征:由于次生铁硫酸盐矿物的生成及其对SO_4~(2-)的吸附,从上游拦泥坝(RS2)到水楼下(RS5)河段河水中SO_4~(2-)含量从2250 mg/kg降低至250 mg/kg,显著降低。但是在RS2~RS5河段河水和沉积物中δ34S为-1.24‰至-1.16‰,这说明次生铁硫酸盐矿物的生成和吸附过程,不会产生明显的分馏效应。另外在农田(S1至S5)中交换性硫的δ34S变化介于-3.23‰~+3.40‰,未呈现规律性的分布特征,并且后期的耕作方式(旱地与稻田)对SO_4~(2-)的含量和分馏特征影响不显著。(4)次生铁硫酸盐矿物中重金属的溶出机制:在AMD环境中,次生铁硫酸盐矿物(黄钾铁矾)形成过程中其化学结构中的Fe3+和SO_4~(2-)易被其他离子(如Cu2+和Cr O42-)所取代。实验合成了Cu2+和Cr O42-分别取代部分Fe3+和SO_4~(2-)的黄钾铁矾矿物。研究发现,p H变化对次生铁硫酸盐矿物的稳定性和重金属的溶出影响较大:铜铬在p H=1的溶出量显著高于p H=10;两个p H条件下,铬的溶出在大约4 d达到平衡,溶解的Cr O42-在p H=1和10的情况下分别与溶液中高浓度的Fe3+(1.74 mmol/L)与磁赤铁矿络合吸附在矿物表面从而阻碍了矿物的进一步溶解。铜铬元素的溶出摩尔比发现,Cr O42-在矿物中的溶出速率显著高于Cu2+,这种溶解的不一致性主要是因为铜溶后会先形成高稳定Cu O6八面体存在,后于铬的溶出。Cr O42-能够较快被溶出,但是溶出后易被吸附或者络合,阻碍矿物及自身的溶出;Cu2+溶出存在滞后性,但是不易于质子化或形成络合物,随着矿物溶解会持续溶出。因此黄钾铁矾矿物中重金属的溶出主要是受到酸度、取代离子的性质以及取代位点的结构稳定性的影响。综上所述,AMD中高浓度的硫进入土壤后会增加土壤中各种形态硫含量并主要以交换态和酯键硫的形式被赋存到土壤之中,清水灌溉促进了土壤中交换性硫酸根的解吸以及酯键硫的矿化;次生铁硫酸盐矿物中重金属的溶出主要受酸度、取代重金属离子的性质以及取代位点的影响。
[Abstract]:Acid mine wastewater (acid mining drainage, AMD) has the characteristics of low P H, high sulphate, high iron and heavy metal. AMD pollute downstream farmland through surface runoff, infiltration and agricultural irrigation, resulting in serious acidification, heavy metal pollution and heavy metal secondary mineral generation. Since, scholars have conducted a lot of research work on the distribution of heavy metals in contaminated soil, AMD and the migration of heavy metal toxicity, but the main companion species, sulfur distribution, migration and transformation and stability of heavy metal rich secondary minerals are rare. Although sulfur is not toxic, the transfer and transformation of sulfur has an important effect on soil acidification and the release of heavy metals. This paper takes Guangdong province Dabaoshan Polymetallic Sulfide mine in AMD contaminated paddy field as the research object, from the type, the paddy soil sulfur speciation, migration, transformation of sulfate fractionation of sulfur isotope and different acidity on the secondary minerals in the aspects such as the release of heavy metals for paddy soil in mining area of metal sulfide sulfur the migration of heavy metals in secondary iron sulfate mineral dissolution mechanism. The main research results are as follows: (1) AMD pollution in paddy soil irrigation of sulfur in time and space and form distribution characteristics: total sulfur from upstream to downstream of AMD contaminated the Heng Shi River showed a gradually decreasing trend, but in the paddy soil along the river from upstream to downstream cold bridge (S1) Xu Wu (S5) exchange of sulfur and total sulfur did not show the regularity of distribution. Although S1~S5 has not used the Heng Shi River irrigation, the exchangeable sulfur and total sulfur in the soil are 2~20 times and 1.5~2.8 times of the soil of the double stone village (S6) which is not irrigated by AMD, so exchangeable sulfur and total sulfur can be used as markers for AMD irrigation. In addition, there is a peak of exchangeable sulfur (934 mg/kg) in the depth of 20~30cm in the soil profile of the upper dam village (S3). The 2012-2014 year study found that the periodic change of exchangeable sulfur in S3 soil profile was not significant, and the highest exchange sulfur content in 20~30cm in 2014 was 1207mg/kg. Analyzing the physical and chemical properties of soil, it is found that the main reason for the occurrence of sulfate is the low P H, the large specific surface area, the high content of amorphous iron and the high content of powder. In the S3 soil profile, reduced inorganic sulfur (mainly chromium reduction sulfide) is mainly distributed on the surface (0~20 cm). The reason is that the surface total carbon and total nitrogen provide energy and electrons for sulfate reduction. Different forms of sulfur in the soil profile was significantly difference in reducing inorganic sulfur sulfur and carbon sulfur bond is mainly distributed in the surface soil, the adsorbed sulfur mainly in the depth of 20~30cm, ester sulphur in each layer has a higher content of 630~1065 mg/kg AMD, the sulfur in the soil profile into the irrigation main form of sulfur and exchange ester sulphur. (2) AMD in SO_4~ contaminated soil (2-) migration pathway: SO_4~ (2-) (0~1000 mg/kg) adsorption experiment, found on the dam of AMD village irrigation (5 layer soil 0~80 cm depth) are not SO_4~ (2-) adsorption, but a large number of SO_4~ (2-) by desorption the surface soil (0~20cm) desorption ratio up to 52%~86%. This is mainly because the SO_4~ (2-) in different forms of soil profile, in the surface soil of the high concentration of organic matter and phosphate (450 mg/kg) by competitive adsorption to occupy the SO_4~ (2-) adsorption sites, SO_4~ (2-) forms the main water soluble (88%); in the middle layer (soil 20~40 cm (H-O-H) - V) and amorphous iron oxide layer complex adsorption amounts of SO_4~ (2-), speciation is mainly adsorbed. In addition, the adsorption of SO_4~ (2-) in each layer has reached saturation and contains water soluble sulfur, which is not adsorbed, and its main source is the mineralization of organic sulfur (ester bond sulphur). The isotope analysis results show that the 34S surface soil water soluble sulfur and adsorbed sulfur value of -4.60% and -5.67%, is lower than the minimum value of the stone cross -1.03%, due to the reduction of plant uptake and microbial will only improve soil SO_4~ (2-) - 8 34S, and organic sulphur mineralization the release of a large number of SO_4~ (2-) - Delta 32S, Delta 34S and reduce the content of water soluble sulfur and adsorbed sulfur value. Therefore, the main way of migration and transformation of the current sulfate irrigation is: desorption of adsorbed state and water soluble state into the soil solution. The ester bond sulfur released in the early stage also releases SO_4~ (2-) to the soil solution under mineralization. (3) the fractionation characteristics of sulfur in river and farmland of mining area: due to the formation of secondary iron sulfate minerals and their adsorption on SO_4~ (2-), the content of SO_4~ (2-) in the river from upstream to RS2 (RS5) reaches 250 mg/kg, decreasing from 2250 mg/kg to 250 mg/kg. But in the RS2~RS5 River and river sediments, the delta 34S is -1.24 per thousand to -1.16 per thousand, which indicates that the generation and adsorption process of secondary iron sulfate minerals will not produce obvious fractionation effect. In addition, in the farmland (S1 to S5), the change of the delta 34S of exchangeable sulfur is -3.23% ~+3.40 per thousand, showing no regular distribution characteristics. Moreover, the late farming mode (dry land and paddy field) has no significant effect on the content and fractionation characteristics of SO_4~ (2-). (4) the dissolution mechanism of heavy metals in secondary iron sulphate minerals: in the AMD environment, the Fe3+ and SO_4~ (2-) in its chemical structure are easily replaced by other ions, such as Cu2+ and Cr O42-, during the formation of secondary iron sulphate minerals. The potassium ferric vitriol minerals, Cu2+ and Cr O42-, which were substituted for partial Fe3+ and SO_4~ (2-) respectively, were synthesized. The study found that P H changes on the secondary iron sulfate mineral stability and leaching of heavy metals affected: copper chromium in P H=1 dissolution rate was significantly higher than that of P H=10; two P H under the condition of chromium dissolution in about 4 d to reach equilibrium, the dissolution of Cr O42- in P H=1 and 10. Respectively with high concentration of Fe3+ (1.74 mmol/L) and Magnetic Hematite adsorption on the mineral surface and thus hinder the further dissolution of minerals. Dissolving mole ratio of copper and chromium elements
【学位授予单位】：华南理工大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：X53;X753

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