【作者】 周元祥；

【导师】 岳书仓；

【作者基本信息】 合肥工业大学 ， 矿物学岩石学矿床学， 2009， 博士

【摘要】 金属矿山尾矿库是亟待开发利用的土地资源,也是潜在的环境污染源。如何开发利用尾矿库,减少环境污染,是目前国际上普遍关注的问题。本文对铜陵地区几个典型尾矿库的地球化学特征进行了研究,通过实地采样分析和实验室实验模拟,探讨了尾矿库重金属迁移和分布规律以及环境效应,并提出了尾矿库复垦的对策。为尾矿库的复垦提供理论根据。研究区铜尾矿的酸中和能力强。浸取水的初始pH对尾矿重金属的溶出几乎没有影响。金属元素的初始溶出速率有一定差异,一般为Zn>Pb>Mn>Cu>Ni>Cr>As>Hg。由于水中酸度被很快中和,pH值上升,使已溶出的重金属离子发生二次反应,生成金属氢氧化物或络合物沉淀析出,最终水中的离子总量趋于稳定。本次工作获得了不同重金属元素的浸出浓度变化的数学模型;风化后尾砂残余重金属含量的变化与堆积时间成正比。尾砂中金属矿物风化释放出的金属离子在自然降水作用下缓慢向下淋滤。由于不同层位尾砂的含氧量不同,尾砂的风化氧化程度不同。不同元素淋滤迁移速度不同。部分重金属元素可能会在50-60cm深度产生二次富集。相比较而言,尾砂中Cu、As、Hg、Cd、Pb的向下迁移速度较快。经过二十多年的淋滤,浅层尾砂中的这些元素明显下降;Zn、Cr的淋滤速度略慢于前四种元素;不论尾砂中Co、Ni的基本上是同步变化;Mn相对比较稳定;值得注意的是,虽然尾砂中孔隙水呈中性偏碱性,但是Pb的迁移速率比预期要快。长期风化氧化后尾矿库尾砂残余重金属含量的空间分布有明显差异。尾砂在风化氧化过程中释放出的金属离子不仅向下迁移,也随地表径流和潜水流动在水平方向产生一定迁移。金属离子的淋滤量及迁移速度与风化氧化程度、降水时间和降水量有关,也与浸水时间有着密切关系,处于径流通道上的表层尾砂金属含量明显降低;尾矿库边缘的尾砂粒度较粗,虽然堆积时间较长,各层位尾砂中的重金属含量还是明显高于其他点。而地势最低的点,Zn、As、Cd等在尾砂表层二次沉积,形成局部富集,下层尾砂中也出现了二次向下迁移的峰值。杨山冲尾矿库尾砂经过20多年的风化氧化和淋滤作用,110cm以内尾砂中的重金属元素的易于淋滤部分大多被淋失,Cu、Mn、Pb、As、Hg、N5、Co、Cr以残渣态为主要赋存形式,所占比例均>35%;其次为铁锰氧化态;Zn、Cd则以铁锰还原态为主,其次为残渣态。表层尾砂中元素的铁锰氧化态的含量均较高;Ni、Co的强有机态所占比例较高。相对而言,林冲尾矿库尾砂经过更长时间的风化淋滤和植物改造,除表层尾砂由于植物富集造成少数元素含量增高,以及60cm处少数元素出现二次富集现象以外,150cm以上大多数金属元素含量已经趋于稳定,变化幅度很小;正在使用中的相思谷尾矿库尾砂元素含量垂向变化大。可见尾矿库尾砂经长期堆存后和复垦后,重金属含量下降幅度大,残留的重金属元素多以铁锰氧化态、强有机态和残渣态形式存在,对环境的危害大幅度减小。尾矿库复垦对重金属元素分布和迁移的影响十分明显,仅仅恢复植被的杨山冲尾矿库,由于草基本上不采收,影响的是其根系能够到达的区域,一部分元素被草吸收,最后随着草枯萎残留在表层,造成表层尾砂中该元素的异常升高;对于大规模耕作复垦的林冲尾矿库,经过多年翻耕、施肥,尾砂中含氧量增加,有机质含量增加,微生物活动增强,尾砂的风化氧化速度提高。重金属元素含量也明显下降,只是作物落叶造成个别元素表层元素含量相对于下层略微升高。因此,大规模耕作对尾矿库尾砂的改性作用很大,而仅表面植草只能减少扬沙危害,并不能从根本上改变尾砂性状,还可能造成部分元素表面富集,影响尾矿库的进一步改造和复垦。研究表明:相思谷尾矿库泄露的水和尾砂对相思河水质没有产生大的影响,相思河水质仍能满足地表水环境质量标准(GB3838-88)中Ⅳ类水的要求,可以用于农灌。但必须澄清后再灌溉,淤积在河底的大量尾砂在汛期可能对沿河低洼地区的土壤产生一定影响。凤凰山尾矿库下风向500m范围内的土壤均不同程度的受到尾矿库扬尘的影响。离尾矿库距离越近,其受到的影响也就越大,即土壤中重金属总量越高。尾矿库泄露水和露采区扬尘共同影响区域,各污染源对土壤重金属含量增加的贡献可以根据其扩散规律进行理论模拟和分离,计算出各自的贡献。计算结果表明:该露采区扬尘影响明显的范围约为半径300米,二者对不同金属元素的贡献有所不同。该区域在汛期有时处于淹没状态,洪水和携带的尾砂对该区域土壤有一定影响。通过对不同位置土壤中重金属赋存状态的分析,发现重金属元素的离子交换态含量随着离露采区的距离增加而明显降低。处于离子状态较易随水迁移,所以残留在土壤中的含量很少;腐殖酸结合态含量同样普遍偏低;各点金属的铁锰氧化态占了较大比重。实验证明:在连续酸性降雨条件下,尾砂覆盖土壤中尾砂释放的重金属可以影响到70cm深度。金属离子在土壤中的迁移速率不同。迁移过程中部分金属离子被吸附在土壤中,故短期对地下水的影响并不是很大,但是Hg、Pb的影响不可忽视。对淋出液和不同部位土壤中重金属含量的比较分析可知,不同金属在土壤中迁移、吸附的量差别很大。尾矿中含量较高的Cu的溶出量和迁移的速度并不大;Pb、Hg的迁移能力则相对较强,能够大部分被淋滤迁移出来,可能引起地下水环境的污染,应予以重视。Cr的迁移能力比较弱,不容易下渗到浅层地下水中,但易造成土壤Cr污染。Zn的迁移能力较强,土壤对其吸附作用也较强,导致土壤和淋出液中的Zn含量普遍升高。种子发芽毒性试验结果表明:尾砂中重金属元素对叶类蔬菜种子的发芽率影响也不大,均能取得较好发芽率,尾矿砂上种植林木和经济作物是可行的。在尾矿砂中加入土壤、EDTA或PAM改良后,能够改变尾砂层的结构,提高其保水、保肥能力。试验配土添加EDTA或PAM后,植物生长状态良好。经对比测试,PAM性能较好,能够有效抑制植物对Cu、Pb、Zn的吸收。而且保水保肥性能良好。尾矿库的复垦工作应分阶段逐步进行。首先采取一定工程措施强化重金属元素的氧化淋滤;然后由边缘向中心逐步推进进行初期植被恢复;在尾矿库闭库的前5—10年以种植草本和木本植物为主,目的的抑制扬沙,改良土壤;10年以后根据土壤中重金属含量的变化可以逐步种植经济作物。尾矿库边缘区域尾砂粒径较大,金属矿物风化氧化速度较慢,要适当采取掺土改良。如果工程措施适当及时的话,可大大缩短复垦时间。更多还原

【Abstract】 The metal mine tailings impoundments are a kind of land resource which should be rehabilitated and utilized urgently, and they are also a potential contamination source. How to rehabilitate and utilize the tailings impoundments and reduce environmental contamination is a problem which attracts people’s attention all over the world. In this paper, the geochemical characters of several representative tailings impoundments in the region of Tongling are studied. The heavy metal transfer rule and environmental effect are researched by sample analyzing and making simulation laboratory experiment, and technological measures for utilizing of tailings impoundments are put forward. The study results provide a theoretic basis for utilizing of tailings impoundments. The conclusions are as follows.In the study area, acid-neutralization capacity of copper tailings is stronger. The initiatory pH of water exerts little effect on the lixiviation of the elements. The initial lixiviation rate of metallic elements were different, commonly, Zn>Pb>Mn>Cu>Ni>Cr>As>Hg. For the reason that acid in water was neutralized rapidly, heavy metal ions lixiviated were able to take part in the second reaction, and metal hydroxides produced were deposited. When lixiviating was in dynamic equilibrium with depositing, the quantity of total ions became a constant. The mathematic models for describing the lixiviation of different heavy metals were obtained in this work.The contents of remaining metals in tailings weathered are in direct proportion to accumulating time. When metallic minerals of tailings have been weathered, metal ions were eluviated down slowly by rainfall. Because the oxygen content in different layers of the tailings dump is not same, the degree of weathering of tailings is different. The transfer rate of different elements in a layer of tailings was dissimilar. Some heavy metal elements might get secondarily enriched in 50. The transfer rates of Cu, As, Hg, Cd, and Pb were faster comparatively. After eluviating over a 20-year period, the contents of these elements in the shallow tailings have decreased obviously. The eluviating rates of Zn and Cr were slower than the above elements. The contents of Co and Ni have changed simultaneously. The content of Mn was steady relatively. It is noteworthy that the transfer rate of Pb was faster in tailings layers than in soils though pH of the pore water was alkalescent.The distribution of remaining heavy metal contents in the space is different due to a long period of weathering. The metal ions transferred not only in the perpendicular direction but also in the horizontal direction with the flow of surface runoff and underflow. The quantity of metal ions and their transfer rates are related to the weathering process, precipitation time, and rainfall, and also related closely to the inundating time. At the route-way of runoff, the metal contents in surface tailings decreased obviously. At points in the edge of tailings impoundments, tailings particle sizes were bigger relatively, and although it has been a long time of weathering, the heavy metal contents in each layer of tailings were greater than other points obviously. At the low-lying area, Zn, As, and Cd deposited at the surface of tailings secondly, resulting in metal ions enrichment; and the peak values of some elements due to secondary transfer also appeared at some positions of lower layers.Through weathering and eluviating over a 20-year period, the easily eluviating fraction of most heavy metals in the tailings above 110 cm in depth have eluviated in the Yangshanchong impoundment. The major existing state of Cu, Pb, Mn, As, Hg, Ni, Co, and Cr was the residual state with the fraction being greater than 35%, and the second was the oxidation state of both iron and manganese. The major existing state of Zn and Cd was the oxidation state of both iron and manganese. In the surface tailings, the contents of the metals in the oxidation state of both iron and manganese were higher, while the fraction of the organic-bound state that Ni and Co existed was bigger. Comparatively, the copper tailings of the Linchong impoundment experienced weathering, eluviating and reclaiming with plants for a much longer time, the contents of metal elements have been changed obviously. Except that the contents of minority elements have risen due to plants enrichment and some elements got secondarily enriched at the 60 cm layer, most metal contents of tailings above 150 cm became steady. In the Xiangsigu impoundment which is being used, metal elements contents in the tailings have changed in perpendicular. It is obvious that heavy metal contents in tailings can be reduced evidently after the tailings were piled and rehabilitated over a long period of time. The existing states of remaining metal elements were the residual state, the oxidation state of both iron and manganese, and the organic-bound state, and the harm to environment was reduced obviously.Impoundment rehabilitation influences the distribution and transfer of heavy metals obviously. For the Yangshanchong impoundment where vegetation came back only, the effect depth is that grass roots can arrive at. Some elements could be absorbed by grasses, and remained on the surface of tailings as grasses perished, so the contents of some elements in surface tailings rose singularly. For the Linchong impoundment which has been rehabilitated and cultured in full scale for years, the oxygen content in the tailings layers has increased, the content of organic substance has been increased, the activity of microorganism is enhanced, and the rate of tailings weathering has increased. Therefore heavy metal contents in tailings were reduced clearly except that the content of one or two elements rose slightly as compared with the lower layer, which may be a result of defoliation. Thus full scale culturing is important for improving the characters of tailings, while surface planting of grass can just decrease dust flying upwards, but the characters of tailings can not be improved fleetly, and even some elements may get enriched again in the surface of tailings, which may produce bad influence on the rehabilitation of tailings impoundments.The investigation proved that leaked water and tailings did not influence obviously the quality of water in the Xiangsi river. The quality of water in the Xiangsi river satisfies the requirement of IV class water in the environmental quality standard of surface water (GB3838-88), and the water can be used to irrigate, but should be clarified. A quantity of tailings depositing at the bottom of the river may influence the soil in the low-lying area along the river. The soil in the area bounded with 500 m leeward of the Xiangsigu impoundment has been influenced by flying dust. The less the distance, the greater the influence, that is, the heavy metal contents in the soil is higher than others.For the area influenced by both leaking water of tailings impoundments and flying dust of opencast working, the emission source’s contribution to increasing metal contents in soils can be simulated and separated according to its diffusion rule. Investigation proved that the area bound influenced by flying dust of opencast working was 300 m. Each factor’s contribution to every metal element was different. The area has been submerged during the raining season. Flooding and the tailings carried by the river water could influence the soil in that area. By analyzing the existing state of metal elements in soil samples of different points, it was found that the contents of metal elements in the exchangeable state decreased with lessening of the distance. Because metals in the ion state could be easily transferred, the remaining contents in soil were less. The contents of metal elements in the humic acid combined state were also lower. At all points, the contents of metal elements in the oxidation state of both iron and manganese were major.The results of eluviating experiment prove that in the soil which was covered with tailings, the metals leached from tailings could influence 70 cm in depth under the continuous acid rainfall condition. Different elements have different rates of transfer. Some elements were adsorbed by soils in the course of transfer, and these elements had less influence on groundwater in a short term, but it is important that the effect of Hg and Pb should not neglected. By comparing the metal contents in the eluviating water sampled at different time with those in the soils at different sections, it is found that the quantity of metal elements leached and adsorbed was different distinctively. The Cu the content of which is higher in tailings eluviated and transfered less. The transferring ability of Pb and Hg in soil was biggish, and most of them eluviated, so attention should be paid to that Pb and Hg may cause groundwater contamination. The transferring ability of Cr was feeblish, and it can not easily move to groundwater, but can cause soil contamination. The transferring ability of Zn in soil was biggish, and the sorption of Zn by soil was also bigger, so the Zn content in soils and eluviating water had risen.The result of experiment on the toxic effect of metal elements on seed germination proved that metal elements in tailings have less influence on the germination rate of greenstuffs. It is possible to grow trees and economic crops on copper tailings. After the tailings were mixed with soil, EDTA, or PAM, the structure of tailings layers would be improved, and their ability of keeping water and fertilizer was raised. After the tailings were mixed with EDTA or PAM, plants grew well. Comparative analysis shows that both EDTA and PAM can restrain plants from absorbing certain metal elements. Comparatively, the capability of PAM was better, and it could restrain plants from absorbing three metal elements availably, and its capability of keeping water and fertilizer was better.The work of tailings impoundment rehabilitating should be carried out step by step. First some technological measures can be used to strengthen oxidating and eluviating of heavy metal elements, and to accelerate improving of soil in tailings impoundment. Second, initial vegetation rehabilitating can be made progressively from the edge to the center of tailings impoundments. Trees and grasses can be planted mainly to restrain flying dust and improve tailings during the initial 5-10 years. According to the change of heavy metal contents in tailings, economic crops can be planted after 10 years. The tailings particle sizes are bigger in the edge of tailings impoundments for the rate of metallic mineral weathering and oxidating is slower, so it is necessary that tailings should be mixed with soils for improving. If the technological measures are appropriate and just in time, the time of rehabilitating can be shortened.更多还原