|关键词||矿山开采 河流 沉积物 重金属 释放 Wasp模型|
金是亲硫元素，其与多种金属伴生，金矿开采产生的大量尾矿废石的风化氧化，以及受到严重污染的沉积物在环境条件变化后的释放，是金矿区多种重金属污染的主要来源。利用超滤离心的方法和地球化学平衡模型MinteQ的模拟对As和Fe的形态进行了分析，在上游河道（0-11.4 km）砷和铁主要以胶体态的形式存在，而在下游河道（11.4-23.3 km）二者主要以真溶解态的形式存在。本文中罗山河河道中砷的地球化学反应过程大致可以分为以下三个阶段：（1）黄铁矿（FeS2）和其他含砷矿物的风化氧化造成砷和铁等释放到河水中；（2）当超过水铁矿的溶解度时，风化氧化释放的铁就会很容易发生沉淀作用;（3）最后水铁矿通过脱水作用产生针铁矿和赤铁矿。由含砷矿物风化氧化释放到水体中的As通过吸附、共沉淀等作用再次吸持在水铁矿、针铁矿和赤铁矿等矿物的表面。因此对不同河段，必须根据其地球化学特征选取更合理的的治理措施。
在界河上游4 km的位置，沉积物中As、Zn、Cu、Pb在含量很高，另外，在界河中游17-19 km的河段沉积物中As、Zn、Cu也特别高。重金属高值区与金矿分布密切相关，结合实地勘察表明采矿废渣和废水的排放是重金属的主要来源。沉积物中As的赋存形态沿程变化较大，主要是可还原态和残渣态，上游三个点可还原态含量逐渐减少，而残渣态含量逐渐增多。酸溶解态的Zn含量最高，在采样点LS12之后的样点，酸溶解态Zn的含量远远高于最上游两个采样点。Cu的不同形态沿河变化比较大，在最上游的LS17和LS16两点，Cu主要以酸溶解态的形式存在，在中游河道沉积物中有机和硫化物结合态的Cu的含量明显增多，最下游的JH06点可还原态的Cu含量最高。
四种沉积物中重金属As、Zn、Cu、Cd、Mn释放趋势相似，淋出液中各元素浓度逐渐降低。平衡-动力学反应迁移模型可以很好模拟这些元素的动力学释放过程，并且也可以较好地重现两次停止通液（Stop-flow）的实验结果。通过模型拟合得到的沉积物中各种元素的动力学反应速率反映了它们具有不同的反应机理。在元素的快速释放阶段它的释放是由平衡反应位点和动力学反应位点共同控制的，而之后的长时间持续的慢速的释放是由动力学反应位点控制的。四种沉积物中缓冲能力最强的是JH27，整个淋洗过程中，JH27中三种pH溶液的淋出液pH都在7左右，只有pH 3的淋出液pH有较小的降低，pH 9和pH 6.5的淋出液的pH基本相同。这说明沉积物与淋洗液之间发生了酸碱中和反应，造成了多种重金属的大量释放。
WASP7模型中通过调节河水流量和孔隙水流量的数据对五个连续采样点和沿河采样中示踪剂Li都获得了较好的模拟结果。利用示踪试验获得的界河上游水文数据，对重金属Zn和As的溶解态和总量进行了模拟，取得了很好的模拟结果。总量Zn和As的模拟值和实测值之间的相关系数都是0.98，溶解态Zn和As的模拟值和实测值之间的相关系数都是0.97。另外，在距离O点3 km的河段存在的明显污染源中Zn和As的污染负荷分别为13.2和0.64 kg day-1，对下游河道存在潜在的威胁，应该优先治理。WASP模型可以应用到其他流域用于模拟重金属和其他污染物的迁移和归趋，从而协助我们评价污染物的来源、迁移、沉积物-水界面作用，应用该模型为重金属污染治理的科学决策提供支持。
The heavy metal pollution in mining area is actually the surface geochemical process of heavy metal elements reactivation, migration and accumulation in the mine-river system under the common action of human and nature. To clarify the source, chemical composition, migration and transformation of heavy metals in mining area is of great significance. It helps us to understand the formation mechanism, distribution law of heavy metal pollution and carry out prevention and control work. The Jiehe River is located in Zhaoyuan, Shandong Province, originated in the southwest of Linglong mountain which has the most abundant of gold resources in this mining area. Long-term of large-scale gold mining has caused serious heavy metal pollution in the river basin. In this study, the sampling survey, indoor simulation experiment, field tracer test combined with model simulation method was used. We analyzed the speciation and distribution of heavy metals in water and sediment of Jiehe River, the dynamic release process of heavy metals from contaminated sediment, and the load of pollution source and heavy metal transport in the upstream. The main formation is as follows:
Au is a thiophil element, which is associated with a variety of metals. The main sources of heavy metal contamination in gold mining area are the weathering and oxidation of tailings and waste rocks produced by gold mining, as well as the release of contaminated sediment by the changing of environmental conditions. We analyzed the speciation of As and Fe using the method of ultrafiltration and the the geochemical equilibrium model MinteQ. The result shows that As and Fe were mainly in colloidal forms at stream reach 0-11.4 km, and in downstream reach (11.4-23.3 km) they were mainly in true dissolved forms. We suggest three steps the geochemical reaction process of As in this study area: (1) oxidation of pyrite (FeS2) and As-bearing minerals released As and Fe into stream water; (2) dissolved Fe easily precipitated when the solubility of ferrihydrite [Fe(OH)3] was exceeded under the conditions of this study; (3) further dehydration of Fe(OH)3 generated goethite [FeO(OH)] and hematite (Fe2O3). The As released by As-bearing minerals was adsorbed or co-precipitated again by ferrihydrite, goethite, and hematite. Therefore, it is necessary to select more reasonable treatment measures according to the geochemical characteristics of different river sections.
There are high content of As, Zn, Cu and Pb in the sediment of Jiehe River collected from the 4 km position, in addition, in the middle reaches (17-19 km), particularly high content of As, Zn and Cu is also found. The high value area of heavy metals is closely related to the distribution of gold deposits, and combined with the field survey, the main sources of heavy metals are the discharge of mining waste and waste water.The speciation distribution of As changed a lot along the stream reach, mainly in the reducible state and residual state, the content of reducible state in the three samples in the upper reaches reduced gradually, and the content of residual state is gradually increasing. Zn is mainly in acid extratable forms. The content of acid dissolved Zn in LS12 is much higher than that of the two sampling points of LS16 and LS17. Relatively larger change of Cu speciation along the stream reach, Cu mainly exists in the form of acid dissolved in sediments LS16 and LS17, organic and sulfide content of Cu increased significantly in mid-stream sediments, Cu mainly existed in reducible state in JH06 sediment of downstream.
The release of As, Zn, Cu, Cd, Mn from four sediments showed a similar trend, with each element concentration decreased gradually. The equilibrium-kinetic reactive transport model was successfully used to simulate the dynamic process of heavy metals release, and it can also reproduce the two stop liquid (Stop-flow) experimental results. The kinetic reaction rates of various elements in the sediment obtained from the model can reflect the different reaction mechanism. During the rapid release of the element, its release is controlled by the common action of the equilibrium reaction sites and the kinetic reaction sites, while during the slow release of the element, its release is controlled by the kinetic reaction sites. The acid neutralization capacity of sediment JH27 is much stronger than the other three sediments. In the leaching process, the leachate pH was about 7 for JH27 sediment after using three kinds of injection liquid pH solution. Only a little decrease for leachate pH of JH27 using injection liquid pH 3. The pH of leachate using injection liquid pH 9 and 6.5 was almost the same. This shows that acid and alkali neutralization reaction between sediment and leaching solution, it is likely to cause a large number of heavy metal release.
By regulating the flow of surface water and pore water in the WASP7 model, a good model result of the trace Li data of the five continuous sampling points and along the river were obtained. The river upstream hydrological data obtained by tracer test was used to simulate the dissolved and total amount of Zn and As, and it obtained a very good result of simulation. The correlation coefficient between the simulated and measured values of Zn and As were 0.98, and the correlation coefficient between the simulated and measured values of dissolved Zn and As were 0.97. In addition, the presence of Zn and As pollution loads in the river reach 3 km downstream from O were 13.2 and 0.64 day-1 kg. It is a potential threat to the downstream river and should give priority to governance. The WASP model can be applied to other basins for the transport and fate of heavy metals and other pollutants, to help us evaluate the sources, transport and sediment-water interaction. Application of the model to provide support for scientific decision making of heavy metal pollution control.
|蔡永兵. 金矿区河流水-沉积物中重金属的地球化学特征及反应迁移模拟[D]. 北京. 中国科学院大学,2016.|