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汞(Hg), 因具有持久性和长距离迁移的特征,被世界公认为全球性的污染物,对生态系统和人类健康造成严重影响,因而备受关注[1 − 2]. 现有研究表明,有色金属开采和冶炼是人为汞排放的最大源头之一[3 − 5]. 尽管黑色金属矿石中汞含量通常较低,但黑色金属矿物开采规模相对较大,其冶炼加工过程中释放量也较大,因此,黑色金属矿物采冶过程中的汞排放对环境的影响不容忽视,而锰作为黑色金属的典型代表,在黑色金属锰的一系列原矿开采和冶炼加工等过程中对环境造成的汞污染状况如何?现有的研究仍显不足. 据估算,韩国全国初级锰冶炼厂汞的排放量可达到每年644.0 kg [6]. 挪威的Si-Mn合金冶炼的工厂中发现锰矿石中汞含量很高,大量的汞通过燃烧废气向大气环境中排放[7]. 锰冶炼生产加工过程中,大约50%的汞被直接释放到大气环境,大量的汞伴随锰矸石、粉煤灰等以固体废物的形式输出[6,8].
前期研究发现,锰矿采矿和电解锰厂等人为工矿活动向环境中释放了大量汞,锰矿中的汞被迁移进入河流环境在沉积物中产生累积[9]. 然而,锰矿开采过程中产生的锰矸石是典型一般固体废物,由于锰矸石产生量大,露天堆放占用大量林地和耕地等土地资源. 在风化、淋溶、自燃等作用下,锰矸石中重金属容易在大气、土壤和水生态环境进行迁移和转化. 对锰矿采矿区的锰矸石堆场采样预实验发现,天然锰矿采矿的原矿和锰矸石堆场的尾矿中汞含量较高,分别为2.5 mg·kg−1、12.9 mg·kg−1,初步认为锰矿开采过程可能产生大量的汞向周围环境排放. 为从源头上摸清锰矿开采过程产生的锰矸石向环境中排放汞状况,以秀山县溶溪镇某大型锰矿开采企业的锰矸石为研究对象,开展锰矸石中汞的静态浸溶和动态淋溶实验研究,考察静态浸泡和动态淋溶对锰矸石中汞的溶出特征,揭示锰矸石中汞在不同温度、pH值、不同粒径、不同降水作用方式下的溶出释放规律,为研究锰矿区环境中汞的地球化学特征具有极其重要意义.
锰矿区典型汞排放源——锰矸石中汞溶出排放特征
Characteristics of mercury dissolution and discharge in manganese gangue, a typical mercury emission source in manganese mining areas
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摘要:
为掌握锰矿开采产生的锰矸石向环境中排放汞状况,以某大型锰矿开采企业的锰矸石为研究对象, 开展锰矸石中汞的静态浸泡和动态淋溶特征研究. 静态浸泡实验分别考察不同粒径(6—20 目、20—100目、大于100 目)、pH值(4.0、4.8、5.6),浸泡时间(10—180 min)、固液比(1∶16、1∶8、1∶5.3、1∶4、1∶3.3、1∶2.7)、温度(25、35、45 ℃)对锰矸石中汞溶出特征影响. 动态淋溶实验采取在淋溶柱内分别装入6—20 目、20—100 目,以及大于6 目混合锰矸石样品各300 g,温度为25 ℃,以1.0 mL·min−1淋溶速度,每间隔24 h连续加模拟酸雨(pH为4.0)进行淋溶实验,共计反复淋滤38 d. 实验结果表明:在静态浸泡实验中,锰矸石中汞的浸出量随浸泡时间增加而增加,固液比越小,浸出量越大;温度升高,浸出量增大. 酸性条件有利于增加锰矸石中汞的迁移性,粒径较小的锰矸石拥有更大的比表面积,与浸泡溶液的接触面积越大,锰矸石中汞更易于溶解析出. 固液比为1∶2.7时,不同粒径锰矸石中汞浸出量均为最大,表明较大的降雨量和积水量可能增加锰矸石中汞的溶出释放风险. 在动态淋溶实验中,不同粒径锰矸石中淋溶汞浓度变化显著,且均在13—38 d时间范围内,呈逐渐变小的相似释放规律;淋溶后的溶液均呈现酸度增大. 通过估算,每年每吨锰矸石尾矿大约溶出汞量为375.9 mg,锰矿原矿开采人为活动过程均会向环境中排放大量的汞. Abstract: To investigate the mercury emission of manganese gangue produced by manganese ore mining to the environment, this thesis was based on the research on the static immersion and dynamic leaching characteristics of manganese gangue from a large manganese mining enterprise. In static immersion experiments, the effects of different particle sizes (6—20 mesh, 20—100 mesh, greater than 100 mesh), pH value (4.0, 4.8, 5.6), immersion time (10—180 min), solid-liquid ratio (1:16, 1:8, 1:5.3, 1:4, 1:3.3, 1:2.7) and temperature (25, 35, 45 °C) on the dissolution characteristics of mercury in manganite were investigated respectively. The dynamic leaching experiment was performed by loading 300 g of manganese gangue samples with 6—20 mesh, 20—100 mesh and the mixed sample with more than 6 mesh in the leaching column at a temperature of 25 °C under a leaching rate of 1.0 mL·min−1, and continuously adding simulated acid rain (pH 4.0) every 24 h, for a total of 38 days of repeated leaching. The results showed that in the static immersion experiment, the leaching amount of mercury in manganese gangue increased with the increasing immersion time, and the leaching amount increased with smaller solid-liquid ratio and higher temperature. Acidic conditions were conducive to increasing the mobility of mercury in manganese. Manganese gangue with smaller particle size had a larger specific surface area, and the larger the contact area with the immersion solution, the easier it was for the mercury in the manganese gangue to dissolve and desorb. At a solid-liquid ratio of 1:2.7, the amount of mercury leached from manganese gangue with different particle sizes was the largest, indicating that heavy rainfall and water accumulation may increase the risk of mercury dissolution and release from manganese gangue. In the dynamic leaching experiment, the concentration of leached mercury in manganese gangue of different particle sizes changed significantly, showing a similar gradually decreasing release within 13—38 d. After leaching, the solution showed increased acidity. It is estimated that the amount of mercury dissolved per ton of manganese gangue tailings per year is about 375.9 mg, and large amounts of mercury will be released into the environment during manganese raw ore mining.-
Key words:
- manganese gangue /
- mercury /
- static leaching /
- dynamic leaching
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