冻-融及干-湿循环对采矿废石风化产酸影响的试验研究

Experiments on the weathering effects of freezing-thawing and drying-wetting circulation on the mining waste rock behaviors

为研究我国东北地区典型气候条件对采矿废石酸性排水的影响,以辽宁省本溪市红透山铜矿废石为研究对象,探讨了干-湿循环和冻-融循环作用对采矿废石风化产酸的影响。黄铁矿(FeS2)在废石中的平均质量分数为23.51%,是主要的产酸硫化矿物。利用自制淋溶试验设备开展了为期120 d(共计20次)的冻-融循环、干-湿循环及淋溶试验,对不同试验条件下铜矿废石淋溶液的pH值、酸度、电导率以及Ca2+、Mg2+、SO2-4、总Fe及Cu2+质量浓度进行了测试分析。结果表明,相对于干-湿循环作用而言,单纯的冻-融循环作用不会对废石的风化产酸产生明显影响。试验过程中冻-融循环作用下废石淋溶液的pH值基本维持在5左右,干-湿循环作用下废石淋溶液的pH值则保持在4.5左右。由于风化产酸程度较高,干-湿循环作用下黄铁矿风化所形成的总Fe、SO2-4质量浓度分别为冻-融循环下的8.5倍和1.6倍;Cu2+的质量浓度约为冻融循环条件下Cu2+质量浓度的5.2倍。冻-融循环及干-湿循环条件下,氧气及水分穿透黄铁矿外"包裹层"的时间分别为60 d和80 d。因此,与南方相对温暖湿润的气候类型相比,我国东北地区冰冻期长、丰水期短的气候类型可在一定程度上抑制废石风化产酸的形成。

The present paper is aimed at introducing the results of our experimental study over the effects of drying-and-wetting weathering circulation on the mining waste rock behaviors by taking the Acid Mine Drainage of mining waste rocks of Hongtou Mountain Copper Mine of Benxi, Liaoning, as a case study sample. As is known, the waste rocks of the Hongtou Mountain Copper Mine in Benxi, have to experience the weathering influence of environmental factors under the local weather conditions. In this paper, we have given a series of leaching experiments under the freezing-thawing and drying-wetting circulated laboratory conditions and made a detailed discussion over the effects of the natural environmental factors on the changes of such rocks. The XRD analyses of the waste rock samples indicate that the Pyrite （FeS 2 ） serves as dominating sulphate mineral of the samples, which account for 23.51% of the average presence of the waste rocks. Based on our self-developed leaching device, we have established three different laboratory conditions, including freezing-thawing circulation, drying-wetting recycling and reference condition （without freezing-thawing and drying-wetting circulations） parameters 20 times as harsh as the natural freezing-thawing/drying-wetting weathering cycles in our experiments, which were let to be exposed to and continued for a period of 120 days. During the said period, monitoring and observation activities were done to the samples in terms of the pH value, acidity, conductivity and the mass concentration of Ca ^2＋ , Mg ^2＋ , SO4^2- , the total Fe and Cu^2＋ within the range of the leachate change. The results of our experiments indicate that, as compared with the drying-wetting effects made in the natural condition, the simple freezing-thawing cycles wouldn＇t have made noticeable effects on the waste rocks. The pH value of the leachate under the experimental freezing-thawing cycles tends to be around 5 whereas that of the leachate from natural drying-wetting cycles has been worked out as 4.5. Due to the relatively higher weathering acidity under the experimental conditions, the mass concentration of the total Fe and SO4^2- , coming from the chemical weathering experimental conditions of the pyrite, were found to be as 8.5 times and 1.6 times as that under the natural freezing-thawing cycles. Under the effects of lower pH value, the Cu^2＋ of the leachate tends to have a higher mass concentration. By the end of the experiments, the mass concentration of Cu^2＋ has been found as high as 146.6 μg/L, which reached approximately 5.2 times as high as that under the natural conditions. The time limit of oxygen and water has been found broken through the outer integument of the pyrite inner core under the freezing-thawing and drying-wetting cycles turned out to be 60 days and 80 days respectively. Thus, it can be concluded that, as compared with the warm and humidity climate conditions in south of China, the long frozen period and short wet season in the north-eastern of China tend to restrict the weathering acidity and the acid mine drainage of the mining waste rocks.