Special Column of Mine Ecological Restoration
Acid mine drainage and its associated heavy metal pollution are the most important mine pollution problems in pyrite−bearing mining areas and the most difficult to comprehensively treat. In order to find out the white pollution and causes of aluminum mining rivers from abandoned stone coal mines in the Haoping river basin, satellite remote sensing interpretation, non−fixed−wing UAV aerial survey, sample collection and analysis, and dynamic monitoring of water quality in major river sections have been carried out since 2021. The results show that, ①white pollution of aluminum is common in rivers in the study area, and three patterns can be seen: the two channels are mixed with river water with different pH degrees to form white water belts; after the natural fall of the river water, white pollutants are formed on the rock surface of the riverbed; river water naturally evolves to form acidic water, acidic sulfur water, and acidic white water. ②Aluminum ion pollution in river water was widespread and seriously exceeded the standard, the average content of Al ions in 216 river waters was 8.6 mg/l, the sample exceeded the standard rate by 65.8%, and the average excess rate of Al ions in the three river waters of 19 river sections was 90.48%. ③ The aluminum in the river comes from the result of the acid water dissolution of feldspar in the stone coal mine and its surrounding rock, and the flowing water at the bottom of the waste residue pile is the main source of pollution of the river aluminum. ④ Aluminum ions in river water have a significant negative correlation with pH, and the greater the acidity of river water, the higher the content of aluminum ions in river water; after the formation of white amorphous gels in river water, the content of aluminum ions in river water decreased significantly. The increase in the pH of river water is the main factor in the formation of white pollutants in rivers. The white pollutants of aluminum in river water have amorphous characteristics, complex chemical composition, and are complex compounds composed of sulfate, hydroxide and aluminum. The white amorphous gel of aluminum has the ability to adsorb heavy metal ions in river water. The research results can have important theoretical and practical application value for the pollution prevention and control of aluminum in the research area.
Acid mine drainage (AMD) is a difficult point in the prevention and control of environmental pollution in sulfide ore deposits, has attracted the attention of scholars at home and abroad. Numerous scholars have studied secondary minerals in AMD in different mining areas. In order to understand the formation and evolution of secondary minerals in AMD, it provides scientific basis for AMD pollution prevention and control. This paper briefly reviews the types of secondary minerals, the formation order of secondary minerals, and the formation, characteristics, environmental hazards and significance of secondary minerals in aluminum phase in AMD under different environments. There are currently three main types of secondary minerals associated with AMD, including: iron−phase secondary minerals, aluminum−phase secondary minerals and other−phase secondary minerals. The pH, Eh and temperature in AMD have a controlling effect on the formation of secondary minerals. Fe− and Al−phase secondary minerals have strong adsorption capacity for several metals in AMD, which can achieve a certain degree of water self−purification. At present, due to the high formation conditions of AMD and unstable mineral phases, there are limited research results on aluminum−phase secondary minerals and “acidic white water” in AMD. Therefore, the study of aluminum−phase secondary minerals and “acidic white water” can better analyze the formation and evolution mechanism of acidic sulfonated water and acidic white water in rivers in the stone coal mines area of Haoping river basin from the perspective of prevention and control, as well as the geochemical process of heavy metal adsorption by aluminum−phase secondary minerals.
To investigate the water pollution effects of a molybdenum mine’s concentrated mining area in southern Shaanxi Province with a 20–year mining history on the surrounding environment, this study collected water quantity and quality test data for 25 tailings pond acid drainage outlets, including the contents of nine heavy metal elements such as mercury, cadmium, arsenic, lead, copper, zinc, manganese, iron, and molybdenum, to evaluate the compound pollution caused by multiple sources and multiple heavy metals. Using the single pollution index and comprehensive index method, this study compared and analyzed the results with the“Comprehensive Wastewater Discharge Standard (GB 8978–1996)”and the“Surface Water Environmental Quality Standard (GB 3838–2002)”, and calculated the single heavy metal element pollution load based on the amount of discharged water. Furthermore, on the basis of the equal–weight index method, this study used the environmental quality standards as a benchmark and, according to the principle of "the importance of the standard value determines its importance," introduced a three–scale indirect matrix to calculate the relative weights of the nine elements, including Fe, and their pollution loads to determine the environmental risk value of a tailings pond. Finally, this study determined the pollution contribution rate of the 25 tailings ponds to the receiving water body, and provided suggestions for the prioritization of tailings pond pollution source control in the next step, based on the pollution load and environmental risk value, to provide a reference for the formulation of relevant follow–up treatment plans.
The sulfate concentration of the water body in the Ziyang stone coal mining area exceeds the standard, and the pollution is becoming more and more serious. Identifying the source of sulfate pollution is extremely important for the prevention of pollution and the guarantee of drinking water safety. The production mechanism of acid wastewater was analyzed and identified using sulfate and oxygen stable isotopes. The results show that the sulfate produced by the sulfide oxidation of stone coal was the main source of sulfate in acid wastewater. Calculated by the IsoSource mass conservation model, the contribution rate of acid wastewater to groundwater sulfate is about 36.5%. The application of multiple isotopes provides a new approach for the comprehensive identification of sulfate sources in acid wastewater and the quantitative study of its impacts on groundwater and provides a scientific basis for mine development and ecological environmental protection and restoration.
River water heavy metal pollution has always been a hot spot problem in the field of environmental pollution prevention and control. The heavy metal content in the water of the Chenjiagou river in a stone coal mining area in Qinling exceeded the standard seriously, but the source of heavy metals was unknown, which caused trouble for pollution control. In order to find out the source and temporal and spatial changes of heavy metals in the Chenjiagou river, surface water samples such as Phase II river water, waste stone coal mine drainage and waste residue pile leaching water were collected, and the pollution index method, principal component analysis and Pearson correlation analysis methods were used to study the degree and spatial distribution of heavy metal pollution in river water, and the sources of heavy metals in river water were analyzed. The results show that the heavy metal content of the river water at the source of Chenjiagou (control point) can reach the Class I standard of surface water, and the heavy metal content in the middle reaches is significantly increased by the drainage of waste stone coal mines and the leaching water of waste residue pile in the middle reach, and the heavy metal content in the river water before entering the main stream is 3.5~312 times that of the control point; the heavy metals such as Cd, Cu, Zn, Ni, and Mn in the river water are homologous, all from the mine drainage and waste residue leaching water in the upper reaches of the river. The spatial distribution of heavy metal content in river water is related to geological bodies, pollution source distribution, river pH, salinity and other factors. The research results provide a scientific basis for the prevention and control of heavy metal pollution in Chenjiagou river.