Study On Release Rule And Pollution Risk Of Heavy Metals From The Gold Mine Tailings Pond

The gold mine tailings are mostly stored in the tailings ponds as solid waste.If the pollution prevention measures are not in place,heavy metals in the tailings will migrate to soil and water bodies through wind transport,rainwater leaching,surface runoff,and other ways,affecting the safety of the surrounding environment,and can enter the surrounding residents through oral intake,respiration and skin contact,threatening human health.Therefore,this thesis addresses the hot issue of heavy metal pollution of tailings(solid waste),takes tailings in a gold mine tailings pond as the research object,and systematically carries out research related to the meso-structure characteristics and permeability of the tailings,the release rules and distribution characteristics of heavy metals,the risk assessment of the surrounding groundwater and soil around the tailings pond,through a combination of laboratory analysis,similar experiments,theoretical analysis,and numerical simulation.The main research results are as follows.1)The grain composition,permeability,and porosity of tailings were experimentally determined;based on CT scanning technology,image processing,and three-dimensional reconstruction method,a three-dimensional model of tailings pores and particles were established,and the validity of the model was verified with experimental measurements;the characteristics of tailings particles and pores structure were analyzed from the perspective of meso-structure,and a multi-dimensional characterization system of tailings meso-structure was formed with average particle size,porosity,sphericity,and fragmentation index as the main characteristic parameters;the fragmentation index was introduced into the KozenyCarman empirical equation to establish the theoretical calculation model of tailings permeability coefficient.2)The heavy metal content and morphological distribution characteristics of the tailings were measured,and the heavy metals studied in the leaching experiment were determined as Mn,Zn,Pb,and Cd;the heavy metal leaching device of the tailings was developed,and the dynamic leaching experiments of the tailings under different rainfall flow rates and pH conditions were carried out to obtain the heavy metal concentration release rule and cumulative release characteristics of the tailings,and by improving the control equation of heavy metal release mechanism,the release process of each heavy metal element under different conditions segmentally described,and the release mechanism of heavy metal in the tailings of the gold mine was revealed.Based on the exponential decay relationship between the concentration of heavy metals and the total volume of leachate,a heavy metal leaching release model for the tailings was established to predict the total annual average release and the annual average release concentration of Mn,Zn,Pb and Cd under the rainfall conditions of the tailings pond.3)Based on the dynamic leaching experiment of tailings,the water content and heavy metal distribution characteristics of tailings with different rainfall pH,flow rate,leaching cycle,and leaching column depth were studied,combined with probability statistics and the transformation process of heavy metals in the solid phase of tailings and liquid phase of leaching solution,the vertical distribution law of heavy metal content in the tailings under leaching conditions was revealed;the Sparrow search algorithm(SSA)was introduced to optimize the extreme learning machine(ELM)and combined with the vertical distribution results of heavy metal content in the tailings under leaching conditions,the SSA-ELM vertical distribution prediction model of heavy metal content was constructed,and the prediction accuracy was evaluated to predict the distribution characteristics of heavy metal content under different influencing factors.4)Visual MODFLOW groundwater numerical simulation software was used to establish the hydrogeological conceptual model of the tailings pond and its surroundings,and the heavy metal elements in the leaching experiment were used as the pollution factors and the heavy metal release predicted by the leaching release model was used as the source strength to simulate the heavy metal transport with groundwater after the leakage of the tailings pond,to predict the transport range,the maximum transport distance and the impact degree of heavy metal pollutants at different times;the contamination of civil wells in the surrounding villages was monitored,and the risk of contamination was evaluated using groundwater quality standards.5)The soil samples around the tailings pond were collected to analyze the characteristics of heavy metal pollution in the soil;the heavy metal content within the soil was interpolated by using ArcGIS to obtain the spatial distribution law of heavy metals and analyze the sources of heavy metal pollution;different evaluation methods were used to assess the risk of soil heavy metal pollution and human health.Thus,the risk level of heavy metal contamination in soil was determined.The research results of this thesis provide data support for the evaluation of heavy metal pollution and the formulation of prevention and control measures,and also enrich the theory and methods of heavy metal release and distribution of gold mine tailings,which are of practical significance for the protection of environmental safety and the health of residents around tailings ponds.