底板岩性对煤矸石充填体重金属元素迁移影响规律数值模拟

近年来煤矸石充填采煤技术作为煤矿绿色开采技术之一得到了较大规模的推广应用。煤矿采空区中的煤矸石充填体长期处于偏酸性或偏碱性矿井水环境中,其富含的重金属元素有向底板迁移进而影响地下水的风险。通过煤矸石静态浸泡实验,利用ICP测试浸泡液中重金属元素浓度,确定了煤矸石浸泡液中的主要重金属为铍(Be)、锰(Mn);运用COMSOL Multiphysics建立了不同底板岩性(泥岩、花岗岩、砂岩、灰岩)条件下的煤矸石重金属元素迁移数值模拟计算模型;以Mn元素为例分析了重金属元素在不同岩性底板中的扩散距离及浓度分布,得到了重金属元素扩散距离与底板岩层渗透系数的关系。结果表明:未铺设黏土垫层时泥岩、花岗岩、砂岩、灰岩底板中Mn元素在底板中的扩散距离分别为5.2,12.5,16.0,19.0 m,铺设黏土垫层后Mn元素扩散距离为0.9,2.8,5.2,9.1 m,分别下降了82.69%,77.60%,67.50%,52.10%。

Numerical simulation on migration effects of heavy metal elements in coal gangue backfilling body caused by the lithology of coal seam floor

In recent years,coal gangue backfill mining technology has been widely applied as one of the green mining technologies.The coal gangue filling in goaf has been in the acidic or alkaline mine water environment for a long time,its heavy metal elements in goaf have the risk of migrating to the floor and polluting groundwater.In this paper,through the static immersion test of coal gangue,the concentration of element in soaking solution was determined by ICP.The main heavy metals components in coal gangue were Be and Mn.A numerical simulation model for the migration of heavy metals in coal gangue under different floor lithology (mudstone,granite,sand-stone and limestone) was established by using COMSOL and Multiphysics.Taking Mn as an example,the diffusion distance and concentration distribution of heavy metal element in different rock floors were analyzed,and the relation between the diffusion distance of heavy metal element and the permeability coefficient of floor rock was obtained.The results show that the diffusion distance of Mn element in the bottom plate is 5.2 m,12.5 m,16 m and 19 m,respectively,when the clay cushion is not laid on the mudstone,granite,sandstone and limestone.After laying clay cushion,the diffusion distance of Mn element is 0.9 m,2.8 m,5.2 m and 9.1 m,and decreases by 82.69%,77.60%,67.50%,52.10% respectively.