古土壤层对煤矸石淋滤液中典型污染物的防污性能

Antifouling property of the paleosol layer to the contaminants in the coal gaugue leachate

黄土区是我国重要的煤炭生产区,古土壤层在黄土区包气带中广泛发育。煤炭开采和洗选过程中会产生大量煤矸石,其中露天堆放的煤矸石在长期降水淋滤作用下会释放出含有大量污染物的淋滤液,对矿区周围的地下水造成污染。黄土区煤矸石淋滤液在进入到地下含水层之前,必将流经过古土壤层。要准确评价煤矸石淋滤液对地下含水层的影响,必须确定古土壤层对煤矸石淋滤液中污染物的防污性能。通过开展室内渗透试验和批式吸附试验,研究了古土壤对煤矸石淋滤液中典型污染物Mn^(2+),Zn^(2+),Cu^(2+)和SO_(4)^(2-)的阻隔情况。渗透试验结果显示,煤矸石淋滤液作用下古土壤试样的渗透系数在0.852×10^(-9)~1.01×10^(-9) m/s,比使用蒸馏水渗透时得到的渗透系数降低了1.5倍以上。古土壤试样渗透系数之所以会降低,是因为煤矸石淋滤液与古土壤之间发生了化学反应,生成新的沉淀物淤堵了古土壤试样中的孔隙。批式吸附试验结果显示,古土壤能够吸附Mn^(2+),Zn^(2+),Cu^(2+),吸附过程符合非线性的Freundlich模型;古土壤层中黏土矿物与重金属之间的离子交换反应,是古土壤吸附重金属的主要途径。古土壤颗粒呈电负性,与SO_(4)^(2-)之间存在相互排斥作用,几乎不吸附SO_(4)^(2-)。使用POLLUTE V7软件模拟预测了煤矸石淋滤液中典型污染物击穿古土壤层的时间,结果显示,厚度为1.0 m的古土壤层对污染物的有效阻隔时间可以达到10 a以上。总体而言,古土壤层具有较强的防污性能,能够限制污染物向含水层迁移,因此在进行黄土区煤矸石堆场地下水环境影响评价及污染防控时,有必要考虑古土壤层产生的影响。

Loess region is an important coal producing region in China.The paleosol are widely developed in vadose zone in the loess areas.A large amount of coal gangue will be produced in the process of coal mining and washing,among which the coal gangue stacked in the open dump will release a large number of pollutants under the long-term leaching effect,causing pollution to the underground water around the mining area.The leachate produced in coal gaugue dump will flow through the paleosol before it arrives to aquifer.Thus,in order to understand the accurate environmental effect of the coal gaugue leachate on the aquifer,the antifouling property of the paleosol needs to be assessed.Hydraulic conductivity tests and batch adsorption tests were conducted to evaluate the antifouling property of paleosol for Mn^(2+),Zn^(2+),Cu^(2+) and SO_(4)^(2-) in coal gaugue leachate.The results of hydraulic conductivity tests show that the hydraulic conductivity of paleosol ranges between 0.852×10^(-9) and 1.01×10^(-9) m/s,which is lower than the values obtained using distilled water as permeation solution.The decreases in the hydraulic conductivity should be attributed to pore plugging resulting from the production of precipitates.The batch adsorption test demonstrate that paleosol can adsorb Mn^(2+),Zn^(2+) and Cu^(2+) and the adsorption processes are well described by Freundlich model.The adsorption of heavy metals on the paleosol is mainly through ion-exchange reaction.The adsorption capacity of paleosol for SO_(4)^(2-) is so small that can be ignored.This may be attributed to the negative surface of the paleosol,which produces a repulsion between the paleosol surface and the SO_(4)^(2-)ions.POLLUTE V7 was used to simulate and predict the time of typical pollutants in coal gangue leachate to penetrate the paleosol.The model results show that the paleosol with 1.0 m thickness can protect aquifer for 10 years from polluting.In general,the paleosol used in the present study is an effective barrier to limit the flow of coal gaugue leachate.Therefore,the potential effect of the paleosol layer should be considered when conducting the groundwater environmental impact assessment and pollution control of coal gangue dump in the loess area.