改性土-膨润土阻隔墙阻控离子型稀土矿氨氮污染

Resistance and control of ammonia nitrogen pollution of ionic rare earth ores with modified soil-bentonite barrier

以土-膨润土为阻隔材料,使用硅灰及水泥对其进行固化改性,研究改性后阻隔墙对离子型稀土矿原地浸矿氨氮污染的阻控效果。通过了解阻隔墙材料的渗透性能、力学性能,并结合阻隔材料对氨氮的吸附效果、穿透效果和数值模拟结果,探讨改性土-膨润土阻隔材料对氨氮污染的阻控性能。结果表明:硅灰改性土-膨润土阻隔材料,最佳质量配比为硅灰∶土=1∶10,最佳含水率为67.80%;改性阻隔材料生成的铝硅酸盐提高了阻隔墙防渗性能,渗透系数为2.36×10-9 m·s-1;CaCO3提高了材料的力学性能,使抗压强度达到0.896 MPa;改性阻隔材料对氨氮的吸附过程符合准二级动力学模型及Langmuir等温模型。这说明该吸附过程以化学吸附为主,并且该吸附是放热过程。在不同氨氮浓度的穿透下,渗透系数呈逐渐减小的趋势,实验期间并未达到穿透浓度。利用Visual MODFLOW数值模型对阻隔墙的阻控效果进行模拟发现,7300 d后NH4+扩散范围小,未穿透阻隔墙。硅灰改性土-膨润土阻隔墙用于对离子型稀土矿氨氮污染阻控的效果较好。

In this study,silica fume and cement were used to perform the curing and modification of the barrier material of soil-bentonite,the control effect of modified barrier on ammonia nitrogen pollution caused by in-situ leaching of ionic rare earth ore was investigated.Through analyzing the permeability and mechanical properties of the barrier material,and the adsorption and penetration effects of the barrier material on ammonia nitrogen,as well as the numerical simulation results,the resistance and control properties of the modified soil-bentonite barrier material on ammonia nitrogen pollution were discussed.The results showed that for silica fume modified soil-bentonite barrier material,the optimal mass ratio of silica fume to soil was 1∶10,and the optimal moisture content was 67.80%.The permeability of the barriers was improved by the aluminosilicate yielded in modified barrier material,and the corresponding hydraulic conductivity was 2.36×10-9 m·s-1.CaCO3 improved the mechanical properties of the material and its compressive strength reached 0.896 MPa.The adsorption process of ammonia nitrogen by the modified barrier material conformed to the quasi-second-order kinetic model and the Langmuir isothermal model,which indicated that the adsorption process was dominated by chemical adsorption and exothermic process.Under the penetration of different ammonia nitrogen concentrations,the permeability coefficient gradually decreased,while the penetration concentration was not reached during the experiment.Visual MODFLOW numerical model was adopted to simulate the barriers,and the results indicated NH4+ runing.The silica fume modified soil-bentonite barrier has a good effect on ammonia nitrogen pollution control in ionic rare earth minerals.