Resistance and control of ammonia nitrogen pollution of ionic rare earth ores with modified soil-bentonite barrier
GONG Rui1,2,, YE Changwen1,2,,, CHENG Rong3, JI Xing1,2, SHU Rongbo3, YANG Jinfei1,2, ZHOU Jinqiu1,2 1.State Key Laboratory of Geohazard Prevention and Geoenvironment Protection, Chengdu University of Technology, Chengdu 610059, China 2.State Environmental Protection Key Laboratory of Synergetic Control and Joint Remediation for Soil & Water Pollution, Chengdu University of Technology, Chengdu 610059, China 3.Institute of Comprehensive Utilization of Minerals, Chinese Academy of Geological Sciences, Chengdu 610041, China
Abstract: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 that the diffusion range of ${\rm{NH}}_4^ + $ was small and the barrier wall was not penetrated after 7 300 d simulation runing. The silica fume modified soil- bentonite barrier has a good effect on ammonia nitrogen pollution control in ionic rare earth minerals. Key words:ammonia nitrogen pollution/ ionic rare earth ore/ pollution control/ silica fume recycling/ modified soil-bentonite/ numerical simulation.
图1阻隔墙改性前后的XRD图谱 Figure1.XRD pattern of barriers before and after modification
图5Visual MODFLOW数值模型模拟设置阻隔墙前后预测污染羽分布 Figure5.Pollution plume distribution before and after using the barrier wall predicated by Visual MODFLOW numerical model simulation
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1.State Key Laboratory of Geohazard Prevention and Geoenvironment Protection, Chengdu University of Technology, Chengdu 610059, China 2.State Environmental Protection Key Laboratory of Synergetic Control and Joint Remediation for Soil & Water Pollution, Chengdu University of Technology, Chengdu 610059, China 3.Institute of Comprehensive Utilization of Minerals, Chinese Academy of Geological Sciences, Chengdu 610041, China Received Date: 2019-10-10 Accepted Date: 2020-03-01 Available Online: 2020-05-12 Keywords:ammonia nitrogen pollution/ ionic rare earth ore/ pollution control/ silica fume recycling/ modified soil-bentonite/ numerical simulation Abstract: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 that the diffusion range of ${\rm{NH}}_4^ + $ was small and the barrier wall was not penetrated after 7 300 d simulation runing. The silica fume modified soil- bentonite barrier has a good effect on ammonia nitrogen pollution control in ionic rare earth minerals.
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