Adsorption characteristics and influencing factors of ammonium nitrogen on yellow soil around informal landfill
ZHAO Li1,,, ZHANG Yanxia2, AO Liang1, YIN Zhenzhen1 1.Chongqing Institute of Ecological Environment Science, Chongqing 401147, China 2.State Power Investment Group Yuanda Environmental Protection Engineering Co. Ltd., Chongqing 401122, China
Abstract:To investigate the influence of soil in vadose zone around an informal landfill on the migration of ammonium nitrogen from soil to groundwater, batch experiments were employed to characterize the adsorption thermodynamics and kinetics of water-soluble ammonium, exchangeable ammonium, fixed ammonium and total ammonium, as well as the influences of temperature, pH and coexisting cations. In combination with the desorption tests, the fix ability of yellow soil to ammonium was also determined. The results showed that adsorption kinetics properties of different forms of ammonium were similar, but the adsorption process was different, the order of adsorption rate and the time reaching adsorption equilibrium was following: water-soluble ammonium, fixed ammonium and the exchangeable ammonium. The thermodynamic process of ammonium adsorption conformed to the Langmuir model, and the maximum adsorption capacities of total ammonium, water soluble ammonium, exchangeable ammonium and fixed ammonium were 696.49 mg·kg?1, 363.50 mg·kg?1, 245.64 mg·kg?1 and 112.50 mg·kg?1 at 25 ℃, respectively. The increase of temperature could accelerate the adsorption process and inhibit the increase of adsorption capacity, lower temperature was favorable to the adsorption and fixation of ammonium nitrogen. pH showed no significant effect on the total amount of ammonium adsorption by yellow soil, which could change the composition of ammonium nitrogen in soil by affecting the adsorption of water-soluble ammonium and exchangeable ammonium. Addition of Ca2+ could significantly decrease the adsorption amount of water-soluble ammonium and exchangeable ammonium by competing the adsorption points in the soil, and promote the desorption correspondingly. The results indicated that the soil around the informal landfill could effectively prevent the migration of low concentration ammonia nitrogen to groundwater, and lower temperature, higher pH, and lower concentration of cations were beneficial to enhance the protection performance of vadose zone on ammonia nitrogen. Key words:yellow soil/ ammonium forms/ adsorption characteristics.
图1各形态铵吸附动力学曲线 Figure1.Absorption kinetic curves of ammonium forms
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1.Chongqing Institute of Ecological Environment Science, Chongqing 401147, China 2.State Power Investment Group Yuanda Environmental Protection Engineering Co. Ltd., Chongqing 401122, China Received Date: 2020-02-13 Accepted Date: 2020-05-19 Available Online: 2020-09-05 Keywords:yellow soil/ ammonium forms/ adsorption characteristics Abstract:To investigate the influence of soil in vadose zone around an informal landfill on the migration of ammonium nitrogen from soil to groundwater, batch experiments were employed to characterize the adsorption thermodynamics and kinetics of water-soluble ammonium, exchangeable ammonium, fixed ammonium and total ammonium, as well as the influences of temperature, pH and coexisting cations. In combination with the desorption tests, the fix ability of yellow soil to ammonium was also determined. The results showed that adsorption kinetics properties of different forms of ammonium were similar, but the adsorption process was different, the order of adsorption rate and the time reaching adsorption equilibrium was following: water-soluble ammonium, fixed ammonium and the exchangeable ammonium. The thermodynamic process of ammonium adsorption conformed to the Langmuir model, and the maximum adsorption capacities of total ammonium, water soluble ammonium, exchangeable ammonium and fixed ammonium were 696.49 mg·kg?1, 363.50 mg·kg?1, 245.64 mg·kg?1 and 112.50 mg·kg?1 at 25 ℃, respectively. The increase of temperature could accelerate the adsorption process and inhibit the increase of adsorption capacity, lower temperature was favorable to the adsorption and fixation of ammonium nitrogen. pH showed no significant effect on the total amount of ammonium adsorption by yellow soil, which could change the composition of ammonium nitrogen in soil by affecting the adsorption of water-soluble ammonium and exchangeable ammonium. Addition of Ca2+ could significantly decrease the adsorption amount of water-soluble ammonium and exchangeable ammonium by competing the adsorption points in the soil, and promote the desorption correspondingly. The results indicated that the soil around the informal landfill could effectively prevent the migration of low concentration ammonia nitrogen to groundwater, and lower temperature, higher pH, and lower concentration of cations were beneficial to enhance the protection performance of vadose zone on ammonia nitrogen.