Adsorption of NH4+-N on Chinese loess: Non-equilibrium and equilibrium investigations

Haijian Xie; Shaoyi Wang; Zhanhong Qiu; Jianqun Jiang

doi:10.1016/j.jenvman.2017.07.016

Adsorption of NH₄⁺-N on Chinese loess: Non-equilibrium and equilibrium investigations

J Environ Manage. 2017 Nov 1;202(Pt 1):46-54. doi: 10.1016/j.jenvman.2017.07.016. Epub 2017 Jul 14.

Authors

Haijian Xie¹, Shaoyi Wang², Zhanhong Qiu³, Jianqun Jiang⁴

Affiliations

¹ College of Civil Engineering and Architecture, Zhejiang University, Hangzhou, 310058, China. Electronic address: xiehaijian@zju.edu.cn.
² College of Civil Engineering and Architecture, Zhejiang University, Hangzhou, 310058, China. Electronic address: zoexcalibur@zju.edu.cn.
³ College of Civil Engineering and Architecture, Taizhou University, Taizhou, 317000, China. Electronic address: qiuzhanhong@tzc.edu.cn.
⁴ College of Civil Engineering and Architecture, Zhejiang University, Hangzhou, 310058, China. Electronic address: jianqun@zju.edu.cn.

PMID: 28715681
DOI: 10.1016/j.jenvman.2017.07.016

Abstract

NH₄⁺-N is a crucial pollutant in landfill leachate and can be in high concentrations for a long period of time due to anaerobic condition of landfills. The adsorption properties of NH₄⁺-N on the Chinese loess were investigated using Batch test. The influences of ammonium concentration, temperature, reaction time, slurry concentration, and pH on the adsorption process are evaluated. Adsorption kinetics and isotherm behaviors were studied by applying different models to the test data to determine the adsorption parameters. The equilibrating duration was shown to be less than 60 min. The data on adsorption kinetics can be well fitted by the pseudo-second-order kinetics model. According to the Langmuir isotherm model, the adsorption capacity of Chinese loess about NH₄⁺-N was predicted to be 72.30 mg g^-1. The uptake of NH₄⁺-N by Chinese loess was considered to be the type of physical adsorption on the basis of D-R isotherm analysis. The optimal pH and slurry concentration are 4 and 2 g/50 ml, respectively. According to the calculated values of free energy, enthalpy and entropy change, the adsorption process is determined to be exothermic. The disorder of the system appeared lowest at temperature of 308.15 K. The predicted Gibb's free energies also indicate the adsorption process is endothermic and spontaneous. The FTIR spectrum and EDX analysis showed the adsorption process of NH₄⁺ involves cation exchange and dissolution of calcite.

Keywords: Ammonium adsorption; Equilibrium; Kinetics; Landfill leachate; Loess; Thermodynamics.

MeSH terms

Adsorption
Hydrogen-Ion Concentration
Kinetics
Temperature
Thermodynamics
Water Pollutants, Chemical*

Substances

Water Pollutants, Chemical