Lead adsorption on loess under high ammonium environment
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RESEARCH ARTICLE
Lead adsorption on loess under high ammonium environment Shaoyi Wang 1 & Jiawei Wu 1 & Jianqun Jiang 1 & Shakil Masum 2 & Haijian Xie 1 Received: 8 March 2020 / Accepted: 8 September 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Lead (Pb) is one of the most toxic, hazardous pollutants available in landfill leachate. Loess-amended soil buffers are found suitable and effective in attenuating migration of Pb and the other trace metals. High concentration of ammonium (NH4+ > 1000 mg/l) is also reported in landfill leachate, and therefore, it is essential to investigate the transport of lead under such condition. In this study, the mechanisms and the capacity of loess to adsorb Pb under high NH4+ concentration were investigated. Adsorption isotherm test data were obtained for 25 °C, 35 °C and 45 °C. The maximum adsorption capacity is estimated to be 2101.97 mg/g at 25 °C and 4292.8 mg/g at 45 °C under 1000 mg/l NH4+. The binding sites of Pb on loess are positively related to each other at low temperatures (25–35 °C). The thermodynamic analysis indicates that adsorption process is endothermic and nonspontaneous and the system randomness increases with reaction time. The kinetic test data, fitted with a pseudo-second-order kinetic model and an intraparticle diffusion model, suggests that removal of Pb is driven by both membrane and intraparticle diffusions. The SEM, XRD and FTIR analyses indicate flocculation, precipitations as well as some ion exchange processes, which perhaps combinedly increases adsorption of both NH4+ and Pb in loess. The two kinds of precipitations are involved for the removal of Pb. The precipitations of PbCO3, Pb(OH)2 and PbCO3·2H2O are formed by the reactions between calcite and lead. The other precipitation of white basic salt (Pb2O(NO3)2) is formed by the reactions among Pb2+, NO3− and aqueous ammonia under alkaline environment of loess slurry. Keywords Landfill leachate . Loess . NH4+ . Pb . Multi-component adsorption . Membrane diffusion
Introduction Landfill and mining operations often pollute the surrounding environment by releasing a large amount of hazardous contaminants. The heavy metals, such as lead (Pb), Zn, Cd, Cr and Ni, are of great concerns due to their environmental mobility and toxicity towards human and other living beings (Yang et al. 2018). Among those, Pb is significant, as it can, even at low concentrations, damage blood-forming systems leading to anaemia (Sarkar 2002), as well as lung, stomach and bladder cancers (Shaik and Jamil 2009). High concentration of Pb usually occurs in landfills during the acetogenic Responsible Editor: Tito Roberto Cadaval Jr * Haijian Xie [email protected] 1
College of Civil Engineering and Architecture, Zhejiang University, Hangzhou 310058, China
2
Geoenvironmental Research Centre, Cardiff University, S Glam, Cardiff, Wales CF24 3AA, UK
stage, when the low-pH environment, created by the acetogenic process, enhances the mobility of Pb (Kim et al. 2002). Besides the heavy metal pollutants,
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