Surface mole-ratio method to distinguish surface precipitation and adsorption on solid-liquid interface

Jinshan Wei; Xiaoguang Meng; Yonghui Song; Qiantao Shi; Xianghua Wen; George Korfiatis

doi:10.1016/j.jhazmat.2020.122781

Surface mole-ratio method to distinguish surface precipitation and adsorption on solid-liquid interface

J Hazard Mater. 2020 Oct 5:397:122781. doi: 10.1016/j.jhazmat.2020.122781. Epub 2020 Apr 22.

Authors

Jinshan Wei¹, Xiaoguang Meng², Yonghui Song³, Qiantao Shi⁴, Xianghua Wen⁵, George Korfiatis⁴

Affiliations

¹ State Key Joint Laboratory of Environmental Simulation and Pollution Control, School of Environment, Tsinghua University, Beijing, China. Electronic address: jwei7@stevens.edu.
² Center for Environmental Systems, Stevens Institute of Technology, Hoboken, NJ, USA. Electronic address: xmeng@stevens.edu.
³ State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing, China. Electronic address: songyh@craes.org.cn.
⁴ Center for Environmental Systems, Stevens Institute of Technology, Hoboken, NJ, USA.
⁵ State Key Joint Laboratory of Environmental Simulation and Pollution Control, School of Environment, Tsinghua University, Beijing, China.

PMID: 32388096
DOI: 10.1016/j.jhazmat.2020.122781

Abstract

The enhancement effects of phosphate (P) on Pb removal by adsorbents have been attributed to co-adsorption of P and Pb, the formation of P-Pb surface ternary surface complexes, and surface precipitation of P and Pb. However, distinguishing adsorption from surface precipitation in multi-adsorbate systems has been a challenge. For the first time, a surface mole-ratio (SMR) method was established and applied for delineating Pb-P precipitation and Pb adsorption on an acrylic amine fiber (AAF) adsorbent. In elaborating the SMR method, we developed Pb removal experiments by mixing solutions containing 0.2 g/L of AAF, 6 and 12 μmol/L P, and 0-35 μmol/L Pb. When the removed Pb/P (μmol/μmol) was plotted as a function of the equilibrium Pb (μmol/L), the SMR diagram exhibited a turning-point similar to the Pb/P mole ratio of 5/3 = 1.67 in pyromorphite (Pb₅(PO₄)₃OH) precipitate. The SMR diagram indicated that when the Pb concentration increased, the precipitate formed first; after all P formed precipitates, Pb was removed by adsorption. The precipitation and adsorption processes were further confirmed by other SMR diagrams, FTIR, SEM-EDX, and XRD analysis. The SMR method will have broad applications in determining the removal mechanisms of multi-adsorbates by adsorbents and coagulants, and stabilization mechanisms of heavy metals in soils. With the development and application of more modern in-situ characterization techniques, SMR method will be more effective.

Keywords: Adsorption; Lead removal; Phosphate; Precipitation; Surface; Surface mole-ratio method.