Effects of Fe3+ and Ca2+ on sorption of phenanthrene by Humin in karst soil, Southwest China

Humin (HM) is the main organic matter component to affect the migration and transformation of polycyclic aromatic hydrocarbons (PAHs) in soil. The study on influence of the morphology change of inorganic ions on the adsorption of PAHs in soil and its organic matter is still rare at microscopic scale. In this paper, yellow soil humin (YS-HM) and lime soil humin (LS-HM) were chosen as samples, then Fe3+ and Ca2+ were added into samples to facilitate the precipitation by changing the existing conditions of ions, and the mechanism by which inorganic precipitation changed adsorption capacity of karst soil was analyzed from the microscopic scale. The results showed that the adsorption capacity of HM reduced with the inorganic precipitation increasing. The precipitation of Ca2+ and Fe3+ both reduced the adsorption capacity of YS-HM and LS-HM by 61.71% and 71.83% on average, respectively. The results of scanning electron microscope-energy dispersive spectrometry (SEM-EDS) and pore analysis showed that the HM porosity decreased after formation of Ca2+ and Fe3+ precipitation. According to the value of Freundlich parameter n, it may be because the precipitation or colloid of Ca2+ and Fe3+ filled micropores and covers high-energy adsorption sites of the HM. This research provides theoretical support for studying the PAHs migration and bioavailability of Calcium-rich in karst soil.