Exploring the Sorption Mechanism of Ni(II) on Illite: Batch Sorption, Modelling, EXAFS and Extraction Investigations

The sorption mechanism of nickel (Ni) at the illite/water interface was investigated using batch, sorption modelling, extended X-ray absorption fine structure (EXAFS), and extraction approaches. The results showed that Ni(II) sorption on illite was strongly dependent on pH, contact time, temperature, and initial Ni(II) concentration. At a low initial Ni(II) concentration, the ion exchange species of equivalent to X2Ni degrees and the inner-sphere complexes including equivalent to (SONi+)-O-s, equivalent to (SONi+)-O-w and equivalent to (SONiOH)-O-w degrees species are observed on the sorption edges of Ni(II) on illite. As the initial Ni(II) concentration increased to 1.7 x 10(-3) mol/L, precipitates including surface-induced precipitation of s-Ni(OH)(2) and amorphous Ni(OH)(2) became more significant, especially under neutral to alkaline conditions. EXAFS analysis confirmed that Ni-Al layered double hydroxide (LDH) can gradually form with an increase in the contact time. At pH 7.0, alpha-Ni(OH)(2) was produced in the initial stage and then transformed to the more stable form of Ni-Al LDH with increasing contact time because of the increased Al3+ dissolution. With an increase in temperatures, alpha-Ni(OH)(2) phase on illite transformed to Ni-Al LDH phase, indicating a lower thermodynamic stability compared to Ni-Al LDH phase. These results are important to understand the geochemical behaviors to effectively remediate soil contaminated with Ni(II).