Strong binding of heavy metals in fayalite of copper smelting slags: Lattice site substitution

A deep understanding of the binding relationship between Fe2SiO4 and heavy metals from the perspective of lattice site substitution is essential to improve the theoretical knowledge regarding heavy metals binding in copper smelting slags (CSS). Here, we proposed the lattice site substitution behavior of heavy metals in Fe2SiO4 by preparing MFe2SiO4 (M = Cu, Pb, and As). X-ray diffraction refinement, scanning electron microscopy, and Fourier transforminfrared spectroscopy analysis showed that heavy metals were involved in the formation of Fe2SiO4 during the smelting process. Compared with pure Fe2SiO4, the fine structure of M-Fe2SiO4 was significantly changed by the lattice substitution of heavy metals. X-ray photoelectron spectroscopy and Raman and Mossbauer spectra combined with Density Functional Theory calculation confirmed that the divalent metal elements including Cu and Pb were bound to the Fe2SiO4 lattice by replacing M2 site. However, the trivalent As element could substitute both the positions of M2 site and part of the central Si atom through a charge compensation mechanism. Overall, the proposed lattice site substitution behavior of heavy metals in Fe2SiO4 could enrich the theory of the lattice substitution of heavy metals in CSS, also further provide guidance for the comprehensive disposal of CSS.