(Na, Pb)-Jarosite nucleation and growth on anglesite: Implications for inhibition of Pb releasing.

The mobility and bioavailability of Pb can be significantly reduced by Pb-bearing minerals encapsulation in jarosite-group minerals, especially in sulfate-rich environments. However, the kinetic pathways and mechanisms of jarosite-group minerals formations on Pb-bearing mineral surfaces are not well understood. Here, time-resolved heterogeneous (Na, Pb)-jarosite nucleation and growth on anglesite were explored to gain insights into the encapsulation mechanisms. The initial dissolution of anglesite were clearly distinguished, and for the first time, the facet-specific heterogeneous nucleation of (Na, Pb)-jarosite on anglesite was demonstrated. Density functional theory calculations revealed higher adsorption energies and electronic interactions of FeSO4+ complex on anglesite (020), (140), (110) facets, attributed to the preferential nucleation of (Na, Pb)-jarosite on these facets, which resulted in effective passivation of the facets resistant to dissolution. An interpretation was proposed where (Na, Pb)-jarosite grew via a particle-attachment pathway involving the formation of amorphous intermediate, and subsequently, it transformed to the crystalline phase by solid-state conversion. These observations might improve the mechanistic understanding of interface interactions between slightly soluble Pb-bearing minerals and iron minerals, with implications for Pb immobilization in sulfate-rich environments.