In situ recombination and recovery of photovoltaic waste Si through a mechanochemical strategy for application in Hg<sup>0</sup> removal: Effect and mechanism.

Abstract

The discharge of untreated photovoltaic waste silicon powders (PWSP) causes significant environmental challenge and resource wastage. This work accomplished the recovery and sustainable application of PWSP for Hg⁰ removal through a one-step mechanochemical strategy. It also determined the mechanisms of mechanochemistry in PWSP recovery and Hg⁰ removal. We found all the examined silicon particles, those with a size of ≥140 mesh exhibited the greatest Ag enrichment and good Hg⁰ removal performance due to their sound surface structure and abundant active components. Interestingly, these silicon particles displayed excellent Hg⁰ removal efficiency (98.3 %) and good tolerance to simulated flue gas (SFG + HCl) after ball-milling. Here, we found that ball-milling induced the enhancement of (111) adsorption plane, the appearance of lattice distortion and defects, the improvement of physical-properties as well as the exposure of -OH, O∗ (Oα, Oβ, and Oγ) and Ag∗(Ag-OH and Ag⁺), contributing to the recombination of PWSP and efficient mercury removal. This work disclosed that the de-agglomeration of Ag cluster and an increase in oxygen density induced electron transfer (0.56e) from Ag to Si, triggering the recovery of PWSP. Moreover, iner-diffusion adsorption kinetic (R² = 0.997), high affinity reaction (Ag-Hg), low energy barrier (0.4eV) and electron exchange (0.33e) facilitated mercury immobilization (Hg⁰→HgO) and SFG + HCl tolerance. This work provides a facile, simple and sustainable way to recycling PWSP for Hg⁰ removal, which aligns the principles of sustainable energy development and environmental protection.