Effectiveness of conventional and emerging methods for the physicochemical reactivation of passivated mercury in artisanal and small-scale gold mining: a systematic review with a technical and environmental focus

Abstract

This study presents a systematic review of the technical effectiveness and environmental sustainability of conventional and emerging methods for the physicochemical reactivation of passivated mercury in artisanal and small-scale gold mining (ASGM). Following the PRISMA 2020 guidelines, 27 primary studies initially meeting the eligibility criteria were identified. Subsequently, through manual search and citation chasing, 23 additional relevant references were incorporated, resulting in a final corpus of 50 sources for evidence synthesis. The findings indicate that conventional mechanical methods present a technical recovery limit ranging from 30% to 50% due to the phenomenon of surface passivation. In contrast, emerging technologies, particularly selective electroreduction, achieve coalescence restoration rates exceeding 90%, while the overall set of emerging methods shows an average gold capture efficiency of 76.9% (p < 0.01). However, correlation analysis reveals a moderate inverse association between technical efficiency and operational portability (ρ = −0.50). The available evidence suggests that electroreduction offers one of the most balanced approaches for implementing circular economy models, although its large-scale field adoption depends on the implementation of modular systems at an operational scale.