CO₂ fluxes in the chemical weathering of carbonate-hosted tailings ponds, Panxi valley, Sichuan province, China

Growing and intensified mining activities in China have produced substantial quantities of carbonate-bearing tailings wastes. Rapid chemical weathering of these wastes, accompanied by active CO₂ fluxes (CO₂ absorption and degassing), have the potential to positively or negatively influence the emissions arising from the mining sector. However, few prior studies have examined these processes and effects. Herein, we present a systematic investigation of the chemical and mineral composition, hydro-geochemistry, and isotopes of four tailings ponds and filtrates in Panxi valley, Sichuan province, China. Our results reveal that significant rock–water interactions have occurred in carbonate-hosted tailings with active carbonate and silicate dissolution. The abundance of sulfuric acid in the dissolved load, derived from sulfide oxidation, provides a non-negligible portion of protons for chemical weathering. The influences on cationic weathering, therefore, were found to be carbonic–carbonate weathering > sulfide–carbonate weathering > sulfide–silicate weathering > mineral processing inputs > nature inputs > atmospheric inputs. Exoreic river basin tailings have the potential to fix atmospheric CO₂ and provide a valuable strategy toward China’s carbon neutrality goals. However, inland/arid area mining also has the potential to risk net CO₂ degassing and hence encumber the mining industry’s carbon performance.