Iron-Bearing Natural Minerals Maifanite and Limonitum Drive Sulfur-based Autotrophic Denitrification Enhancement and Electron Recycling via Sulfide

Iron-bearing natural minerals (maifanite and limonitum) significantly enhanced sulfur-based autotrophic denitrification (SAD) performance. Denitrification efficiency was markedly improved, with nitrate removal efficiency increased by 1.3 to 1.6-fold and nitrite accumulation suppressed by 20.5%-29.0%, attributed to enhanced electron transfer and elevated nitrate reductase activity facilitated by mineral-derived trace elements and Fe(III)/Fe(II) redox shuttling. Critically, biogenic sulfide derived from sulfur disproportionation was effectively immobilized as FeS precipitates through microbially mediated biomineralization. Limonitum, with higher iron content, achieved superior electron recovery (83.7%) via FeS formation, reducing aqueous sulfide by 43.8% compared to control. Microbial community evolution was selectively driven by mineral amendments, enriching key functional genera (Sulfurimonas, Thiobacillus) and iron-cycling taxa (Simplicispira). These findings establish a dual-function mechanism: enzymatic activation for accelerated denitrification and in-situ electron recycling via sulfide fixation. Limonitum emerges as a sustainable amendment for groundwater remediation, concurrently resolving nitrate pollution and sulfide byproduct challenges in permeable reactive barriers.