Toward sulfur retention and H 2 S mitigation in composting: elucidating and validating the molecular pathway of Fe( ii )/Fe( iii )-driven sulfur incorporation into humic acid

Fe( iii ) drives sulfur oxidation and stable fixation in humic acid, boosting sulfur–HA by 58.04% and slashing H 2 S emissions by 94.68%, while Fe( ii ) leads to unstable intermediates. This work aids sulfur pollution control and waste resource recovery.