Sulfide Immobilization: Investigating the Impact of a Protective Sulfide-Bearing Layer Formed by Siderite (FeCO₃)

Sulfate-rich wastewater poses ecological hazards to freshwaterecosystems, and sulfate is highly regulated in many Minnesota lakes.Biological sulfate reduction results in the reduction of sulfate tosulfide, and this process is used to remediate acid mine drainage.Theoretically, the aqueous sulfide can be immobilized into a solid-phasematerial and removed from the aqueous system. This study focuses onsulfide immobilization using iron-bearing waste minerals. Specifically,the extent of reaction of siderite (FeCO3), an abundantferrous mineral in some mining wastes, with sulfide was studied. Mildlyacidic batch reactors containing powdered siderite were consecutivelyinjected with a sodium sulfide solution. Solid reaction products wereidentified and characterized using powder X-ray diffraction, scanningand transmission electron microscopy, and energy-dispersive X-rayspectroscopy. Mackinawite (FeS) appeared to be the most abundant product,with greigite (Fe3S4) also detected. Resultsreveal that the immobilization capacity of sulfide by siderite islimited by the concentration of the Fe2+(aq) presentedin the system immediately before the initial sulfide exposure as theFe(2+)(aq) levels are not replenished after sulfidation.These results improve our understanding of the sulfidation of sideriteand provide insight to improve the viability of using siderite-containingmining waste rock in a sulfate remediation technology.