Tungsten-induced alteration of schwertmannite transformation and its implications for tungsten mobility in acid mine drainage.

Tungsten (W) mobility in acid mine drainage (AMD) may be strongly influenced by its interactions with schwertmannite (Sch), a metastable sulfate-bearing Fe(III) oxyhydroxide that can effectively scavenge oxyanion-forming contaminants. During aging, Sch gradually transforms into more stable Fe(III) phases, such as goethite, which may substantially alter the mobility and retention of associated contaminants. However, the fate of W during Sch transformation remains unclear. This study investigated W redistribution during Sch aging and examined whether W loading altered the temporal development of Fe mineral phases. Batch aging experiments were conducted at pH 3.5 and 60 ℃ using W-free and W-loaded Sch suspensions. Sch gradually transformed into goethite in both systems. However, W loading altered the transformation in a stage-dependent manner. During the early stage, the W-loaded system exhibited approximately 15% higher sulfate release and earlier development of goethite-related features than the W-free system. During the later stage, the development of crystalline goethite was attenuated. W was initially released into solution and subsequently reassociated with the solid phase. The residual W fraction increased to approximately 38% by day 30. The later redistribution of W coincided with attenuated development of crystalline goethite. Overall, the results reveal a stage-dependent relationship between Sch transformation and W partitioning under accelerated aging conditions and provide a geochemical basis for assessing W retention and mobility in AMD-related systems.