Thallium(I) retention in porous media is restricted by elevated Mn(II) and Fe(III) loadings: Insights into suitability between media and microbial communities.

In tailings permeated by leachate containing thallium (Tl), manganese oxides (MnOx) are recognized as critical substances in immobilizing Tl and preventing its further migration into groundwater. However, dissolved Mn(II) and Fe(III) also exist in micro-oxic environments. The effects and mechanisms of the increased levels of these coexisting ions, driven by environmental processes such as rainfall leaching, on Tl(I) retention remain largely unclear. This study established two systems using natural manganese sand and limestone sand as porous media, demonstrating that the elevated Mn(II)/Fe(III) loadings weakened Tl(I) retention. Redundancy analysis identified media type and depth as primary factors shaping microbial communities, which subsequently influenced Tl(I) immobilization. Manganese sand exhibited superior recovery capacity compared to limestone sand under higher Mn(II) and Fe(III) loadings. Co-occurrence network analyses revealed that media-microorganism suitability governs microbial community structure and heavy metal retention efficiency. Hydraulic impact and dissolved organic/inorganic cations reduced MnOx content, while the higher retention capacity of manganese sand was attributed to the presence of microorganisms with higher activity and abundance, as well as an increased abundance of microbial-generated MnOx. This study offers novel insights into the mechanisms underlying Tl(I) retention in tailings, which is crucial for comprehending its environmental fate.