Critical Metal Adsorption by Biotic and Abiotic Hydrous Manganese Oxides: Implications for Acid Mine Drainage Resource Recovery

Acid mine drainage (AMD) remediation facilities can produce treatment byproducts with near ore grade concentrations of rare-earth elements (REEs), cobalt, and manganese. High concentrations of these critical metals in treatment solids are often associated with hydrous manganese oxides (HMOs) through adsorption and/or coprecipitation. Chemical and microbial oxidation processes can influence HMO formation, mineralogy, and sorption efficiency. Here, we investigate the adsorption of rare-earth elements and yttrium (REY), cobalt, and nickel over 31 days by (1) abiotic HMO (δ-MnO2 and c-disordered H+ birnessite) produced by chemical oxidation and (2) bitotic HMO produced by Mn-oxidizing fungi, Paraphaeosphaeria sporulosa and Stagonospora sp. After 31 days, ∼70% of REY was adsorbed by abiotic HMO, whereas >99% of REY was adsorbed by biotic HMO and/or fungal biomass within 7 days. Biotic HMO also adsorbed ∼30% Ni and ∼75% Co; however, Co and Ni adsorption by abiotic HMO was negligible. Both biotic and abiotic HMOs were initially poorly crystalline. However, over the course of the experiment, abiotic HMO was transformed to more crystalline phases, resulting in a reduced adsorption capacity and significant desorption of Co and Ni. In contrast, the biotic HMO remained stable and resistant to structural changes over time. This study demonstrates that biotic HMOs are highly efficient at adsorbing Co and REY and that fungal biomass can also play a significant role in this process, particularly for REY.

酸性矿山排水（Acid mine drainage, AMD）修复设施可产生含有接近矿石品位浓度的稀土元素（rare-earth elements, REEs）、钴与锰的处理副产物。这些关键金属在处理固体中的高浓度通常通过吸附和/或共沉淀作用与水合氧化锰（hydrous manganese oxides, HMOs）相结合。化学与微生物氧化过程会影响水合氧化锰的形成、矿物学特征以及吸附效能。本研究针对为期31天的吸附实验展开探究，分别考察两类水合氧化锰对稀土元素与钇（rare-earth elements and yttrium, REY）、钴及镍的吸附行为：其一为通过化学氧化制备的非生物水合氧化锰（abiotic HMO，包含δ-MnO₂与c无序H+水钠锰矿）；其二为产锰氧化真菌——多孢副菲氏霉（Paraphaeosphaeria sporulosa）与Stagonospora属（Stagonospora sp.）所生成的生物水合氧化锰。实验进行31天后，非生物水合氧化锰仅吸附了约70%的REY，而生物水合氧化锰和/或真菌生物质在7天内即可吸附超过99%的REY。生物水合氧化锰同时还吸附了约30%的镍与约75%的钴，而非生物水合氧化锰对钴与镍的吸附量则可忽略不计。两类水合氧化锰初始均为低结晶度状态，但在实验过程中，非生物水合氧化锰会转变为结晶度更高的物相，导致其吸附能力下降，并引发钴与镍的显著解吸。与之相反，生物水合氧化锰则始终保持稳定，且随时间推移不易发生结构变化。本研究表明，生物水合氧化锰对钴与REY具备极高的吸附效率，且真菌生物质也可在该吸附过程中发挥重要作用，对于REY而言尤为如此。