Sustainable Minerals Institute, Environment Centres (CMLR), University of Queensland, Brisbane, QLD 4072, Australia.
Sustainable Minerals Institute, Environment Centres (CMLR), University of Queensland, Brisbane, QLD 4072, Australia; College of Resources and Environmental Sciences, China Agricultural University, Beijing 100193, China.
Sci Total Environ. 2019 May 1;663:216-226. doi: 10.1016/j.scitotenv.2019.01.317. Epub 2019 Jan 25.
Effective neutralization of strongly alkaline conditions in bauxite residues (BR) is the fundamental step to initiate the process of eco-engineering BR into growth substrate (or soil-like medium) for direct phytostabilization with pioneer plant species. The present study aimed to evaluate the effectiveness of microbial decomposition of organic matter (OM) (i.e., biomass residues) in neutralizing the strong alkalinity of residues under saturated conditions, together with the regulatory role of calcium sulfate (CaSO) addition. Admixing OM (i.e., sugarcane mulch, Lucerne hay) alone in the BR significantly lowered the porewater pH from 11.4 to around 9.0 by Day 7, which persisted until the end of incubation (Day 28). The pH reduction in the porewater of OM-amended BR coincided with the production of acidic organic compounds (mainly acetic acid). Diverse species of organotrophic bacteria (e.g., Enterobacteriales, Pasteurellales, Lactobacillales, and Streptophyta) were found to have colonized in the OM-amended BR, but which were dominated by haloalkaliphilic bacteria (e.g., Halomonas and Bacillaceae). The CaSO addition in the OM-amended BR further lowered pH to 8.3 in the porewater. Besides, the bioneutralization effects resulted in dramatic reduction (>90%) of soluble Al in the porewater, which is a prerequisite to lowering Al toxicity in plants. At the same time, the levels of major cations (i.e., K, Ca, Mg) in the porewater were elevated by the OM + CaSO amendment, which would facilitate subsequent leaching of these soluble salts to lower the salinity in the BR, and improve the diversity of organotrophic bacterial communities in the amended BR.
有效中和铝土矿残渣（BR）中的强碱性条件是启动生态工程将 BR 转化为先锋植物物种直接稳定化的生长基质（或类似土壤的介质）的基本步骤。本研究旨在评估微生物分解有机物（OM）（即生物质残渣）在饱和条件下中和残渣强碱性的有效性，以及硫酸钙（CaSO）添加的调节作用。单独在 BR 中添加 OM（即甘蔗覆盖物、紫花苜蓿干草）可将孔水 pH 值从 11.4 显著降低至约 9.0，直至培养结束（第 28 天）。OM 改良 BR 中孔水的 pH 值降低与酸性有机化合物（主要是乙酸）的产生相吻合。在 OM 改良 BR 中发现了多种有机营养细菌（例如肠杆菌目、巴氏杆菌目、乳杆菌目和木霉菌目）定殖，但以耐盐碱性细菌（例如盐单胞菌和芽孢杆菌科）为主。在 OM 改良 BR 中添加 CaSO 可进一步将孔水的 pH 值降低至 8.3。此外，生物中和作用导致孔水中可溶性 Al 的大幅减少（>90%），这是降低植物中 Al 毒性的前提。同时，OM+CaSO 改良剂提高了孔水中主要阳离子（即 K、Ca、Mg）的水平，这有利于随后这些可溶性盐的淋溶，降低 BR 中的盐分，并改善改良 BR 中有机营养细菌群落的多样性。
