Study on the removal of iron (II) and manganese (II) in acidic mine drainage by red mud: Performance and mechanism.

Red mud is an environmental burden during the alumina production process. To mitigate the hazards associated with red mud storage, this study investigated the utilization of alkaline red mud as a treatment agent for acidic mine drainage (AMD) with high concentrations of Fe(II) and Mn(II). This study explored the influence of reaction times, addition amounts of red mud, and pH values on the removal efficiency of Fe (II) and Mn(II) from high-concentration AMD. Various parameters such as suspended solids levels, effluent pH, and zeta potentials were measured to meet discharge standards. The adsorption mechanism of red mud was examined using SEM, XRD, EDX, XPS, and 3D-EEM analysis. Optimal conditions were determined as a reaction time of 2 h, pH value of 5.01 and the addition of 100 g/L red mud, achieving effective removal of Fe(II) (reduced from 1000 to 0.224 mg/L) and Mn (II) (reduced from 20 to 1.03 mg/L). The treated AMD meets discharge standards with reduced suspended matter content of 37.4 mg/L. These findings provided valuable insights for the utilization of red mud waste in engineering applications.

Hierarchical porous structured polysulfide supported nZVI/biochar and efficient immobilization of selenium in the soil.

Soil pollution with selenium is a significant environmental problem in several areas of the world, which extremely affects the growth of plants and human health. Thus, it is necessary to find an effective method to immobilize selenium in the soil to make it less bioavailable and less accessible. In this study, the low-cost biochar-supported nanoscale zero-valent iron and polysulfide (PS-nZVI@BC) are produced and used for the immobilization of selenium (Se) in soil. The FTIR, UV-Vis, XRD, VSM, SEM and XPS techniques validate surface properties and morphology of PS-nZVI@BC. Introduction of S2- led to the in-situ formation of FeS on the surface of the biochar supported zero valent iron. Two intense Bragg peaks (2θ) of 40.5°, 44.5° were corresponded to Fe0 basal plane, indicating the presence of nZVI in nZVI@BC and PS-nZVI@BC. The modified biochar presents a magnetic saturation value of 0.008 emu/mg, reasonably less than the reported values of bare nZVI. The soil immobilization showed that the PS-nZVI@BC is more effective for the control of selenium than the biochar and nZVI@BC. The available selenium content decreased by 77.29% in PS-nZVI@BC amended soil after 30 days. From sequential extraction procedure (SEP) results, it was observed that PS-nZVI@BC promoted the conversion of more accessible Se (water-soluble and exchangeable fractions) into the less accessible forms (acid-soluble, organic, and residual fractions) to reduce the toxicity of Se. Surface sorption, reduction and complexation were dominant mechanisms for Se immobilization. Hence, PS-nZVI@BC is promising and effective for immobilizing Se in contaminated soils and improving the soil properties.

Three decades of changes in water environment of a large freshwater Lake and its relationship with socio-economic indicators.

Tai Lake (Ch: Taihu) has attracted international attention forcyanobacteria blooms. However, the drivers of cultural eutrophication, especially long-term socio-economic indicators have been little researched. The results of research demonstrate how socio-economic development affected quality of water and how it has been improved by anthropogenic activities. This study described variability in indicators of water quality in Tai Lakeand investigated thedrivers. Significant relationships existed between concentrations of annual mean total nitrogen (TN), total phosphorous (TP), chemical oxygen demand (COD) and biological oxygen demand (BOD), and population, per capital gross domestic production (GDP) and sewage discharge (p < 0.05). However, mechanisms causing change varied among TN, TP, COD and BOD. Before 2000, the main contributors to increases in concentrations of TN were human population, GDP and volumes of domestic sewage discharges. After 2000, discharges of industrial sewage become the primary contributor. After 1998, the regressions of annual mean TN, TP and COD on per capital GDP, population and domestic sewage discharge were reversed compared to the former period. Since 1999, an apparent inverted U-shaped relationship between environmental pollution and economic development has developed, which indicated that actions taken by governments have markedly improved quality of water in Tai Lake. The statistical relationship between BOD and per capital GDP didn't conform to the Kuznet curve. The U-shaped Kuznet curve may offer hope for the future that with significant environmental investments a high GDP can be reached and maintained without degradation of the environment, especially through appropriate management of industrial sewage discharge.