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Heavy metal pollution such as cadmium and arsenic in water seriously threatens human health and safety, and the removal of Cd/As combined pollution is more difficult. In this work, the performance of mechanically activated calcite composite FeSO4 to remove Cd/As combined pollution was investigated by Cd/As combined pollution removal test in water. It was found that mechanically activated calcite can significantly improve the removal efficiency of Cd/As combined pollution in water. The results showed that the removal rate of Cd and As can reach 99% in 30 min by activated calcite composite FeSO4. The removal mechanism of Cd/As combined pollution in water by activated calcite and FeSO4 was studied by SEM-EDS, XPS, and XRD. The results showed that the crystallinity and dissolution activity of calcite were changed by mechanical activation, and the hydrolysis of calcite to produce CO32- and OH- was enhanced. OH- promoted the formation of a stable iron oxide bound precipitate of FeSO4 with arsenic, and CO32- binded with cadmium to form a stable precipitate of cadmium carbonate.

Exploring eco-environmental quality dynamics in the Daihai Lake Basin has significant implications for the conservation of ecological environments in the semi-arid and arid regions of northern China. Based on the Google Earth Engine (GEE) platform, the remote sensing ecological index (RSEI) was constructed by coupling Landsat SR remote sensing data from 1985 to 2022. The spatial significance of the RSEI was analyzed using linear regression equations and an F-test. The spatial correlation, distribution characteristics, and driving factors behind the RSEI were explored using Moran's index and a geodetector. The results indicated that (1) the RSEI was appropriate for evaluating eco-environmental quality in the Daihai Lake Basin. (2) From 1985 to 2022, the eco-environmental quality of the Daihai Lake Basin exhibited a positive trend but remained subpar. (3) A positive spatial autocorrelation was demonstrated for eco-environmental quality with increasing spatial aggregation. (4) Significant eco-environmental quality degradation (slope < 0) occurred primarily in Sanyiquan Town in the northeastern region of the basin and in Tiancheng Township in the southeastern region. Conversely, a notable improvement (slope > 0) was predominantly observed in Yongxing and Liusumu in southwestern Daihai. (5) The improvement in the ecological environment of the Daihai Lake Basin was primarily attributed to an increase in NDVI and WET and a decrease in NDBSI and LST. The interaction between NDVI and LST had the greatest explanatory power for the ecological environment. Among the external driving factors, DEM (elevation) was the dominant factor in the RSEI and had the strongest explanatory power. The interaction between DEM and LST was the most significant, and the driving factors were enhanced. This study provided a theoretical basis for the sustainable development of the Daihai Lake Basin, which is crucial for the local ecological environment and economic development. [ABSTRACT FROM AUTHOR]

Coagulation with aluminum salts is an important method for fluoride removal from groundwater. However, the hydration of aluminum salts generating a large number of H+ usually leads to limited defluorination performance due to the optimum pH of active aluminum phase for fluoride removal around 5.5–6.5. In this work, enhanced fluoride removal from groundwater through precise regulation of active aluminum phase by CaCO3 was investigated. Precipitation products were characterized by XPS, FTIR, XRD, and SEM, respectively, and the mechanism of the high fluoride removal efficiency was discussed and compared with the traditional coagulation of Al2(SO4)3. In the Al2(SO4)3 + CaCO3 (ASCC) system, CaCO3 can stably regulate the pH at the optimum range for active aluminum phase existence and has the best fluoride removal effect. CaCO3 accurately regulated the activity of the aluminum phase by slowly releasing OH− and fine tuning pH, thereby achieving effective fluoride removal. Undissolved CaCO3 particles exist as the carrier of defluorination flocs to accelerate precipitation and improve stability. The work here provides a new method for fluoride removal and may shed light on the application of CaCO3 coagulants for other pollutants. [ABSTRACT FROM AUTHOR]

Cd(II) pollution in water will cause serious threats to the environment and human health. The general remediation protocol for Cd(II) pollution by hydroxide (Ca(OH)2 or NaOH) is still faced with filtering difficulties and high effluent pH. To develop an applicable method for the Cd(II) removal in water, we prepared an activated calcium carbonate (CaCO3) material by changing the crystallinity, particle size, and surface activity of CaCO3, and investigated the corresponding Cd(II) removal capacity from aqueous solutions. The results showed that more than 99.9% of Cd(II) was removed within 10 min in an initial concentration of 50 mg L−1. Moreover, the effluent pH is close to neutral after removal of Cd(II), and the sediment is filtered well. Comparative experiments and characterizations have demonstrated that the excellent Cd(II) removal performance of activated CaCO3 is due to the mechanical activation changes the surface activity of the original stable CaCO3, promotes the slow-release dissolution equilibrium of the active carbonate groups, and thus the coprecipitation of cadmium hydroxide and cadmium carbonate on CaCO3 particles. This research demonstrates that mechanical activation of CaCO3 could be used as a repair material for efficient removal of heavy metal pollution in water, which can solve the problems of filtration and high effluent pH of alkaline precipitation. [ABSTRACT FROM AUTHOR]