Following ion-adsorption rare earth mining, the residual tailings experience considerable heavy metal contamination and gradually evolve into a pollution source. Therefore, the leaching characteristics and environmental impact of heavy metals in ion-adsorption rare earth tailings require immediate and thorough investigation. This study adopted batch and column experiments to investigate the leaching behaviour of heavy metals in tailings and assess the impact of tailings on paddy soil, thereby providing a scientific basis for environmental protection in mining areas. The results showed that Mn, Zn, and Pb contents were 431.67, 155.05, and 264.33 mg·kg^-1, respectively, which were several times higher than their respective background values, thereby indicating significant heavy metal contamination in the tailings. The batch leaching experiment indicated that Mn and Pb were priority control heavy metals. Heavy metals were divided into fast and slow leaching stages. The Mn and Pb leaching concentrations far exceeded environmental limits. The DoseResp model perfectly fitted the leaching of all heavy metals from the tailings (R² > 0.99). In conjunction with the findings of the column experiment and correlation analysis, the chemical form, rainfall pH, ammonia nitrogen, and mineral properties were identified as the primary factors controlling heavy metal release from tailings. Rainfall primarily caused heavy metal migration in the acid-extraction form from the tailings. The tailing leachate not only introduced heavy metals into the paddy soil but also caused the transformation of the chemical form of heavy metals in the paddy soil, further exacerbating the environmental risk posed by heavy metals. The study findings are significant for environmental conservation in mining areas and implementing environmentally friendly practices in rare earth mining.

The use of high-concentration ammonium sulfate leaching agent for the mining of ion-absorbed rare earth ore will change the soil environment properties, thereby inducing the release of associated heavy metals. Serious manganese pollution has been observed in the environment of rare earth mining areas, but the environmental chemical process of manganese in the raw ore soil has not been fully recognized. In this study, a sequential extraction experiment showed that the manganese in the soil included acid extractable form, reducible form, oxidizable form, and residual form, among which residual form and reducible form were the main forms. According to the release kinetics experiment, the release process of manganese included the fast release and slow release, which was controlled by multiple diffusion mechanisms and could be optimally fitted with the Elovich equation. The treatment of ammonium sulfate leaching agent could reduce the proportion of reducible form and increase the proportion of residual form, but there was no significant change in other forms. In addition, batch release experiments indicated that leaching factors (the initial concentration and initial pH of leaching agent, and temperature) could affect the release of manganese. Lower pH and higher temperature were not conducive to the stability of manganese and significantly aggravated the release amount. Excessive initial concentration had a certain inhibitory effect on the release amount, but the effect was weak. Considering the significant effect of initial pH and temperature on the release of manganese, during the mining process of ion-absorbed rare earth, controlling the initial pH of leaching agent and reducing the mining scale in the hot summer are the key measures to manage the release risk of manganese.

The value-added utilization of waste resources to synthesize functional materials is important to achieve the environmentally sustainable development. In this paper, the biochar supported graphene oxide (BGO) materials were prepared by using navel orange peel and natural graphite. The optimal adsorption parameters were analyzed by response surface methodology under the conditions of solution pH, adsorbent dosage, and rotating speed. The adsorption isotherm and kinetic model fitting experiments were carried out according to the optimal adsorption parameters, and the mechanism of BGO adsorption of Pb²⁺ was explained using Scanning Electron Microscope (SEM-EDS), X-ray Photoelectron Spectroscopy (XPS), X-ray Diffraction (XRD), and Fourier Transform Infrared Spectroscopy (FTIR). Compared with virgin biochar, the adsorption capacity of Pb²⁺ on biochar supported graphene oxide was significantly increased. The results of response surface methodology optimization design showed that the order of influence on adsorption of Pb²⁺ was solution pH > adsorbent dosage > rotating speed. The optimal conditions were as follows: solution pH was 4.97, rotating speed was 172.97 rpm, and adsorbent dosage was 0.086 g. In the adsorption–desorption experiment, the desorption efficiency ranged from 54.3 to 63.3%. The process of Pb²⁺ adsorption by BGO is spontaneous and endothermic, mainly through electrostatic interaction and surface complexation. It is a heterogeneous adsorption process with heterogeneous surface, including surface adsorption, external liquid film diffusion, and intra-particle diffusion.

Due to the steep slope and short concentration time of flow in mountainous areas, the water environment of headwaters is easily disturbed by human activities. The spatial-temporal variation of the water environment is a key issue for the implementation of river restoration. This study aims to explore the spatial-temporal characteristics of water quality and its pollution sources of the headwaters of the Dongjiang River. Water quality monitoring data over the past 6 years were collected and analyzed using principal component analysis, equal standard pollution load, and multivariate statistical analysis. The results show that the water quality presents significant spatial heterogeneity, where the water quality in the middle and lower reaches is poor. The concentrations of ammonia nitrogen and total phosphorus in the middle and lower reaches were 18.3 and 9.5 times higher than those in the upper reaches, respectively. The water quality has tended to improve recently because of ecological compensation and environmental management. Correlation analysis shows that there were significant positive relationships among major pollutants. Critical source areas were identified, which implies that the most polluted area is located in the middle reaches. Studies have also shown that the water pollution mainly comes from livestock and poultry breeding, industrial sewage discharge, and cultivated land. Controlling the scale of construction land and adjusting the industrial structure is one of the main measures for eradicating water environment problems in headwaters in mountainous areas.