Graphene oxide and chitosan microspheres modified with α–FeO(OH) (α–FeO(OH)/GOCS) are prepared and utilized to investigate the performance and mechanism for Cr(VI) removal from aqueous solutions and the possibility of Fe secondary pollution. Batch experiments were carried out to identify the effects of pH, mass, and volume ratio (m/v), coexisting ions, time (t), temperature (T), and Cr(VI) initial concentration (C₀) on Cr(VI) removal, and to evaluate adsorption kinetics, equilibrium isotherm, and thermodynamics, as well as the possibility of Fe secondary pollution. The results showed that Cr(VI) adsorption increased with C₀, t, and T but decreased with increasing pH and m/v. Coexisting ions inhibited Cr(VI) adsorption, and this inhibition increased with increasing concentration. The influence degrees of anions and cations on the Cr(VI) adsorption in descending order were SO₄²⁻ > PO₄²⁻ > NO₃⁻ > Cl⁻ and Ca²⁺ > Mg²⁺ > Mn²⁺, respectively. The equilibrium adsorption capacity of Cr(VI) was the highest at 24.16 mg/g, and the removal rate was 97.69% under pH = 3, m/v = 1.0 g/L, T = 298.15 K, and C₀ = 25 mg/L. Cr(VI) adsorption was well fitted to a pseudo-second-order kinetic model and was spontaneous and endothermic. The best fit of Cr(VI) adsorption with the Langmuir and Sips models indicated that it was a monolayer and heterogeneous adsorption. The fitted maximum adsorption capacity was 63.19 mg/g using the Sips model under 308.15 K. Cr(VI) removal mainly included electrostatic attraction between Cr(VI) oxyanions with surface Fe–OH₂⁺, and the adsorbed Cr(VI) was partially reduced to Cr(III) and then precipitated on the surface. In addition, there was no Fe secondary pollution during Cr(VI) adsorption.

A magnetite graphene oxide chitosan (MGOCS) composite microsphere was specifically prepared to efficiently adsorb As(III) from aqueous solutions. The characterization analysis of BET, XRD, VSM, TG, FTIR, XPS, and SEM-EDS was used to identify the characteristics and adsorption mechanism. Batch experiments were carried out to determine the effects of the operational parameters and to evaluate the adsorption kinetic and equilibrium isotherm. The results show that the MGOCS composite microsphere with a particle size of about 1.5 mm can be prepared by a straightforward method of dropping FeCl₂, graphene oxide (GO), and chitosan (CS) mixtures into NaOH solutions and then drying the mixed solutions at 45 °C. The produced MGOCS had a strong thermal stability with a mass loss of 60%) and other metals, showing a great advantage in the treatment of heavy metal-contaminated water.

Mineral extraction can significantly affect the groundwater flow and hydrochemical environment. However, for hilly areas, significant ground elevation changes and complex geological conditions make it difficult to accurately analyze and predict the impact of mineral mining. This study takes the Nuodong rare earth mining area as an example. Based on field investigations and experiments, GOCAD software (version 2022) was used to establish a geological model in combination with GMS numerical simulation software, which was used to build a groundwater flow model and a solute transport model. The flow model in the hilly area indicated that the absolute error between the simulated and measured water levels of each observation well is 0.554 m. The solute-transport model showed that the maximum pollutant concentration of ammonia-nitrogen (NH₃-N) in the liquid injection area, stream area, and village area monitoring wells reaches 139.15, 27.9, and <0.5 mg/L, respectively. During the mining period, streams in the area are affected by NH₃-N, which threatens the safety of the water for mine area residents. To control pollutant transport, two stages of pumping were adopted to reduce NH₃-N concentrations in groundwater. After adopting the first stage, the peak concentration of the stream area monitoring wells decreased significantly, with the maximum peak concentration decreasing from 27.9 mg/L to 5.51 mg/L. Based on the results of the first stage of the pump-out treatment, a second stage was adopted. The model results showed that the peak concentration of NH₃-N pollutants discharged into the stream is less than 0.5 mg/L. The results provide a theoretical basis and reference for groundwater monitoring and pollution control after mining in this area.

Antimony (Sb), as a toxic heavy metal, has drawn worldwide attention, and its efficient removal from water has become increasingly urgent. In this study, an iron-modified alkaline lignin chitosan (Fe-ALCS) gel bead is prepared by the freeze-drying method to remove Sb(III) from the aqueous solution. The static adsorption experiment discusses the various environmental influences on the adsorption performance of Fe-ALCS for Sb(III) removal. The adsorption mechanism is explored by combining adsorption kinetics, isothermal adsorption, and characterization methods (such as FTIR, XRD, XPS, etc). The results show that the equilibrium adsorption capacity of Sb(III) decreases with the increase in pH and mass–volume ratio. With the increase in the initial Sb(III) concentration, Q_e showed a rapid increasing trend in the range of 50–100 mg/L and continued to rise with the extension of contact time (t), reaching the maximum value at 3540 min. Under the optimal conditions of pH = 3, m/v = 1.0 g/L, and C₀ = 20 mg/L, the removal efficiency (R_e) value is 95.07%, which is still approximately 86.8% after five adsorption–desorption cycles. The maximum adsorption capacity is 266.58 mg/g fitted by the Langmuir model. The adsorption mechanism is mainly related to the iron-based active site of Fe–O(OH), where the O–H on its surface undergoes ligand exchange with Sb(OH)₃ to form a stable Fe–O–Sb coordination structure. Additionally, C–OH, C–O, and other functional groups in ALCS also contribute to Sb adsorption. Fe-ALCS is an environmentally friendly, renewable, and convenient biomass adsorbent with good potential for wastewater treatment.

The problem of chromium contamination, especially Cr(VI), in acidic wastewater has drawn significant attention, requiring effective and sustainable remediation measures. In this study, tannic-acid/Fe₃O₄-modified corn straw biochar (Fe-TA-CSB) is prepared by a grinding-calcination method to remove Cr(VI). The factors influencing the removal effect of Fe-TA-CSB are investigated through static adsorption experiments. The removal mechanism is explored by combining adsorption kinetics, isothermal adsorption, and thermodynamics, as well as characterization methods. The results show that the removal efficiency of Cr(VI) increases with the increase in pH, contact time (t), and solid–liquid ratio (m/v), but decreases with the increase in initial concentration (C₀). Under optimal conditions of TA/Fe₃O₄ mass ratio = 12.5%, pH = 3.0, m/v = 1.0 g/L, and C₀ = 10 mg/L, the removal efficiency value is 94.02%, which is approximately 81.44% after four adsorption–desorption cycles. The adsorption behavior is fitted well by the Sips isotherm model and Elovich kinetics model, suggesting the adsorption process of heterogeneous monolayer chemisorption. The removal mechanism of Cr(VI) by Fe-TA-CSB involves electrostatic interaction with Cr(VI), reduction in Cr(VI) to Cr(III) through C–O and Fe(II), and complexation of reduced Cr(III) with the introduced Fe–O and phenolic hydroxyl groups. Fe-TA-CSB is an environmentally friendly and renewable adsorbent with good potential for the treatment of acidic wastewater.

Microplastics (MPs) resulting from plastic fragmentation with a size less than 5 mm have become one of the main pollutants endangering the water environment. Therefore, it is necessary to know about the abundance and size distribution of MPs in sewage waters and their relationship with water quality. In this study, water samples are collected from 20 sewage outlets in Guilin, China to analyze the abundance and morphology of the MPs and their hydrochemical characteristics. Multivariate statistical analyses are conducted to identify the major factors related to the MP distribution in sewage water samples. Results showed that MPs in sewage water samples are mainly composed of fiber and film, and about 67.8% are sized <0.3 mm. The abundance is in the range of 6 (±1)–47 (±3) items/L. The correlation analysis presents that the abundance of MPs is weakly correlated with hydrochemical parameters and metal ions due to the complexity of the abundance data. The redundancy analysis indicates that the MP morphology distribution is significantly affected by NO₃–N, Zn, Ca, and Cu contents, and the MP size distribution is mainly related to Zn, Ca, and Cu contents. Adsorption kinetics are analyzed using pseudo-first-order, pseudo-second-order, and intraparticle diffusion models, revealing that the adsorption process is predominantly governed by chemisorption for smaller MPs (0.3–0.5 mm), while larger MPs (1.0–5.0 mm) are constrained by internal diffusion. Isothermal adsorption experiments are fitted using Langmuir and Freundlich models, indicating that the adsorption of nutrients (NH₃–N, TN, TP) and metal ions (Ca, Mg, Cu, Pb, Zn) on MPs follows a monolayer adsorption mechanism, with smaller MPs showing higher adsorption capacities due to their larger specific surface areas. This study highlights the occurrence characteristics and environmental influencing factors of MPs in sewage water, which may be significant for future studies on the pollution control of MPs.