MXene has drawn widespread attention as a potential material for electrode use in capacitive deionization (CDI). However, the applications of MXene are limited by its property of low electrical capacity. Herein, a MnO₂/MXene composite was firstly evaluated in a capacitive deionization system, in which the MnO₂ acts as intercalation-type pseudocapacitive electrodes to enhance the electrical capacity, and MXene provides an electron conduction highway network that improves the charge transfer of the MnO₂. The result showed that the low-crystallinity MnO₂ with irregular particles was well-distributed on the surface of the MXene. The desalination capacity of 30.5 mg·g⁻¹ is achieved at a voltage window of 1.2 V, which was higher than that of the reported pure MXene and MnO₂. The electrical double-layer (EDL) capacitive and the diffusion-controlled processes are the main charge storage mechanisms, and the EDL contribution provides 50.3% to the total capacitance. This result suggests a promising direction for further applying a MnO₂/MXene composite in CDI.

The safe disposal of hazardous waste from zinc hydrometallurgy, such as jarosite residue, is crucial for the sustainable development of the industry. The chemical, structural and morphological properties of jarosite residue from zinc smelting were studied by a combination of various characterizations, and environmental stability was evaluated using the toxicity characteristic leaching procedure (TCLP), Chinese standard leaching tests (CSLT) and long-term leaching experiments (LTLE). Phase composition analysis revealed that zinc ferrite and sodium jarosite were the main phases present in the jarosite residue. TCLP and CSLT analyses indicated that the Zn and Pb contents exceeded their respective toxicity identification standards by more than 30 times and 8 times, respectively, exceeding the threshold values of the standard. The LTLE results demonstrated that Pb concentrations continued to exceed the standard limits, even after long contact times. This study has paramount significance in the prediction of jarosite residue stability and the evaluation of its potential for secondary environmental pollution.

Lead is the main toxic factor in jarosite residue. It is important to study the release behavior of lead from simulated lead-bearing jarosite (SLBJ) for predicting the stability of jarosite residue and its secondary pollution to the environment. To identify the technical issues and limitations associated with its safe disposal, a comprehensive analysis of the chemical, structural, and morphological characteristics of SLBJ was conducted using various detection techniques including XRF, XRD, SEM-EDS, FTIR, XPS, etc. The environmental stability of SLBJ was assessed through the toxicity characteristic leaching procedure (TCLP), Chinese standard leaching tests (CSLT), and a long-term leaching experiment (LTLE). Phase composition analysis revealed that the primary components of SLBJ are sodium jarosite and lead sulfate. TCLP and CSLT results indicated that lead content surpassed the toxicity identification standard limit by more than 47 times. Furthermore, LTLE indicated that the lead concentration surpassed the standard limit about 15 times after prolonged contact time. This study is of great significance for predicting the stability of jarosite residue and its secondary pollution to the environment.

The release of heavy metals during coal combustion may pose potential hazards to the surrounding environment and human health. In this study, we investigated the migration characteristics and ecological risks of heavy metals during the combustion of two distinct raw coal samples (C1 and C2) sourced from Shanxi Province. The analytical results demonstrate significant differences in volatilization behavior between the samples, with total heavy metal release rate ranging from 30.25% to 98.92% for C1 and from 17.77 to 98.16% for C2. Four elements—Cd, As, Pb, and Hg—exhibited preferential migration to fly ash fractions A1 and A2, displaying higher transfer coefficients compared to other monitored heavy metals. Chemical speciation analysis revealed that elemental release behavior was predominantly governed by residual phases (2.2–81.4%), Fe-Mn oxide-bound forms (3.7–45.6%), and sulfate-associated fractions (1.3–56.8%). Combustion temperature showed nonlinear positive correlations with the volatilization rates of Cd, As, Pb, and Hg. Hg volatilization decreases at a combustion temperature below 600 °C, whereas for Cd, As, and Pb, this temperature is below 800 °C. Ecological risk indices (RI) indicate substantial contamination potential in fly ash matrices: A1 (RI = 285.32) is dominated by Hg (I_geo = 1.9, $E_r^i$ = 224) with a notable contribution from Cd ($E_r^i$ = 51), whereas A2 (RI = 246.67) showed a predominance of Cd (I_geo = 1.6, $E_r^i$ = 138) over Hg ($E_r^i$ = 94.4). These findings underscore the need for optimized combustion parameters and enhanced particulate filtration systems to mitigate environmental impacts associated with coal-fired power generation.