Geochemical properties, heavy metals and soil microbial community during revegetation process in a production Pb-Zn tailings.

Lead-zinc (Pb-Zn) tailings pose a significant environmental threat from heavy metals (HMs) contamination. Revegetation is considered as a green path for HM remediation. However, the interplay between HM transport processes and soil microbial community in Pb-Zn tailings (especially those in production) remain unclear. This study investigated the spatial distribution of HMs as well as the crucial roles of the soil microbial community (i.e., structure, richness, and diversity) during a three-year revegetation of production Pb-Zn tailings in northern Guangdong province, China. Prolonged tailings stockpiling exacerbated Pb contamination, elevating concentrations (from 10.11 to 11.53 g/kg) in long-term weathering. However, revegetation effectively alleviated Pb, reducing its concentrations of 9.81 g/kg. Through 16 S rRNA gene amplicon sequencing, the dominant genera shifted from Weissella (44%) to Thiobacillus (17%) and then to Pseudomonas (comprising 44% of the sequences) during the revegetation process. The structural equation model suggested that Pseudomonas, with its potential to transform bioavailable Pb into a more stable form, emerged as a potential Pb remediator. This study provides essential evidence of HMs contamination and microbial community dynamics during Pb-Zn tailings revegetation, contributing to the development of sustainable microbial technologies for tailings management.

A critical review on the migration and transformation processes of heavy metal contamination in lead-zinc tailings of China.

The health risks of lead-zinc (Pb-Zn) tailings from heavy metal (HMs) contamination have been gaining increasing public concern. The dispersal of HMs from tailings poses a substantial threat to ecosystems. Therefore, studying the mechanisms of migration and transformation of HMs in Pb-Zn tailings has significant ecological and environmental significance. Initially, this study encapsulated the distribution and contamination status of Pb-Zn tailings in China. Subsequently, we comprehensively scrutinized the mechanisms governing the migration and transformation of HMs in the Pb-Zn tailings from a geochemical perspective. This examination reveals the intricate interplay between various biotic and abiotic constituents, including environmental factors (EFs), characteristic minerals, organic flotation reagents (OFRs), and microorganisms within Pb-Zn tailings interact through a series of physical, chemical, and biological processes, leading to the formation of complexes, chelates, and aggregates involving HMs and OFRs. These interactions ultimately influence the migration and transformation of HMs. Finally, we provide an overview of contaminant migration prediction and ecological remediation in Pb-Zn tailings. In this systematic review, we identify several forthcoming research imperatives and methodologies. Specifically, understanding the dynamic mechanisms underlying the migration and transformation of HMs is challenging. These challenges encompass an exploration of the weathering processes of characteristic minerals and their interactions with HMs, the complex interplay between HMs and OFRs in Pb-Zn tailings, the effects of microbial community succession during the storage and remediation of Pb-Zn tailings, and the importance of utilizing process-based models in predicting the fate of HMs, and the potential for microbial remediation of tailings.

Single/co-adsorption and mechanism of methylene blue and lead by ß-cyclodextrin modified magnetic alginate/biochar.

Due to the high biological toxicity, the concurrent elimination of lead (Pb (II)) and methylene blue (MB) has become a challenging problem. Therefore, a newly ß-cyclodextrin (ß-CD) modified magnetic alginate/biochar (ß-CD@MBCP) material was developed. Comprehensive characterizations proved the successful coating of ß-CD onto MBCP surface by microwave-aided fabrication. The ß-CD@MBCP achieved high-efficiency uptake for contaminants under a wide pH scope. In the dual system, Pb (II) elimination was facilitated with the presence of MB, due to the active sites provided by MB. In the presence of Pb (II), MB uptake was inhibited due to the electrostatic repulsion between positively charged MB and Pb (II). Electrostatic attraction and complexation contributed to capturing Pb (II), while π-π interactions, host-guest effect, and H-bonding were important in MB elimination. After four cycles, ß-CD@MBCP maintained comparatively good renewability. Findings demonstrated that ß-CD@MBCP could be an effective remediation material for Pb (II)/MB adsorption from aqueous environments.

The geochemical and mineralogical controls on the release characteristics of potentially toxic elements from lead/zinc (Pb/Zn) mine tailings.

Large quantities of lead/zinc (Pb/Zn) mine tailings were deposited at tailings impoundments without proper management, which have posed considerable risks to the local ecosystem and residents in mining areas worldwide. Therefore, the geochemical behaviors of potentially toxic elements (PTEs) in tailings were in-depth investigated in this study by a coupled use of batch kinetic tests, statistical analysis and mineralogical characterization. The results indicated that among these studied PTEs, Cd concentration fluctuated within a wide range of 0.83-6.91 mg/kg, and showed the highest spatial heterogeneity. The mean Cd concentrations generally increased with depth. Cd were mainly partitioned in the exchangeable and carbonate fractions. The release potential of PTEs from tailings was ranged as: Cd > Mn > Zn > Pb > As, Cd > Pb > Zn > Mn > As and Cd > Pb > Mn > Zn > As, respectively, under the assumed environmental scenarios, i.e. acid rain, vegetation restoration, human gastrointestinal digestion. The results from mineralogical characterization indicated that quartz, sericite, calcite and pyrite were typical minerals, cumulatively accounting for over 80% of the tailings. Sulfides (arsenopyrite, galena, and sphalerite), carbonates (calcite, dolomite, cerussite and kutnahorite), oxides (limonite) were identified as the most relevant PTEs-bearing phases, which significantly contributed to PTEs release from tailings. A combined result of statistical, geochemical and mineralogical approaches would be provided valuable information for the alteration characteristics and contaminant release of Pb/Zn mine tailings.

Activation of Persulfate for Degrading Tetracycline Using the Leaching Residues of the Lead-Zinc Flotation Tailing.

Inappropriate disposal of leaching residues from the lead-zinc tailings recovery process may result in environmental pollution. Its recycling and reuse remain a prevalent topic in environmental science and technology. It was roasted to prepare leaching residues-based materials (TLRS) in this work, and the TLRS were creatively used as the catalyst to active sodium persulfate (PS) to degrade organic pollutants. Degradation of tetracycline using the TLRS-PS system was evaluated, and the treating parameters were optimized. Roasting resulted in the exposure of active sites on TLRS surface, in which transition metals can donate electrons to PS to form SO4·-. SO4·- can further react with OH- to form ·OH. Formation of these radicals was confirmed by both quenching experiments and EPR analysis. Under optimized conditions, 85% of the TC can be degraded in 3.0 h, and ~50% of degraded TC was mineralized to CO2 and H2O. The performance of TLRS barely changed after four reuses, suggesting the chemical stability of TLRS. The presence of dissolved substance in the water matrix could weaken the performance of the TLRS-PS system. A mechanism of TC degradation was proposed based on the experimental results and literature. These preliminary results provide us new insight on the reuse of lead-zinc flotation tailings.

Bacterial networks mediate pentachlorophenol dechlorination across land-use types with citrate addition.

Soil microorganisms play a crucial role in the bioremediation of pentachlorophenol (PCP)-contaminated soils. However, whether and how soil bacterial networks with keystone taxa affect PCP dechlorination is not well understood. The present study investigated the effects of citrate on soil bacterial networks mediating PCP dechlorination by direct and indirect transformation in iron-rich upland and paddy soils. The rates of PCP dechlorination and Fe(II) generation were accelerated by citrate addition, particularly in the paddy soils. Network analysis revealed that the topological properties of bacterial networks were changed by citrate addition; more modules and keystone taxa were significantly correlated with PCP dechlorination and Fe(II) generation in the networks. Random forest modeling indicated that Clostridiales was the most important bacterial order; it was significantly involved in both the direct and indirect pathways of PCP dechlorination. Citrate addition had less influence on the balance between the direct and indirect pathways of PCP dechlorination in the upland soils, whereas it enhanced biological PCP dechlorination more directly and efficiently in the paddy soils. Our results suggested that land-use type and citrate addition play a critical role in controlling the biogeochemical mechanisms of PCP dechlorination.

Carbon sources mediate microbial pentachlorophenol dechlorination in soils.

In this study, experiments were performed using network analysis to investigate the effects of different carbon sources, including blank, citrate, glucose and lactate, on indigenous bacterial communities and on the pentachlorophenol (PCP) dechlorination in two soils. Kinetics results demonstrate that PCP dechlorination is significantly enhanced by adding citrate/lactate, but to a lesser extent by adding glucose. High-throughput sequencing results revealed that Firmicutes and Proteobacteria were the dominant groups in these four different treatments during the PCP dechlorination, whereas random forest analysis indicated that the orders Clostridiales, Haloplasmatales, Bacillales, Pseudomonadales and Gaiellales were the critical bacterial orders in modules that were significantly correlated with PCP dechlorination. Among them, the relative abundance of Clostridiales dramatically increased in both citrate and lactate treatment, further accelerating the PCP dechlorination. Addition of citrate/lactate as the carbon source increased the bacterial co-occurrence network density, average clustering coefficient and modularity. Moreover, more modules significantly correlated with PCP dechlorination in the citrate/lactate networks compared with the glucose/blank networks. Random forest modeling suggested that Clostridiales played a critical role in these functional modules. Taken together, our results provide insight into the biological mechanism of the impact of exogenous carbon sources on PCP dechlorination pathways by modifying soil bacterial networks.