Dynamic elution of residual ammonium leaching agent from weathered crust elution-deposited rare earth tailings by magnesium chloride.

The release of residual ammonium (RA) leaching agent from weathered crust elution-deposited rare earth tailings would cause serious environmental pollution, and it was necessary to efficiently remove it from the ore body before the mine closure. In this study, occurrence states of the RA were determined and dynamic elution of RA from rare earth tailings by using magnesium chloride as eluent was investigated. Effects of initial concentration, pH, flow rate, and particle size on the ammonium removal efficiency were investigated, and variations of ammonium occurrence states before and after elution were determined. Lastly, elution mechanism was discussed. Results showed that removal efficiency of RA by magnesium chloride was significantly higher than that by deionized water, and elution efficiency of RA could reach about 95.7% at the optimum laboratory experiment conditions. Energy dispersive spectrometer (EDS) analysis illustrated that the residual ammonium was replaced by Mg2+ during the elution process, and occurrence state experimental results showed that 94.0% of water-soluble and adsorbable ammonium was eluted. The empirical kinetic equation of eluting RA by magnesium chloride was established as 1-2/3α-(1-α)2/3= 0.02*C00.6t. This study provided a valuable method for reducing environmental pollution caused by the release of the residual ammonium from the rare earth tailings.

Selective recovery of glyphosine from glyphosate mother liquor using a modified biosorbent: Competitive substitution adsorption.

Here, an easy to prepare, environmentally friendly, and highly efficient biosorbent was synthesized for the selective recovery of glyphosine from glyphosate mother liquor. Batch adsorption and continuous fixed-bed column experiments were conducted to determine its adsorption properties and evaluate its potential towards practical applications. The results showed that the biosorbent exhibited a fast adsorption rate and high adsorption capacity (296.1 mg/g) toward glyphosine. Further, the biosorbent performed better under acidic conditions, and was easily regenerated using an alkaline solution, maintaining a high removal efficiency even after 5 adsorption-desorption cycles. Competitive adsorption experiments in binary and ternary systems revealed that the biosorbent showed a higher adsorption affinity toward the target glyphosine compared with glyphosate and phosphorous acid (which are the other main constituents of glyphosate mother liquor), enabling the selective recycling of glyphosine. These observations were further supported through density functional theory (DFT) calculations of the adsorption energy. Moreover, fixed-bed column experiments showed that the prepared biosorbent could maintain its high performance in actual glyphosate mother liquor. Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) analyses revealed that the adsorption mechanism is strongly associated with electrostatic attraction and hydrogen bonding between -NH3+ and glyphosine. Overall, the prepared biosorbent can be considered as an excellent candidate for the selective recovery of glyphosine from complicated industrial wastewater systems.

Evaluation of different factors on metal leaching from nickel tailings using generalized additive model (GAM).

Compared with sulfide tailings, the oxidation and transformation of certain substances in oxidized tailings into more soluble forms may affect the bioaccumulation and biomagnification properties and enhance the risk of toxic effects in the ecosystem. This study aimed to apply the generalized additive model (GAM) to evaluate factors affecting heavy metal leaching from nickel (Ni) tailings. We created an orthogonal experiment table (L18(37)) to evenly distribute the different combinations of factor values. The Ni tailings were immersed in solutions with different combinations of factor values for 16 d, and samples were taken on days 1, 2, 4, 7, 11, and 16 to measure the pH and heavy metal concentration of the leachate. The GAM was used to fit the concentration of heavy metals of the leachate and the initial factors of the leaching solution. The results showed that the pH and Cr concentration of the leachate increased with time and stabilized after 1 d (pH of approximately 7), while the Mn, Ni, and Tl concentrations gradually decreased and stabilized after peaking on the first day. An analysis of the GAM results showed that the Cr concentration was highly sensitive to the solid-liquid ratio (F = 127.8) and tailing particle size (F = 10.7). The Cr concentration of the leachate was significantly higher when exposed to a high solid-liquid ratio or a fine particle size, whereas the Mn, Ni, and Tl concentrations were highly sensitive to the KCl concentration and solid-liquid ratio (F = 77.4, 146.9, and 315.9 respectively). The GAM identified interactions between key factors, which have complex and strong effects on the leaching of tailings and the migration of heavy metals, either promotional or antagonistic. The prediction of the minimum Cr leaching concentration shows that GAM can be used to determine the conditions associated with minimum leaching concentrations of heavy metals and to effectively predict the metal concentrations of leachate. As such, the results of this study can be applied to the management of nickel tailings.

Sustainable and efficient stabilization/solidification of Pb, Cr, and Cd in lead-zinc tailings by using highly reactive pozzolanic solid waste.

Lead-zinc tailings (LZTs) are industrial by-products containing a large number of heavy metals that seriously harm the ecological environment and human health. This study was performed to propose a sustainable and efficient method for immobilizing Pb, Cr, and Cd in LZTs by using solid waste. To better assess the immobilization performance and mechanism, the leaching toxicity, fraction distribution, unconfined compressive strength, environmental risk assessment, and hydration products were explored. The LZTs were mixed and molded with different constituents of ground granulated blast furnace slag (GGBFS) and rice husk ashes (RHAs) at different curing temperatures. Results suggest that ≥99% of the Pb, Cr, and Cd were immobilized mainly in the form of residual fractions in the LZTs. The amounts of Pb, Cr, and Cd in the bioavailable fractions notably decreased by approximately 99.83%, 99.58%, and 97.05%, respectively. After stabilization/solidification (S/S) disposal, Pb, Cr, and Cd showed low to even no risk. The RHAs were effective to stabilize Pb, and GGBFS was effective to stabilize Cr. However, both materials showed almost equal effects to Cd. Ettringite, C-S-H gel, and portlandite were the main hydration products to immobilize Pb, Cr, and Cd, and these hydration products provided a source of strength. Honey-comb or reticular network C-S-H gel possessed higher specific surface area, higher pore volume, and bigger pore size than the other materials. The proposed method could explain the sustainability and efficiency of the S/S of Pb, Cr, and Cd in LZTs by using RHAs. This study opens up new perspectives for disposing heavy metal by using accessible agricultural solid waste (i.e., RHAs) in rural areas, and the solidified block shows certain economic benefits.

Multiple environmental risk assessments of heavy metals and optimization of sludge dewatering: Red mud-reed straw biochar combined with Fe2+ activated H2O2.

In this study, Fe-rich biochar (RMRS-BC) was prepared from red mud and reed straw to improve sludge dewatering and transformation of heavy metals (HMs, including Cd, Cr, Cu, Pb, and Zn). The optimal concentrations of RMRS-BC, Fe2+, and H2O2 to promote sludge dewaterability were identified by response surface methodology (RSM). The optimal dosages of RMRS-BC, Fe2+, and H2O2 were 74.0, 104.9, and 75.7 mg/g dry solids (DS), respectively. The corresponding capillary suction time (CST) and water content of sludge cake were 14.3 s and 51.25 wt%. For the improvement mechanism, heterogeneous and homogeneous Fenton reactions occurred due to RMRS-BC and Fe2+ activating H2O2. The extracellular polymeric substances (EPS) decomposed into dissolved organic matter (proteins and polysaccharides), thereby promoting the transformation of bound water to free water and further reducing the water content of the sludge cake. The research quantitatively assessed the environmental risk of heavy metals in the conditioned sludge cake based on bioavailability and ecotoxicity, pollution levels and potential ecological risks. Compound conditioning using RMRS-BC, Fe2+, and H2O2 could significantly improve the solubility and reduce the leaching toxicity of HMs. In general, RMRS-BC combined with Fe2+ to activate H2O2 provided an effective method to enhance sludge dewaterability and reduce HMs risk.

Simultaneous removal of lead, manganese, and copper released from the copper tailings by a novel magnetic modified biosorbent.

Potentially toxic elements including lead (Pb), manganese (Mn), and copper (Cu) released from copper tailings would cause severe long-term environmental risks and potential threats to human health. To prevent these negative effects caused by the release of the metals, a novel magnetic carboxyl groups modified bagasse with high adsorption affinity and strong magnetism was synthesized through an in-situ precipitation method and used to simultaneously remove Pb, Mn, and Cu from the eluate of copper tailings. Results showed that release of Pb, Mn, and Cu from the copper tailings was pH, time, and particle size dependent, and maximum concentrations of them released in the eluate was 1.7, 1.9, and 4.1 mg L-1 under weak acid conditions. Batch adsorption experiment showed that the as-synthesized magnetic modified bagasse could selectively absorb Pb, Mn, and Cu from a complex solution with adsorption capacity of 137.3, 13.1, and 90.0 mg g-1, respectively. X-ray photoelectron spectroscopy (XPS) and energy dispersive spectroscopy-mapping (EDS-mapping) demonstrated that Pb, Mn, and Cu interacted with the magnetic modified biosorbent mainly through coordination and ion exchange. Column experiments showed that higher than 99.5% of the released Pb, Mn, and Cu could be simultaneously removed by the magnetic modified bagasse, and the maximum concentrations of them released in the eluate of the copper tailings were all decreased to lower than 0.01 mg L-1, which reached the discharge standards. After recycled by a magnet, the magnetic modified bagasse could be collected easily and used repeatedly. Because of the high efficiency and easy recovery, the used method had great practical application value in removal of potentially toxic elements released from metallic tailings.

Citrobacter arsenatis sp. nov., an arsenate-reducing bacterium isolated from freshwater sediment.

A novel arsenate-reducing bacterium, LY-1T, was isolated from freshwater sediment in Huangshi, China. Morphological analysis indicated that the cells were shaped like rods and were gram-negative. The major fatty acids (> 10%) were C16:0, summed feature 3 (C16:1 ω7c, C16:1 ω6c) and summed feature 8 (C18:1 ω7c, C18:1 ω6c). An assessment of the phylogeny based on 16S rRNA gene sequences indicated that the strain LY-1T belonged to the genus Citrobacter, while further analysis based on the recN gene indicated that LY-1T occupies a distinct phylogenetic niche within the Citrobacter genus. Moreover, average nucleotide identity and digital DNA-DNA hybridization between the strain LY-1T and the type strains of closely related species of the genus Citrobacter (C. europaeus, C. brakii, C. portucalensis, C. freundii, C. werkmanii, C. cronae, C. youngae, C. pasteurii, C. tructae, C. gillenii, and C. murliniae) were 85.8-93.8% and 31.2-56.9%, respectively. In addition, the LY-1T strain's capacity to metabolize various compounds and its characteristic G + C content of 51.9% were also distinct from other species of the Citrobacter genus. These discriminatory features cumulatively indicate the LY-1T strain as a new species within the Citrobacter genus. We propose the species name Citrobacter arsenatis for this new species, with LY-1T (= CCTCC AB 2019169T = KCTC 72440T) as the type strain.

Vertical distribution and occurrence state of the residual leaching agent (ammonium sulfate) in the weathered crust elution-deposited rare earth ore.

Weathered crust elution-deposited rare earth ore (WCE-DREO) are rich in middle and heavy rare earth, and ammonium sulfate ((NH4)2SO4) was often used as leaching agent to leach rare earths by in-situ leaching method. However, much of (NH4)2SO4 would remained in the ore body during the leaching process, and release of it would cause seriously environmental pollution after the mine closure. To efficiently remove it, the rare earth ore properties and vertical distribution and occurrence state of the residual leaching agent at mine roof (GP1), mine waist (GP2), and mine foot (GP3) with different depth were investigated and efficient elution method was proposed in this study. Results showed that the rare earth ore mainly consist of quartz, clay minerals (halloysite, illite, and kaolinite) and rock-forming minerals, and pH and moisture contents of them were ranged from 4.0 to 5.0 and 10-20%, respectively. Residual agent was mainly enriched in the middle and deep layer of the ore body with the main form of ammonium nitrogen (NH4+-N), and content of it at the three sites followed the order of GP1>GP3>GP2, which was related to the content of the clay minerals and the moisture. Occurrence state experimental results illustrated that about 95% of the NH4+-N existed as water-soluble ammonium (WS-AN) and adsorbable ammonium (AS-AN), and 5% of it existed as fixed ammonium (FX-AN), and concentration ratio of them was in order: WS-AN > AS-AN â‰« FX-AN. Based on the results above, MgCl2 solution was used as an eluent to remove the leaching agent from the ore, and results showed that higher than 90% of residual ammonium could be removed from the ore by it. This study provided a valuable guidance for the residual leaching agent removal from the WCE-DREO body.

Enhanced sludge dewaterability by Fe-rich biochar activating hydrogen peroxide: Co-hydrothermal red mud and reed straw.

This study proposed Fe-rich biochar (RMRS-BC) produced by the co-hydrothermal treatment of red mud and reed straw, industrial waste and agricultural waste, as a novel sludge conditioner. It had been proven that heterogeneous and homogeneous Fenton reactions occurred during the sludge conditioning process, in which RMRS-BC activated H2O2 to improve sludge dewaterability. Results demonstrated that the optimal condition was 7.5 wt% dry solids (DS) of RMRS-BC at a mass ratio of 1:1 combined with H2O2. The corresponding water content of sludge cakes and the capillary suction time reduction efficiency were 57.88 wt% and 69.76%, respectively. The Fe3O4 supported in the RMRS-BC structure was used as a catalyst to produce heterogeneous reaction, and the Fe2+ leached from the RMRS-BC after acidification happened homogeneous reaction. Double Fenton reaction in sludge conditioning enhanced the production efficiency of ·OH, the sludge flocs were dispersed into smaller particles, more bound water from the extracellular polymeric substances (EPS) was released, and sludge dewaterability performance was improved. Another main mechanism for enhancing dewaterability was to use RMRS-BC as a skeleton builder to reduce the compressibility of sludge cakes and facilitated free water to flow out. In summary, the Fenton oxidation method activated by RMRS-BC is feasible in improving sludge dewatering.

An integrated geospatial correlation analysis and human health risk assessment approach for investigating abandoned industrial sites.

An integrated geospatial correlation analysis (GCA)-human health risk assessment (HHRA) approach was developed to investigate abandoned industrial sites featured by heterogeneous contamination data. Critical areas of high health risk concerns can be prioritized for remediation using the integrated approach. An abandoned chemical complex site in Hubei, China was investigated as a case study. GCA and HHRA were performed using soil and groundwater sampling data collected in 2016 and 2019. Benzene, chlorobenzene, dichlorobenzenes, 2-nitrochlorobenzene, and α-hexachlorocyclohexane were determined to be critical contaminants in soil. The 2019 sampling data revealed new contaminated locations that were not found in the 2016 sampling campaign. High concentrations (89.81-386.55 mg/L) of vinyl chloride were also found in groundwater samples. Several critical location clusters of high concentrations of dichlorobenzenes, chlorobenzene, and α-hexachlorocyclohexane were found within the site according to the GCA outcomes. These contaminants could pose significant cancer and non-cancer risks to onsite workers. The critical areas were ranked according to cancer and non-cancer risks estimated by HHRA, respectively, for informed remediation planning. Among the critical contaminants, α-hexachlorocyclohexane, 2-nitrochlorobenzene, and 1,4-dichlorobenzene in soil, as well as vinyl chloride in groundwater, contributed a predominant part to the total health risk. The integrated approach can be used to assess the contamination of other similar abandoned industrial complex sites.

The experimental optimization and comprehensive environmental risk assessment of heavy metals during the enhancement of sewage sludge dewaterability with ethanol and Fe(â ¢)-rice husk.

The optimal concentrations of ethanol, Fe3+ and rice husk (RH) to enhance sludge dewaterability were determined by response surface methodology (RSM). Results showed the optimal concentrations of ethanol, Fe3+ and RH were 22.2 g/g DS, 239.9 mg/g DS and 348.9 mg/g DS, respectively, and the CST reduction efficiency reached 72.3%. The transformation behavior and mechanism of the heavy metals (HMs) during conditioning process were determined in terms of total HMs content, leaching tests, and fraction distribution. The environmental risk of HMs was quantitatively evaluated after conditioning in terms of bioavailability and ecotoxicity, potential ecological risks, and pollution levels. Results showed that the high ecological risk of HMs in raw sludge cake is primarily dominated by Cd and the use of Fe3+ alone negatively affected the immobilization of HMs and reduction of leaching toxicity. However, after repeated conditioning with Fe3+ and ethanol, the total HMs content reduction values in sludge cake were 75%, 93%, 100%, 91%, and 74% for Pb, Cr, Cd, Zn, and Cu, respectively. The potential ecological risk index (PERI) and geoaccumulation indicated low or no overall environmental risk after repeated conditioning. Particularly, the risk of Cd was reduced from high risk to low risk after repeated conditioning according to the PERI. Ethanol/Fe3+-RH can effectively reduce HMs risk from the sludge cake in the dewatering tests.

Mechanism investigations into the effect of rice husk and wood sawdust conditioning on sewage sludge thermal drying.

This study attempts to employ wood sawdust and rice husk as biorenewable conditioners to improve the efficiency and energy consumption of sewage sludge thermal drying, besides revealing the mechanism of drying. Response surface methodology (RSM) approach has been used to optimize the operational parameters (drying temperature and dose of conditioners). Investigations into the thermal performance, water distribution and morphological of sludge have been used to explain the improvements obtained in the properties of drying with the addition of biomass. The optimal conditions found out were: 10% rice husk and 10% wood sawdust at 120 °C, which resulted in drying time to reduce by 17.64% with the energy consumption savings by 46.37% for the conditioned sludge. Also, the mechanism on the roles of these additives has been found out as follows: (1) Addition of biomass enhances the thermal conductivity of the conditioned sludge, leading to improvements in its heat transfer capacity; (2) Bound water → free water and strongly bonding water → weakly bonding water, due to cationic osmotic effects; (3) Structures with rigidity and porosity provide sufficient passages for the vapors to escape.

Distribution and phytotoxicity of soil labile aluminum fractions and aluminum species in soil water extracts and their effects on tall fescue.

Soil acidification can alter the biogeochemistry of ecosystems and adversely affect biota; however, there are still many debates about the toxicity of aluminum (Al) fractions and Al species in soil:water extracts to plants. In this study, five crude soils with different pH values (4.92-8.51) were collected, seeded with tall fescue and grown in rhizosphere boxes for 120 days. Then, soil properties, labile Al fractions and Al species in soil:water extracts were determined, and their toxicities to plants were analyzed. Our study showed that a stable exchangeable Al fraction (ExAl) pool exists and is supplied by other labile Al fractions. Dissolution of Al from adsorbed hydroxyl-Al fraction (HyAl) and organic-Al fraction (OrAl) may play important roles in soil Al toxicity, as HyAl and OrAl account for major parts of soil labile Al. Additionally, Al3+ and mononuclear hydroxyl-Al species in soil:water extracts have few effects to plants. Nevertheless, high negative correlations were found between Al-F- complexes and tall fescue biomass, indicating their toxicity in the natural soil environment. Thus, in many cases, Al3+ toxicity should not be emphasized because of its lower activity in soil water extracts. Moreover, toxicities of AlF3(aq) and AlF4- to plants should be emphasized, because they have been confirmed in soil water extracts in this study.

Zero-carbon inertization processes of hazardous mine tailings: Mineral physicochemical properties, transformation mechanism, and long-term stability.

Hazardous mine tailings (HMTs) dam failures can cause devastation to the ecology environment, people's lives and property, which require expensive and complicated remediation engineering systematacially. A cheap and sustainable inertization disposal is proposed for de-risking HMTs without any carbon emissions, stabilizing hazardous heavy metal cations within safety minerals and also sequestering CO2 in the process, simultaneously. Herein, lead-zinc tailings as target HMTs were inertized by using waste rice husk ashes (RHAs) and carbide slag (CS) with a certain ratio, and lead-zinc tailings hardened pastes (LZTHPs) were investigated based on the experimental performance, analytical characteristics, and simulation diffusion methods, to deeply unveil the minerals transformation mechanisms and long-term stability from the cation perspectives. Results revealed that LZTHPs' compressive strength ranged from 1.04-4.73 MPa and leaching toxicity concentrations of Pb, Zn, Cr, and Cd reached 0.03 mg/L, 1.78 mg/L, 0.01 mg/L, and 0.01 mg/L, respectively. C-S-H gels (Type I and II), cation hydroxides and CO2 mineralization carbonates were the hydrates in LZTHPs. Pb (86%), Zn (78%), Cr (76%), and Cd (65%) were immobilized as residual state, and CO2 mineralization capacity was 0.16 kg/kg. The diffusion coefficient of Pb, Zn, Cr, and Cd below 4.48 × 10-10 cm2/s, 1.39 × 10-10 cm2/s, 4.72 × 10-10 cm2/s, and 0.30 × 10-12 cm2/s, which would be sufficient in most scenarios to adequately stabilize tailings. Diffusion control is the leaching mechanism of cations. After 100 years of simulation diffusion, the diffusion areas of Pb, Zn, Cr, and Cd are 1.33 × 10-3∼1.49 cm2, 2.47 × 10-4∼0.48 cm2, 2.47-8.61 × 10-4 cm2, and 1.49 cm2, respectively, and the environmental impact of LZTHPs was negligible. This study provides promising solutions for alleviating hazardous tailings dangerous, achieving sustainable development with zero-carbon emission, implying the concept of eliminating waste by waste, synchronously.

Preparation of Cementitious Materials from Mechanochemically Modified Copper Smelting Slag Compounded with High-Aluminum Fly Ash.

Copper smelting slag discharged from mining and high-aluminum fly ash generated during the combustion of coal for energy production are two typical bulk solid wastes, which are necessary to carry out harmless and resourceful treatment. This research proposed an eco-friendly and economical method for the co-consumption of copper smelting slag and high-aluminum fly ash. Cementitious materials were compounded with copper smelting slag and high-aluminum fly ash as the main materials were successfully prepared, with a 28-d compressive strength up to 31.22 MPa, and the heavy metal leaching toxicity was below the limits of the relevant standards. The optimum mechanical properties of the cementitious materials were obtained by altering the material proportion, ball mill rotation speed, and CaO dosage. Under the combined effect of mechanical ball milling at a suitable speed and chemical activation with a certain alkali concentration, the prepared cementitious materials had an initial activation. The pastes of the cementitious materials generated a gel system during the subsequent hydration process. The two steps together improved the mechanical strength of the cured products. The preparation was simple to operate and offered a high stability of heavy metals. The heavy metal contaminants were kept at a low content throughout the process from raw materials to the prepared cured specimens, which was suitable for application in practical environmental remediation projects and could provide effective solutions for ecological environment construction.

Research on Utilizable Calcium from Calcium Carbide Slag with Different Extractors and Its Effect on CO2 Mineralization.

With the increasing accumulation of alkaline industrial solid waste, the mineralization of CO2 using alkaline industrial solid waste has broad application prospects. Carbide slag is highly alkaline and contains a large amount of calcium elements, making it an excellent material for CO2 mineralization. Our idea was to acquire qualified products and fast kinetics by integrating carbide slag utilization and carbon reduction. The reaction route was divided into two steps: calcium extraction and carbonization. In order to achieve efficient extraction of utilizable calcium, we selected NH4Ac as the extraction agent, which has the advantage of buffer protection and environmental friendliness due to being an acetate radical. The extraction efficiency of utilizable calcium exceeded 90% under the conditions of L/S 20:1 and NH4+/Ca2+ 2:1. In the carbonization process, the crystal forms of CaCO3 synthesized by direct carbonation, acid extraction, and ammonium salt were characterized. The formation mechanism of vaterite in ammonium solution and the influence of impurities (Al3+, Mg2+) on the crystal transformation were revealed. This study provides technical support for using alkaline industrial waste to prepare high-purity vaterite. Therefore, alkaline industrial waste can be efficiently and sustainably utilized through CO2 mineralization.

Investigation of waste alkali-activated cementing material using municipal solid waste incineration fly ash and dravite as precursors: Mechanisms, performance, and on-site application.

The proper treatment of municipal solid waste incineration fly ash (MSWIFA) is a crucial concern due to its hazardous nature and potential environmental harm. To address this issue, this study innovatively utilized dravite and black liquor to solidify MSWIFA. The semi-dry pressing method was employed, resulting in the production of waste alkali-activated cementing material (WACM). This material demonstrated impressive compressive and flexural strength, reaching 45.89 MPa and 6.55 MPa respectively, and effectively solidified heavy metal ions (Pb, Cr, Cu, Cd, and Zn). The leaching concentrations of these ions decreased from 27.15, 10.36, 8.94, 7.00, and 104.4 mg/L to 0.13, 1.05, 0.29, 0.06, and 12.28 mg/L, respectively. The strength of WACM increased by 3 times compared to conventionally produced materials. Furthermore, WACM exhibited excellent long-term performance, with acceptable heavy metal leaching and minimal mechanical degradation. Experimental and theoretical analyses revealed the heavy metal solidification mechanisms, including chemical binding, ion substitution and physical encapsulation. Finally, the on-site application of WACM confirmed its feasibility in meeting both environmental and strength requirements.

Efficient carbamazepine degradation by modified copper tailings and PMS system: Performance evaluation and mechanism.

It is a green and sustainable path to establish cheap solid waste-based catalyst to establish peroxymonosulfate (PMS) catalytic system for the degradation of carbamazepine (CBZ) in water. In this study, durable copper tailing waste residue-based catalyst (CSWR) was prepared, and efficient CSWR/PMS system was constructed for catalytic degradation of CBZ for first time. The morphology and structure of CSWR changed from clumps to porous and loose amorphous by alkali leaching and medium temperature calcination. The reconstructed surface of the CSWR exposes more active sites promotes the catalytic reaction and increases the degradation rate of CBZ by more than 39.8 times. And the CSWR/PMS achieved a CBZ removal of nearly 99.99 % in 20 min. In particular, perovskite-type iron-calcium compounds were formed, which stimulated the production of more HO• and SO4•- in the system. DFT calculation shows that CSWR has stronger adsorption energy and electron transfer ability to PMS molecules, which improved the degradation efficiency of the system. In general, this study proposed a means of high-value waste utilization, which provided a new idea for the preparation of solid waste based environmental functional materials and is expected to be widely used in practical wastewater treatment.

Pollution control performance of solidified nickel-cobalt tailings on site: Bioavailability of heavy metals and microbial response.

There has been increasing attention given to nickel-cobalt tailings (NCT), which pose a risk of heavy metal pollution in the field. In this study, on site tests and sampling analysis were conducted to assess the physical and chemical characteristics, heavy metal toxicity, and microbial diversity of the original NCT, solidified NCT, and the surrounding soil. The research results show that the potential heavy metal pollution species in NCT are mainly Ni, Co, Mn, and Cu. Simultaneous solidification and passivation of heavy metals in NCT were achieved, resulting in a reduction in biological toxicity and a fivefold increase in seed germination rate. The compressive strength of the original tailings was increased by 20 times after solidification. The microbial diversity test showed that the abundance of microbial community in the original NCT was low and the population was monotonous. This study demonstrates, for the first time, that the use of NCT for solidification in ponds can effectively solidification of heavy metals, reduce biological toxicity, and promote microorganism diversity in mining areas (tended to the microbial ecosystem in the surrounding soil). Indeed, this study provides a new perspective for the environmental remediation of metal tailings.

Phosphorus-based soil prophylactics for managing Pb contamination in soil: Slow-release kinetics and microbiological effects.

Soil remediation poses significant challenges due to its spatial heterogeneity, surpassing the complexities of atmospheric and water remediation. This study introduces an innovative approach to prevent soil heavy metal pollution by developing three phosphorus slow-release heavy metal soil prophylactic agents (SLPs) - Sap-11, Sap-12, and Sap-21. At a liquid-to-solid ratio of 1:20, the three types of SLPs achieve phosphorus sustained slow release amounts of 1.586 g/L, 4.259 g/L, and 1.444 g/L within 30 days, respectively. Over a cultivation period of 120 days, after amendment with the three SLPs, the surface soil demonstrates stabilization capacities for Pb of 29.56 mg/g, 46.24 mg/g, and 25.77 mg/g, respectively, representing enhancements of 283.64 %, 500.12 %, and 250.74 % compared to the control. Firstly, the direct contribution of P (up to 3.778 mg/g) released from SLPs chemically binding with Pb, and secondly, a significant proportion of the indirect contribution originating from the microbial activity and soil organic matter. In summary, SLP emerges as an effective strategy for soil heavy metal management, stabilizing heavy metals by stimulating the soil's inherent physiological and biochemical reactions. This approach provides a practical solution for the application of P-containing materials and introduces novel perspectives for soil heavy metal management strategies.