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.

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.

Submicron tourmaline enhanced the solidification of municipal solid waste incineration fly ash by chemical structure reorganization and stabilized heavy metals.

Municipal solid waste incineration fly ash (MSWIFA) exsits in large quantitities and contains pollutants such as heavy metal. While solidification is one of the most effective methods for treating MSWIFA, this application is limited by cost, subsequent treatment, and simultaneous immobilization of anions and cations. This research demonstrated that under a certain initial pressure (20 MPa), a gelation reaction involving ball milling-modified tourmaline powder, a small amount of cement clinker, and MSWIFA forms a stable consolidated body and significantly reduces the risk of heavy metal dissolution. The consolidated MSWIFA can easily be formed into unfired bricks in large-scale pilot production, and a response surface model was used to optimize the experimental parameters. When the mass ratio of tourmaline: cement clinker: MSWIFA was 15:15:200 (mixed with a moisture content of 13 to 15 %), the compressive strength of the consolidated body reached 13 MPa, and the amounts of Cr and Pb leached decreased from 12 mg/L to 0.1 mg/L and 25 mg/L to 0.3 mg/L, respectively. The consolidated form contained a new mineral phase (Ca3Si2O7·3H2O, Ca10Mg0.8(SiO4)0.6O2Cl, and CaCl2∙Ca(OH)2·H2O) with a high compressive strength. Notably, the soluble PbSO4 in the MSWIFA was converted into relatively stable PbSiO3, and Cr(VI) was lattice-wrapped. This study was the first to demonstrate that tourmaline synchronously passivates Pb(II) and Cr(VI) in fly ash in the solid phase, with a low cost and requires no subsequent treatment. This study provided a novel technical path for recycling MSWIFA. Eventually, leaching of the heavy metals Pb, Cr, Cu, Cd, and Zn from the solids achieved concentrations less than 0.25, 1.5, 0.5, 0.15, and 100 mg/L.

A novel expansive soil hardener: performance and mechanism of immersion stability.

Aiming at the existing problems of poor treatment effect and immersion stability of expansive soils, a slag soil hardener (SSH, developed by Wuhan University, China) was combined with different additives to dispose in this study. The free expansion rate, compressive strength, and immersion stability of samples were compared, and the influences of different additives, curing age, and dry density on the process and mechanism of improvement were discussed. The experimental results indicated that SSH combined with quicklime had the best improvement effect on expansive soils, in which the mass ratio of raw materials was: expansive soil/SSH/quicklime = 92/4/4, and the free expansion rate decreased from 45.90% to 4.4%, compressive strength increased from 2.53 MPa to 6.69 MPa, and there was no splitting after immersion under this ratio. FTIR spectroscopy, XPS and SEM were performed to analyze the characteristic functional groups, structural forms, and morphology of samples to study the mechanism of improvement, which showed that SSH greatly reduced the proportion of montmorillonite in the whole system and further enhanced the mechanism of ion exchange, soil particle connection, and coating protection. The research can provide theoretical reference for engineering the application of expansive soil area in rainy climate and has dual economic and environmental benefits.

Acid rain-dependent detailed leaching characteristics and simultaneous immobilization of Pb, Zn, Cr, and Cd from hazardous lead-zinc tailing.

In acidic medium, hazardous heavy metals of lead-zinc tailing (LZT) are easily leachable and mobilizable. Thus, the hazard, amount, form, and complexity of the leached heavy metals under acidic precipitation become a major environmental concern. This work investigates the gangue minerals, toxicity, speciation, leaching characteristics of heavy metals in LZT under simulated acid rain, as well as immobilization effects and mechanisms using a sustainable binder. In LZT, dolomite, quartz, calcite, and muscovite are the main gangue minerals, tiny hazardous metallic minerals were absorbed in the surface. The results revealed that Pb, Zn, Cr, and Cd were the predominant harmful elements, particularly Pb and Zn. Zn is leached completely and is the concerned hazardous element under simulated acid rain. In the acid rain neutralization ability test, the amount of leachable Pb, Cr, Ca, and Si maintained in equilibrium, leached Zn, Cd, Al, and Mg depended on the addition of acid. Pb and Ca were sedimented in residues. Immobilization of Pb, Zn, Cr, and Cd depended on the stability of Ca(OH)2/C-S-H of hydrates, and 70% LZTHP after curing 7 days can be used for some practical engineering projects. This work opens up deeply understandings for the leached heavy metals under acidic precipitation and improves the sustainable and safe in the field of immobilization of heavy metals.

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.

High-efficiency degradation of phthalic acid esters (PAEs) by Pseudarthrobacter defluvii E5: Performance, degradative pathway, and key genes.

Phthalic acid esters (PAEs) are a class of biologically accumulated carcinogenic and teratogenic toxic chemicals that exist widely in the environment. This study, Pseudarthrobacter defluvii E5 was isolated from agricultural soils and showed efficient PAEs-degradation and -mineralization abilities for five PAEs, and encouraging PAEs tolerance and bioavailable range for dibutyl phthalate (DBP) and bis(2-ethylhexyl) phthalate (DEHP) (0.25-1200 mg/L). The complete catalytic system in E5 genome enables PAEs to be degraded into monoester, phthalate (PA) and Protocatechuic acid (PCA), which eventually enter the tricarboxylic acid cycle (TCA cycle). The preferred PAEs-metabolic pathway in soil by E5 is the metabolism induced by enzymes encoded by pehA, mehpH, pht Operon and pca Operon. For the first time, two para-homologous pht gene clusters were found to coexist on the plasmid and contribute to PAEs degradation. Further study showed that P. defluvii E5 has a broad application prospect in microplastics-contaminated environments.

Stabilization and passivation of multiple heavy metals in soil facilitating by pinecone-based biochar: Mechanisms and microbial community evolution.

Soil contamination by multiple heavy metals and As is one of the major environmental hazards recognized worldwide. In this study, pinecone-biochar was used for stabilization and passivation of Pb, Cu, Zn, Cr, and As in contaminated soil around a smelter in Hubei province, China. The stabilization rate of heavy metals in soil can exceed 99%, and the leaching amount can meet the national standard of China (GB/T 5085.3-2007, less than 5, 100, 100, 15, and 5 mg/L, respectively.) within 90 days. The study confirmed that the addition of pinecone-biochar and the coexistence of indigenous microorganisms can effectively reduce the bioavailability of heavy metals. Among the heavy metals, As(III) can be oxidized to As(V) and then stabilized, and other heavy metals can be stabilized in a complex and chelated state characterized by X-ray photoelectron spectroscopy. After pinecone-biochar was added, the abundance of microbial community and intensity of metabolic activities became vigorous, the types and contents of dissolved organic matter increased significantly. A novel innovation is that the addition of pinecone-biochar increased the Bacillus and Acinetobacter in soil, which enhanced the function of inorganic ion transport and metabolism to promote the passivation and stabilization of heavy metals throughout the remediation process.

Selective recovery of manganese from electrolytic manganese residue by using water as extractant under mechanochemical ball grinding: Mechanism and kinetics.

This research aimed to address the issue of residual manganese in electrolytic manganese residue (EMR), which is difficult to recycle and can easily become an environmental hazard and resource waste. This research developed a method for the efficient and selective recovery of manganese from EMR and the removal of ammonia nitrogen (ammonium sulfate) under the combined action of ball milling and oxalic acid. The optimum process parameters of this method were obtained through single-factor experiment and response-surface model. Results showed that the recovery rate of manganese can exceed 98%, the leaching rate of iron was much lower than 2%, and the leaching rates of manganese and ammonia nitrogen after EMR ball grinding were 1.01 and 13.65 mg/L, respectively. Kinetics and mechanism studies revealed that ammonium salts were primarily removed in the form of ammonia, and that insoluble manganese (MnO2) was recovered by the reduction of FeS and FeS2 in EMR under the action of oxalic acid. Iron was solidified in the form of Fe2O3 and Fe2(SiO3)3. The technology proposed in this research has great industrial application value for the recycling and harmless treatment of EMR.

Analysis of driving factors on China's industrial solid waste generation: Insights from critical supply chains.

Industrial solid waste (ISW) poses a huge potential threat to human health and the environment. To prevent pollution at its source, it is necessary to analyze the socioeconomic drivers and identify the key supply chains that cause changes in ISW generation. In this study, based on monetary input-output tables (MIOTs) in China from 2011 to 2015, structural decomposition analysis (SDA) was used to study the influence of socioeconomic drivers on common industrial solid waste (CISW) and hazardous waste (HW) generation. Structural path decomposition (SPD) was used to further trace the effects of drivers at the supply chain level and obtain more meaningful results for policy formulation. Economic expansion was found to play the most crucial role in the increase in total ISW generation while the reduction of generation intensity effectively slowed the growth trend. From the final demand perspective, fixed capital formation contributed the most to ISW generation growth, accounting for 65.05% of the total final demand effect. Construction was the primary trigger. For CISW, the supply chain with the greatest overall influence was "metal ore mining industry → fixed capital formation" (including intermediate consumption of metal smelting, general and special machinery, and construction), reflecting how fixed capital formation indirectly affected the metal ore mining industry. The supply chain with the greatest influence on HW generation was "paper industry → exports." Based on the findings, corresponding policy adjustments are proposed.

A novel method for solidification/stabilization of Cd(II), Hg(II), Cu(II), and Zn(II) by activated electrolytic manganese slag.

This study was aimed at removing and stabilizing heavy metals (HgII, ZnII, CuII, and CdII). A novel material (named A-EMS) for heavy metal removal was proposed by ball grinding activated electrolytic manganese slag (EMS) with low content of sodium hydroxide. For different application scenarios, the two physical properties of the materials were developed: the powdery A-EMS (powder) was used to remove heavy metals from wastewater. In addition, the blocky A-EMS (porous brick) was used to build barrier walls for tailings ponds to prevent heavy metals from flowing out. The maximum removal amount of Hg(II) Cd(II), Zn(II), and Cu(II) by A-EMS were 475.35, 77.72, 259.70, and 203.20 mg/g in 30 min. The heavy metals ions were removed and fixed on A-EMS mainly through ion exchange and some forms of electrostatic adsorption and hydroxyl complexation. After consolidating the heavy metals, the compressive strength of the materials can reach 20 Mpa and the leaching toxicity met the national standard of China (GB/T 3838-2002) in 60 days. These excellent properties made A-EMS widely used to remove heavy metals in wastewater and to intercept and solidify heavy metals in mine wastewater.

Biodegradation of phthalic acid esters (PAEs) by Cupriavidus oxalaticus strain E3 isolated from sediment and characterization of monoester hydrolases.

Phthalic acid esters (PAEs) are teratogenic and carcinogenic and mainly metabolized by microorganisms in sediment. A novel strain, Cupriavidus oxalaticus strain E3, was isolated and characterized from sediment for PAEs degradation. The transformation of dibutyl phthalate (DBP) and bis(2-ethylhexyl) phthalate (DEHP) as the sole carbon source by strain E3 was systematically studied in the darkness through the kinetic studies and analysis of intermediates. After the initial lag pause of 5 h-8 h, the strain efficiently degraded 87.4%-94.4% of DBP and 82.5%-85.6% of DEHP at an initial amount of each phthalate of 200 mg/L after 60 h of incubation. The biodegradation rate of DBP and DEHP followed a first-order kinetic model, and degradation rate constants (k) of them by E3 were 1.37 and 0.86 d-1, respectively. Gas chromatography-mass spectrometry (GC-MS) results revealed that the tentative PAEs degradation pathway, included the transformation from PAEs to phthalic acid (PA) and the complete mineralization of PA. In the phase of PAEs to PA, DBP with short sides reduced the chain length via hydrolyzation, and DEHP with long sides reduced the chain length via hydrolyzation and ß-oxidation. The 3D model of monoester hydrolase from C. oxalaticus was predicted and used for docking with mono-2-ethylhexyl phthalate (MEHP) and mono-n-butyl phthalate (MBP). The docking results showed that the conserved catalytic triplet structure (Ser140, His284, and Asp254) acted as active sites and participated in degrading PMEs. This study provided novel insights into the mechanisms of PAEs degradation at a molecular level and widened the scope of functional bacteria by isolating strain E3.

Contamination and health risk assessment of heavy metals in China's lead-zinc mine tailings: A meta-analysis.

The lead-zinc areas of China have faced serious foulteousqulated heavy metal pollution. In this study, data on As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn concentrations in China's lead-zinc mine tailings were collected and screened from published literature (2015-2020). The contamination assessments, geographical distributions, and health risk assessments of the eight heavy metals were analyzed. The results revealed that the mean concentrations of As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn exceeded the corresponding background values for soils. Moreover, most of the lead-zinc mine tailing areas contaminated by heavy metals were located in the southern and eastern regions of China. The health risk assessment results indicated that oral ingestion was the main exposure route of heavy metals in the mine tailings, and children were more vulnerable to adverse effects. For a single metal, As and Pb presented high non-carcinogenic risks, and As and Cu presented the unacceptable carcinogenic risks. This study provides a timely analysis proving the urgent necessity of the treatment of heavy metal pollution in lead-zinc tailings in China.

Barrier effect of coal bottom ash-based geopolymers on soil contaminated by heavy metals.

Coal bottom ash (CBA) was modified on the basis of the engineering problems of low resource utilization of CBA and difficulty in treating HMS through alkali activation to synthesize geopolymers and solidify heavy metal-contaminated soil (HMS). The optimal values of geopolymers were selected through response surface methodology. Their mineral compositions, microstructure, and binding energy were determined through X-ray diffraction, X-ray photoelectron spectroscopy, and scanning electron microscopy tests, respectively. The stress-strain curve, the leaching concentration and fraction of heavy metals, and the solidifying mechanism for remolded soil were determined through unconfined compressive strength, leaching toxicity, sequential chemical extraction, and infrared (IR) spectroscopy tests, respectively. Based on these experiments, the following conclusions were presented. The optimum ratios of CBA-based geopolymers were n(Si) : n(Al) = 2.666, n(Na) : n(Al) = 0.687, and n(water) : n(binder) = 2.422. The X-ray curves of the geopolymers were obvious hump-like protuberances at diffraction angles of 20-35° and had a dense amorphous structure on the surface. The maximum binding energies of Si 2p and Al 2p decreased to 101.03 and 72.89 eV, respectively. A 3D network polymerized because of strong geopolymerization. The maximum axial stress of the remolded soil was 104.91% higher than that of the undisturbed soil, and the leaching concentration decreased by more than 45.88%. The leaching toxicity met the requirements of standard GB 5085.3-2007. The proportion of the acid-extractable fraction of heavy metals in the remolded soil decreased, whereas the proportion of residual fraction increased. The stretching vibration of Si-O-Si (Al) and the bending vibration of Si-O-Si appeared in the IR spectrum. The soil particles were completely encapsulated by a hardened geopolymer structure, thereby forming a multilayer space-skeleton barrier structure that could greatly improve the mechanical properties.