Synergistic Effect In Reduction Research Articles

Necessary CO2 emissions improvement based on rural residential coal/stove-specific coal combustion and prefectural-differentiation synergistic effect of pollutants and carbon emission reduction

Rural residential coal combustion (RRCC) is an important CO2 emission source in rural areas and these emissions vary greatly by coal and stove types. The lack of CO2 emission estimations for different coal-stove combinations restricts refinement and region-differentiated synergistic reduction of pollution and CO2 emissions from RRCC. This study established the coal and stove specific CO2 emissions inventory of RRCC based on investigated coal combustion of various coal and stove types, taking the region of Hebei in China as an example. The synergistic reduction effect of CO2 and pollutants was evaluated using 4 emission reduction scenarios. CO2 emission was 67.4% higher than estimates of RRCC based on the Statistical Yearbook and IPCC emission factors. The combination of bituminous coal and an advanced coal stove was the greatest contributor (62.1%) to CO2 emissions. Bituminous coal burnt in home Arcola has the highest per capita hourly and per unit calorific value CO2 emission, 2.3 and 2.4 times higher than the combination of anthracite briquette coal and pit coal stove and the combination of bituminous coal and an advanced coal stove, respectively. Except for NOx and CO, the coal-stove combination with the lowest per capita hourly and per unit calorific value emissions is anthracite briquette coal and an advanced coal stove. Scenario analysis shows that updated coal stoves feature the highest pollutant emission reduction, but greater CO2 and NOX emissions. For individual cities, synergistic pollution and carbon reduction is seen in Tangshan and Qinhuangdao, and organic carbon, CO, and SO2 have better synergistic positive reduction with CO2, while NOX has shown a negative effect with CO2 in other cities with the best coal and stove update scenario. Compared with the coal and stove update scenario, emission reduction effects with clean fuel substitution varies across cities. This study is helpful to understand the possible non-synergy of pollutant and CO2 reduction in the process of RRCC management. Attention should be given to issues related to the synergistic control plan of pollution and CO2 reduction for RRCC with local adaptation.

Selenium–phosphorus modified biochar reduces mercury methylation and bioavailability in agricultural soil

Biochar is a frequently employed for solidifying and stabilizing mercury (Hg) contamination in soil. However, it often results in an elevated presence of soil methylmercury (MeHg), which introduces new environmental risks. Consequently, there is a necessity for developing a safer modified biochar for use in Hg-contaminated soil. This study employed sodium selenite (at a safe dosage for soil) and hydroxyapatite to modify straw biochar (BC) based on the interaction between selenium (Se) and phosphorus (P). This process led to the formation of Se-modified biochar (Se-BC), P-modified biochar (P-BC), and Se and P co-modified biochar (Se-P-BC). Additionally, solvent adsorption experiments and pot experiments (BC/soil mass ratio: 0.5 %) were conducted to investigate the impacts of these soil amendments on soil Hg methylation and bioavailability. Se and P co-modification substantially increased the surface area, pore volume, and Hg adsorption capacity of BC. BC treatment increased the simulated gastric acid-soluble Hg, organo-chelated Hg, and MeHg in the soil. Conversely, Se-P-BC significantly reduced these forms of Hg in the soil, indicating that Se-P-BC can transform soil Hg into less bioavailable states. Among the different biochar treatments, Se-P-BC exhibited the most pronounced reductions in soil MeHg, total Hg, and MeHg in water spinach, achieving reductions of 63 %, 71 %, and 70 %, respectively. The co-modification of Se and P displayed a synergistic reduction effect in managing soil Hg pollution, which is associated with the increase of available Se in the soil due to phosphorus addition. The significantly reduced dissolved organic carbon and the abnormally high SO42− concentration in the soil of Se-P-BC treatment also inhibited Hg methylation and bioavailability in the soil. In summary, Se-P-BC substantially increased reduction percentage in plant Hg content while mitigating the risk of secondary pollution arising from elevated soil MeHg.

The synergistic reduction effect of PM2.5 and CO2: evidence from national key ecological functional areas in China.

China faces the dual pressure of haze pollution control and carbon emission reduction. The goals of national key ecological functional areas (NKEFAs) are to improve ecological quality and enhance ecological supply. In this paper, a time-varying difference-in-differences model is used to assess the impact of NKEFAs on PM2.5 and CO2 by the panel data of prefecture-level cities of China and then investigate the synergistic reduction effect. This quasi-natural experiment reveals that NKEFAs can effectively reduce both PM2.5 and CO2 and then achieve the synergistic emission reduction effect. Land use pattern optimization and productivity enhancement are identified as key drivers for promoting this synergistic effect. This effect is observed in NKEFAs of water conservation and soil conservation types, as well as in the northern region, middle and lower reaches of the Yangtze River, and southeast coastal areas of the southern region. This study provides valuable theoretical references and empirical insights for realizing a synergistic status of environmental improvement and low-carbon transformation.

Process Path for Reducing Carbon Emissions from Steel Industry—Combined Electrification and Hydrogen Reduction

This review focuses on the energy structure of iron and steel production and a feasible development path for carbon reduction. The process path and feasible development direction of carbon emission reduction in the iron and steel industry have been analyzed from the perspective of the carbon–electricity–hydrogen ternary relationship. Frontier technologies such as “hydrogen replacing carbon” are being developed worldwide. Combining the high efficiency of microwave electric-thermal conversion with the high efficiency and pollution-free advantages of hydrogen-reducing agents may drive future developments. In this review, a process path for “microwave + hydrogen” synergistic metallurgy is proposed. The reduction of magnetite powder by H2 (CO) in a microwave field versus in a conventional field is compared. The driving effect of the microwave field is found to be significant, and the synergistic reduction effect of microwaves with H2 is far greater than that of CO.

Analysis of emission evolution and synergistic reduction effect of air pollutants and CO2 from Chinese coal-fired power plants

The coal-fired power industry is the largest coal-consuming sector in China, and it serves as a significant source of air pollutants and carbon emissions. In this study, we investigated the evolution of air pollutants and CO2 emissions originating from coal-fired power plants (CFPPs) from 2013 to 2020 based on a unit-based bottom-up inventory, and then we quantitatively assessed their combined reduction effects from 2013 to 2060. Our findings indicated that air pollutant emissions experienced a rapid decrease from 2013 to 2020, with nearly 46.0%–64.2% of the reduction occurring within the years 2013–2017. However, CO2 emissions displayed a slight increase during the same period. The top five provinces with the most robust synergistic reduction effects for both air pollutants and CO2 were Jiangsu, Hebei, Henan, Shanxi, and Shandong. The primary measures to the reduction in CO2 emissions were energy structure adjustment and energy conservation and consumption reduction. By 2060, emissions of PM2.5, SO2, NOx, Hg, and CO2 had decreased by 57.9–92.1%, 26.0–80.6%, 18.1–69.4%, 26.6–86.3%, and 35.8–76.1% compared to the levels in 2020, respectively. As the emission reduction process advanced, the reduction effect on CO2 became more pronounced within the synergistic process. We believe that our highly detailed emission inventory comprehensively captures the historical evolution of PM2.5, SO2, NOx, Hg, and CO2 emissions from CFPPs. Furthermore, the scenario analysis results we have obtained will be instrumental in supporting policy development aimed at achieving the synergistic reduction of air pollutants and carbon emissions.

Can Policy Instruments Achieve Synergies in Mitigating Air Pollution and CO2 Emissions in the Transportation Sector?

The transportation sector has significantly contributed to greenhouse gas and air pollutant emissions. Consequently, there is an urgent need to investigate strategies to synergize the reduction in CO2 and pollutant emissions in this sector. Using panel data from 30 provinces in China over the period from 2005 to 2018, this study employs spatial econometric models and mediation effect models to investigate the synergistic effects of carbon markets and environmental regulations on carbon reduction and pollution control in the transportation sector, along with the underlying transmission mechanisms. The results are as follows: (1) Carbon markets can achieve synergistic reduction effects in both CO2 emissions and pollutant emissions, whereas environmental regulations can reduce pollutant emissions alone in the transportation sector. (2) The synergistic reduction effects of carbon markets and environmental regulations in the transportation sector exhibit regional heterogeneity. The central region can realize synergistic reductions, while the western and eastern regions may experience an increase in CO2 and pollutant emissions and cross-regional transfers. (3) Carbon markets can achieve synergistic reduction effects in the transportation sector by influencing the industrial structure at the provincial level, transportation supply and demand at the sectoral level, and green willingness at the individual level.

Has China achieved synergistic reduction of carbon emissions and air pollution? Evidence from 283 Chinese cities

Confronted with the dual pressures of carbon emissions and air pollution, examining their synergistic effects becomes increasingly paramount in China. This study verifies and quantifies the bidirectional synergistic effects between reductions in carbon emissions and air pollutants (SO2 and PM2.5) at the city level. We also analyzed the spatial spillover of this effect among cities, investigating the dynamic evolution, heterogeneity, and underlying mechanisms of both synergistic reduction and increase effects across different time scales. Key findings include: 1) Carbon emission mitigation causes greater synergistic reduction effect than pollution reduction; 2) Carbon emission reduction has a more significant synergistic effect on SO2 than PM2.5; 3) Synergistic effects vary across city types. Cities with higher resource endowments, lower administrative levels, smaller populations, and lower economic status show greater synergistic effects; 4) The synergistic effects demonstrate significant positive spatial spillovers across cities, with local reductions in carbon and sulfur emissions spurring sulfur emission reductions in neighboring regions; 5) Synergistic reduction effects between carbon and air pollutant emissions exhibit temporal delays, while their synergistic increase effects are pronounced in both short and long terms; 6) R&D investment mitigates synergistic increase effects, while the impact of energy efficiency on synergistic reduction effects shows an inverted U-curve relationship. Our findings offer valuable insights for policymakers seeking to simultaneously tackle climate change and environmental pollution more effectively.

New insights into the degradation of nitrobenzene by activated persulfate with sulfidated nanoscale zero-valent iron: Synergistic effects of reduction and reactive oxygen species oxidation

In recent years, nitrobenzene (NB) leakage has emerged as one of the most pressing environmental issues related to groundwater contamination that requires immediate attention. This study aimed to combine S-nZVI reduction with persulfate (PDS) oxidation for NB degradation in aquatic environment. The strong synergistic effect of reduction and oxidative degradation of NB in the S-nZVI/PDS system was demonstrated for the first time. To throughly investigate the mechanism of PDS activation by S-nZVI, chemical quenching tests, detection of electron spin resonance (ESR), and monitoring of oxidant consumption were conducted. According to the results, the reactive oxygen species in the reaction system originated predominantly from the presence of ≡Fe2+ on the surface of S-nZVI and from the free state of Fe2+ in the co-activation of PDS in solution. The main role of S(-II) on the surface of S-nZVI is to enhance the electron transfer ability and act as an electron donor to facilitate the conversion between Fe2+ and Fe3+. In addition, density functional theory calculations was used to reveal the reactive sites of NB and clarify the possible degradation pathways of NB. The results of this study will deepen the understanding of the mechanism of S-nZVI driven persulfate activation and provide fundimental support for the future practical application of the S-nZVI/PDS system for the remediation of nitrobenzene contaminated groundwater.

One-step leaching mechanism for total elemental recovery from spent lithium-ion batteries utilizing ethylene diamine tetraacetic acid

A process capable of leaching full component valuable metals including Ni, Co, Mn, and Li from spent lithium-ion batteries (LIBs) without additional reducing agents has been proposed. As a strong chelating organic acid, ethylene diamine tetraacetic acid (EDTA) is suitable for recovering up to 99.9 % of each metal element under optimal conditions of EDTA concentration of 0.5 M, liquid-solid ratio of 30:1 mL g−1, the temperature of 353 K, and leaching duration of 2 h. Kinetic analysis shows that the entire leaching process is controlled by the chemical reaction, accompanied by the apparent activation energy of 56.6 kJ mol−1 for Ni, 68.2 kJ mol−1 for Co, 49.5 kJ mol−1 for Mn, and 53.0 kJ mol−1 for Li, respectively. The thermodynamic mechanism indicates that EDTA acts as a proton chelating agent and Fe/Al exhibits a synergistic reduction effect during leaching process. In addition, the whole process is divided into three stages, where the behavior of each substance is specified. The individual ions in the leachate are separated by precipitation with different reagents and the filtrate can be recycled for the next stage of leaching, which also provides a novel approach for an industrial one-step leaching process.

Cooperation between specialized cropping and livestock farms at local level reduces carbon footprint of agricultural system: A case study of recoupling maize-cow system in South China

Decoupling of crop and livestock production has become increasingly common in the world during to past decades. The cooperation between specialized crop and livestock farms have been paid more attention for the development of sustainable agriculture. This study assumed that rebuilding the linkage between specialized crop and livestock farms through cooperation at the local level would decrease agricultural GHG emissions. Therefore, we designed a cooperative crop-livestock farming model (CCLS) in South China by recoupling the cow farm with the sweet maize cultivation farms around it to demonstrate the hypothesis based on carbon footprint (CF) method. The CFs under two cooperative scenarios (CCLS20 and CCLS50) were compared with the corresponding decoupling models (DCLS20 and DCLS50). Results showed that CCLS significantly reduced GHG emissions from cropping systems in comparison to DCLS primarily by increasing the soil organic carbon storage while decreasing accumulative N2O emissions. In specific, the CFs of CCLS20 and CCLS50 were 48.78% and 623.34% lower than DCLS20 and DCLS50, respectively. The yield-based CFs of CCLS20 and CCLS50 were 66.30% and 165.99% lower than DCLS20 and DCLS50, respectively. Meanwhile, the CF of the cow farm in CCLS20 and CCLS50 were 8.80% and 8.22% lower than that in DCLS20/50 by lowering relative GHG emissions of straw supply in roughage forage and shortening manure storage time in the manure management process. Finally, the yield-based CF in CCLS20 and CCLS50 were 67.68% and 168.51% lower than the DCLS20 and DCLS50, respectively, demonstrating that the cooperation between specialized planting and livestock farms at local level reduced the CF of the agricultural production chain by the synergistic reduction effects of GHG emissions in cropland, livestock rearing and transportation processes. The results would provide a quantitative understanding of the net GHG emission of cooperative crop-livestock system at the local level in China and valuable information for the development of sustainable farming system in the world.

Study on the synergistic effect of air pollution prevention and carbon emission reduction in the context of "dual carbon": Evidence from China's transport sector

The transportation sector has significantly contributed to greenhouse gas and air pollutant emissions. Based on the Kaya constant equation and the LMDI decomposition model, A synergistic reduction effect model of transportation tailpipe Environmental negative externalities emissions is constructed to adopt the inter-provincial panel data of China from 2005 to 2019. The synergistic reduction emission impact and indirect drivers between air pollution and carbon emission are analyzed. The results show that the drivers of the synergistic impact are mainly energy efficiency and industrial structure. Significant synergistic emission reduction effects exist in eastern China, western China, medium-sized transportation markets, and less developed tourism regions. Further, increasing environmental regulation can improve the synergistic reduction impact of the transportation sector's air pollutants and carbon emissions. This paper provides theoretical support for winning the battle of pollution prevention and control and achieving the "dual carbon" goal in the new era.

Microwave-ultra-fast recovery of valuable metals from spent lithium-ion batteries by deep eutectic solvents

The large-scale use of electric vehicles produced massive discarded lithium-ion batteries, containing many recyclable valuable metals and toxic and harmful substances. Biodegradable and recyclable deep eutectic solvent (DES) is considered a green recycling technology for spent LIBs. Herein, we proposed a microwave-enhanced approach to shorten the leaching time in the urea/lactic acid: choline chloride: ethylene glycol DES system. The dipole moments induced by urea or lactic acid on LiCoO2 surface increased over two orders of magnitude under the high electric field. Because of this, over 90 % of Li and Co can be fast leached at 4 min and 160 W in the urea/lactic acid: choline chloride: ethylene glycol DES system. Meanwhile, we established two models to explain the leaching mechanism of metal ions from their leaching kinetics and micro-level behavior, and named them dot-etching and layer-peeling processes, respectively. By further analyzing, we found that the dot-etching can be attributed to the synergistic effect of reduction and coordination, which caused the surface of leaching residues porous. The layer-peeling process depends on neutralization, and the leaching residues had a smooth surface in this process. This work highlights the effect of microwave-enhanced strategy and DES surface chemistry on spent electrode materials recovery.

A 2D mesoporous hydrazone covalent organic framework for selective detection and ultrafast recovery of Au(III) from electronic waste

Developing a material that can simultaneously detect and recover Au(III) is economically desirable. Herein, we constructed a two-dimensional mesoporous fluorescent covalent organic framework named TY-Hz COF by integrating 1,3,6,8-tetra(4-formylphenyl)pyrene (TY) and terephthalic dihydrazide (Hz) into a π-conjugated framework for simultaneous detection and recovery of Au(III). The TY-Hz COF suspension can rapidly (10 s) and sensitively response to Au(III) with electron transfer-induced fluorescence quenching and visual color change from bright yellow to dark green, and the limit of detection is as low as 17 nM. Moreover, TY-Hz COF can capture more than 92 % Au(III) in the solution with extremely fast kinetics (within 2 min) and excellent selectivity with a maximum adsorption capacity of 1008.30 mg g−1. It is worth mentioning that TY-Hz is the first type of COF that achieves Au(III) detection, adsorption and chemical reduction simultaneously. Mechanistic studies reveal that the detection and adsorption behaviors can be attributed to the synergistic effect of reduction, coordination interaction between neutral amide functional groups and Au(III), and hydrogen bonding between protonated amides and AuCl4-. These results suggest that TY-Hz COF shows great potential for Au(III) detection and recovery in electronic waste (e-waste).

Cr(VI) adsorption and reduction by magnetite-humic acid adsorption complexes under mildly acidic conditions: Synergistic/antagonistic mechanism and multi-step reaction model

Ubiquitous Fe-OM complexes in subsurface environments have substantial retention effects on Cr(VI) migration; however, whether these effects follow the superposition principle remains unclear, particularly for Fe(II)-containing minerals. In this study, Cr(VI) adsorption and reduction by magnetite-humic acid (HA) adsorption complexes (MHAs) were investigated under mildly acidic conditions, and MHAs were found to have antagonistic adsorption and synergistic reduction effects on Cr(VI). Based on the Raman mapping characterization, the MHAs surface was extremely heterogeneous, consisting of two types of sites: (A) magnetite covered by HA and (B) bare magnetite without HA. Owing to the coverage of the magnetite surface by HA, the adsorption and reduction by magnetite was depressed with an antagonistic efficiency of 8 %–70 %, varying with the amount of adsorbed HA. In contrast, the synergistic reduction of Cr(VI) by the HA component at site (A) was observed, resulting in a synergistic factor of up to 44, which could be attributed to the molecular fractionation and functionality activation of HA on the magnetite surface according to the fluorescence excitation-emission matrix combined with parallel factor analysis and density functional theory calculations. Accordingly, a multi-step kinetic model of Cr(VI) adsorption and reduction by MHAs based on antagonistic and synergistic effects was established to quantitatively simulate the Cr(VI) interfacial behavior (R > 0.9). This study is instructive for accurately assessing the effect of Fe-OM complexes on Cr(VI) migration and benefits the development of remediation materials for Cr(VI)-contaminated soils and groundwater.

Reaction characteristics and kinetics of phosphogypsum decomposition via synergistic reduction effect of composite reducing agent

Reaction characteristics and kinetics of phosphogypsum decomposition via synergistic reduction effect of composite reducing agent

Reaction mechanism of antibiotic bacteria residues as a green reductant for highly efficient recycling of spent lithium-ion batteries

In this study, antibiotic bacteria residues (ABRs) is proposed as a novel green reducing agent and it is found that the reducing agent can realize the efficient recovery of the valuable metals in spent cathode powder (SCP), reduce the environmental pollution and realize the high-value utilization of the biomass waste. The leaching efficiency of Ni, Co, Mn and Li can reach 99.57%, 98.50%, 98.99% and 99.90% respectively under the optimal conditions of 3 mol L−1 H2SO4, mass ratio of ABRs to SCP of 0.8:1, liquid/solid ratio of 30:1 mL g−1, the temperature of 363 K and time of 2.5 h. Leaching kinetics results shows that the reaction process is controlled by the chemical reaction with apparent activation energy exceeding than 40 kJ/mol. More importantly, the detailed ABRs leaching mechanism is proposed that the metabolite of CaC2O4 and reducing sugar in ABRs provide a synergistic reduction effect on the recovery of valuable metals. Furthermore, acid leaching residue can be regenerated to obtain lithium-ion anode materials with excellent electrochemical properties. The entire process is a sustainable green recycling strategy by using waste ABRs waste to treat spent lithium-ion batteries (LIBs), recovering valuable metals efficiently and minimizing environmental pollution.

Beneficial effects of Se/Zn co-supplementation on body weight and adipose tissue inflammation in high-fat diet-induced obese rats.

This research investigated the effect of co‐supplementation of selenium with zinc on weight control and the inflammatory and oxidative status in relation to obesity. Male Wistar rats (N = 32) were randomly divided into four groups after induction of obesity model: 1) “Zn” was supplemented with zinc sulfate (15 mg/kg BW), 2) “Se” supplemented with selenium as sodium selenate (0.5 mg/kg BW), 3) “Zn + Se” which received Zn (15 mg/kg BW) + Se (0.5 mg/kg BW), and 4) “HFD” as the control group. The intervention was done for eight weeks. At the end of treatment, serum and tissue level of Zn, Se, SOD, GSH‐Px, MDA, leptin, TNF‐α, and IL‐6 was evaluated. Weight and food intake were significantly reduced in the Se group(p < .001), while in the Zn group, weight gain due to obesity was prevented compared to the control group (p = .48). There was a significant and stronger increase in SOD, GSH‐Px levels and a remarkable decrease in MDA, leptin, TNF‐α, and IL‐6 in the group receiving the combination of two supplements than either alone(p < .001). Leptin had a positive correlation with inflammatory factors and lipid peroxidation marker and showed an inverse relationship with Zn and Se levels and anti‐oxidative enzymes(p < .05). The analysis showed the mediating role of leptin in the effects of zinc. Co‐supplementation of selenium and zinc may have a synergistic effect in reduction of oxidative and inflammatory markers. Regarding the effect of zinc on inflammatory factors and lipid peroxidation, leptin can play a mediating role.

A novel preparation of S-nZVI and its high efficient removal of Cr(VI) in aqueous solution

The chitosan-stabilized biochar supported S-nZVI (CS@BC/S-nZVI) composite with low aggregation and superior antioxidation were successfully synthesized by liquid-phase reduction method for the outstanding removal of Cr(VI) from wastewater and characterized by SEM, BET, FTIR, XRD, and XPS. The optimized synthesis parameters of CS@BC/S-nZVI were determined as a 0.14 molar ratio of S/Fe and a 0.25 mass ratio of BC/Fe. The CS@BC/S-nZVI possessed a specific surface area of 199.246 m2/g and an average pore size and pore volume of 1.186 nm and 0.272 cc/g. The CS@BC/S-nZVI could remain reductive activity after Cr(VI) removal and present a remarkable tolerance to the coexisting ions during Cr(VI) removal. The adsorption data were fitted well by the pseudo-second order model and the Langmuir model. The removal of Cr(VI) by CS@BC/S-nZVI was an exothermic process with prominent Cr(VI) removal capacities of 244.07 mg/g at 120 min and 221.84 mg/g at 15 min at 25 ℃. Further mechanism analysis proved that the binding of Cr(VI) to CS@BC/S-nZVI was mainly a synergistic effect of reduction and electrostatic attraction. Overall, these findings shed new light on the research of a novel S-nZVI compound and revealed the potential practical application of CS@BC/S-nZVI in the future heavy metal removal from wastewater.

Effect of the reduction–mineralization synergistic mechanism of Bacillus on the remediation of hexavalent chromium

Through the synergistic effect of reduction and mineralization by Bacillus strain T124, hexavalent chromium (Cr(VI)) is reduced to a state with lower toxicity, where stable mineralization occurs, and this results in the reduction of the migration and bioavailability of Cr(VI) in the environment. In this study, a chromium (Cr)–resistant mineralization strain, Bacillus thuringiensis T124, was selected from the soil around an electroplating company, and the mechanism underlying the reduction–mineralization of Cr by this strain was studied. The reduction process mainly occurred on the cell wall membrane. The reducing enzymes were found in each component of the strain; however, a majority of them were internal. The strain could tolerate and reduce the toxicity of Cr toward itself. On fitting the data to enzyme kinetics, the K m was found to be 2925.03 μmol·L −1 , V m was 7.48 mg·(h·L) −1 , and urease activity was 66.4 U·mL −1 . The final mineralization of Cr(VI) by the strain yielded CaCO 3 and Ca 10 Cr 6 O 24 (CO 3 ). The proposed mechanism is that Cr(VI) is reduced by biological reductase, which reduces the toxicity of Cr and indirectly increases urease activity of the strain. Urease can decompose the substrate to form a CaCO 3 precipitate with Ca(II). Cr replaces a part of the lattice of CaCO 3 to mineralize Cr, thereby forming a Ca Cr coprecipitate. These minerals occupy a part of the binding site of the strain. The reduction–mineralization synergistic mechanism thus plays an important role in the immobilization of Cr(VI) on the cell wall of the strain. • Bacillus strain T124 reductase can reduce Cr(VI) to Cr(III), reducing the toxicity of Cr. • The Cr ion was captured during the formation of CaCO 3 and fixed in the lattice. • Cr(VI) can be fixed as Ca 10 Cr 6 O 24 (CO 3 ), with a good crystal form and stable structure. • The reduction-mineralization system has a synergistic effect, which can better repair Cr (VI).

Synergistic/antagonistic effects and mechanisms of Cr(VI) adsorption and reduction by Fe(III)-HA coprecipitates

Widespread Fe(III)-humic acid (HA) coprecipitates (FHCs) have substantial impacts on the adsorption and reduction of Cr(VI) in soils and sediments, but whether this process is equal to the sum of their individual components remains unknown. In this study, ferrihydrite (Fh)- and HA-like FHCs (C/Fe<3 and C/Fe>3, respectively) were synthesized by controlling the initial C/Fe ratios (0.5–18) to explore the potential synergistic/antagonistic effects during the adsorption and reduction of Cr(VI). According to the results, antagonistic effects on Cr(VI) adsorption (5%−80%) were observed on Fh- and HA-like FHCs, where the antagonistic intensity increased with increasing HA proportions, respectively caused by the more serious occupation of adsorption sites and the stronger electrostatic repulsion to Cr(VI). Notably, significant synergistic reduction effects (5%−650%) occurred on Fh-like FHCs were found to be achieved by the activation of low-molecular HA (0.1–0.3 kDa) with primary/secondary hydroxylic groups, which might be induced by the inductive effect of Fh on complexed HA molecules according to density-functional theory (DFT) calculation. While slight antagonistic reduction effects (2%−45%) by HA-like FHCs were attributed to the decreasing accessibility of Cr(VI) to reductive phenolic groups, which might be blocked within FHC particles or complexed with Fe(III) ions through cation bridges.