Preparation of non-sintered permeable bricks using electrolytic manganese residue: Environmental and NH3-N recovery benefits

Synergistic solidification and mechanism research of electrolytic manganese residue and coal fly ash based on C-A-S-H gel material

Electrolytic manganese residue (EMR) is known for high concentrations of Mn2+, NH4+, and heavy metals. Failure to undergo benign treatment and landfill disposal would undeniably lead to negative impacts on the quality of the surrounding ecological environment. This study sought to mitigate the latent environmental risks associated with EMR using a cooperative solidification/stabilization (S/S) method involving coal fly ash (CFA). Leveraging leaching toxicity tests, the leaching behavior of pollutants in electrolytic manganese residue-based geopolymer materials (EMRGM) was determined. At the same time, mechanistic insights into S/S processes were explored utilizing characterization techniques such as XRF, XRD, FT-IR, SEM-EDS, and XPS. Those results confirmed significant reductions in the leaching toxicities of Mn2+ and NH4+ to 4.64 μg/L and 0.99 mg/L, respectively, with all other heavy metal ions falling within the permissible limits set by relevant standards. Further analysis shows that most of NH4+ volatilizes into the air as NH3, and a small part is fixed in the EMRGM in the form of struvite; in addition to being oxidized to MnOOH and MnO2, Mn2+ will also be adsorbed and wrapped by silicon-aluminum gel together with other heavy metal elements in the form of ions or precipitation. This research undeniably provides a solid theoretical foundation for the benign treatment and resourceful utilization of EMR and CFA, two prominent industrial solid wastes.

Enabling efficient and economical degradation of PCDD/Fs in MSWIFA via catalysis and dechlorination effect of EMR in synergistic thermal treatment

Catalytic thermal treatment is an efficient and low-energy consumption method for degrading polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) in municipal solid waste incineration fly ash (MSWIFA). However, catalysts with high activity are expensive, difficult to separate and reuse from the treated MSWIFA, and they usually pose a risk of heavy metal pollution. Herein, a synergistic thermal treatment method of MSWIFA and electrolytic manganese residue (EMR) at relatively low temperatures was proposed after an in-depth analysis of their mineralogy composition to achieve detoxification of PCDD/Fs in MSWIFA. The mass and WHO-TEQ degradation efficiencies of PCDD/Fs significantly increased from -92.79% and -51.46%-98.57% and 96.10%, respectively, by the addition of electrolytic manganese residue (EMR) with an MSWIFA/EMR ratio of 3:7 in the thermal treatment of MSWIFA at 250 °C for 60 min. The WHO-TEQ concentration of PCDD/Fs in the treated sample decreased to 3.7 ng WHO-TEQ/kg, meeting the European end-of-waste criteria (20 ng WHO-TEQ/kg). The excellent degradation effect of EMR on PCDD/Fs in MSWIFA could be attributed to two aspects: 1) the manganese oxides in EMR has a catalytic effect on the degradation of PCDD/Fs; 2) the NH3 generated by the decomposition of (NH4)2SO4 in EMR is conducive to the degradation and resynthesis inhibition of PCDD/Fs. Besides, the thermodynamic calculations indicated that CaClOH in MSWIFA played a crucial role in the decomposition of (NH4)2SO4 in EMR. In addition, the degradation pathways and mechanisms of PCDD/Fs-homologues under the synergistic effect of manganese oxides, ammonia, and thermal field were investigated through comparative analysis of concentration and fingerprint of PCDD/Fs.

Innovative co-treatment technology for effective disposal of electrolytic manganese residue

Electrolytic manganese residue (EMR) stockpiles contain significant amounts of Mn2+ and NH4+-N which pose a risk of environmental pollution. For EMR safe disposal, an innovative approach is proposed that involves direct sodium silicate-sodium hydroxide (Na2SiO3-NaOH) collaborative technology. This approach utilises Na2SiO3 and NaOH as the solidifying agent and activator, respectively, to treat EMR without hazardous effects. The study also provides insights into the kinetics of Mn2+ leaching under the effect of Na2SiO3-NaOH. Leaching efficiency was determined by varying parameters such as stirring rate, reaction temperature, pH of the initial solution, Na2SiO3 concentration, and reaction time to investigate the efficacy of this method. The study indicates that the co-treatment technology of Na2SiO3-NaOH can achieve maximum solidification efficiencies of 99.7% and 98.2% for Mn2+ and NH4+-N, respectively. The process can successfully solidify Mn2+ by synthesising Mn(OH)2 and MnSiO3 in an alkaline environment under optimal conditions including stirring rate of 450 rpm, initial solution pH of 8, test temperature of 40 °C, test time of 420 min, and Na2SiO3 content of 5%. The findings of this study have confirmed that surface chemistry plays a vital role in regulating the test rate and the proposed equation accurately describes Mn2+ leaching kinetics. Overall, the co-treatment technology involving Na2SiO3-NaOH is a viable solution for EMR resource utilisation without compromising environmental safety. This method has the potential to be implemented for other waste streams with comparable compositions, ultimately promoting the sustainable management of waste.

Study of microscopic properties and heavy metal solidification mechanism of electrolytic manganese residue-based cementitious materials

Electrolytic manganese residue (EMR) is a solid waste that contains a significant amount of soluble manganese and ammonia nitrogen, which can pose risks to human health if improperly disposed of. This study aimed to prepare cementitious materials containing abundant ettringite crystals by mixing EMR with various proportions of granulated blast furnace slag (GBFS) and alkaline activators (CaO, Ca(OH)2, clinker, NaOH). The resulting cementitious material not only utilized a substantial amount of EMR but also exhibited comparable strength to ordinary Portland cement. The optimal ratios were determined through mechanical testing. Additionally, the leaching toxicity of cementitious materials was assessed using ICP-MS (inductively coupled plasma mass spectrometer) tests. The microscopic properties, hydration, and mechanism of heavy metal solidification in the cementitious materials were evaluated using XRD (X-ray diffraction), SEM (scanning electron microscope), EDS (energy-dispersive spectrometer), FTIR (Fourier transform infrared spectroscopy), and TG (thermogravimetric) techniques. The results showed that the optimal ratio for the cementitious materials was 60% EMR, 36% GBFS, and 4% Ca(OH)2. The hardened mortar exhibited compressive strengths of 34.43 MPa, 41.3 MPa, and 50.89 MPa at 3 days, 7 days, and 28 days, respectively, with an EMR utilization rate of 60%. The hydration products of EMR-based cementitious materials were C-(A)-S-H, AFt, and ferromanganese compounds, which contribute to the mechanical strength. The Mn2+ and NH4+-N contents of raw EMR were 1220 and 149 mg/L, respectively. Nonetheless, the leaching of Mn2+ and NH4+-N in the alkali-EMR-GBFS system was significantly below the limits set by the Chinese emission standard GB8978-1996. Within this system, C-(A)-S-H and AFt could physically adsorb and displace heavy metals, Ca6Mn2(SO4)2(SO3)2(OH)12·24H2O could replace Al ions with Mn ions, and ferromanganese compounds Fe2Mn(PO4)2(OH)2·(H2O)8 and MnFe2O4 could chemically precipitate Mn2+.

Study on the Performance and Mechanism of Cement Solidified Desulfurization Manganese Residue

Desulfurized manganese residue (DMR) is an industrial solid residue produced by high-temperature and high-pressure desulfurization calcination of electrolytic manganese residue (EMR). DMR not only occupies land resources but also easily causes heavy metal pollution in soil, surface water, and groundwater. Therefore, it is necessary to treat the DMR safely and effectively so that it can be used as a resource. In this paper, Ordinary Portland cement (P.O 42.5) was used as a curing agent to treat DMR harmlessly. The effects of cement content and DMR particle size on flexural strength, compressive strength, and leaching toxicity of a cement-DMR solidified body were studied. The phase composition and microscopic morphology of the solidified body were analyzed by XRD, SEM, and EDS, and the mechanism of cement-DMR solidification was discussed. The results show that the flexural strength and compressive strength of a cement-DMR solidified body can be significantly improved by increasing the cement content to 80 mesh particle size. When the cement content is 30%, the DMR particle size has a great influence on the strength of the solidified body. When the DMR particle size is 4 mesh, the DMR particles will form stress concentration points in the solidified body and reduce its strength. In the DMR leaching solution, the leaching concentration of Mn is 2.8 mg/L, and the solidification rate of Mn in the cement-DMR solidified body with 10% cement content can reach 99.8%. The results of XRD, SEM, and EDS showed that quartz (SiO₂) and gypsum dihydrate (CaSO₄·2H₂O) were the main phases in the raw slag. Quartz and gypsum dihydrate could form ettringite (AFt) in the alkaline environment provided by cement. Mn was finally solidified by MnO₂, and Mn could be solidified in C-S-H gel by isomorphic replacement.

Study on Physical Properties of Desulfurized Electrolytic Manganese Residue Cement and Properties of Mortar

The desulfurized electrolytic manganese residue (DMR) was prepared by calcination and desulfurization of industrial waste electrolytic manganese residue, and the original DMR was ground to prepare DMR fine powder (GDMR) with specific surface areas of 383 m²/kg, 428 m²/kg, and 629 m²/kg. The effects of particle fineness and content of GDMR (GDMR content=0%, 10%, 20%, 30%) on the physical properties of cement and the mechanical properties of mortar were studied. After that, the leachability of heavy metal ions was tested, and the hydration products of GDMR cement were analyzed using XRD and SEM. The results show that the addition of GDMR can regulate the fluidity and water requirement for the normal consistency of cement, delay the hydration process of cement, increase the initial setting and final setting time of cement, and reduce the strength of cement mortar, especially the strength of early age mortar. As the fineness of GDMR increases, the reduction of bending strength and compressive strength decreases, and the activity index increases. The content of GDMR has a significant effect on short-term strength. With the increase in GDMR content, the strength reduction degree becomes higher and the activity index decreases. When the content of GDMR was 30%, the 3D compressive strength and bending strength decreased by 33.1% and 29%. When the content of GDMR in cement is less than 20%, the maximum limit of leachable heavy metal content in cement clinker can be met.

Progress in comprehensive utilization of electrolytic manganese residue: a review

Electrolytic manganese residue (EMR) is a solid waste produced in the process of electrolytic manganese metal (EMM) production. In recent years, the accumulation of EMR has caused increasingly serious environmental problems. To better understand the state of EMR recycling in recent years, this paper used a comprehensive literature database to conduct a statistical analysis of EMR-related publications from 2010 to 2022 from two perspectives: harmless green treatment and resource utilization. The results showed that the research on the comprehensive utilization of EMR mainly focused on the fields of chemical hazard-free treatment and manufacturing building materials. The related studies of EMR in the fields of biological harmlessness, applied electric field harmlessness, manganese series materials, adsorbents, geopolymers, glass-ceramics, catalysts, and agriculture were also reported. Finally, we put forward some suggestions to solve the EMR problem, hoping that this work could provide a reference for the clean disposal and efficient utilization of EMR.

Release characteristics of heavy metals from electrolytic manganese residue under varying environmental factors

High levels of manganese (Mn) and other heavy metals from electrolytic manganese residue (EMR) stockpiled would be released into the environment under natural conditions. A batch-leaching test was carried out to investigate the release characteristics of heavy metals from EMR with different storage times under simulated environmental conditions such as acid rain with different pH (3.0, 4.5, 5.6, and 7.0) at contact times of 1, 2, 4, 6, and 12 h; liquid to solid ratio (L/S) (5:1, 10:1, 20:1, and 30:1); and temperature (15, 25, 35, and 45 °C). The results showed that low pH (3.0 and 4.5) and high temperature (35 and 45 °C) could significantly promote heavy metal leaching from EMRs and increasing the L/S ratio above 20:1 mL/g significantly decreased heavy metal leachate concentrations due to dilution effect. Cr, Mn, and Pb concentrations in leachate increased almost continuously throughout the leaching process, while Zn decreased slightly at the 12th hour. Meanwhile, heavy metal concentrations in EMR1 (fresh EMR) were higher than in EMR2 (out stockpiled for more than 3 months). The concentrations of Mn, Pb, and Zn in leachates from EMRs at pH 3.0 and 4.5 leaching far exceeded the allowable maximum discharge concentrations for pollutants of the integrated wastewater discharge standard in China (GB8978-1996) by 57.5-59.0, 1.3-4.3, and 1.1-1.8 and 53.5-56.0, 3.04-7.25, and 1.0-1.91 times, respectively. Additionally, the Mn concentrations from both EMR leachates at pH 7.0 were above the national safe emission threshold. The morphological structure of EMRs changed after leaching, and XRD analysis showed the disappearance of MnO₂, SiO₂, FeS₂, and CaSO₄. The XPS revealed that Cr, Mn, Pb, and Zn existed as Cr³⁺, MnO, PbSO₄, and ZnSiO₃, respectively, after leaching. The study concluded that Mn, Pb, and Zn from EMRS leached by acid rain might pose a high potential environmental risk. Therefore, developing appropriate disposal techniques for EMR is necessary to prevent heavy metal pollution.

Effect of Phanerochaete chrysosporium inoculation on manganese passivation and microbial community succession during electrical manganese residue composting

Electrolytic manganese residue poses potentially threats to the environment and therefore needs eco-friendly treatment. Composting has been reported to effectively passivate heavy metals and alleviate their ecotoxicity. Observation of the Mn concentration during composting indicated that the mobility of Mn was significantly reduced, with the easily extraction fraction (acid extractable and easily reduction fraction) of Mn in the control pile (pile 1 without Phanerochaete chrysosporium inoculation) and treat pile (pile 2 with Phanerochaete chrysosporium inoculation) decreasing by 17% and 29%, respectively. The inoculation of Phanerochaete chrysosporium prompted the passivation of manganese, prolonged the thermophilic period, and enriched the microbial community structure, which was attributed to the rapid growth and reproduction of thermophilic bacteria. Moreover, Phanerochaete chrysosporium inoculation promoted the effect of pH on the stabilization of Mn, but the opposite contribution of organic matter. This study would provide a new perspective for remediating EMR contaminated soil via composting.

Manganese Pollution and Its Remediation: A Review of Biological Removal and Promising Combination Strategies

Manganese (Mn), as a cofactor of multiple enzymes, exhibits great significance to the human body, plants and animals. It is also a critical raw material and alloying element. However, extensive employment for industrial purposes leads to its excessive emission into the environment and turns into a significant threat to the ecosystem and public health. This review firstly introduces the essentiality, toxicity and regulation of Mn. Several traditional physicochemical methods and their problems are briefly discussed as well. Biological remediation, especially microorganism-mediated strategies, is a potential alternative for remediating Mn-polluted environments in a cost-efficient and eco-friendly manner. Among them, microbially induced carbonate precipitation (MICP), biosorption, bioaccumulation, bio-oxidation are discussed in detail, including their mechanisms, pivotal influencing factors along with strengths and limitations. In order to promote bioremediation efficiency, the combination of different techniques is preferable, and their research progress is also summarized. Finally, we propose the future directions of Mn bioremediation by microbes. Conclusively, this review provides a scientific basis for the microbial remediation performance for Mn pollution and guides the development of a comprehensive competent strategy towards practical Mn remediation.

Water column leaching recovery manganese and ammonium sulfate from electrolytic manganese residue: extremely low water consumption toward practical applications

Regional contamination by electrolytic manganese residue (EMR) not only composes a serious environmental problem but also leads to severe valuable resources waste. Directly recovering manganese and ammonium sulfate is a promising way, but it is still challenging to efficiently recover without high water consumption. Herein, a recovery method based on water column leaching under extremely low water consumption was firstly reported. The effect of continuous leaching and intermittent leaching on leaching behaviors, leaching trends, and spatial variations of (NH₄)₂SO₄ and Mn with depth after leaching were fully investigated. Results indicated that some Mn-bearing soluble salts which covered on the surface of SiO₂ in the micropores could be fully dissolved and transported out of the micropores in the EMR with the help of rest periods in the method of intermittent leaching, resulting in higher leaching efficiencies with comparison to continuous leaching, 73.50% of Mn and 67.71% of (NH₄)₂SO₄ and 71.57% of Mn and 65.40% of (NH₄)₂SO₄ were recovered by intermittent leaching and continuous leaching, respectively. This work demonstrates a practical approach to recover valuable materials from industrial solid wastes.

Properties and Microstructural Characteristics of Manganese Tailing Sand Concrete

In this work, manganese tailing sand concrete (MTSC) was prepared using manganese tailing sand (MTS) in replacement of river sand (RS) to alleviate the shortage of RS resources and achieve clean treatment and high-value resource utilization of manganese tailing stone. The effects of MTS content on the slump, mechanical strength, air void characteristics, hydration products and micromorphology of MTSC were studied experimentally. The leaching risk of harmful substances in MTSC was also explored by testing the concentration of Mn²⁺. The results show that the utilization of MTS reduces the slump of MTSC to a certain extent. When the MTS content is lower than 40%, the gypsum introduced by MTS and C₃A in cement undergoes a hydration reaction to form ettringite, which decreases the number of pores with a diameter less than 0.1 mm and promotes strength development in MTSC. Additionally, when the MTS content exceeds 40%, the large amount of gypsum reacts to form more ettringite. The expansive stress generated by the ettringite severely damages the pore structure, which is not conducive to the mechanical properties of MTSC. In addition, the leaching of hazardous substances in MTSC is insignificant, and the incorporation of cement can effectively reduce the risk of leaching hazardous substances in MTSC. In summary, it is completely feasible to use MTS to replace RS for concrete preparation when the substitution rate of MTS is less than 40%, with no risk of environmental pollution. The results and adaptation in the concrete industry can reduce the carbon footprint, which is in line with the current trend in civil and materials engineering.

Microstructure, Electromagnetic Properties, and Microwave Absorption Mechanism of SiO2-MnO-Al2O3 Based Manganese Ore Powder for Electromagnetic Protection

Considering the electromagnetic protection needs of important ground buildings, exploring the electromagnetic wave (EMW) absorption performance of manganese ore powder (MOP) building materials is an effective way to overcome its low added value and difficulty in popularizing. Here, choosing filling ratios commonly used in building materials such as autoclaved bricks, MOP/paraffin samples with 20%, 40%, and 60% mass fraction of MOP were prepared, and electromagnetic properties were analyzed at 2−18 GHz using the coaxial method. The results show that 60 wt% sample has the best absorption performance, with a minimum reflection loss (RLmin) value of −22.06 dB at 15.04 GHz, and the effective absorption bandwidth (EAB, RL < −10 dB) reaches 4.16 GHz at a 7.65 mm absorber thickness, covering most of the Ku-band region. The excellent microwave absorption performance of MOP is due to its multi-oxide forming multi-interface structure and rough surface, which can not only form abundant dipole and interfacial polarization under the action of EMW, but also reflect and scatter the incident EMW, prolong the transmission path, and enhanced the absorption of microwaves. This study demonstrates that MOP building materials can have excellent microwave absorption properties, thus becoming a new way to address harmful manganese residue; for example, autoclaved bricks, which can not only improve the added value of manganese residue building materials but also can be consumed on a large scale. It provides a new idea to solve the harm of manganese residue.

Study on the Mechanical and Leaching Characteristics of Permeable Reactive Barrier Waste Solidified by Cement-Based Materials

The durability against wet-dry (w-d) cycles is an important parameter for the service life design of solidified permeable reactive barrier (PRB) waste. This study introduces the potential use of cement, fly ash, and carbide slag (CFC) for the stabilization/solidification (S/S) of PRB waste. In this study, solidified PRB waste was subjected to different w-d cycles ranging in times from 0 to 10. By analyzing the mass loss, the unconfined compressive strength (UCS), initial resistivity (IR), and the Mn2+ leaching concentration under different durability conditions, the results demonstrate that these variables increased and then tended to decrease with the number of w-d cycles. The UCS of contaminated soil is significantly correlated with IR. Moreover, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD) analyses indicate that the hydration products calcium silicate hydrate (C-S-H) and ettringite (AFt) are the main reasons for the enhancement of the UCS. However, the increase in Mn2+ concentration leads to a decrease in hydration products and the compactness of solidified soil, which has negative effects for the UCS and the leaching ion concentration. In general, the durability exhibited by the PRB waste treated with S/S in this paper was satisfactory. This study can provide theoretical guidance for practical engineering applications.

Screening of silicon-activating bacteria and the activation mechanism of silicon in electrolytic manganese residue

Electrolytic manganese residue (EMR) is a kind of solid waste with a high silicon content. Most of the silicon in EMR, however, exist in the state of SiO₂, which cannot be directly absorbed by plants. Currently, it is very challenge to recover the silicon from EMR. In this study, a preliminary screening of strains with silicon-activating ability was conducted, and four strains were screened out and isolated from the soil around the tailings pond of EMR. Then, single factor experiments were conducted to obtain the optimal growth conditions of the four strains, and the results indicated that the Ochrobactrum sp. T-07 had the best silicon-activating ability from EMR after nitrosoguanidine mutagenesis (Ochrobactrum sp. T-07-B). The available silicon (in terms of SiO₂) in the leaching solution was up to 123.88 mg L^-1, which was significantly higher than that produced by Bacillus circulans and Paenibacillus mucilaginosus, the two commercial available pure culture strains. Results of direct/indirect contact experiments between Ochrobactrum sp. T-07-B and EMR revealed that bioleaching was promoted under the synergistic effect of bacteria growth on the surface of and metabolism within EMR. The newly isolated strains with silicon-activating effect are different from the existing-known silicate bacteria and may be used for more efficient silicon activation in silicate minerals.

A critical review on approaches for electrolytic manganese residue treatment and disposal technology: Reduction, pretreatment, and reuse

Electrolytic manganese residue (EMR) has become a barrier to the sustainable development of the electrolytic metallic manganese (EMM) industry. EMR has a great potential to harm local ecosystems and human health, due to it contains high concentrations of soluble pollutant, especially NH₄⁺ and Mn²⁺, and also the possible dam break risk because of its huge storage. There seems to be not a mature and stable industrial solution for EMR, though a lot of researches have been done in this area. Hence, by fully considering the EMM ecosystem, we analyzed the characteristics and eco-environmental impact of EMR, highlighted state-of-the-art technologies for EMR reduction, pretreatment, and reuse; indicated the factors that block EMR treatment and disposal; and proposed plausible and feasible suggestions to solve this problem. We hope that the results of this review could help solve the problem of EMR and thus promote the sustainable development of EMM industry.

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.

Tailings after Iron Extraction in Bayer Red Mud by Biomass Reduction: Pozzolanic Activity and Hydration Characteristics

Bayer red mud (BRM) is a kind of solid waste with high hematite content, and its effective utilization is difficult due to the special physicochemical properties. In this work, Fe₂O₃ in BRM was reduced to Fe₃O₄ by biomass, and iron concentrate and high activity tailings were obtained after magnetic separation. The pozzolanic activity and hydration characteristics of the tailings were systematically studied. The results showed that the relatively stable polymerization structures of Si-O and Al-O in BRM are destroyed under the effect of biomass reduction at 650 °C, and some fracture bonds and activation points are formed in the structures. The aluminosilicate phases in the BRM were easy to transform into the active substances of Si and Al. The pozzolanic activity of tailings is greatly improved, and its pozzolanic activity index is 91%. High polymerization degree of gel and ettringite are formed since more active substances and alkali in the tailings promote the hydration reaction of cement-based cementitious materials, which made cementitious materials have dense matrix, good mechanical properties, and environmental performance. This work has realized the full quantitative utilization of BRM and provided a feasible way for the resource utilization of BRM.

Electrolytic manganese residue-based cement for manganese ore pit backfilling: Performance and mechanism

Slag backfilling with electrolytic manganese residue (EMR) is an economical and environmentally-friendly method. However, high ammonium-nitrogen and manganese ions in EMRs limit this practice. In this study, a method of highly efficient simultaneous stabilization/solidification of ultrafine EMR by making EMR-based cementitious material (named EMR-P) was proposed and tested via single-factor and response surface optimization experiments. Results show that the stabilization efficiency of NH₄⁺ and Mn²⁺ were above 95%, and the unconfined compressive strength of the EMR-P was 18.85 MPa (megapascal = N/mm²). The mechanistic study concluded that the soluble manganese sulfate and ammonium sulfate in EMR were converted into the insoluble precipitates of manganite (MnOOH), gypsum (CaSO₄), MnNH₄PO₄·H₂O, and struvite (MgNH₄PO₄∙6 H₂O), leading to the stabilization of NH₄⁺ and Mn²⁺ in the EMR-P. Leaching tests of EMR-P indicated that NH₄⁺, Mn²⁺, and others heavy metals in the leachate were within the permitted level of the GB/T8978-1996. The novelty of this study includes the addition of phosphate and magnesium ions to precipitate ammonium-nitrogen and the combination between calcium ions (from CaHPO₄∙2 H₂O) and sulfate (from the EMR) to form calcium sulfate to improve the stability and unconfined compressive strength of cementitious materials (EMR-P).

Mechanical Properties and Toxicity Risks of Lead-Zinc Sulfide Tailing-Based Construction Materials

The leaching residue of the lead-zinc sulfide tailing (LRT) is the only residue generated from the tailing leaching recovery process; it is a typical hazardous material for its high heavy-metal contents and high acidity. Due to the large output of LRT, and because its main components are Ca, Si, and Al, the preparation of building construction materials with LRT was studied. The results showed that when the LRT addition is less than 47%, with the ordinary Portland cement (OPC) and fly ash (FA) added and the curing conditions appropriate, the strength values of the tested specimens meet the M15 Class of the autoclaved lime sand brick standard (GB/T 16753-1997). The carbonization coefficient and drying shrinkage of the specimen were 0.79 and smaller than 0.42, respectively. As the SEM, TG, and XRD analysis have shown, the LRT can chemically react with additives to form stable minerals. The heavy metal contents that were leached out well met the limits in GB5085.3-2007. Based on the high addition of the LRT, the good strength and lower heavy metals were leached out of the prepared test specimen, and the tailing could be reused completely with the leaching recovery and the LRT reuse process. LRT can be used to replace OPC, allowing more sustainable concrete production and improved ecological properties of LRT.

Efficient removal of diethyl dithiocarbamate with EDTA functionalized electrolytic manganese residue and mechanism exploration

The recycling of solid wastes is obligable as it can reduce the environmental pollution and prevent the diffusion of secondary pollution. In this study, a novel cheap adsorbent was prepared by modifying electrolytic manganese residue (EMR) with EDTA. The maximum adsorption capacity of adsorbents for diethyl dithiocarbamate (DDTC) was 133.46 mg/g under initial pH of 7.32 at room temperature. Adsorption kinetics study revealed the DDTC adsorption on EDTA-EMR is mainly controlled by chemisorption and isotherm studies implied the adsorption is a monolayer process. Mechanism exploration found that the DDTC molecules could enter into the holes of EDTA-EMR, and the transition metal-based sorption sites were crucial for the target molecule immobilization and chelation. High pH value (> 10) was found to have inhibited the adsorption capacity of adsorbent, which should be due to the fact that the decreasing of functional groups on adsorbents surface and the competition between DDTC and OH^-. The ionic strength has negligible effect on the adsorption and the as-synthesized adsorbents showed excellent performance after five cycles. The overall results reveal that EDTA-EMR is a promising adsorbent ascribed by its low cost, good recyclability and excellent adsorption capacity.

Binary reaction behaviors of red mud based cementitious material：Hydration characteristics and Na+ utilization

Bayer red mud (RM) occupies a large amount of land, which excessive Na⁺ seriously damages groundwater resources. In this research, a RM based cementitious material (RMC) composed of RM and ordinary Portland cement (OPC) was developed. It is interesting to find that a binary reaction consisting of cement hydration and geopolymer reaction in RMC. The mechanical and Na⁺ consolidation rate of RMC were improved by the synergistic effect of binary reaction. The results indicated that the compressive strength of RMC is the highest and reaches 32.5R OPC when the mass ratio of CaO/(SiO₂+Al₂O₃) is 1.37, and the Na⁺ leaching concentration is environmentally acceptable. The 7 days compressive strength of RM-based cementitious material No.2 (RMC2) can reach 93.80% of that of 28 days. As the predominant hydration products, cement hydration product (Ca₅(SiO₄)₂(OH)₂) and geopolymer (CaAl₂Si₂O₈·2H₂O and Na₃Al₃Si₃O₁₂·2H₂O) were principally responsible for the strength development of RMC2 at 7 days. The optimal densification microstructure and [SiO₄] polymerization structure was presented in RMC2. The supreme Na⁺ consolidation rate was 99.23% in RMC2 due to the cooperation of physical fixation and [Si(Al)O₄] charge balance principle. This paper provides a fresh theoretical guidance for the utilization of RM and its Na⁺ in building materials.

Utilization of Spent FCC Catalyst as Fine Aggregate in Non-sintered Brick: Alkali Activation and Environmental Risk Assessment

This study focuses on the recycling of a spent fluid catalytic cracking (FCC) catalyst to produce catalyst-based non-sintered bricks (CN-bricks) for the recovery of its aluminosilicate components and the solidification of heavy metals. The effects of the content of cement (10–20%), the proportion of FCC (10–40%), and the type of an activator (NaOH/Na₂SiO₃/Na₂SO₄) on the performance of a CN-brick were investigated in terms of the mechanical strength and leaching behavior. The results show that an optimal binder system of 20% cement + Na₂SO₄ could promote the compressive strength up to 42.3 MPa; the proportion of an optimal spent FCC catalyst of 20% could achieve the lowest porosity and water absorption. The microscopic mechanism of a cementitious process was analyzed by x-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM), proving that C-S-H and ettringite (AFt) are the two main hydration products of a CN-brick. Na₂SO₄ is superior to NaOH or Na₂SiO₃ as an activator since Na₂SO₄ takes advantage of the aluminum-rich property of a spent FCC catalyst and specifically promote the formation of a needle-like AFt. Quantitative environmental risk assessment for the utilization of a CN-brick on roads was carried out based on the leaching test of a toxicity characteristic leaching procedure (TCLP), NEN 7371 maximum availability test, and the hazard Index (HI) identification, and a final HI 0.0045 (<1.0) indicates an acceptable risk for environment and nearby residents as CN-bricks are utilized on roads for 30 years.

Co-sintering MSWI fly ash with electrolytic manganese residue and coal fly ash for lightweight ceramisite

The MSWI fly ash (FA) is classified as hazardous waste and electrolytic manganese residue (EMR) as the harmful industrial waste. FA, water-washed FA (WFA), EMR and coal fly ash (CFA) were co-recycled to form lightweight MFCE ceramisites. The effects of FA, WFA and mixed MSWI fly ash on ceramisites were discussed. The approach to mixing FA and WFA increased the recycling amount of MSWI fly ash. The optimal mixture of 34.5% EMR, 24.1% CFA, 20.7% FA and 20.7% WFA sintered at 1160 °C for 12 min with a procedural heating rate (10 °C/min) and belonged to Class 800 artificial lightweight aggregate (GB/T 17431.1-2010); the quantity of MSWI fly ash in ceramisite was as high as 41.4%. Volatilization rates of Cd, Pb, Cu, Zn, Mn and Cr for ceramisite were higher 75.0, 24.2, 62.7, 133, 343 and 764% than FA respectively, attributed to the co-existence of chlorides and sulfates. The remained Zn, Cu, Pb, Mn and Cr were exchanged with Mg²⁺/Ca²⁺/Al³⁺ of diopside and wollastonite to form residual fractions. Our findings provided a feasibility method of co-recycling MSWI fly ash and electrolytic manganese residue to produce green lightweight aggregates.

Species identification and mutation breeding of silicon-activating bacteria isolated from electrolytic manganese residue

A strain of silicon-activating bacteria was isolated from electrolytic manganese residue (EMR); identified as a species of Ochrobactrum by integrated microscopic morphological characteristics, biochemical index determination, and clone analysis (i.e., results of 16S rRNA sequence); and temporarily named as Ochrobactrum sp. T-07 (T-07). The optimal growth conditions of the strain T-07 were obtained as follows: temperature of 30 °C, initial pH of 7.0, shaking speed of 180 rev. min^-1, and loading volume of 100 mL. In order to enhance its activation activity of silicon, T-07 went through the ultraviolet (UV) mutagenesis and nitrosoguanidine (NTG) mutagenesis breeding, and the mutant strain T-07-B with higher activity was obtained. Under the optimal fermentation condition (leaching time of 20 days, temperature of 30 °C, initial pH of 7, pulp concentration of 5%, shaking speed of 180 rev. min^-1, and particle diameter of EMR ≤ 180 μm), the available silicon content in the supernatant reached 98.8 mg L^-1, which was 2.4 times of the original strain T-07. Therefore, T-07 can be used as a good backup in developing biological silicon fertilizer for plants.

Quantitative source identification and apportionment of heavy metals under two different land use types: comparison of two receptor models APCS-MLR and PMF

At present, many researchers are increasingly aware of the importance of using models to identify heavy metal (HM) pollution sources. However, on the performance and application of different source identification models to HMs under different land use types had been studied little. In this study, comparison of absolute principal component scores-multiple linear regression (APCS-MLR) and positive matrix factorization (PMF) models and their application characteristics in identifying pollution sources were carried out by using 11 HMs in Zhongwei City farmland and Shizuishan industrial park, Ningxia. The results indicated that HM pollution in farmland mainly came from pesticides, fertilizers, and deposition of the Yellow River, while the pollution in industrial park mainly originated from atmospheric deposition and various industrial productions. The APCS-MLR model had the problem of less identification sources and the difficulty to explain the complex pollution, while the PMF model not only identified more pollution sources, but also distinguished heavy metal-related sources for two different land use types and different industrial production conditions. It is of great significance the formulation of agricultural-related pesticides' and chemical fertilizers' rational use and various industrial production-related raw materials put in and emission control strategies.

A low cost of phosphate-based binder for Mn2+ and NH4+-N simultaneous stabilization in electrolytic manganese residue

Electrolytic manganese residue (EMR) is a solid waste remained in filters after using sulfuric acid to leaching manganese carbonate ore. EMR contains high concentration of soluble manganese (Mn²⁺) and ammonia nitrogen (NH₄⁺-N), which seriously pollutes the environment. In this study, a low cost of phosphate based binder for Mn²⁺ and NH₄⁺-N stabilization in EMR by low grade-MgO (LG-MgO) and superphosphate was studied. The effects of different types of stabilizing agent on the concentrations of NH₄⁺-N and Mn²⁺, the pH of the EMR leaching solution, stabilizing mechanisms of NH₄⁺-N and Mn²⁺, leaching test and economic analysis were investigated. The results shown that the pH of the EMR leaching solution was 8.07, and the concentration of Mn²⁺ was 1.58 mg/L, both of which met the integrated wastewater discharge standard (GB8978-1996), as well as the concentration of NH₄⁺-N decreased from 523.46 mg/L to 32 mg/L, when 4.5 wt.% LG-MgO and 8 wt.% superphosphate dosage were simultaneously used for the stabilization of EMR for 50 d Mn²⁺ and NH₄⁺-N were mainly stabilized by Mn₃(PO₄)₂·2H₂O, MnOOH, Mn₃O₄, Mn(H₂PO₄)₂·2H₂O and NH₄MgPO₄·6H₂O. Economic evaluation revealed that the treatment cost of EMR was $ 11.89/t. This study provides a low-cost materials for NH₄⁺-N and Mn²⁺ stabilization in EMR.

An innovative method for manganese (Mn2+) and ammonia nitrogen (NH4+-N) stabilization/solidification in electrolytic manganese residue by basic burning raw material

High concentrations of manganese (Mn²⁺) and ammonia nitrogen (NH₄⁺-N) in electrolytic manganese residue (EMR) have seriously hindered the sustainable development of electrolytic manganese industry. In this study, an innovative basic burning raw material (BRM) was used to stabilize/solidify Mn²⁺ and NH₄⁺-N in EMR. The characteristics of EMR and BRM, stabilize mechanism of NH₄⁺-N and Mn²⁺, and leaching test were investigated. The concentrations of NH₄⁺-N and Mn²⁺ were 12.8 mg/L and 0.1 mg/L, respectively, when the solid liquid ratio was 1.5:1, and the mass ratio of EMR and BRM was 100:10, at the temperature of 20 °C reacting for 12 h Mn²⁺ was mostly solidified as bustamite ((Mn,Ca)Si₂O₆), groutite (MnOOH) and ramsdellite (MnO₂). NH₄⁺-N was mostly recycled by (NH₄)₂SO₄ and (NH₄)₃H(SO₄)₂. Leaching test results indicated that the concentrations of heavy metals were within the permitted level for the integrated wastewater discharge standard (GB8978-1996). Economic evaluation revealed that the cost of EMR treatment was $ 10.15/t by BRM. This study provided a new research idea for EMR harmless disposal.

Preparation and Component Optimization of Resin-Based Permeable Brick

The present study aims to prepare resin-based permeable bricks with micron-sized pores using fine aggregate with a particle diameter of 0.08–0.6 mm and bisphenol-A epoxy resin, a polymer binder. The properties of the binder, the characteristic parameters of the aggregate, and the micro pore structure of the brick were studied in order to break through the limitations of traditional porous permeable materials. The dynamic mechanical properties of resin were analyzed by dynamic mechanical analysis (DMA). The frequency parameter of particle size of 10 kinds of aggregate from different regions were obtained by digital image processing, and the characteristic parameter (aggregate distribution coefficient α) was obtained by modified Gaussian distribution. The microstructure of porous brick was analyzed by scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDS). The test results show: (1) the glass transition temperature (Tg) of the resin is 61 °C; (2) the parameters of aggregate particle group will affect the performance of porous permeable materials; (3) the minimum effective pore diameter of the permeable brick is 30 μm, the maximum permeable rate is 6.22×10−2 cm/s and the compressive strength is 41.08 MPa. The conclusions of this study will provide an important reference for permeable materials in the micron-scale pore range and the selection of binder and aggregate materials.