Electrolytic Manganese Research Articles

Synergistic preparation and application in PCU of α-calcium sulfate hemihydrate whiskers from phosphogypsum and electrolytic manganese residue

The α-calcium sulfate hemihydrate whiskers (α-CSHWs) were first prepared using phosphogypsum (PG) and electrolytic manganese residue (EMR) as raw materials for coating urea, demonstrating excellent controlled-release properties. The effects of different reaction conditions on α-CSHWs, achieved by optimizing the reaction time, the concentrations of NH4+, Mn2+, and other factors, were discussed. Results showed that when the EMR content was 25 wt%, the reaction temperature was 100 °C, and the reaction time was 3 h, α-CSHWs with a length-to-diameter ratio of 39 were obtained. Through experiments and density functional theory (DFT), the mechanism of α-CSHWs preparation was elucidated. The results show that the addition of EMR reduces the content of impurity ions PO43− and F− in PG while introducing NH4+ and Mn2+. Interestingly, both NH4+ and Mn2+ can reduce the nucleation time of α-CSHWs, while PO43−, Mn2+, and F− are more likely to adsorb on the (0 0 6) crystal plane of α-CSHWs, NH4+ readily adsorbs on the (4 0 0) crystal plane. The controlled-release performance of modified α-CSHWs incorporated into polyurethane-coated urea (PCU) was investigated, and it was found that the addition of Mα significantly prolonged the nutrient release period, with the period extending up to 116 days for coatings of 5wt% and above. This work not only enhances the efficiency of PG and EMR utilization but also serves as a reference for the straightforward synthesis and application of α-CSHWs.

Adsorbed hydroxyl radicals dominated peroxymonosulfate activation in acetaminophen degradation using modified electrolytic manganese anode slime: Catalyst evaluation and free radical identification

A new type of catalyst based on electrolytic manganese anode slime (EMAS) for heterogeneous peroxymonosulfate (PMS) activation in acetaminophen (APAP) degradation was prepared. The EMAS was modified by washing, pickling, and calcination to produce the DEMAS200 catalyst, and multi-types of refractory organic matter could be degraded by the DEMAS200/PMS system, of which 20 mg/L APAP can be removed within 4 min. A radical activation mechanism based on PMS was proposed through a series of APAP degradation experiments and material characterization. By quenching, probing, PMSO experiments, and electron paramagnetic resonance (EPR), the major contribution of various reactive oxygen species (ROS) (such as ·OHfree, SO4·−, high-valent Mn species, 1O2 and O2·−) was excluded, and ·OHads was verified as the major ROS. Nuclear magnetic resonance (NMR) was applied to identify active hydrogen using the D2O exchange method to qualitatively identify the presence of ·OHads, which was determined by comparing the appearance and disappearance of chemical shifts at 1.90 ppm (active hydrogen) and 7.96 ppm (hydrogen at the benzene ring on TPA). In this study, the modified EMAS was innovatively introduced for PMS activation in the degradation of APAP, and NMR technology successfully identified the presence of different hydroxyls.

Immobilization mechanism of Mn2+ in electrolytic manganese residue using sintered ceramsites prepared by alkali-mechanical-roasting method

Currently, sufficient information is unavailable on using electrolytic manganese residue (EMR) to prepare sintered ceramsites for immobilization of manganese in EMR. This study used EMR, Na2CO3, and montmorillonite (MMT) as raw materials to prepare ceramsites with the influence of alkalinity, sintering temperature, and sintering time on the investigated ceramsite properties. Under the optimal conditions (i.e., C-2 h= EMR content: 50%, Na2CO3 content: 25%, sintering temperature: 1050℃, sintering time: 2 h), the cylinder compressive strength, porosity, bulk density and apparent density of the ceramsites reached 25.03 MPa, 54.72%, 0.748 g/cm3 and 2.056 g/cm3. The presence of mesoporous pores within the ceramsites made them suitable for adsorption as biocarriers. The leaching concentration of Mn2+ from the ceramsites was 2.26 mg/L, lower than the third grade in standard (GB 8978–1996), suggesting that heavy metals are stabilized within the ceramsite. The main immobilization mechanism in the ceramsites included the formation of a new crystalline phase including jacobsite (Fe2MnO4) and liquid phase encapsulation. The involvement of certain impurities such as Mg2+ in the formation of crystalline phases can influence Mn2+ immobilization. This research not only offers valuable insights into the safe and valuable utilization of EMR but also provides a novel method for preparing ceramsites.

Enhanced recovery of high-purity Fe powder from iron-rich electrolytic manganese residue by slurry electrolysis

Enhanced recovery of high-purity Fe powder from iron-rich electrolytic manganese residue by slurry electrolysis

Adsorption of Phosphate by Two-Step Synthesis of Ceramsite from Electrolytic Manganese Residue/Dredged Sludge.

Carrying out research on the management of electrolytic manganese residue (EMR) is necessary to maintain the environment and human health. The dredged sludge (DS) and water hyacinth (WH) generated from dredging projects are potential environmental threats, and therefore suitable methods need to be found for their treatment. In this study, ceramsite was prepared by a two-step low-temperature firing method using DS and EMR as raw materials, WH as a pore-forming additive, and aluminate cement as a binder for the adsorption of phosphorus from wastewater. The optimal ratio and process parameters of the ceramsite were determined by mechanical and adsorption properties. The static adsorption experiments were conducted to study the effect of ceramsite dosage and solution pH on the removal of phosphorus. At the same time, dynamic adsorption experiments were designed to consider the influence of flow rate on its actual absorption effect, to explore the actual effect of ceramsite in wastewater treatment, and to derive a dynamic adsorption model that can provide technical support and theoretical guidance for environmental management.

Hydration characteristics and pollutant solidification mechanism of full solid waste electrolytic manganese residue super sulfate cement

In this study, electrolytic manganese residue (EMR) rich in soluble manganese, ammonia nitrogen, and sulfate was combined with carbide slag (CS) and granulated blast furnace slag (GBFS) to produce Full Solid Waste Electrolytic Manganese Residue Super Sulfate Cement (FWS-EMR-SSC). The compressive strength, hydration mechanism, microstructure, hydration kinetics, and pollutant solidification mechanism of FWS-EMR-SSC were investigated. The study revealed that the optimal ratio was 4% carbide slag, 40% EMR, and 56% GBFS, achieving a compressive strength of 38.34 MPa at 28 days. This was due to the release of OH- from carbide slag, causing EMR to dissolve large amounts of SO42- and Ca2+, while GBFS accelerated the release of Ca2+, Si2+, Al3+, leading to the formation of abundant AFt and C-(A)-S-H gel, providing strength to FWS-EMR-SSC. The heat release rate and cumulative heat of the FWS-EMR-SSC system were lower than Ordinary Portland Cement (OPC). Additionally, compared to OPC, the second exothermic peak rate was significantly reduced and delayed in the FWS-EMR-SSC system due to the exothermic release of gypsum, retarding effects, and pronounced generation of AFt. The simulation of FWS-EMR-SSC hydration kinetics using the Krstulović-Dabić model revealed that FWS-EMR-SSC underwent the NG-I-D process. Gypsum retarded the nucleation and crystal growth stages of NG, while AFt had a significant impact on the D diffusion stage. The C-(A)-S-H, AFt gel, and iron-manganese compounds (Fe2Mn(PO4)2(OH)2·(H2O)8, MnFe2O4) generated in the FWS-EMR-SSC system could undergo ion exchange and chemical precipitation with Mn2+. Meanwhile, NH3-N transformed into NH3 release, ensuring that the leaching toxicity of FWS-EMR-SSC met the Chinese standard limits of GB8978-1996 for wastewater discharge.

Ammonia removal and simultaneous immobilization of manganese and magnesium from electrolytic manganese residue by a low-temperature CaO roasting process.

A large amount of open-dumped electrolytic manganese residue (EMR) has posed a severe threat to the ecosystem and public health due to the leaching of ammonia (NH4+) and manganese (Mn). In this study, CaO addition coupled with low-temperature roasting was applied for the treatment of EMR. The effects of roasting temperature, roasting time, CaO-EMR mass ratio and solid-liquid ratio were investigated. The most cost-effective and practically viable condition was explored through response surface methodology. At a CaO: EMR ratio of 1:16.7, after roasting at 187°C for 60 min, the leaching concentrations of NH4+ and Mn dropped to 10.18 mg/L and 1.05 mg/L, respectively, below their discharge standards. In addition, the magnesium hazard (MH) of EMR, which was often neglected, was studied. After treatment, the MH of the EMR leachate was reduced from 60 to 37. Mechanism analysis reveals that roasting can promote NH4+ to escape as NH3 and convert dihydrate gypsum to hemihydrate gypsum. Mn2+ and Mg2+ were mainly solidified as MnO2 and Mg(OH)2, respectively. This study proposes an efficient and low-cost approach for the treatment of EMR and provides valuable information for its practical application.

Recovery of manganese as spinel MgMn2O4 cathode material from electrolytic manganese residue by Na2CO3 hydrothermal-roasting process

Recovering high-value-added Mn products from electrolytic manganese residue (EMR) is prominent due to the scarcity of Mn resource and its increasing importance in various industries. In this study, we explored Mn and Mg recovery from EMR for the synthesis of cathode material MgMn2O4 for the first time through Na2CO3 hydrothermal-roasting method. Na2CO3 concentration and roasting temperature were found to significantly affect the morphology and structure of MgMn2O4. Both flower-like MgMn2O4 (f-MMO) and hollow MgMn2O4 (h-MMO) were synthesized under optimized conditions. Additionally, the electrochemical performances of MgMn2O4 as cathode material of magnesium-ion batteries were evaluated. Both f-MMO and h-MMO showed superior rate performance. High initial reversible capacity can be achieved (237.5 mAh/g), and still retain 157.7 mAh/g after 40 cycles at 100 mA/g and 76 mAh/g after 500 cycles at 500 mA/g. This work inspires the way for recovering Mn from EMR as energy storage material.

Regeneration of waste Zn-MnO2 batteries: Value-added transformation to regenerate essential materials for sustainable battery manufacturing

Zn-MnO2 batteries have a 3–5 year shelf life and make up 75 % of portable batteries. Disposing of spent batteries is a global issue and demand for MnO2 cathode material is growing 9.6 % annually, causing increased resource use and potential toxic metal leaching risk. Eco-efficient practices are needed to reduce environmental impact through recycling and reusing end-of-life products. Herein, electrolytic manganese dioxide (EMD) of spent Zn-MnO2 batteries was recycled using a thermochemical process where the structure of EMD was upgraded resulting in improving its electrochemical performance. The applicability of the recycled EMD as cathode into a new battery was explored by examining the discharge behaviour of the Zn-MnO2 cell made in KOH electrolyte and the results were compared with the performance of an original battery/EMD. In the recycled EMD cell, γ-MnO2 transformed to Zn2Mn7O8.H2O upon discharge (with a capacity of 213 mAh.g−1) and no Mn3O4 was observed, whereas in the original EMD, discharge resulted in the formation of mainly ZnMn5O4 and Mn3O4 (with a capacity of 175 mAh.g−1). The reversibility of the intercalation of cations into the structure of γ-MnO2 and their rechargeability was further examined via charge-discharge cycles using LiOH electrolyte where the recycled EMD exhibited enhanced behaviour. This indicates that in the recycled EMD, ZnMnO2 was able to revert to the original γ-MnO2, whereas in the original EMD, the formed Mn3O4 seemed to be irreversible resulting in the poor rechargeability behaviour of such batteries. Conclusively, the proposed method is a more efficient solution for reducing environmental impacts in value-added manufacturing due to its fewer steps compared to conventional techniques.

Enhanced removal of iron from iron-rich manganese ore leaching solution: A promising strategy by seed-induced

Enhanced removal of iron from iron-rich manganese ore leaching solution has become a bottleneck limiting the development of the electrolytic manganese industry. Herein, iron-rich electrolytic manganese residue (IREMR) as a seeding to enhance iron removal. The results showed that the iron removal efficiency was 99.97 % with only manganese loss of 1.5 % whenadding 1 g/L IREMR. Compared with the traditional conditions of electrolytic metal manganese enterprise, it demonstrated several environmental advantages: lower manganese loss (from 16 % to 1.5 %), less IREMR produced (64.45 %), faster filtration speed (from 0.0013 to 0.1966 mL/s.cm2). Based on multiphase equilibria modelling and strengthening mechanism analysis, enhanced iron removal by seed-induced can reduce the formation of ammonium-alum complex salts and prevent the formation of Fe(OH)3 colloid. In addition, IREMR as seeding applied in the iron removal process can accelerate the formation of goethite and hematite to shorten the nucleation cycle. This strategy is important for source reduction and resource utilization of electrolytic manganese residue.

Electrolytic manganese residue-biochar composite for simultaneous removal of antimony and arsenic from water: Adsorption performance and mechanisms

Antimony (Sb) and arsenic (As) pollution in the water environment pose a threat to the ecological environment and human health. A lot of studies have been conducted on the removal of pollutants from water by modified biochar, but little attention has been paid to the simultaneous removal of Sb and As from water. This study aimed to simultaneously remediate the water contaminated by Sb and As and realize the resource utilization of solid waste. Herein, electrolytic manganese residue (EMR)-biochar composite (EB) was prepared by a one-step pyrolysis method using the mixture of EMR and distillers grains for the removal of As(III, V) and Sb(III, V) from water. The results indicated that the optimal pyrolysis temperature and EMR to distillers grains mass ratio for EB removal of As(III, V) and Sb(III, V) were 750 °C and 3∶1, respectively. The removal of As(III, V) and Sb(III, V) by EB was inhibited to varying degrees by HCO3−, PO43−, and humic acid. The maximum adsorption capacities of EB for As(III), As(V), Sb(III), and Sb(V) were 40.92, 40.54, 34.36, and 9.42 mg/g, respectively. The main adsorption mechanisms of As(III, V) and Sb(III, V) included complexation, hydrogen bonding, and pore filling. Compared with other engineered biochar composites, EB can be utilized not only as a potential adsorbent to treat water contaminated with As(III, V) and Sb(III, V), but also to enable the hazard-free treatment and resource utilization of EMR and distillers grains, achieving the goal of treating pollution with waste. Future studies on the remediation performance and mechanisms of EB for practical Sb and As co-contaminated soil and water are necessary.

Enhanced green remediation and refinement disposal of electrolytic manganese residue using air-jet milling and horizontal-shaking leaching

The reclamation and reuse of electrolytic manganese residue (EMR) as a bulk hazard solid waste are limited by its residual ammonia nitrogen (NH4+-N) and manganese (Mn2+). This work adopts a co-processing strategy comprising air-jet milling (AJM) and horizontal-shaking leaching (HSL) for refining and leaching disposal of NH4+-N and Mn2+ in EMR. Results indicate that the co-use of AJM and HSL could significantly enhance the leaching of NH4+-N and Mn2+ in EMR. Under optimal milling conditions (50 Hz frequency, 10 min milling time, 12 h oscillation time, 400 rpm rate, 30 ℃ temperature, and solid-to-liquid ratio of 1:30), NH4+-N and Mn2+ leaching efficiencies were optimized to 96.73% and 97.35%, respectively, while the fineness of EMR was refined to 1.78 µm. The leaching efficiencies of NH4+-N and Mn2+ were 58.83% and 46.96% higher than those attained without AJM processing. The AJM used strong airflow to give necessary kinetic energy to EMR particles, which then collided and sifted to become refined particles. The AJM disposal converted kinetic energy into heat energy upon particle collisions, causing EMR phase transformation, and particularly hydrated sulfate dehydration. The work provides a fire-new and high-efficiency method for significantly and simply leaching NH4+-N and Mn2+ from EMR.

Preparation of slow-release fertilizers by electrolytic manganese residue and alkali-activated laterite-based geopolymers: Mn release effects on Guizhou white tea seedlings growth

Electrolytic manganese residues (EMR) and alkali-activated laterite-based geopolymers were used to prepare slow-release fertilizers (SRFs) and the physicochemical properties and Mn release behavior of EMR-laterite-based SRFs (SRFs-LA) were studied. MnSO4·H2O in EMR transforms into CaMnSi2O6, MnO2 and (NH4)2Mn(SO4)2·6H2O after SRFs-LA synthesis. Geopolymers can slow Mn release through ion exchange and can physically encapsulate Mn-containing minerals. Mn release from the SRFs-LA system was primarily influenced by a combination of non-Fick diffusion and skeleton erosion. A comparative pot experiment was also conducted between SRFs-LA and SRFs prepared using alkali/acid-activated geopolymers with EMR (SRFs-alGo/SRFs-acGo) to examine the fertilization efficiency of Guizhou white tea seedlings. Compared with Mg(II), Mn(II) not only played a dominant role in the competitive root absorption process from the soil to the interior of seedlings, but also impeded Fe transportation by regulating the expression of citrate transporters. The slow release of Mn from SRFs-alGo and SRFs-LA could benefit tea seedling growth and protein and photosynthetic pigment synthesis, whereas EMR treatments with Mn burst release damaged the antioxidant system owing to the excessive accumulation of reactive oxygen species in leaves. The Mn released from SRFs-acGo may approach the tolerance limit of tea seedlings growth. The order of fertilizer efficiency for young Guizhou white tea seedlings was as follows: SRFs-LA > SRFs-alGo > SRFs-acGo. Moreover, the cost of SRFs-LA prepared using laterite instead of metakaolin as an active silicon–aluminum source could be reduced by approximately $18.7/t.

Mechanical properties and environmental characteristics of the synergistic preparation of cementitious materials using electrolytic manganese residue, steel slag, and blast furnace slag

The high content of heavy metals in electrolytic manganese residue (EMR) makes it difficult to utilize in engineering, and direct disposal can pose a threat to the environment. This study uses EMR as a raw material combined with steel slag (SS) and blast furnace slag (GGBS) to prepare electrolytic manganese residue-based cementitious material (ESGM) under the action of an alkali activator (NaOH), and studies the effects of the EMR to SS ratio and alkali activator concentration on the flowability, setting time, compressive strength, and toxic leaching of ESGM. In addition, XRD, FTIR, SEMEDS, and MIP were used to study the microscopic characteristics of ESGM and its stabilization/solidification mechanism for heavy metals. The results indicate that an increase in EMR content will reduce the fluidity and setting time of the slurry, while an increase in alkali activator concentration will increase the fluidity of the slurry and reduce the setting time. When the content of EMR, SS, and GGBS is 50%, 20%, and 30%, respectively, and the concentration of alkali activator is 0.2, the strength of ESGM reaches its maximum, reaching 23.0 MPa in 28 days. The heavy metal leaching in ESGM is lower than the allowable range of Chinese standard GB 89781–996, and the material meets environmental requirements. The microscopic analysis showed that the ESGM gelling products were mainly C-(A)-S-H and N-A-S-H gels, and the formation of ettringite was also observed. Mn2+ in EMR was mainly stabilized in ESGM in the form of MnO2 and H2Mn8O16·2.4 H2O.

Exploration of the effects of electrolytic manganese residue on the environmental, economic, and engineering performance of magnesium oxychloride cement: A possible utilization method of electrolytic manganese residue

The widespread use of magnesium oxychloride cement (MOC) can effectively solve the waste problem in the potash industry. However, its poor water resistance limits its practical application. Electrolytic Manganese Residue (EMR), as a solid waste from manganese metal smelting, requires an effective utilization method. In this work, we have attempted to incorporate EMR into MOC after its treatment in order to improve the water resistance of MOC and increase the utilization rate of EMR. The addition of EMR to MOC increased the density of MOC. The incorporation of EMR did not significantly reduce the strength of the MOC samples. The incorporation of EMR reduced the relative content of magnesium oxide in the specimens and EMR can be used as a source of soluble Al, Si and Fe to produce insoluble amorphous gels. The combined effect resulted in an effective improvement in the water resistance of the samples. The 28-day water immersion strength of the EMR100 can reach 38.3 MPa, and its water resistance coefficient was 82.10%. The appropriate doping of EMR can improve the pore structure of the specimens, reduce the porosity and refine the pore size distribution. Carbon emission per unit compressive strength and cost per unit compressive strength were used as evaluation indices of environmental and economic benefits. A high dosage of EMR-incorporated MOC resulted in low cost and carbon emission, especially the strength of the specimen after water immersion as a strength index. Taking into account the strength after 14 days of air curing and 28 days of water immersion, the advantages of cost per unit compressive strength and carbon emission per unit compressive strength of EMR100 were further extended and reduced by 86.23% and 22.15% respectively compared to the benchmark group. The heavy metal curing of EMR was evaluated by ion leaching test, and the result showed that MOC effectively cured the heavy metal ions in EMR and reduced the environmental risk of EMR. The good performance of EMR in MOC systems not only provides an effective breakthrough for the efficient utilization of EMR and its heavy metal curing, but also effectively improves the performance of MOC and reduces the production cost.

Using Mn/Fe enriched-roots of P. Stratiotes to synthesize multi-metallic catalysts for activating peroxymonosulfate to degrade bisphenol A

Aquatic plants used for phyto-extracting toxic metals from water are often enriched in certain metals and recycling these metal-enriched plants will achieve the sustainable application of phytoremediation/phytoextraction technology. The present study systematically explores the potential recycling of Mn-enriched-roots of P. Stratiotes used in the treatment of electrolytic manganese residue leachates as catalysts for activating peroxymonosulfate [1] to degrade organics in water. The effects of heat treatment temperature and atmosphere on the catalyst activity were first investigated and the results indicate that catalyst prepared in air at 400 °C contains active Mn(IV) while Mn(IV) was not detected in the catalyst prepared in N2 at the same temperature, and thereby catalyst obtained in air under 400 °C (MF400) performs better catalytic activity in degrading bisphenol A (BPA). The removal of BPA was found to reach 99.9 % in the MF400/PMS system at 120 min. The BPA degradation pathways were inferred by density flooding calculations (DFT) and then confirmed by liquid chromatography-mass spectrometry coupled detection, indicating that the radical pathway depending on·OH, SO4− and·O2– is the mechanism for BPA degradation in the MF400/PMS system. The ECOSAR assessment reveals that most BPA degradation intermediates are less toxic than their parent molecule. This work provides a simple and effective way for recycling Mn/Fe enriched aquatic plants used in phytoextraction process.

Utilisation of electrolytic manganese residue as a sulphate activator in producing concrete blocks with high-volume fly ash

Electrolytic manganese residue has been largely generated and accumulated, which poses a threat to the sustainable development of the electrolytic manganese metal industry. This paper explores the feasibility of utilising pretreated electrolytic manganese residue and fly ash in the production of concrete blocks. The pretreated electrolytic manganese residue is used as an activator to react with the alumina and portlandite in the mixture. The volume of permeable voids, compressive strength, and drying-wetting performance of the blocks were estimated, followed by the characterisation of their microstructure and the leaching behaviour of hazardous elements. The results show that replacing sand with 0–30 wt% pretreated electrolytic manganese residue can improve the blocks' compressive strength and reduce the volume of permeable voids due to the filler effect of pretreated electrolytic manganese residue and the promoted formation of ettringite. However, increasing the pretreated electrolytic manganese residue content compromises the blocks’ water resistance due to the presence of gypsum. Substituting 0–30 wt% of ordinary Portland cement with fly ash in the blocks contributes reactive SiO2 and Al2O3 to the system with the pretreated electrolytic manganese residue as a sulphate activator. This further facilitates the formation of ettringite which can bridge micro-particles and fill pores, enabling the concrete blocks with ordinary Portland cement and fly ash to attain comparable properties to those with ordinary Portland cement only. Moreover, leaching tests demonstrate that hazardous elements in electrolytic manganese residue can be efficiently immobilised in concrete blocks. The incorporation of 0–30 wt% fly ash enhances the solidification of Mn in the blocks due to the intensified ion substitution and physical encapsulation emanating from the facilitated formation of ettringite. Overall, this paper showcases a sustainable technical pathway for the utilisation of electrolytic manganese residue in concrete blocks with high-volume fly ash.

Insight into a novel composite biosorbent by incorporating chitosan into electrolytic manganese residue for Cr(VI) removal from aqueous solutions

A novel adsorbent was obtained by using a typical solid waste electrolytic manganese residue (EMR) and a green material chitosan (CS) for the Cr(VI) removal from the aqueous environment. The tagged mineral phases and elements in the EMR were successfully detected in the synthesized composites according to the XRD and SEM-EDS results. Furthermore, the characteristic peak of metal and hydroxyl group binding appeared at 779 cm−1, and the Si-O bending vibration at 454 cm−1 in the FT-IR pattern of the synthesized composites indicating the functional Fe and Mn hydroxyl groups and the silicates in EMR were all successfully grafted onto the CS. This obtained composite showed a high Cr adsorption capacity with a maximum adsorption capacity of 133.64 mg·g−1, and the Cr(VI) removal rate could maintain a high level of 94.6 % after five adsorption–desorption cycles. Its adsorption isotherm matched with the Langmuir model, and the adsorption kinetics followed the pseudo-first-order model. According to the response surface CCD model, the optimal conditions for Cr(VI) removal were pH at 2, contact time at 53.0 min, and initial concentration at 100 mg·L-1. For the removal mechanism, Cr(VI) anions could be easily electrostatic adsorbed by –NH3+, or chelated with the Fe and Mn oxides. Meanwhile, partial Cr(VI) (∼35.7 %) was reduced into Cr(III) by the abundant hydroxyl group of chitosan on the surface of the as-obtained materials, and then the free Cr(III) could be easily chelated with three chitosan monomers. This work opens up a novel and green methodology to modify chitosan and reuse the solid waste EMR.

Glass-ceramics prepared from desulfurized electrolytic manganese residue and the nucleation promotion effect of calcium fluoride in glass phase transition

Electrolytic manganese residue (EMR) is toxic industrial solid waste. Electrolytic manganese enterprises have established a desulfurization and sulfuric acid production process to address its storage risks leaving desulfurized EMR (DEMR). In this study, DEMR was used as a raw material to prepare glass-ceramics. A method of melting and one-stage heat treatment was used to realize controlled crystallization of diopside, with calcium fluoride sludge (FS) as a nucleating agent. The impact of CaF2 on the glass network structure, as well as on the microstructure and performance of the glass-ceramics, are discussed. CaF2 can greatly improve the nucleation ability of glass precursors. When the addition of FS is small, the phase transition of glass is dominated by the diffusion of atoms and growth of diopside, forming dendritic crystals. When introducing more FS, the glass-ceramics form smaller island-shaped crystals due to many nucleation sites. The prepared glass-ceramics show excellent mechanical properties and chemical stability. Its hardness exceeds 6.5 GPa, with bending strength over 110 MPa. The acid resistance of glass-ceramics is higher than 99.5%, and the toxic metals in the raw materials are stable solidified. This study perfects the technology of EMR desulfurization pretreatment, which provides an effective graded recycling approach for EMR.

Utilization of ground granulated blast-furnace slag and electrolytic manganese residue as a low-carbon cementitious material

Ground granulated blast-furnace slag (GGBS) is a common substitute for ordinary Portland cement (OPC). However, GGBS–OPC lacks early strength when OPC content is low (<50%). A new cementitious material called GGBS–OPC–EMR (GOE) was developed by adding electrolytic manganese residue (EMR) to address this issue. Tests were conducted using XRD, SEM, and TG to analyze the micro-structural mechanisms of strength development in GOE. Environmental and economic evaluations were conducted, including CO2-eq (carbon dioxide equivalent) analysis, leaching tests, and economic analysis. Results showed that mixture of GGBS, OPC, and EMR in a 4:2:1 ratio increased the unconfined compressive strength by 25% after 28 days compared to OPC while reducing cement consumption by 70%. Major hydration products in GOE were C–S–H and ettringite (AFt), with approximately 14% EMR promoting AFt production. GOE reduced CO2-eq emissions by 35.9% and saved $46.6/ton compared to OPC. Leaching tests demonstrated GOE's ability to stabilize heavy metals, sulfate, and ammonia nitrogen.