Solidification/stabilization of electrolytic manganese residue using phosphate resource and low-grade MgO/CaO

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.

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.

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 phase evolution and promoting the pozzolanic activity of electrolytic manganese residue during calcination

Electrolytic manganese residue (EMR) is a harmful by-product in the electrolytic manganese industry. Calcination is an efficient method for disposing EMR. In this study, thermogravimetric-mass spectrometry (TG-MS) combined with X-ray diffraction (XRD) was used for analysing the thermal reactions and phase transitions during calcination. The pozzolanic activity of calcined EMR was determined by the potential hydraulicity test and strength activity index (SAI) test. The leaching characteristics of Mn were determined by TCLP test and BCR SE method. The results showed that MnSO₄ was converted into stable MnO₂ during calcination. Meanwhile, Mn-rich bustamite (Ca_0.228Mn_0.772SiO₃) was converted into Ca(Mn, Ca)Si₂O₆. The gypsum was transformed into anhydrite and then decomposed into CaO and SO₂. Additionally, the organic pollutants and ammonia were completely removed following calcination at 700 °C. The leaching concentration of Mn decreased from 819.9 mg L^-1 to 339.6 mg L^-1 following calcination at 1100 °C. The chemical forms of Mn were transformed from acid-soluble fraction to residual fraction. The pozzolanic activity tests indicated that EMR1100-Gy maintained a complete shape. The compressive strength of EMR1100-PO reached 33.83 MPa. Finally, the leaching concentrations of heavy metals met the standard limits. This study provides a better understanding for the treatment and utilization of EMR.

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 mutual harmless treatment of electrolytic manganese residue and red mud

Electrolytic manganese residue (EMR) and red mud (RM) are solid waste by-products of the metal manganese and alumina industries, respectively. Under long-term open storage, ammonia nitrogen and soluble manganese ions in EMR and alkaline substances in RM severely pollute and harm the environment. In order to alleviate the pollution problem of EMR and RM. In this study, the alkaline substances in RM were used to treat ammonia nitrogen and soluble manganese ions in EMR. The results confirm the following suitable treatment conditions for the mutual treatment of EMR and RM: EMR-RM mass ratio = 1:1, liquid-solid ratio = 1.4:1, and stirring time = 320 min. Under these conditions, the elimination ratios of ammonia nitrogen (emitted in the form of ammonia gas) and soluble manganese ions (solidified in the form of Mn3.88O7(OH) and KMn8O16) are 85.87 and 86.63%, respectively. Moreover, the alkaline substances in RM are converted into neutral salts (Na2SO4 and Mg3O(CO3)2), achieving de-alkalinisation. The treatment method can also solidify the heavy metal ions-Cr3+, Cu2+, Ni2+, and Zn2+-present in the waste residue with leaching concentrations of 1.45 mg/L, 0.099 mg/L, 0.294 mg/L, and 0.449 mg/L, respectively. This satisfies the requirements of the Chinese standard GB5085.3-2007. In the mutual treatment of EMR and RM, the kinetics of ammonia nitrogen removal and manganese-ion solidification reactions are controlled via a combination of membrane diffusion and chemical reaction mechanisms.

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.

A new basic burning raw material for simultaneous stabilization/solidification of PO43--P and F- in phosphogypsum

Phosphogypsum (PG) contains a lot of soluble phosphate (PO₄^3--P) and fluorine ion (F^-), which seriously has hindered the sustainable development of the phosphorous chemical industry. In this study, a new burning raw material (BRM) as an intermediate product in the cement production process was used for PO₄^3--P and F^- stabilize in PG. The stabilizing mechanism of PO₄^3--P and F^- were investigated by Fourier Transform infrared spectroscopy (FT-IR), X-ray diffractometer (XRD), Scanning Electron Microscopy (SEM), X-ray fluorescence (XRF) and X-ray spectroscopy system (XPS). The effect of PG and BRM weight ratio, solid-to-liquid ratio, reaction time, and reaction temperature on the concentrations of PO₄^3--P and F^- were studied. The results showed that the concentration of F^- in the PG leaching solution was 8.65 mg/L and the stabilizing efficiency of PO₄^3--P was 99.78%, as well as the pH of the PG leaching solution was 8.12 when the weight ratio of PG and BRM was 100:2, and the solid to liquid ratio was 4:1, reacting for 24 h at the temperature of 30 ℃. PO₄^3--P and F^- were mostly solidified as Ca₅(PO₄)₃F, CaPO₃(OH), Ca₅(PO₄)₃(OH), Ca₂P₂O₇·2H₂O, CaSO₄PO₃(OH)·4H₂O, CaF₂, and CaFPO₃·2H₂O. Leaching test results indicated that the concentrations of PO₄^3--P, F^- and heavy metals were less than the integrated wastewater discharge standard (GB8978-1996). This study provides a new harmless treatment method for PG.

Manganese stabilization in mine tailings by MgO-loaded rice husk biochar: Performance and mechanisms

Leachable metal in abandoned mine tailings may be toxic to vegetation, affecting effective ecological restoration. In this study, MRB was synthesized through MgCl₂·6H₂O wet impregnation followed by duplicate slow pyrolysis. Manganese tailings were mixed with MRB, rice husk biochar (RB), and MgO at a dosage of 0-5%, followed by 90-day incubation. Toxicity characteristic leaching procedure and sequential leaching were used to analyze the leachability and species of Mn in tailings, while a stabilization mechanism was proposed with the support of the characterization of the tailings before and after amendment. Results suggested MRB addition significantly decreased leachable Mn by 63.8%, reducing from 59.88 mg/L to 21.68 mg/L, while only a 14.39% reduction was achieved by rice husk biochar (RB). The sharp decline of leachable Mn after 90-day mixing was contributed by the transformation from labile to stable fractions. A microporous biochar matrix along with the uniform dispersion of MgO active component were both responsible for the better Mn stabilization. Only less than 10% of the variation in substrate pH was observed with the increase of MgO loading or incubation time. Linear correlation analyses indicated substrate pH's strongl negative relationship with leachable Mn and moderately positive relationship with residual fraction. Characterization results revealed that MRB exhibited different stabilization mechanisms in mine tailings, where Mn was likely to be stabilized by direct interaction with active MgO or indirect alkaline precipitation to form stable MgMn₂O₄, Mn(CH₃COO)_2, and MnO(OH)₂. This work validated the promoting potential of recycling agricultural biomass waste for the amendment of manganese mine tailings.

Heavy metal removal using an advanced removal method to obtain recyclable paper incineration ash

Various agents, including ethylenediaminetetraacetic acid, oxalic acid, citric acid, and HCl, were applied to remove heavy metals from raw paper incineration ash and render the ash recyclable. Among these prepared agent solutions, ethylenediaminetetraacetic acid showed the highest efficiency for Pb removal, while oxalic acid showed the highest efficiencies for Cu, Cd, and As removal. Additionally, three modes of an advanced removal method, which involved the use of both ethylenediaminetetraacetic acid and oxalic acid, were considered for use at the end of the rendering process. Among these three modes of the advanced removal method, that which involved the simultaneous use of ethylenediaminetetraacetic acid and oxalic acid, i.e., a mixture of both solutions, showed the best heavy metal removal efficiencies. In detail, 11.9% of Cd, 10% of Hg, 28.42% of As, 31.29% of Cu, and 49.19% of Pb were removed when this method was used. Furthermore, the application of these three modes of the advanced removal method resulted in a decrease in the amounts of heavy metals eluted and brought about an increase in the CaO content of the treated incineration ash, while decreasing its Cl content. These combined results enhanced the solidification effect of the treated incineration ash. Thus, it was confirmed that the advanced removal method is a promising strategy by which recyclable paper incineration ash can be obtained.

Resource utilization from solid waste originated from oil-based shale drilling cutting during shale gas development

With the large-scale development of shale gas, oil-based drilling fluids are widely used, generating significant amounts of solid wastes from oil-based shale drilling cutting (OBSDC). These solid wastes are biologically toxic and are difficult to degrade. The current treatment methods do not meet the requirements for oily sludge. This study begins with pyrolysis of OBSDC in order to use it as an external admixture for preparing cement slurry for resource utilization. The research results showed that when the OBSDC content was increased to 35%, the mechanical properties of developed cement were favourable. Evaluating the cement sheath integrity showed that the OBSDC cement met the subsequent production requirements for a casing with an internal pressure of 50.01 MPa, applicable for cementing surface casings as well as technical casings. The active SiO₂ and feldspar in OBSDC after pyrolysis promoted the hydration reaction of cement and accelerated the crystallization of C-S-H, which in turn complemented the cement mechanical properties. When OBSDC was in the proper dosage range, the particle gradation characteristics further optimized the pore structure of the cement matrix and increased the cement strength.

Synergistic solidification/stabilization of electrolytic manganese residue and carbide slag

Electrolytic manganese residue (EMR) contains high concentrations of NH₄⁺ and heavy metals, such as Mn²⁺, Zn²⁺, Cu²⁺, Pb²⁺, Ni²⁺ and Co²⁺, while carbide slag (CS) contains high amount of OH^- and CO₃^2-, both posing a serious threat to the ecosystem. In this study, EMR and CS synergistic stabilization/solidification (S/S) was discussed science CS could stabilize or solidify EMR and simultaneously reduce its corrosive. The results showed that after the synergistic S/S for 24 h when liquid-solid ratio was 17.5% and CS dosage was 7%, Mn²⁺ and NH₄⁺ leaching concentrations of the S/S EMR were below the detection limits (0.02 mg/L and 0.10 mg/L) with a pH value of 8.8, meeting the requirements of the Chinese integrated wastewater discharge standard (GB 8978-1996). Mn²⁺ was stabilized as MnFe₂O₄, Mn₂SiO₄, CaMnSi₂O₆, and NH₄⁺ escaped as NH₃. Zn²⁺, Cu²⁺, Pb²⁺, Ni²⁺ and Co²⁺ in EMR can also be stabilized/solidified because of the react with OH^- and CO₃^2- in CS. Chemical cost was only $ 0.54 for per ton of EMR synergistic harmless treatment with CS. This study provided a new idea for EMR cost-effective and environment-friendly harmless treatment.

Property of concrete made of recycled shale gas drilling cuttings

Exploration and development of shale gas generate a lot of water-based drilling cuttings (WDC), which can then be used in concrete engineering. This work studied mix ratio optimization, mechanical properties, leaching characteristics and the microstructure of the WDC concrete. The results showed that the pH and COD values of these WDC were slightly above 9.0 and 60, respectively. All other indices satisfied the first grade standard of Chinese standard GB8978. On the other hand, a moderate amount of WDC can be improved concrete properties, especially its workability and compressive strength. When the water-binder ratio is 0.52 and the sand ratio is 41%, we can obtain C25 strength grade and 130 ~ 140 mm slump grade concrete by adding high efficiency water reducing agent and fly ash. XRD and SEM analysis showed that the silica and aluminum oxide in WDC reacted with calcium hydroxide to form secondary hydration products: C-S-H gel and ettringite, which are conducive to the formation of concrete strength and solidified the heavy metals and other contaminants. EDX analysis found it is known that the hydration products in WDC concrete can bind metal elements well. The environmental leaching test shows that the recycled WDC added to concrete products as aggregate and admixture is very environmentally friendly and sustainable.

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.

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).

Hazard-free treatment of electrolytic manganese residue and recovery of manganese using low temperature roasting-water washing process

A combined low-temperature-roasting and water-washing process is investigated as a hazard-free method to treat electrolytic manganese residue (EMR) and recover manganese. In this study, the phase transformation characteristics and a thermodynamics analysis of the low temperature roasting process of EMR are evaluated. In addition, the effects of temperature and time on the phase transformation of EMR in the roasting process and the washing characteristics of roasted EMR samples are also investigated. Results reveal that some unstable phases within EMR are transformed into more stable phases depending on the treatment time/temperature conditions used and EMR roasted for 60 min at 600 °C (R_60min/600°C) exhibit the highest rate of manganese recovery, 67.12 %. After 25 min of deionized water washing, the concentration of manganese in solution from R_60min/600°C material become stable, whereas after 6 washing cycles the concentration of manganese in the solution is < 0.005 g/L. The R_60min/600°C material with three wash cycles results in a manganese-water solution concentration that is suitable for use in electrolytic manganese metal production. Finally, toxicity leaching tests show that the concentrations of ions present in the leaching solution are all lower than the regulatory limits mandated by the Chinese Integrated Wastewater Discharge Standard GB 8978-1996.

Bio-leaching of manganese from electrolytic manganese slag by Microbacterium trichothecenolyticum Y1: Mechanism and characteristics of microbial metabolites

The related microbial metabolomics on biological recovery of manganese (Mn) from Electrolytic Manganese Slag (EMS) has not been studied. This study aimed at open the door to the metabolic characteristics of microorganisms in leaching Mn from EMS by using waste molasses (WM) as carbon source. Results show Microbacterium trichothecenolyticum Y1 (Y1) could effectively leach Mn from EMS in combination with using waste molasses as carbon and energy sources. For the first time, Y1 was identified to be capable of generating and then metabolizing several organic acids or other organic matter (e.g., fumaric acid, succinic acid, malic acid, glyoxylic acid, 3-hydroxybutyric acid, glutaric acid, L(+)-tartaric acid, citric acid, tetrahydrofolic acid, and L-methionine). The production of organic acids by Y1 bacteria was promoted by EMS with the carbon source. This study demonstrated for the first time that metabolic characteristics and carbon source metabolic pathways of Y1 in bioleaching of Mn from EMS.

Carbonating MgO for treatment of manganese- and cadmium-contaminated soils

Ordinary Portland cement (OPC) and lime are commonly used to treat soils contaminated by heavy metals, such as cadmium (Cd) and manganese (Mn). However, the production of these two binders is not sustainable, consuming high energy and emitting high carbon dioxide (CO₂). In this contest, this study proposed a novel and sustainable method of carbonating magnesia (MgO) for treatment of Cd- and Mn-contaminated soils, which can sequester CO₂ and immobilize Cd and Mn in the soils. To validate the method, a range of experiments were performed. First, MgO and CO₂ were used to treat contaminated soils. Then, the properties of the treated soils were evaluated by unconfined compressive strength test, one stage batch leaching test, X-ray diffraction test, and thermogravimetric analysis. It was found that the carbonation process of MgO-treated soils was decelerated by Mn, but not significantly decelerated by Cd. After carbonation, multiple magnesium carbonates were formed in both contaminated soils, and CdCO₃ was formed in the Cd-contaminated soil, while MnCO₃ was not confidently determined in the Mn-contaminated soil. Both Cd and Mn negatively affected the strength of carbonated MgO-treated soils; nevertheless, if the concentration of Cd or Mn was not more than 8000 mg/kg, 5% MgO-treated soils after carbonation could meet the strength requirement of higher than 1000 kPa. The treatment decreased the Cd leachability to be below the limit for non-hazardous wastes. The leached concentration of Mn was decreased to be lower than the limit of drinking water.

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.

Heavy Metal Immobilization Studies and Enhancement in Geotechnical Properties of Cohesive Soils by EICP Technique

Soil treatment methods to cope with ever-growing demands of construction industry and environmental aspects are always explored for their suitability in different in-situ conditions. Of late, enzyme induced calcite precipitation (EICP) is gaining importance as a reliable technique to improve soil properties and for contaminant remediation scenarios. In the present work, swelling and permeability characteristics of two native Indian cohesive soils (Black and Red) are explored. Experiments on the sorption and desorption of multiple heavy metals (Cd, Ni and Pb) onto these soils were conducted to understand the sorptive response of the heavy metals. To improve the heavy metal retention capacity and enhance swelling and permeability characteristics, the selected soils were treated with different enzyme solutions. The results revealed that EICP technique could immobilize the heavy metals in selected soils to a significant level and reduce the swelling and permeability. This technique is contaminant selective and performance varies with the nature and type of heavy metal used. Citric acid (C6H8O7) and ethylene diamine tetra-acetic acid (EDTA) were used as extractants in the present study to study the desorption response of heavy metals for different EICP conditions. The results indicate that calcium carbonate (CaCO3) precipitate deposited in the voids of soil has the innate potential in reducing the permeability of soil up to 47-fold and swelling pressure by 4-fold at the end of 21 days of curing period. Reduction in permeability and swell, following EICP treatment can be maintained with one time rinsing of the treated soil in water to avoid dissolution of precipitated CaCO3. Outcomes of this study have revealed that EICP technique can be adopted on selected native soils to reduce swelling and permeability characteristics followed by enhanced contaminant remediation enabling their potential as excellent landfill liner materials.

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.

Reuse of ammonium sulfate double salt crystals formed during electrolytic manganese production

Ammonium sulfate double salt crystals (ASDSCs) are formed during the electrolytic production of manganese. Typically, the large volume of ASDSCs accumulates in the open air, and this leads to serious environmental pollution and wastage of resources. In this study, we developed a new double-membrane three-chamber electrolysis method. In this method, ASDSCs were dissolved in water and then pretreated stepwise to precipitate manganese(II) carbonate and magnesium carbonate. These precipitates were filtered and the filtrate (mainly ammonium sulfate) was subjected to double-membrane three-chamber electrodecomposition to produce sulfuric acid and ammonia. Further investigations showed that under the optimal conditions of current density of 250 A/m², electrolysis time of 18 h, and temperature of 40 °C, the decomposition rate of ammonium sulfate reached as high as 96.15%. Thus, using this method, ASDSCs can be completely decomposed, which resolves the problem of environmental pollution and provides certain economic benefits to enterprises.

Preparation of road base material by utilizing electrolytic manganese residue based on Si-Al structure: Mechanical properties and Mn2+ stabilization/solidification characterization

Electrolytic manganese residue (EMR) is a potentially harmful industrial solid waste that should be addressed. In the study, the red mud, carbide slag and blast furnace slag were used as stabilization/solidification (S/S) agents to S/S Mn²⁺, and simultaneous reused it as raw material to prepare road base material. The S/S behavior of manganese, unconfined compressive strength (UCS) of road base material with different Al/Si ratios, leaching test and the S/S mechanisms were investigated. The results showed that the Mn²⁺ can be well solidified when the S/S agents reach up to 20 %. The 7-day UCS of the road base material was 6.1 MPa with the Al/Si ratio of 0.48, which meets the highway standards. When Al/Si = 0.48, the formation amount of CaAl₂Si₂O₈·4H₂O and ettringite increased, which promoted the adsorption and wrap of Mn²⁺. The content of active Al^Ⅳ and Al^Ⅵ increased after S/S. Mn₂SiO₄ and Ca₄Mn₄Si₈O₂₄ were produced by the charge balance effect, and the new chemical bond was formed. Meanwhile, the Mn²⁺ is oxidized to more stable MnO₂ to achieve the S/S of Mn²⁺. This research provides an effective way to solidify Mn²⁺ and solves the problem of large-scale utilization of EMR and other solid waste.

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

The present study aims to prepare non-sintered permeable bricks using significant amount of electrolytic manganese residue (EMR), discharged by electrolytic metal manganese industry. Mechanical and environmental properties were investigated. The microstructure was analyzed by means of XRD, FTIR, TG-DSC and SEM-EDS. It was observed that the splitting tensile strength and permeability coefficient of the optimum proportion were 3.53 MPa and 3.2 × 10^-2 cm/s respectively. The main hydration products were found to be ettringite, C-S-H, aluminosilicates and C-A-S-H. The leaching test showed that Mn, Pb, Cd, total Cr and NH₃-N in the non-sintered permeable bricks were solidified up to concentrations lower than groundwater standard. In addition to that, the NH₃-N produced during the process was transformed into ammonia water which was in turn recycled and reused in manganese electrolysis. Besides, non-sintered permeable bricks have been produced at large scale and applied successfully as pavement materials in Songtao, China. Therefore, the use of EMR to produce non-sintered permeable bricks possesses important environmental and economic significance because the process not only utilizes large quantities of EMR and saves EMR disposal cost, but also saves a lot of natural resources and improves the urban environment.

An effective treatment method for phosphogypsum

Phosphogypsum (PG) accumulation occupies huge amounts of land resources and results in serious environmental risks. A new recycling product, the phosphogypsum embedded filler (PGEF) made with calcination-modified phosphogypsum, was developed. The preparation process, hydration mechanism of PG, basic physical performances, environmental safety, engineering application, and cost analysis of the PGEF were studied. The results showed that the stress performance and thermal insulation property of the products were satisfied. Environmental performance tests established their findings that the application of PGEF prepared with calcination-modified PG does not cause any secondary contamination. In addition, the cost of PGEF is far lesser than that of the same volume of reinforced concrete. PGEF prepared with calcination-modified PG has shown a perfect application in cast-in situ concrete hollow floor structure.

Performance of desulfurization ash for the preparation of grouting fire prevention material

The accumulation of desulfurization ash from coal-fired power plants can lead to serious waste of land resources and environmental safety problems. This work presents an experimental study on the feasibility of recycling original desulfurization ash as the main raw materials, and a new green grouting material was prepared. The results indicate that a desulfurization ash-based grouting fire prevention material which was prepared according to the following ingredient design (a water-to-solid ratio of 1.0:1 and a hydroxyethyl cellulose content of 0.09% desulfurization ash, 12% quicklime, 0.6% Na₂SO₄, and 0.05% triethanolamine, 80 °C curing). The slurry's viscosity meets requirements, and its suspension, liquidity, and consolidation strength are better than those of clay under the same conditions. In addition, the grouting material's inhibitor ratio is increased with temperature increase, which means it has good flame retardancy. Environmental performance tests concluded that when desulfurization ash as-recycled admixture is used for the preparation of grouting fire prevention material, from the technique point of view, the environmental safety of them is very good.

An effective treatment method for shale gas drilling cuttings solidified body

The exploration and production of shale gas technology provides a way for utilization of clean fuels. However, during the exploration process of shale gas, enormous amount of drilling cutting was generated and had to be solidified and landfilled. So the accumulation of shale gas drilling cutting solidified body (SGDS)causes severe land resource misuse and environmental complications. This study focuses on the utilization of SGDS as a raw material for the production of cement clinker, and the phase composition, microstructure, and environmental performance of the cement clinker was investigated by X-ray powder diffraction (XRD), scanning electronic microscopy (SEM), energy-dispersive X-ray spectrum analysis (EDX), and soaking test, respectively. The results show that the cement clinker obtained mainly constitutes of typical Portland cement mineral (C₃S, C₂S, C₃A, and C₄AF). The leaching test indicated that the concentration of heavy metal ions in leachate is within the limits allowed by the state "Technical specification for co-processing of solid wastes in cement kiln" (GB 30760-2014). This study therefore provides a benchmark on environmental effects resulting from drilling cuttings and utilization of resources.

Enhanced electrokinetic remediation of manganese and ammonia nitrogen from electrolytic manganese residue using pulsed electric field in different enhancement agents

Electrolytic manganese residue (EMR) is a solid waste generated in the process of producing electrolytic metal manganese and contains a lot of manganese and ammonia nitrogen. In this study, electrokinetic remediation (EK) of manganese and ammonia nitrogen from EMR were carried out by using pulse electric field (PE) in different agents, and sodium dodecyl benzene sulfonate (SDBS), citric acid (CA) and ethylene diamine tetraacetic acid (EDTA) were used as enhancement agents. The removal behavior of ammonia nitrogen and manganese under direct current field (DC) and PE, and the relationship between manganese fractionation and transport behavior, as well as the energy consumption were investigated. The results demonstrated that the removal efficiency of ammonia nitrogen and manganese using PE were higher than DC. SDBS, EDTA and CA could enhance electroosmosis and electromigration, and the sequence of enhancement agent effects were CA, SDBS, EDTA, distilled water. The highest removal efficiency of manganese and ammonia nitrogen were 94.74% and 88.20%, and the effective removal amount of manganese and ammonia nitrogen was 23.93 and 1.48 mg·wh^-1, when CA and SDBS+CA was used as the enhancement agents, respectively. Moreover, electromigration was the main removal mechanism of manganese and ammonia nitrogen in the EK process.

Fractional removal of manganese and ammonia nitrogen from electrolytic metal manganese residue leachate using carbonate and struvite precipitation

A comparative investigation of hydroxide precipitation, sulfide precipitation, carbonate precipitation and the struvite formation process for removing manganese and ammonia nitrogen from electrolytic metal manganese residue leachate (EMMRL) was investigated. Chemical equilibrium model-Visual MINTEQ was applied to simulate the chemical reactions and optimize chemical dosages in manganese and ammonia nitrogen removal. Phase transition, morphology, and valence state of the precipitates were characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), and X-ray Photoelectron Spectroscopy (XPS). Results indicated that carbonate precipitation prior to the other two methods for removal of manganese and ammonia nitrogen. The removal efficiency of manganese was 99.9%, when molar ratio of C to Mn was 1.1:1 at pH 9.5, and manganese was removed in the form of MnCO₃. When molar ratio of P to N was 1.1:1 at pH 9.5, the removal efficiency of ammonia nitrogen was 97.4%, and ammonia nitrogen was removed in the form of struvite. Economic evaluation reveals that the treatment cost was 9.316 $ m^-3 when carbonate and phosphate was used to remove manganese and ammonia nitrogen from EMMRL.

Novel synergy of Si-rich minerals and reactive MgO for stabilisation/solidification of contaminated sediment

Disposal of significant amounts of dredged contaminated sediment poses an economic and environmental problem worldwide. Transforming contaminated sediment into value-added construction materials using low-carbon MgO cement is a sustainable option; however, the weak mechanical strength and unreliable water-solubility of MgO cement restrict its practical engineering applications. This study elucidates the potential role of industrial Si-rich minerals in the performance enhancement of MgO-based products via the promotion of magnesium silicate hydrate (M-S-H) gel formation. Quantitative X-ray diffraction and ²⁹Si nuclear magnetic resonance analyses indicated that compositions and crystallinities of the Si-rich minerals significantly influence the formation and polymerisation of the M-S-H gel. Pulverised fly ash was found to be a promising Si-rich mineral for generating polymeric M-S-H gel, whereas incinerated sewage sludge ash samples demonstrated a low degree of polymerisation, and the use of glass powder samples gave a low yield of M-S-H. The formation of M-S-H gel enhanced the compressive strength and water resistance (strength retention after water immersion). Further experiments demonstrated that Si-modified MgO cement can transform dredged sediment into fill materials with satisfactory mechanical properties and contaminant immobilisation. Therefore, the synergy between reactive MgO and Si-rich industrial waste is a novel option for sustainable remediation and environmental applications.

Co-disposal of MSWI fly ash and electrolytic manganese residue based on geopolymeric system

MSWI fly ash (MSWI FA) and electrolytic manganese residue (EMR) were successfully co-disposed by use of a geopolymeric system. Alkaline products of MSWI FA and NaOH were used to elicit chemical reactions to promote solidification. The best performing formulation of EMR-based geopolymer for immobilization of heavy metals was composed of 75 wt% MSWI FA and 25 wt% EMR with NaOH solution (7.5 M)/solid of 0.5. Solidification was most effective for the heavy metals: Pb > Cu > Cr > Zn > Mn, respectively. The EMR-based geopolymer had high structural stability likely due to the high ratio of SiO₂/Al₂O₃. The Solidification/Stabilization (S/S) mechanism for heavy metals of geopolymers is likely due to alkaline conditions and geopolymeric encapsulation, highlighting the utility and feasibility of this approach.

Simultaneous stabilization/solidification of Mn2+ and NH4+-N from electrolytic manganese residue using MgO and different phosphate resource

This study examined simultaneous stabilization and solidification (S/S) of Mn²⁺ and NH₄⁺-N from electrolytic manganese residue (EMR) using MgO and different phosphate resource. The characteristics of EMR NH₄⁺-N and Mn²⁺ S/S behavior, S/S mechanisms, leaching test and economic analysis, were investigated. The results show that the S/S efficiency of Mn²⁺ and NH₄⁺-N could reach 91.58% and 99.98%, respectively, and the pH value is 8.75 when the molar ratio of Mg:P is 3:1 and the dose of PM (MgO and Na₃PO₄·12H₂O) is 8wt%. In this process, Mn²⁺ could mainly be stabilized in the forms of Mn(H₂PO₄)₂·2H₂O, Mn₃(PO₄)₂·3H₂O, Mn(OH)₂, and MnOOH, and NH₄⁺-N in the form of NH₄MgPO₄·6H₂O. Economic evaluation indicates that using PM process has a lower cost than HPM and HOM process for the S/S of Mn²⁺ and NH₄⁺-N from EMR at the same stabilization agent dose. Leaching test values of all the measured metals are within the permitted level for the GB8978-1996 test suggested when the dose of PM, HPM and HOM is 8wt%.

Statistical optimization and batch studies on adsorption of phosphate using Al-eggshell

This work provides a simple and convenient method to manufacture the sorbent of Al-eggshell. The influence of AlCl3 concentration and pH values as well as the dosage of sorbent and their interactions on adsorption of phosphate was investigated. Therefore, Box–Behnken design coupled with response surface method was adopted to explore the empirical model for phosphate species removal. It was observed that there is an optimal point, C(AlCl3)(0.29 mol/l)–pH(6.12)–dosage(6.72 g/l), for the goal of maximizing phosphate species removal. The second-order polynomial model for phosphate reduction was given as Removal(%) = 96.43 +10.82X1 + 4.29X2 − 0.70X3 + 2.06X1X2 − 1.72X1X3 +8.24X2X3 − 13.10X12 − 17.26X22 − 1.72X32. Contour pictures implied that the interaction between pH values and sorbent dosage was the strongest, followed by C(AlCl3) versus dosage and C(AlCl3) versus pH. The adsorption of phosphate data had a good agreement with the Freundlich isotherm equation at 313 and 323 K. Otherwise, Langmuir–Freundlich model described the best fitness at the temperature of 293, 298, and 303 K. The process of adsorption of phosphate on Al-eggshell fitted a pseudo-second-order kinetic equation, which indicates the exothermic reaction. In conclusion, the present work suggests Al-eggshell as an efficient and environmental friendly sorbent for phosphate species adsorption from aqueous solutions.

Environmental performance, mechanical and microstructure analysis of concrete containing oil-based drilling cuttings pyrolysis residues of shale gas

The overall objective of this research project is to investigate the feasibility of incorporating oil-based drilling cuttings pyrolysis residues (ODPR) and fly ash serve as replacements for fine aggregates and cementitious materials in concrete. Mechanical and physical properties, detailed environmental performances, and microstructure analysis were carried out. Meanwhile, the early hydration process and hydrated products of ODPR concrete were analyzed with X-ray diffraction (XRD), Fourier transform infrared (FT-IR), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). The results indicated that ODPR could not be categorize into hazardous wastes. ODPR had specific pozzolanic characteristic and the use of ODPR had certain influence on slump and compressive strength of concrete. The best workability and optimal compressive strength were achieved with the help of 35% ODPR. Environmental performance tests came to conclusion that ODPR as recycled aggregates and admixture for the preparation of concrete, from the technique perspective, were the substance of mere environmental contamination.