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About 80 % of zinc is produced by “roasting-leaching-purifying-electrodeposition”. Lead-silver and jarosite residues are generated during this process, posing a serious threat to the ecosystem and environment since it contains a lot of heavy metals such as Pb. To better understand metal mobility and toxicity of these two zinc hydrothermal residues, it was analyzed by standard leaching toxicity procedures, bioavailability test and sequential extraction procedures. The results showed that the main phases of lead-silver and jarosite residues are KFe3(SO4)2(OH)6, CaSO4·2H2O, PbSO4, Fe3O4 and ZnFe2O4. These two residues contain a high content of Fe, Pb and Zn and also a significant amount of precious metals, such as Ag and In, showing a great resource potential. Meanwhile, lead-silver and jarosite residues are classified as hazardous waste both in China and the USA since their toxicity leaching concentration of Cd, Pb and Se exceeds the threshold of 1, 5 and 1 ppm. Metals contained in these two residues could easily be released to the environment, especially Cd, Pb and Zn, though metals are mainly in the form of residual, higher than 85 %. In addition, lead-silver and jarosite residues also show a significant biohazardous potential since EDTA and DTPA extractable Zn, Pb, Mn, Cd, Cu and As of these two residues are considerably high. All these results could help the zinc manufactories, governments and also the recycling companies better understand the risk of zinc hydrometallurgical residues and urge them to hind this harm to the ecosystem, and most importantly the human being itself.

Waste printed circuit boards (WPCBs) are usually dismantled, crushed, and sorted to WPCB metal-enriched scraps, still containing an amount of non-metallic materials. This research used slurry electrolysis to refine these WPCB metal-enriched scraps and to examine if a standard ionic liquid, [MIm]HSO4, can replace H2SO4 in the system. The impact of the refinement process on metal migration and transformation is discussed in detail. The results demonstrated that metals in WPCB metal-enriched scraps could be successfully refined using slurry electrolysis, and [MIm]HSO4 can be used to replace H2SO4 in the system. When 80% of H2SO4 was replaced by [MIm]HSO4 (electrolyte of 200 mL, 30 g/L CuSO4·5H2O, 60 g/L NaCl, 130 g/L H2SO4, and 1.624 A for 4 h), the total metal recovery rate is 85%, and the purity, current efficiency, and particle size of cathode metal powder were 89%, 52%, and 3.77 μm, respectively. Moreover, the microstructure of the cathode metal powder was dendritic in the H2SO4-CuSO4-NaCl slurry electrolysis system, whereas at an 80% [MIm]HSO4 substitution rate slurry electrolysis system, the cathode metal powder was irregular and accumulated as small-sized spherical particles. Thus, replacing inorganic leaching solvents with ionic liquids may provide a potential choice for the resources in WPCB metal-enriched scraps.

Electrolytic manganese residue (EMR) contains large quantities of manganese (Mn2+) and ammonia nitrogen (NH4+-N). Phosphogypsum (PG) contains plenty of phosphate (PO43−), fluorine (F−) and some heavy metals. Separate storage of EMR and PG could seriously damage the ecological environment. In this study, synergistic stabilization/solidification (S/S) of EMR and PG was studied. The effects of EMR:PG mass ratio, S/S pH, solid-liquid ratio and temperature on the concentrations of NH4+-N, PO43−, Mn2+ and F− in the leaching solution, and the characteristics of EMR and PG were studied. Meanwhile, the synergistic S/S mechanisms of EMR and PG, and leaching test were investigated. The results showed that the concentrations of F−, PO43−, NH4+-N and Mn2+ in the leaching solution were 4.5 mg/L, 13.6 mg/L, 55.5 mg/L and 0.8 mg/L, respectively, when the mass ratio of EMR to PG was 1:2 and the pH was 9.0 adjusted by MgO after 20 days S/S. Manganese was mainly solidified as Mn3(PO4)2·7H2O and Mn(OH)2, and ammonia nitrogen was mainly stabilized as struvite; fluorine was mainly stabilized as (Mn, Ca, Mg)F2, and phosphate was mainly solidified as (Mn, Ca, Mg)3(PO4)2 and (Mn, Ca, Mg)HPO4. The leaching test results showed that PO43− and NH4+-N were reduced to 13.6 mg/L and 55.5 mg/L, respectively, and the concentrations of all the measured heavy metals and F− were within the permitted level for the GB8978-1996 after 20 days S/S.

Electrolytic metal manganese residue leachate (EMMRL) was produced from long-term deposition of electrolytic metal manganese residue. EMMRL contains huge amount of manganese and ammonia nitrogen which could seriously damage the ecological environment. In this study, a chemical equilibrium model-Visual MINTEQ was used to simultaneously optimize removal of manganese and ammonia nitrogen from EMMRL with chemical precipitation methods. In the laboratory experiment, the effect of different N: P ratios and pH were investigated, and the characterization of the precipitates was characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscope (SEM). The results showed that over 99.9% manganese and 96.2% ammonia nitrogen were simultaneously removed, respectively, when molar ratio of N:P was 1:1.15 at pH 9.5. Moreover, the experimental results corresponded well with the model outputs with respect to ammonia nitrogen and manganese removal. Manganese was mainly removed in the form of MnHPO4·3H2O and manganite, and ammonia nitrogen was mainly removed in the form of struvite. Economic evaluation indicated the chemical precipitation methods can be applied in the factory when the price of precipitation was higher than 0.295 $/kg.

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.

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.

Metal mobility and toxicity of the municipal solid waste incineration (MSWI) fly ash from different seasons in Beijing were studied using leaching toxicity procedures, sequential extraction procedures, and bioavailability procedures. The X-ray diffraction results showed that MSWI fly ash contained CaSO4, CaCO3, and KCl. The Pb, Zn, and Cd contents of MSWI fly ash were high, especially during autumn, being 42, 77, and 1260 times higher than that of their soil backgrounds, respectively. Leaching toxicity experiments showed that MSWI fly ash is hazardous, since Pb exceeded the maximum threshold (5 mg/L). The main alkali metal ions and anions, heavy metals total content, leaching concentration, chemical speciation, and bioavailability varied seasonally. The Pb and Zn leaching concentrations in summer and autumn were higher than that of the other two seasons. Sequential extraction procedures indicated that Pb, Zn, and Cd showed extremely high metal mobility, i.e., the residual states of Pb and Cd in spring were 5.83% and 1.21%, respectively, and that of Zn in autumn was 10.68%. These results will help industries, governments, and the public better understand the risk of MSWI fly ash and will urge them to pay more attention to preventing harm to the ecosystem and human beings.

Superfine copper particles could be directly prepared from waste printed circuit boards by slurry electrolysis. Meanwhile, copper fractal growth could be observed. To better understand this phenomenon, the factors that affect copper dendrites in a point-cathode system were discussed in detail. These results showed that the fractal degree of copper dendrites increased as the increase of applied voltage and the decrease of copper sulfate and gelatin concentrations. Sodium lauryl sulfate and hydrochloric acid concentrations could not significantly impact the fractal degree of copper dendrites, while gelatin concentration could. The minimum copper fractal dimension was 1.069 when gelatin and copper sulfate concentration was 120 mg/L and 0.1 mol/L, respectively with an applied voltage of 11 V. Moreover, the results diffusion-limited aggregation model demonstrated that particle translational speed, particle numbers and binding probability significantly affected copper dendrite patterns. The scanning electron microscopy results indicated that the three additives greatly affected the refinement of the copper crystal. These findings contribute to enrich the theoretical study on metals recovery from e-waste by slurry electrolysis.

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.

Copper is a nonferrous metal closely connected to humans. Approximately 40% of copper is produced by reclaimed copper smelting (RCS). Reclaimed copper smelting fly ash and smelting slag are generated during the RCS process, posing a serious threat to the ecosystem and environment as they contain many heavy metals, such as Cu and Zn. In this study, the metal mobility and toxicity of RCS fly ash and smelting slag were analyzed using standard leaching toxicity procedures, sequential extraction procedures, and bioavailability tests. The results showed that the main phases of RCS fly ash were Cu2(OH)3Cl, FeCl2·2H2O, CuS2, C, CuO, Cu, Ca2SiO4, ZnClO42, Zn(OH)2·0.5H2O, and KFeCl3, and those for smelting slag were SiO2, CaCO3, SiS2, CaAl2Si2O8·4H2O, Cu4O3, CuO, ZnO, NiSO4·6H2O, AlPO4, and Na3Mn(PO4)(CO)3. These two slags contain high contents of Cu, Zn and Fe and trace amounts of heavy metals, such as Ba, Be, Cd, Cr, Ni, As, Pb, Au, Se and Sb. RCS fly ash is classified as hazardous waste in both China and the USA as the toxic leaching concentrations of Pb and Cd exceed the thresholds of 5 and 1 mg L−1. Cu and Zn contained in these two slags can easily be released into the environment, although the residual fraction of Cu and Zn was found to be higher than 65%. Additionally, RCS fly ash and smelting slag also show significant biohazardous potential as the EDTA- and DTPA-extractable Zn, Cu and Se of these two residues are considerably high. The results described above could provide reclaimed copper smelting companies and governments with a better understanding of the risk of RCS fly ash and smelting slag, urging them to stop the slag from harming ecosystems and humans.

In this study, electric field and ball milling were used to leach Mn2+ from low-grade pyrolusite (LGP). The effects of current density, reaction time, reaction temperature, ball-to-powder weight ratio, and ball milling time on the leaching efficiency of Mn2+ from LGP as well as the leaching mechanism were systematically studied. The results showed that the combined use of electric field and ball milling enhanced the leaching of Mn2+ from LGP. The leaching efficiency of Mn2+ reached 97.79% under the optimum conditions of LGP-to-pyrite mass ratio of 1:0.18, current density of 30 mA/cm2, LGP-to-H2SO4 mass ratio of 1:0.4, liquid-to-solid ratio of 5:1, ball-to-powder weight ratio of 1:1, ball milling time of 2 h, temperature of 80 °C, and leaching duration of 120 min. This value was 25.95% higher than that attained without ball milling and 41.45% higher than that attained when neither ball milling nor electric field was employed. Pyrite was fully oxidized to generate additional SO42− and Fe3+, and was further hydrolyzed to form jarosite (KFe3(SO4)2(OH)6) and hydronium jarosite (Fe3(SO4)2(OH)5·2H2O) via ball milling and electric field application. Moreover, the electric field changed the surface charge distribution of the mineral particles and promoted collisions between them as well as the collapse of the crystal lattice, further improving the leaching efficiency of Mn2+ from LGP. This study provided a new method for leaching Mn from LGP.

The objectives of this study were to investigate the adsorption and transfer behaviors of phenanthrene (PHE) and bisphenol A (BPA) in purple paddy soils amended with dissolved organic matter (DOM) derived from rice and canola straw in the West Sichuan Plain of China. In the pristine soil, PHE was preferentially adsorbed on both pristine clayey (L) and sandy (T) paddy soils than BPA, indicating that the retention/adsorption by soils is closely dependent on the chemical properties of organic pollutants (OPs). The noticeably higher adsorption of PHE and BPA on smaller size fraction of the soils (L2 and T2) were observed, possibly due to their higher surface areas and higher content in organic matters with higher aromaticity and hydrophobicity in this soil fraction. The DOMs derived from rice (RDOM) and canola (CDOM) straws possessed remarkable differences in E2/E3 and SUV254 measurements, which reflected that their chemical composition might be different. When CDOM was introduced in the studied soil T1, adsorption of BPA was doubled, but the augment in adsorption was much less impressive with RDOM, showing the nature of derived DOM played an important role. The study also demonstrated that in the fine fraction of clayey soil (L2), the retention of a same OP (PHE) was remarkably dropped when CDOM or RDOM was introduced, whereas in a sandy soil of the same size fraction (T2), the phenomenon was the opposite, suggesting a potential risk that, in certain types of soil, the introduction of straw derived DOMs may enhance the mobility of some OPs. The humification time of straw seems not to affect the adsorptions of OPs in most studied systems. Adsorption kinetics of PHE and BPA in the adsorption systems with derived DOMs were well fitted to the two-step first-order model with radj2 values of 0.994-0.998. Results of this study will provide further comprehensive fundamental data for risk assessment and control of organic pollutants (OPs) in farmland ecosystems.

In industrial electrolytic manganese metal process, the energy consumption closely related to the electrolysis of cathode and anode. The effect of Cl- concentration on electrochemical oscillation a...

Completely separating and recovering metals and nonmetals from waste printed circuit boards (WPCBs) is key to e-waste recycling. Here we proposed a novel approach, slurry or suspension electrolysis, to separate metals and nonmetals from WPCBs. The factors that impact the separation rate during the slurry electrolysis were discussed in detail. The results indicate that CuSO4·5H2O, NaCl, H2SO4, WPCBs dosage, current and time could impact metals separating from WPCBs. Increasing NaCl and H2SO4 concentration and extending electrolysis time could effectively increase the metal and nonmetal separation rate, while increasing WPCBs dosage and current have negative impacts on the metal and nonmetal separation rate. Slurry electrolysis could directly and completely separate and recover metals from WPCBs with a separation rate up to 97.79% under the conditions of 3 g WPCBs dosage in 100 mL electrolyte, 30 g/L CuSO4·5H2O, 40 g/L NaCl, 150 g/L H2SO4, 0.5 A and 9 h. The separated micro-metal powders are mainly Cu, about 86.6%, without any nonmetal powders. Copper recovered is dendritic, with a copper recovery rate up to nearly 99%. Thus, slurry electrolysis shows a prospective future in e-waste reutilization, providing a way to enrich metals for all kinds of urban mines.

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%.

Electrolytic manganese anode slime (EMAS) is a solid waste found in the anode chamber during the production of electrolytic manganese metal, which mainly contains high concentration of manganese and other impurities. In EMAS, γ-MnO2 and δ-MnO2 turned into α-MnO2 after calcination, and the oxide can be dissolved by pickling. The results showed that the specific surface area of EMAS increased from 33.11 m2·g− 1 to 93.53 m2·g− 1, and the micropore volume increased from 0.0129 cm3·g− 1 to 0.0362 cm3·g− 1, as well as the specific capacity and the Open Circuit Voltage (OCV) of EMAS were 249.65 mAh·g− 1 and 1.60 V, respectively, under the condition of calcination temperature 400 °C, calcination time 1 h, sulfuric acid 1 mol·L− 1, pickling temperature 25 °C, pickling time 0.5 h, and liquid-to-solid ratio 8:1.

Municipal solid waste incineration (MSWI) fly ash contains chlorides, heavy metals, and organic pollutants, which requires appropriate disposal to eliminate this risk. In this study, the effects of agents on heavy metals removal from MSWI fly ash by electric field-enhanced washing were systematically studied. The results show that when these fly ashes were washed at a current density of 35 mA/cm2, polarity switching frequency of 40 Hz, Ethylenediaminetetraacetic acid (EDTA) dosage of 0.5 mol/L, and a pH of 2 for 4 h, almost all of the Cd and Ni could be were removed, with a removal efficiency of 100.00% and 99.59%, respectively. Meanwhile, it also shows a significant effect on Cu and Zn, with a removal efficiency higher than 85%. After washing, the results of the sequential extraction procedure showed that the residual forms of Pb, Cu, Zn, Cd, Ni, and As increased obviously. According to GB5085.3-2007, the toxicity of the treated MSWI fly ash were below their thresholds of 5 and 1 mg/L for Pb and Cd, respectively. Thus, a novel technology for heavy metals removal from MSWI fly ash is proposed.

Crystalline silicotitanate (CST) was synthesized via a sol-gel hydrothermal method using Na2Si2O3·9H2O and TiCl4 as silicon and titanium sources. The effects of pH, silicon concentration, hydrothermal temperature, and time on the CST synthesis were studied at a fixed molar ratio of silicon:titanium (0.98:1). Pure nano-CST crystals were synthesized at pH = 12.5, silicon concentration of 5 g L-1, 170 °C for 7 days. The average CST particle size was < 100 nm, with a Sr2+/Cs+ distribution coefficient up to 1.9 × 106 mL g-1/9.4 × 103 mL g-1 under the optimum conditions. In addition, nano-CST absorbed Sr2+/Cs+ over a wide pH range. The nano-CST also displayed a much faster equilibrium time, 4 h, as compared with previous studies. Furthermore, nano-CST adsorption of Sr2+/Cs+ followed a Langmuir adsorption model and was consistent with pseudo-second-order kinetics.

As an indispensable part of printed circuit boards (PCBs), central processing unit (CPU) slots contain a significant amount of precious metals which makes economic sense to recycle these materials. Slurry electrolysis is an attractive approach for electronic waste (e-waste) recycling. In this study, the effect of electrolyte reuse on the recovery of metals (Primarily aluminum, nickel, copper, lead, silver, palladium, platinum and gold), from waste CPU slots by slurry electrolysis is discussed in detail. These results show that metal recovery rate, more than 95% for all 13 cycles, was not affected by slurry electrolyte reuse during metal recycling from waste CPU slots, though the reuse of slurry electrolyte greatly impacted the distribution of metals in the anode residues, electrolyte and cathode metal powders. However, slurry electrolysis recovered metals from waste CPU slots and the effect of electrolyte reuse on the recovery of metals from waste CPU slots is discussed for the first time in this study. This could benefit the recycling process since it could improve cathode metal powders recovery rates by approximately 2 times. The acid usage could be significantly reduced by electrolyte reuse when compared to fresh electrolyte. Therefore, electrolyte reuse is demonstrated and slurry electrolysis is a feasible and potentially economically friendly choice for industrial e-waste recycling.

Waste Electrical and Electronic Equipment (WEEE) contain toxic metals and organic compounds, posing significant threats to human health and environmental quality. The risks vary according to equipment types and components that are influenced by innovations in technical configuration and regulatory policy. To disentangle the relative impacts of these influences in protecting health and environment, we investigated 13 WEEE and 14 components using a life cycle impact assessment procedure. Additionally, we analyzed Waste Mobile Phones (WMPs) and Waste Printed Circuit Boards (WPCBs) from computers manufactured between 2002 and 2010 to identify trends of toxic chemicals and potential adverse impacts associated with technological configurations and regulatory policies. The results show that, among WEEE, Cathode Ray Tube TV presented the highest carcinogenicity and non-carcinogenicity toxicity potential. Waste Air Conditioner posed the highest potential for ecotoxicity. Among electronic components, Waste Organic Light Emitting Diode displays posed the highest potential risk for carcinogenesis, whereas WPCBs from laptop computers posed the highest potential risk for non-cancer diseases. Solid State Drives posed the highest risks for ecotoxicity. Chromium was associated with risk of carcinogenesis and non-cancer diseases; whereas Al and Fe posed the highest potential for ecotoxicological impacts. During the period covered by the study, innovations in technological configurations and regulatory policies demonstrably reduced the potential toxicity risks posed by E-waste, attributable to reduction in the concentrations of toxic organic chemicals in WMPs/WPCBs. These results advance current understanding of strategies to reduce the risks posed by WEEE through coordination of technological innovations and regulatory policies.

Ammonia and manganese were simultaneously removed from electrolytic metal manganese residue leachate using phosphate salt. The influence of different N:P ratios and pH were investigated. Phase transition and decomposing behavior of precipitates and the characterization of the precipitates pyrolysis were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric analysis, differential thermal analysis, and scanning electron microscope. In the laboratory experiment, under the condition of 1:1.15 N:P ratio and 9.5 pH value, removal efficiencies of ammonia and manganese from the residue leachate were achieved 95.0% and 99.9%, respectively, and remaining concentration of orthophosphate was as low as 12 mg L−1. In the process, manganese was first removed as Mn3(PO4)2·7H2O, and then ammonia was removed as NH4MgPO4·6H2O. In addition, MgNaPO4, MgHPO4, Mg2P2O7, Na3PO4 and MnO2 were generated during precipitate pyrolysis process, and the ammonia removal efficiency decreased from 84.0% in the first cycle to 66.0% in the fifth, and manganese removal efficiency was approximately 99.0%. Economic evaluation shows that recycling the precipitates for three times could save 68.4% cost on average, compared to the use of pure chemicals.

In this study, P-LGMgO (low-grade MgO and NaH 2 PO 4 ·2H 2 O), P-CaO (CaO and NaH 2 PO 4 ·2H 2 O), and P-MgCa (low-grade MgO, CaO and NaH 2 PO 4 ·2H 2 O) were used for the solidification/stabilization (S/S) of electrolytic manganese residue (EMR). Relevant characteristics such as ammonia nitrogen and manganese stabilization behavior, unconfined compressive strength (UCS), probable S/S mechanisms, and EMR leaching test were investigated. The results demonstrate that using P-LGMgO had higher stabilization efficiency than P-CaO and P-MgCa for the S/S of EMR at the same stabilization agent dose. The stabilization efficiency of ammonia nitrogen and manganese in the EMR were 84.0% and 99.9%, respectively, and the UCS of EMR was 5.1 MPa using P-LGMgO process after curing for 28 days when the molar ratio of Mg:P was 5:1 and dose of stabilization agent was 12 wt%. In this process, ammonia nitrogen was stabilized by struvite (NH 4 MgPO 4 ·6H 2 O), and manganese by bermanite (Mn 3 (PO 4 ) 2 (OH) 2 ·4H 2 O) and pyrochroite (Mn(OH) 2 ). The leaching test results show that the values of all the measured metals on the 28th day were within the permitted level for the GB8978-1996 test suggested by China’s environmental protection law and the concentration of ammonia nitrogen can be reduced from 504.0 mg L −1 to 76.6 mg L −1 .

In this study, an improved process for leaching manganese from electrolytic manganese residue (EMR) by electro-reduction was developed. The mechanisms of the electro-reduction leaching were investigated through X-ray diffraction, scanning electron microscopy, X-ray fluorescence, and Brunauer Emmett Teller. The results show that the electric field could change the surface charge distribution of EMR particles, and the high-valent manganese can be reduced by electric field. The leaching efficient of manganese reached 84.1% under the optimal leaching condition: 9.2 wt% H2SO4, current density of 25 mA/cm2, solid-to-liquid ratio of 1:5, and leaching time for 1 h. It is 37.9% higher than that attained without an electric field. Meanwhile, the manganese content in EMR decreased from 2.57% to 0.48%.

Ammonia nitrogen- and manganese-contaminated water poses a considerable threat on the safety of water resources. In this work, pulse current (PC) electrolysis, a novel process, was developed to recover manganese and remove ammonia nitrogen from simulation wastewater simultaneously. Accordingly, the parameters of pulse electrolysis, and technological conditions, including temperature, initial pH, and concentration of addition NaCl, were investigated. The results showed that the concentration of manganese in simulation wastewater could be reduced from 160 mg L−1 to 0.2 mg L−1, meanwhile, ammonia nitrogen could be removed from 80 mg L−1 to 0.1 mg L−1 for 2.5 h PC electrolysis at 30 mA cm−2, 1000 Hz, and duty cycle 50% where settled with Ti/SnO2 IrO2 RuO2 electrodes, when the initial pH was 10.0 and NaCl addition was 0.008 mol L−1 at room temperature. Moreover, XRD and SEM analysis showed that manganese dioxide was deposited on the anode, and manganese in simulation wastewater was mainly recovered in the form of manganese dioxide.

In this work, nitrite was developed to simultaneously remove manganese and ammonia nitrogen from wastewater by the electrochemical method. The characteristics of electrolytic reaction were observed via cyclic voltammograms. Moreover, the mole ratio of nitrite and ammonia nitrogen, voltage, and initial pH value, which affected the removal efficiency of ammonia nitrogen and manganese, were investigated. The results showed that the concentration of ammonia nitrogen in wastewater could be reduced from 120.2 to 6.0 mg L−1, and manganese could be simultaneously removed from 302.4 to 1.5 mg L−1 at initial pH of 8.0, the mole ratios of nitrite and ammonia nitrogen of 1.5:1, and voltage of 20 V direct current electrolysis for 4.0 h. XRD analysis showed that manganese dioxide was deposited on the anode, and manganese was mainly removed in the form of manganese hydroxide precipitation in the cathode chamber.

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.

In this study, a new electrochemical method was used to simultaneously efficient removal of Mn2+ and NH4+-N in wastewater with Cu plate as cathode. The effects of various reaction parameters on the concentrations of Mn2+, NH4+-N and by-products (NO3−-N and NO2−-N, free chlorine and residual chlorine), as well as the removal mechanism were investigated. The results showed that the removal efficiencies of Mn2+ and NH4+-N were 99.1% and 92.9%, and the concentrations of NO3−-N, NO2−-N, free chlorine and residue chlorine were 0.73 mg/L, 0.15 mg/L, 0.13 mg/L and 0.63 mg/L reacting for 3 h at room temperature, respectively, when the current density was 10 mA/cm2, the mass ratio of ClO− and Cl− was 1:1, the initial pH was 9. The concentrations of Mn2+, NH4+-N and by-products in wastewater met the integrated wastewater discharge standard (GB8978-1996). In addition, spherical manganese oxide was deposited on the anode plate, and spherical manganese oxide collapsed over electrolysis time. Manganese was mainly removed in the form of MnO, Mn(OH)2 and MnO2. NH4+-N was mainly oxidized to N2. Economic evalution revealed that the treatment cost was 2.93 $/m3.

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.

Removal of hexavalent chromium had attracted much attention as it is a hazardous contaminant. An electrocoagulation-like technology electro-reduction was applied. The chromium (VI) in the wastewater was reduced to chromium (III) by the electron supplied by electricity power and Fe2+, formed from corrosion of steel electrodes in acidic conditions. The mechanism and parameters affecting the reaction were investigated. The results optimized by response surface methodology indicated that the influence of single factor on the reduction efficiency followed the order: A: dosage of H2SO4 &gt, C: reaction time &gt, D: reaction temperature &gt, B: current intensity. The reduction efficiency was hardly affected by current intensity, while it was increased with the increasing of reaction time and acid concentration. The reducing agent, Fe2+ an and extra free electron, acted as a reducing agent and could easily reduce hexavalent chromium to trivalent chromium at high temperatures in an acidic medium.

The objective of this work was the immobilization of soluble manganese (Mn) and ammonium nitrogen (NH4 +-N) leached from electrolytic manganese residue (EMR). Immobilization of Mn was investigated via carbonation using carbon dioxide (CO2) and alkaline additives. NH4 +-N immobilization was evaluated via struvite precipitation using magnesium and phosphate sources. Results indicated that the immobilization efficiency of Mn using CO2 and quicklime (CaO) was higher than using CO2 and sodium hydroxide (NaOH). This higher efficiency was likely due to the slower release of OH− during CaO hydrolysis. The immobilization efficiency of Mn was >99.99 % at the CaO:EMR mass ratio of 0.05:1 for 20-min reaction time. The struvite precipitation of NH4 +-N was conducted in the carbonated EMR slurry and the immobilization efficiency was 89 % using MgCl2 · 6H2O + Na3PO4 · 12H2O at the Mg:P:N molar ratio of 1.5:1.5:1 for 90-min reaction time. A leaching test showed that the concentrations of Mn and NH4 +-N in the filtrate of the treated EMR were 0.2 and 9 mg/L, respectively. The combined immobilization of Mn and NH4 +-N was an effective pretreatment method in the harmless treatment of the EMR.