Chlorine and heavy metals removal from municipal solid waste incineration fly ash by electric field enhanced oxalic acid washing.

Electric field enhanced oxalic acid (H2C2O4) washing was conducted to examine the simultaneously removal efficiency of heavy metals (HMs) and chlorine, especially insoluble chlorine from municipal solid waste incineration fly ash (MSW FA). Results show that chlorine and HMs can be effectively removed with a total chlorine, As, Ni and Zn removal rate of 99.10%, 79.08%, 75.42% and 71.43%, when the electrode exchange frequencies is 40 Hz, current density is 50 mA/cm2, H2C2O4 adding amount is 0.5 mol/L and the reaction time is 4 h. Insoluble chlorine removal efficiency is up to 95.32%, much higher than reported studies. And the chlorine content in the residue is lower than 0.14%. Meanwhile, HMs removal efficiency is remarkable, 41.62%-67.51% higher than that of water washing. The high-efficient removal effect is caused by the constantly changing direction of electrons hitting the fly ash surface, which provides more escape channels for internal chlorine and HMs. These results proved that electric field enhanced oxalic acid washing could be a promising method for removing contaminants from MSWI fly ash.

Enhanced leaching of manganese from low-grade pyrolusite using ball milling and electric field.

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.

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.

A new electrochemical method for simultaneous removal of Mn2+and NH4+-N in wastewater with Cu plate as cathode.

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.

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.

Simultaneous optimizing removal of manganese and ammonia nitrogen from electrolytic metal manganese residue leachate using chemical equilibrium model.

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.

Adsorption behaviors of phenanthrene and bisphenol A in purple paddy soils amended with straw-derived DOM in the West Sichuan Plain of China.

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.

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%.

Simultaneous stripping recovery of ammonia-nitrogen and precipitation of manganese from electrolytic manganese residue by air under calcium oxide assist.

Leaching tests of electrolytic manganese residue (EMR) indicated that high contents of soluble manganese and ammonia-nitrogen posed a high environmental risk. This work reports the results of simultaneous stripping recovery of ammonia-nitrogen and precipitation of manganese by air under calcium oxide assist. The ammonia-nitrogen stripping rate increased with the dosage of CaO, the air flow rate and the temperature of EMR slurry. Stripped ammonia-nitrogen was absorbed by a solution of sulfuric acid and formed soluble (NH4)2SO4 and (NH4)3H(SO4)3. The major parameters that effected soluble manganese precipitation were the dosage of added CaO and the slurry temperature. Considering these two aspects, the efficient operation conditions should be conducted with 8 wt.% added CaO, 60°C, 800 mL min(-1) air flow rate and 60-min reaction time. Under these conditions 99.99% of the soluble manganese was precipitated as Mn3O4, which was confirmed by XRD and SEM-EDS analyses. In addition, the stripping rate of ammonia-nitrogen was 99.73%. Leaching tests showed the leached toxic substances concentrations of the treated EMR met the integrated wastewater discharge standard of China (GB8978-1996).

Enhanced removal of Pb from electrolytic manganese anode slime and preparation of chemical MnO2.

Electrolytic manganese anode slime (EMAS) is produced during the production of electrolytic manganese metal. In this study, a method based on vacuum carbothermal reduction was used for Pb removal in EMAS. A Pb-removal efficiency of 99.85% and MnO purity in EMAS of 97.34 wt.% were obtained for a reduction temperature of 950°C and a carbon mass ratio of 10% for a holding time of 100 min. The dense structure of the EMAS was destroyed, a large number of multidimensional pores and cracks were formed, and the Pb-containing compound was reduced to elemental Pb by the vacuum carbothermal reduction. A recovery efficiency for chemical MnO2 of 36.6% was obtained via preparation from Pb-removed EMAS through the 'roasting-pickling disproportionation' process, with an acid washing time of 100 min, acid washing temperature of 70°C, H2SO4 concentration of 0.8 mol·L-1, liquid-solid mass ratio of 7 mL·g-1, calcination temperature of 60°C and calcination time of 2.5 h. Moreover, the crystal form of the prepared chemical MnO2 was found to be basically the same as that of electrolytic MnO2, and its specific surface area, micropore volume and discharge capacity were all higher than that of electrolytic MnO2. This study provides a new method for Pb removal and recycling for EMAS.HighlightsVacuum carbothermal reduction method was used for Pb removal in EMAS.The removal efficiency of Pb was 99.85%.Chemical MnO2 with excellent discharge performance was prepared using treated EMAS.This study provides a new method for EMAS resource utilization.

Electrolytic manganese residue disposal based on basic burning raw material: Heavy metals solidification/stabilization and long-term stability.

Solidification/stabilization (S/S) is an option for the treatment of electrolytic manganese residue (EMR). Basic burning raw material (BRM) could successfully solidify/stabilize EMR, though heavy metals S/S mechanism and long-term stability remain unclear. Herein, Mn2+ and NH4+ S/S behavior, hydrated BRM and S/S EMR characterization, Mn2+ long-term leaching behavior, phase and morphology changes for long-term leaching were discussed in detail to clarify these mechanisms. Mn2+ and NH4+ leaching concentrations as well as pH value in S/S EMR were respectively 0.02 mg/L, 0.68 mg/L and 8.75, meeting the regulations of Chinese standard GB 8978-1996. Long-term stability of EMR was significantly enhanced after S/S. Mn2+ leaching concentration, Mn2+ migration, Mn2+ cumulative release, Mn2+ apparent diffusion coefficient and conductivity of EMR reduced to 0.05 mg/L, 5.5 × 10-6 mg/(m2·s), ~ 9 mg/m2, 6.30 × 10-15 m2/s and 435 µs/cm. Mechanism studies showed that the hydration of BRM forms OH-, calcium silicate hydrate gels (C-S-H) and ettringite. Therefore, during S/S process, NH4+ was escaped as NH3, Mn2+ was solidified/stabilized as tephroite (Mn2SiO4), johannsenite (CaMnSi2O6) and davreuxite (MnAl6Si4O17(OH)2), and Pb2+, Cu2+, Ni2+, Zn2+ were solidified/stabilized by C-S-H and ettringite via substitution and encapsulation. This study provides a good choice for EMR long-term stable storage.

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 CO32-, 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 CO32- 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.

Application of Machine Learning in a Mineral Leaching Process-Taking Pyrolusite Leaching as an Example.

In this study, several machine learning models were used to analyze the process variables of electric-field-enhanced pyrolusite leaching and predict the leaching rate of manganese, and the applicability of those models in the leaching process of hydrometallurgy was compared. It showed that there was no correlation between the six leaching conditions; in addition to the leaching time, the concentrations of sulfuric acid and ferrous sulfate had great influences on the leaching of pyrolusite. The results of the prediction models showed that the support vector regression model has the best prediction performance, with regression index (R 2) = 0.92 and mean square error = 25.04, followed by the gradient boosting regression model (R 2 > 0.85). In this research, machine learning models were applied to the optimization of the manganese leaching process, and the research process and methods were also applicable to other hydrometallurgical processes for majorization and result prediction.

Toxic footprint and materials profile of electronic components in printed circuit boards.

Waste printed circuit boards (WPCBs) contain valuable material resources and hazardous substances, thereby posing a challenge for sustainable resource recovery and environmental protection initiatives. Overcoming this challenge will require mapping the toxic footprint of WPCBs to specific materials and substances used in manufacturing electronic components (ECs). Therefore, this work collected 50 EC specimens from WPCBs in five ubiquitous consumer products, such as television, refrigerator, air conditioner, washing machine and computer. The work extracted and analyzed metal contents and used leachability assessments based on tests adopted by the regulatory policies from China and the United States. The work found that copper and iron are the most abundant constituents in ECs, with concentrations ranging 5.90-796.62 g/kg and 0-831.53 g/kg, respectively; whereas abundance of precious metal content is in the order of silver > gold > palladium > platinum, with silver concentration ranging 15-5290 mg/kg. The content of marginally-regulated toxic substance arsenic ranged 0-9700 mg/kg; whereas fully regulated toxic metals such as chromium, lead and mercury did not exceed the thresholds set by China and US standards. The work found new toxic threats from arsenic and selenium leached from 20 of 50 ECs exceeding regulatory standards. These results will aid manufacturers and recyclers in protecting workers' health and environmental quality from arsenic and selenium pollution, and should initiate discussion about regulating these toxic components as part of a comprehensive program to reduce the toxic footprint of electronic products.

Metal mobility and toxicity of reclaimed copper smelting fly ash and smelting slag.

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.

Chloride ion inhibition of electrochemical oscillations on the anode of an electrolytic manganese metal cell.

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 at the anode of the electrolytic manganese metal cell was investigated. The results showed that the electrochemical oscillation at the anode was inhibited by Cl-, and the amplitude and frequency of the electrochemical oscillation decreased as the increase of Cl- concentration. When the concentration of Cl- was 2.68 g/L, the cathode and anode electrodes could be effectively activated, and the manganese current efficiency reached its minimum, correspondingly, the power consumption reached its maximum. In addition, the presence of the chloride reduced the production of MnO2 at the anode surface. ClO4- and free ions formed insoluble amorphous structures on the surface of the anode with the increase in reaction time and chloride ion concentration, and the insoluble amorphous structures prevented further generation of MnO2. Thus, electrolytic manganese metal energy consumption decreased.

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.

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.