Thermodynamic simulation of the reaction mechanism of Mn2+ oxidation with an SO2/O2 mixture

Manganese oxides are essential in the production of electronic components and batteries. A promising alternative for their production from secondary sources is the leaching of the Mn and later oxidative precipitation of Mn2+ by an SO2/O2 mixture. The steps involved in this last reaction have not been fully understood. This work presents the reaction mechanism describing the oxidative precipitation of Mn2+ by an SO2/O2 mixture with MnO2 and SO4 2− as reaction products. The analysis was supported in thermodynamic simulations in which the formation and effect of the oxidant species was verified. The proposed reaction mechanism was validated with experimental batch tests and it was found that it describes satisfactorily the oxidation reaction. Experimental evidence revealed that this system is efficient at low concentrations of SO2 in the gas mixture composition; an optimal composition of 7.3% SO2 of the gas mixture was found

Manganese Removal from Sulfuric Acid Leach Solutions of Nickel Laterite Ores

An oxidative precipitation technique using potassium permanganate was explored for the removal of manganese from pregnant leach solution (PLS) generated from the pressure acid leaching (PAL) of nickel laterite ores. The results revealed that the right combination of pH and molar ratio is important in order to achieve maximum removal of manganese (II) with minimum nickel (II) and cobalt (II) losses

Some aspects of nanocrystalline nickel and zinc ferrites processed using microemulsion technique

Nanocrystalline nickel and zinc ferrites synthesised using a microemulsion technique were characterised by high resolution transmission electron microscopy and vibrating sample magnetometry. A narrow and uniform distribution of crystals of size range 5 – 8 nm, distinguished by a clear lack of saturation magnetisation at 9 kOe, were obtained. Also, no coercivity or remanence was observed.

Development of A Hydrometallurgical Process for the Extraction of Cobalt, Manganese, and Nickel from Acid Mine Drainage Treatment Byproduct

Critical minerals (CMs) are defined as crucial elements for the country\u27s economy due to the development of new cutting-edge applications and the risk of an eventual disruption in their supply chain. The unique chemical and physical properties of the CMs have made these elements decisive in the growth of industries such as telecommunications, army, medicine, Aerospace, etc. In 2022, the US Geological Survey established a list of 50 CMs, including manganese, cobalt, nickel, aluminum, magnesium, and others. Of the total of CMs, 26 are 100% imported from outside the United States (Venditti, 2022). Driven by the ever-increasing demand for critical minerals (CMs) and the need to diversify their supply chains, extensive research efforts have been devoted to extracting CMs from various secondary sources, such as fossil fuel (coal ash and refuse), mining tailings, refuse piles, water produced by oil and gas industry, electronic waste (E-waste), and acid mine drainage (AMD), among which acid mine drainage and its treatment byproducts proved to be a viable source. Characterization studies of different AMD and sludge materials indicate the occurrence of CMs containing rare earth elements (REEs), cobalt, manganese, nickel, zinc, aluminum, magnesium, etc. In this context, our research aimed to develop an optimized hydrometallurgical process for extracting multiple individual CM concentrates, including cobalt, manganese, and nickel, from acid mine drainage treatment byproducts. The feedstock used throughout is an REE solvent extraction raffinate loaded with cobalt, manganese, and nickel, with grades corresponding to 38.3 mg/L, 370.7 mg/L, and 69.4 mg/L, respectively, as well as impurity metals such as 3643.1 mg/L of aluminum, 2161.4 mg/L of magnesium, 224.1 mg/L of calcium, and 159.2 mg/L of iron. A hydrometallurgical process developed at the laboratory scale consists of an initial sodium hydroxide precipitation using 2M NaOH until reaching a pH value equal to 5. The approach targeted the upstream removal of impurities such as aluminum and iron and was established by performing stagewise precipitation from an initial pH of 2 to a final value of 12. The optimum pH values were identified by taking samples at each pH setpoint and analyzing the tradeoff between CM recovery and impurity removal. Afterward, a solution with a higher concentration of CMs and lower impurity content was subjected to a new precipitation process with 2M NaOH until reaching pH 10 to generate a precipitated product rich in CMs. The precipitated solids obtained at the pH range of 5 to 10 were treated to separate cobalt and nickel from manganese. The procedure carried out in this stage was a nitric acid washing (HNO3), which was performed under controlled conditions of temperature, time, volume, etc. Two products were obtained in this stage: a dissolved solution with an extractable concentration of cobalt and nickel (393 mg/L and 619.9 mg/L, respectively) and a solid product with a manganese purity of 47.9% by weight. To continue separating cobalt and nickel from remaining impurities, such as magnesium, a new stagewise precipitation with sodium sulfide (Na2S) at 1M was performed to determine the separation feasibility of different elements in the solution. At this stage, three separation steps were determined to generate three solid products: the solid precipitated at the pH range of 1-5 with 5.1 wt.% of cobalt and 8 wt.% of nickel, solids precipitated at pH 5-10 with 20.15 wt.% of manganese, and the solid product at pH 10-12 with 27.49 wt.% of magnesium. Other separation approaches were also evaluated in this study to assess the possibility of separating cobalt from nickel, including oxidative precipitation and solvent extraction. As a result of all these combined studies, the highest cobalt and nickel purity of 9.92 wt.% and 14 wt. % were generated, respectively, in addition to the manganese (47.9 wt. %) and magnesium (27.49 wt. %) products obtained from the developed process

Oxidative precipitation synthesis of calcium-doped manganese ferrite nanoparticles for magnetic hyperthermia

Superparamagnetic nanoparticles are of high interest for therapeutic applications. In this work, nanoparticles of calcium-doped manganese ferrites (CaxMn1−xFe2O4) functionalized with citrate were synthesized through thermally assisted oxidative precipitation in aqueous media. The method provided well dispersed aqueous suspensions of nanoparticles through a one-pot synthesis, in which the temperature and Ca/Mn ratio were found to influence the particles microstructure and morphology. Consequently, changes were obtained in the optical and magnetic properties that were studied through UV-Vis absorption and SQUID, respectively. XRD and Raman spectroscopy studies were carried out to assess the microstructural changes associated with stoichiometry of the particles, and the stability in physiological pH was studied through DLS. The nanoparticles displayed high values of magnetization and heating efficiency for several alternating magnetic field conditions, compatible with biological applications. Hereby, the employed method provides a promising strategy for the development of particles with adequate properties for magnetic hyperthermia applications, such as drug delivery and cancer therapy.This work was funded by the Portuguese Foundation for Science and Technology (FCT) in the framework of the Strategic Funding of CF-UM-UP (UIDB/04650/2020, UIDP/04650/2020), CQUM (UIDB/00686/2020), CICECO Aveiro Institute of Materials (UIDB/50011/2020, UIDP/50011/2020 & LA/P/0006/2020) and by Ministerio de Economía y Competitividad de España (PID2020-113704RB-I00 and PID2020-119242RB-I00), Xunta de Galicia (Centro Singular de Investigación de Galicia—Accreditation 2019-2022 ED431G 2019/06 and IN607A 2018/5 and project ED431C 2020-06), and European Union (EU-ERDF Interreg V-A—Spain-Portugal 0245_IBEROS_1_E, 0712_ACUINANO_1_E, and 0624_2IQBIONEURO_6_E, and Interreg Atlantic Area NANOCULTURE 1.102.531), and the European Union H2020-MSCA-RISE-2019 PEPSA-MATE project. S.R.S. (872233) Veloso acknowledges FCT for a PhD grant (SFRH/BD/144017/2019). Support from MAP-Fis Doctoral Programme is also acknowledged

Mn control in zinc electrowinning process by electrochemical means using Pb-Ag anode

Les conditions optimales pour l'élimination du dioxyde de manganèse (MnO2) en utilisant une anode Pb-0.7 pd% d'Ag ont été étudiées en utilisant des électrolytes simulant les conditions pour le fonctionnement de purification et d'extraction électrolytique. L'effet de la densité, de la température, du pH et de la concentration de manganèse sur l'efficacité du courant de formation de MnO2 et les tensions anodiques ont été étudiés à l'aide d'essais galvanostatiques. La spectroscopie d'émission atomique par plasma micro-ondes (MP-AES) a été utilisée pour mesurer la concentration d'ions manganèse dans les électrolytes. Des essais de voltamétrie linéaire à balayage (LSV) ont été menés pour étudier l'effet de la température et de la concentrations de Mn2+ sur la réaction de dégagement d'oxygène (OER) et la formation de MnO2. La microscopie électronique à balayage avec spectroscopie à dispersion d'énergie (SEM-EDS), la diffraction des rayons X (XRD) et la fluorescence X (XRF) ont été utilisées pour la caractérisation de surface et les compositions chimiques. Les résultats ont montrés que les conditions d'extraction électrolytiques fonctionnels pour éliminer le MnO2 consiste à utiliser la Pb-0.7 pd% d'Ag. L'efficacité de courant (CE) la plus élevée de l'élimination du manganèse était de 21 %, ce qui était obtenu dans l'électrolyte à pH 1 et à une densité de courant de 125 A m-2 à 40 °C après 2 h d'électrolyse. La valeur d'efficacité a été augmentée à 28 % à l'aide d'anodes neuves remplacées toutes les 30 minutes.The optimum conditions for manganese dioxide (MnO2) removal using Pb-0.7 wt.% Ag anode have been investigated using electrolytes simulating the purification and electrowinning operating conditions. The effect of current density, temperature, pH and manganese concentration on the current efficiency of MnO2 formation and anodic voltages have been studied using galvanostatic tests. Microwave plasma atomic emission spectroscopy (MP-AES) has been used to measure the concentration of manganese ions in the electrolytes. Linear sweep voltammetry (LSV) tests were conducted to study the effect of temperature and Mn2+ concentrations on oxygen evolution reaction (OER) and MnO2 formation. Scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS), X-ray diffraction (XRD) and X-ray fluorescence (XRF) were used to study the surface characterizations and chemical compositions. The results revealed that the operating electrowinning conditions are more appropriate for MnO2 removal on Pb-0.7 wt.% Ag surface. The highest current efficiency (CE) of manganese removal was 21 % which obtained in the electrowinning electrolyte at pH 1 at 125 A m-2 at 40 °C after 2 h of electrolysis. The current efficiency value was increased to 28 % using fresh anodes replaced each 30 minutes

Processes controlling metal transport and retention as metal-contaminated groundwaters efflux through estuarine sediments

Factors affecting the transport and retention of Cd, Cr, Cu, Ni, Pb and Zn in acidic groundwaters as they pass through estuarine sediments were investigated using column experiments. Acidic groundwaters caused the rapid dissolution of iron sulfide (AVS) and other iron and manganese phases from sediments that are important for metal binding and buffering. Metal breakthrough to overlying water occurred in the order of Ni\u3eZn\u3eCd\u3e\u3eCu\u3e\u3eCr/Pb. Metal transport increased as the sediment permeability increased, reflecting the low resistance to flow caused by larger sand-sized particles and the decreased abundance of metal adsorption sites on these materials. Metal mobility increased as the groundwater pH decreased, as flow rate or metal concentrations increased, and as the exposure duration increased. Groundwater Cr and Pb were promptly attenuated by the sediments, the mobility of Cu was low and decreased rapidly as sediment pH increased above 4.5, while Cd, Ni and Zn were the most easily transported to the surface sediments and released to the overlying waters. For groundwaters of pH 3, metal migration velocities through sandy sediments were generally 0.5-2% (Cr, Pb), 1-6% (Cu) and 4-13% (Cd, Ni, Zn) of the total groundwater velocity (9-700 m/year). The oxidative precipitation of Fe(II) and Mn(II) in the groundwaters did not affect metal mobility through the sediments. The results indicated that the efflux of acidic and metal-contaminated groundwater through estuarine sediments would affect organisms resident in sandy sediments more greatly than organisms resident in fine-grained, silty, sediments

Distribution of dissolved and particulate Fe in an estuarine system at Bagan Pasir, Perak

The distribution of dissolved iron (dFe) and particulate iron in the estuarine system was studied where in-situ water sampling stations were selected at Bagan Pasir, Perak. The concentration of dFe was 1.17±0.28 mg/L on average at the estuary, while in freshwater samples its concentration was 0.08±0.00 mg/L. This study found that the concentration of particulate Fe in freshwater system was higher than that in the estuary system. The Fe concentration was 0.95±0.03 mg/kg and 0.80±0.18 mg/kg at the freshwater and estuary systems, respectively. We have applied a distribution coefficient (KD) in order to quantify the partitioning of Fe between the particulate (>0.45 µm) and dissolved (<0.45 µm) phases. The KD value of Fe in the freshwater system was much higher compared to that in the estuary, where the KD value was 12.18 in freshwater and 0.48 -1.31 in the estuary. This indicated that Fe in this area has a strong affinity with the particulate phase in a freshwater system and this is probably due to the anthropogenic input. On the other hand, Fe may exist in colloidal or organic ligands which probably originate from surface sediment or a biological process in water columns at the estuarine area

Hydrous Manganese Oxide Doped Gel Probe Sampler for Measuring In Situ Reductive Dissolution Rates. 2. Field Deployment

In situ rates of reductive dissolution in submerged shoreline sediments at Lake Tegel (Berlin, Germany) were measured with a novel hydrous manganese (Mn) oxide-doped gel probe sampler in concert with equilibrium gel probe and sequential extraction measurements. Rates were low in the top 8 cm, then showed a peak from 8 to 14 cm, with a maximum at 12 cm depth. This rate corresponded with a peak in dissolved porewater iron (Fe) at 11 cm depth. Below 14 cm, the reductive dissolution rate reached an intermediate steady value. Lower rates at depth corresponded with increases in operationally defined fractions of carbonate-bound and organic- and sulfide-bound Mn and Fe as detected by sequential extraction. Observed rates of reductive dissolution, which reflect a capacity for Mn reduction rather than actual rates under ambient conditions, appear to correlate with porewater chemistry and sequential extraction fractions as expected in early sediment diagenesis, and are consistent with previous measurements of in situ reductive dissolution rates. Significant downward advection in this bank filtration setting depletes the Mn and Fe oxides in the sediments and enhances the transport of dissolved Fe and Mn into the infiltrating water

Recovery of vanadium pentoxide from spent catalyst used in the manufacture of sulphuric acid

Vanadium has many industrial uses and its contribution to environmental contamination is increasing all the time. Recovery of vanadium pentoxide from spent sulphuric acid catalysts was performed using a three-step process involving acid leaching, oxidation and precipitation. Several different acids were used in the leaching process. Finally, sulphuric acid was used in various concentrations, solid to liquid ratios, stirring times and temperatures. A high solid/liquid ratio in the leaching stage was used to obtain high concentration of vanadium pentoxide and low acid consumption that allowed direct precipitation without the use of extraction by rather expensive organic solvents. Sodium carbonate solution of one mole/liter concentration was used in the precipitation stage. An industrial application including material balance and operating conditions with an overall vanadium pentoxide recovery efficiency of (70%) was proposed