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The leaching characteristics and kinetics of manganese extraction from pyrolusite using black liquor lignin as a reductant in a sulfuric acid medium were explored in this paper. Under the optimal leaching conditions (temperature 363 K, H2SO4 concentration 2.0 mol/L, lignin-pyrolusite mass ratio 1.6, particle size passing an 80-mesh sieve, agitation speed 400 rpm, and leaching time 60 min), manganese leaching efficiency exceeds 96.83%. Kinetic analysis revealed that the leaching of manganese follows an internal-diffusion-dominated kinetic model. The activation energy is calculated as 26.68 kJ/mol, with a pre-exponential factor of 67.91 min−1. Additionally, the reaction orders relative to H2SO4 concentration and LPMR are determined to be 1.56 and 0.97, respectively.

The inefficient leaching of manganese is the main factor hindering the commercialization of the reduction process during manganese recovery using pyrite as the reducing agent. Hence, a new method for improving recovery efficiency and reducing the cost is required. This study uses microwave heating as a strengthening method to extract Mn 2+ from pyrolusite and the leaching conditions are optimized. It was found that the extraction rate of Mn 2+ could reach 95.07% under microwave heating through the conditions of H 2 SO 4 is 1.2 mol/L, m(pyrolusite)/m(pyrite) equals to 10:2, leaching temperature is 90 ℃, and a liquid–solid (L/S) ratio of 10:1. The achieved extraction rate was higher than that of 75.08% under the conventional heating achieved at the same conditions. Besides, experimental studies have found that microwave heating can change the process and direction of chemical reactions, shorten the reaction time, and reduce sulfuric acid. Finally, the kinetic study indicates that the leaching process under microwave heating is controlled by surface chemical reactions. The equation of leaching kinetics is 1 − (1 − x) 1/3  = 3425.32/r 0 ·[H 2 SO 4 ] 1.316 ·[FeS 2 /MnO 2 ] 0.907 ·exp(− 45.03/(RT)·t. The activation energy is 45.03 kJ/mol. Meanwhile, through a scanning electron microscope and particle size analyzer, microwave heating has a significant influence on reducing the ore diameter and increasing the specific surface area of the sample. This study aims to provide an experimental trial case for studying the mechanism of microwave-enhanced leaching process during manganese recovery using pyrite as the reducing agent. The reported kinetics research may guide the development of the industrial application for Mn recovery.

The low-cost Fe(II) reductants used in the leaching of pyrolusite usually cause high concentrations of iron ions in the leaching solution, which are difficult to treat and recover. Herein, a green cyclic leaching process for pyrolusite with recycling and reusing of Fe(II) reductants was developed. Sodium sulfide was introduced to reduce and precipitate iron ions in the leaching solution. Ep-H diagrams show that Fe3+ can be reduced to Fe2+ by S2− and form a precipitate with the high efficiency of 93.09%. Since the main component of the precipitate was ferrous disulfide with reducibility, it was used as a reducing agent for low-grade manganese oxide ores. A total of 97.96% of the manganese was highly reductively leached by the obtained precipitate of 0.28 g·g−1 ore. Furthermore, the leaching efficiency was almost unchanged after five iterations of cyclic experiments. The cyclic leaching process enables the efficient leaching of manganese and the recycling of iron, which provides a green and economic method for the efficient utilization of low-grade pyrolusite resources.

A very low concentration of manganese (Mn) in water is a critical issue for municipal and industrial water supply systems. Mn removal technology is based on the use of manganese oxides (MnOx), especially manganese dioxide (MnO2) polymorphs, under different conditions of pH and ionic strength (water salinity). The statistical significance of the impact of polymorph type (akhtenskite ε-MnO2, birnessite δ-MnO2, cryptomelane α-MnO2 and pyrolusite β-MnO2), pH (2–9) and ionic strength (1–50 mmol/L) of solution on the adsorption level of Mn was investigated. The analysis of variance and the non-parametric Kruskal–Wallis H test were applied. Before and after Mn adsorption, the tested polymorphs were characterized using X-ray diffraction, scanning electron microscope techniques and gas porosimetry analysis. Here we demonstrated the significant differences in adsorption level between MnO2 polymorphs’ type and pH; however, the statistical analysis proves that the type of MnO2 has a four times stronger influence. There was no statistical significance for the ionic strength parameter. We showed that the high adsorption of Mn on the poorly crystalline polymorphs leads to the blockage of micropores in akhtenskite and, contrary, causes the development of the surface structure of birnessite. At the same time, no changes in the surfaces of cryptomelane and pyrolusite, the highly crystalline polymorphs, were found due to the very small loading by the adsorbate.

In this work, a novel method for extraction of manganese from low-grade pyrolusite by a sawdust pyrolysis reduction roasting-acid leaching process was explored. The reduction roasting was studied systematically, and the mechanism was also explored by thermodynamic and phase change analysis. Results indicate that sawdust was rapidly pyrolyzed at 250–450°C to generate a large amount of reducing gases such as CO, CH 4 , and H 2 , which gradually reduced MnO 2 in low-grade pyrolusite to MnO. The reduction process of MnO 2 was identified as MnO 2 →Mn 2 O 3 →Mn 3 O 4 →MnO. It was proved that MnO 2 of low-grade pyrolusite could be reduced effectively to MnO at lower temperature and shorter duration time by sawdust pyrolysis. Meanwhile, the optimum leaching efficiency of 99.45% for manganese could be attained when sawdust dosage was 11% of the mass of low-grade pyrolusite, the roasting temperature was 500°C, and the roasting time was 25 min.

In this study, tartaric acid was identified as an efficient reductant for the reductive leaching of manganese from low-grade pyrolusite ore in an H 2 SO 4 solution. The effect of H 2 SO 4 concentration, tartaric acid concentration, time, and temperature on the leaching efficiency of low-grade pyrolusite ore was investigated. Evidently, when taking into account the various parameter ranges, the greater portion of the increase in efficiency can be attributed to the concentration of tartaric acid and temperature. For instance, by increasing the concentration of tartaric acid within the range of 0 to 0.19 M, the efficiency of manganese has experienced a surge of roughly 62%. In addition, temperature has a favorable impact on the leaching efficiencies of both Mn and Fe; however, the effect is more pronounced for Mn. Specifically, when the temperature is raised from 25 to 85 °C, the leaching efficiency of Mn and Fe rises from 28.9 and 14.3% to 90 and 33.5%, respectively. At optimal leaching conditions (H 2 SO 4 concentration: 1.4 M, time: 150 min, temperature: 85 °C, and tartaric acid concentration: 0.16 M), 94% Mn and 41% Fe were leached. Fourier transform infrared spectroscopy (FTIR) confirmed the breakdown of the strong C=O stretching band for tartaric acid in the presence of H 2 SO 4 and the formation of new bonds at a lower wavelength. Based on the FTIR analysis conducted on the leaching solution, it was observed that the new bands remained consistent when soluble manganese was present. After the impurity removal from leachate, 96% of Mn was precipitated in the form of dioxide manganese by adding potassium permanganate as an oxidant. The results demonstrate that tartaric acid is a practical and efficient reductant for Mn recovery from low-grade pyrolusite ore. Graphical Abstract

The Imini mining district (southern foreland of the intraplate Atlasic belt of Morocco) hosts the largest Mn resources of North Africa, consisting of two laterally extensive bodies of high-grade pyrolusite-rich manganese ore and a third discontinuous medium-grade coronadite-rich Mn ore in a ~ 10–15-m-thick Cenomanian–Turonian dolostone unit. Until now, the origin and timing of the Mn ore have been poorly constrained. New Pb isotopic ratios show that Triassic series (basalts and ferruginous sandstone) are likely the source of the metals. 40Ar/39Ar dating of K-Mn oxides shows that the Mn-rich orebodies formed during at least three periods: late Cretaceous to late Paleocene (> 58 Ma), late Eocene (ca. 36.3 Ma), and early Burdigalian to early Serravalian probably in two pulses at ca. 19–20 Ma and ca. 13 Ma. These periods coincide with three known building phases of the Atlasic relief during late Cretaceous, late Eocene, and the Early(?)-Middle Miocene. We therefore propose the Atlasic tectonics as the first-order control of the Mn mineralization. Periods with regionally high elevations modified the climate to wetter conditions that supplied meteoric water to feed temporary aquifers. Relief building created the required hydraulic head to sustain (1) fluid-rock interaction between O2-poor acidic fluids and the Triassic series, (2) migration of the metal-rich fluid, and (3) to overpressure fluid in the Imini depositional site. The decreasing thickness of Triassic series in front of the Imini anticline forced these low-temperature (< 100 °C) fluids to mix with oxygenated and alkaline ground waters in the karst system and precipitate Mn oxides. The N70°-oriented Atlasic tectonic structure controls the orientation of the Mn deposits. The late Eocene–Early/Middle Miocene uplifts generated additional supplies and/or in situ remobilization of the primary late Cretaceous medium-grade ore to form the high-grade pyrolusite-rich ore.

With the depletion of high-grade manganese ore resources, the efficient utilization of low-grade manganese oxide ore emerges as a significant topic for discussion. Many prior studies have concentrated on the reductive process and the associated kinetics of low-grade manganese oxide ore; however, the ultimate objective of reduction is to produce useful materials. In this paper, we present the preparation of nano-sized manganese oxides from low-grade manganese oxide ore using walnut shell as a reducing agent. The adsorption capacities for basic magenta and methylene blue (MB) were investigated. The experimental results indicate that when the concentration of sulfuric acid is 3 mol L −1 , the amount of walnut shell is 40 g L −1 , the ratio of liquid to solid is 10:1, the leaching time is 150 minutes, and the leaching temperature is 369 K, the leaching efficiency reaches 93.18 pct. The leaching process is controlled by a chemical reaction, with an activation energy of 45.50 kJ mol −1 . Nano-sized manganese oxides can be synthesized from the potassium permanganate oxidation leaching solution after iron removal using potassium sulfate, with α-MnO 2 being the main component. The adsorption process of nano-sized manganese oxide for basic fuchsine follows second-order kinetics and conforms to the Freundlich isotherm adsorption model, demonstrating a maximum adsorption capacity of 144.91 mg g −1 . Conversely, the adsorption process for MB adheres to pseudo-first-order kinetics and also conforms to the Freundlich isotherm adsorption model, with a maximum adsorption capacity of 92.24 mg g −1 .

The radiological characterization of aggregates used in construction materials is essential to determine their suitability from a radiological protection perspective and to ensure their safety for health and the environment. While the activity concentrations of radionuclides present in construction materials are typically determined using gamma spectrometry, an alternative approach involves the development of statistical methods and predictive models derived from the chemical composition of the material. A total of 39 aggregates used in construction of various types (siliceous, carbonatic, volcanic, and granitic) have been analyzed, correlating their chemical compositions obtained through X-ray fluorescence (XRF) with the activity concentrations of natural radionuclides measured via gamma spectrometry using principal component analysis (PCA). The results obtained allowed for the observation of an inversely proportional relationship between the chemical composition of the grouping of siliceous and carbonatic aggregates and the content of radionuclides. However, the set of granitic aggregates showed a strong correlation with the natural radioactive series of uranium, thorium, and 40K. Conversely, the radionuclide content of volcanic aggregates was independent of their chemical composition. The results obtained from the PCA facilitated the development of different models using multiple regression analysis. The chemical parameters obtained in the proposed models were related to the typical mineralogy in each grouping, ranging from primary minerals such as feldspars to accessory minerals such as anatase, apatite, and pyrolusite. Finally, the models were validated using independent samples from those used to determine the models, achieving RSD (%) values ≤ 30% in 50% of the activity concentrations of 226Ra, 232Th(212Pb), and 40K, as well as the estimated ACI.