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Ultrasonic-assisted precipitation was employed to sustainably isolate Fe in the hydrochloric acid lixivium of low-grade laterite for the synthesis of battery-grade iron phosphate. The recovery efficiency of Ni and Co exceeded 99%, while the removal efficiency of the Fe impurity reached a maximum of 95%. Precipitation parameters for the selective isolation of Fe (MgO precipitant, pH 1, 70-80 °C) were optimized and used in ultrasonic precipitation experiments. The use of ultrasonic waves in the precipitation process enhanced micromixing by reducing the size of primary grains and mitigating particle agglomeration, thereby significantly improving the purity of the isolated compound and providing high-quality iron phosphate (FePO4·2H2O). The LiFePO4/C composite prepared from as-precipitated FePO4 exhibited excellent electrochemical performance, with a discharge capacity of 149.7 mAh/g at 0.1 C and 136.3 mAh/g at 0.5 C after 100 cycles, retaining almost 100% cycling efficiency. This novel and facile method for iron removal from laterite acid lixivium not only efficiently removes excess iron impurities leached due to the poor selectivity of hydrochloric acid, but also enables the high-value utilization of these iron impurities. It enhances economic benefits while simultaneously alleviating environmental pressure.
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After the atmospheric hydrochloric acid leaching method is used to treat laterite ore and initially purify it, the extract that results often contains a significant amount of Fe2+ impurities. A novel metallurgical process has been proposed that utilizes microbubble aeration to oxidize Fe2+ ions in laterite hydrochloric acid lixivium, facilitating subsequent separation and capitalizing on the benefits of microbubble technology, including its expansive specific surface area, negatively charged surface attributes, prolonged stagnation duration, and its capacity to produce active oxygen. The study examined the impacts of aeration aperture, stirring speed, oxygen flow rate, pH value, and reaction temperature. Under optimized experimental conditions, which included an aeration aperture of 0.45 µm, stirring at 500 rpm, a bubbling flow rate of 0.4 L/min, pH level maintained at 3.5, and a temperature range of 75-85 °C, the oxidation efficiency of Fe2+ surpassed 99%. An analysis of the mass transfer process revealed that microbubble aeration markedly enhances the oxygen mass transfer coefficient, measured at 0.051 s-1. The study also confirmed the self-catalytic properties of Fe2+ oxidation and conducted kinetic studies to determine an apparent activation energy of 399 kJ/mol. At pH values below 3.5, the reaction is solely governed by chemical reactions; however, at higher pH values (>3.5), both chemical reactions and oxygen dissolution jointly control the reaction.
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As one of the most widely used inorganic fine powder fillers, calcium carbonate is cheap. However, considering its poor light transmittance, it is not suitable to be added to resin matrix composites that require high light transmittance. Aluminum hydroxide has good light transmission and flame retardancy, but it is more expensive than calcium carbonate. CaCO3/Al(OH)3 composites with a core-shell structure that showed a trend toward the performance of aluminum hydroxide not only improved the surface properties of CaCO3, but also increased the added value of CaCO3. In the present paper, CaCO3/Al(OH)3 composites were successfully prepared in sodium aluminate solution via heterogeneous nucleation. Four types of calcium sources, including calcite-type precipitated calcium carbonate, vaterite-type precipitated calcium carbonate, ground calcium carbonate with two different particle sizes as the precursors and supersaturated sodium aluminate solution as the substrate, have been deeply investigated in terms of their influence on the preparation of CaCO3/Al(OH)3 composites. Results showed that the calcium carbonate precursor greatly affected the formation of CaCO3/Al(OH)3 composites. Both the precipitated calcium carbonate and the small particle ground calcium carbonate are likely to undergo anti-causticization and a complexation reaction with it to generate 3CaO·Al2O3·6H2O and 3CaO·Al2O3·CaCO3·11H2O, which go against the coating of calcium carbonate with aluminum hydroxide. Within the experimental range, the use of ground calcium carbonate with a particle size of 400-500 mesh is more suitable as a precursor for the preparation of core-shell CaCO3/Al(OH)3 composites.
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The recent use of cryoprotectant replacement method for solving the easy drying problem of hydrogels has attracted increasing research interest. However, the conductivity decrease of organohydrogels due to the induced insulating solvent limited their electronic applications. Herein, we introduce the Hofmeister effect and electrostatic interaction to generate hydrogen and sodium bonds in the hydrogel. Combined with its double network, an effective charge channel that will not be affected by the solvent replacement, is therefore built. The developed organohydrogel-based single-electrode triboelectric nanogenerator (OHS-TENG) shows low conductivity decrease (one order) and high output (1.02-1.81 W/m2), which is much better than reported OHS-TENGs (2-3 orders, 41.2-710 mW/m2). Moreover, replacing water with glycerol in the hydrogel enables the device to exhibit excellent long-term stability (four months) and temperature tolerance (-50-100 °C). The presented strategy and mechanism can be extended to common organohydrogel systems aiming at high performance in electronic applications.
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The advancement of wearable electronics and environmental awareness requires a wearable triboelectric nanogenerator (TENG) to feature the concepts of sustainability and environmental suitability. While most wearable TENGs are developed based on complex surface modification approaches to avoid the necessity of a physical spacer, herein a nanogap TENG is fabricated based on surface self-modified sustainable polymer films. Compared with poly(lactic acid) (PLA)-based and polycaprolactone (PCL)-based TENGs, the polybutylene succinate (PBS)-based TENG shows the highest output performance, representing up to 3.5-fold that of the reported TENGs based on biodegradable materials with a 0-4 mm spacer, due to the higher content of the ester group and surface roughness resulting from the surface self-modification. The nanogap device is demonstrated as a pressure/angle sensor with acceptable sensitivity for use in health monitoring. More importantly, the environmental suitability of the triboelectric films in air, water, and phosphate buffered saline systems indicates their stability in natural water and saline environments. Moreover, the antibacterial property of the triboelectric films indicates future applications in wearable and implantable electronics. This work demonstrates the potential applications of a biocompatible and environmentally stable TENG in wearable electronics and biomedical systems.
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Highly ordered submicron spherical Fe-MCM-48 was successfully synthesized by a mixed surfactant method using cheap water glass as silica source. The gyroid like structure of MCM-48 was captured by a TEM image for the first time, and it was corresponded well to the previous simulated gyroid model. A tentative mechanism of homogenization cooperative process involving the Helmholtz double electrical layer was purposed. After the loading of metal Ag, the resulting Ag/Fe-MCM-48 catalyst showed good catalytic performance in the catalytic combustion of benzene.
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The trace elements, Ca, Mg, Ba, Co, Cd, Cu, Mn, Pb, Sr, Zn, Al, Fe, Ni, Ti, Si and V, in K2CrO4 were simultaneously determined by inductively coupled plasma atomic emission spectrometry (ICP-AES). Optimum spectral lines were selected for each analyzed element. The matrix effect was studied and eliminated through matrix matching. The results show that the linear correlations of standard curves are good (R2 = 0.998 6-1.000) under the determined conditions. The recoveries of standard addition are in the range of 83.7%-113.0%, and the relative standard deviations are lower than 9.48% (n = 9). Detection limits of these impurities are in the range of 0.075-2. 625 mg x kg(-1). The method is rapid, simple, accurate and credible, so it can be used for the determination of impurities in K2 CrO4 product. The results also show that there is relatively high content of Ca, Mg, Al and Si in K2 CrO4 product, so the K2 CrO4 product can't be directly used for the ion membrane electrochemical synthesis of chromic anhydride and the product must be taken for further purification.
RESUMO
Experimental measurements have been made on the batch ion exchange of Ca(II) and Mg(II) from potassium chromate solution using cation exchanger of Amberlite IRC 748 as K+ form. The ion exchange behavior of two alkaline-earth metals on the resin, depending on contact time, pH, temperature and resin dosage was studied. The adsorption isotherms were described by means of the Langmuir and Freundlich isotherms. For Ca(II) ion, the Langmuir model represented the adsorption process better than the Freundlich model. The maximum ion exchange capacity was found to be 47.21 mg g(-1) for Ca(II) and 27.70 mg g(-1) for Mg(II). The kinetic data were tested using Lagergren-first-order and pseudo-second-order kinetic models. Kinetic data correlated well with the pseudo-second-order kinetic model, indicating that the chemical adsorption was the rate-limiting step. Various thermodynamic parameters such as Gibbs free energy (DeltaG degrees ), enthalpy (DeltaH degrees ) and entropy (DeltaS degrees ) were also calculated. These parameters showed that the ion exchange of Ca(II) and Mg(II) from potassium chromate solution was feasible, spontaneous and endothermic process in nature. The activation energy of ion-exchange (E(a)) was determined as 12.34 kJ mol(-1) for Ca(II) and 9.865 kJ mol(-1) for Mg(II) according to the Arrhenius equation.
