Search Results (76)

High-alumina fly ash may potentially be a valuable source of Ga with a concentration of Ga at 80 mg/kg. Direct adsorption and enrichment of Ga from sulfuric acid leach liquor of high-alumina fly ash is developed in this study. The H-type chelating resin with two carboxy groups exhibited the best adsorption capacity for Ga. The maximum adsorption capacity for Ga was 55 mg/g resin with an adsorption time of 24 h, an initial Ga concentration of 500 mg/L, an adsorption temperature of 55 °C, and an initial acid concentration of 0.1 mol/L. The adsorption process of Ga was in good fit with the Langmuir isotherm and pseudo-second-order reaction kinetics model. The chemical adsorption rate was controlled by an internal diffusion mechanism. The resin had a high selectivity for Ga³⁺ with a K_d over 3600 compared with Fe²⁺, Al³⁺, K⁺, Ca²⁺, and Mg²⁺. The adsorption mechanism was found to be the ion exchange reaction between Ga and H of carboxy and hydroxyl groups. The concentration of Ga in sulfuric acid leach liquor from high-alumina fly ash achieved enrichment from 200 mg/L to 2 g/L. It is an attractive medium for large-scale Ga extraction from high-alumina fly ash. Full article

Magnesium sulfate leaching of ionic rare earth ores is generally characterized by a smooth outflow curve, a long leaching time, and a high impurity content in the leach liquor. To reveal the leaching law of rare earth cations and impurity aluminum ions in the leaching process of ionic rare earth ores in magnesium sulfate, equilibrium leaching and leaching kinetics experiments were carried out using ore samples of five particle sizes (<0.10, 0.10–0.25, 0.25–0.50, 0.50–1.00, and >1.00 mm). Furthermore, prediction models of equilibrium constants and rate constants were constructed based on ion-exchange theory. The results show that the equilibrium constants of the rare earth and aluminum ion-exchange reactions decrease gradually with the increase in the magnesium ion concentration, the decrease in the temperature, and the increase in the surface area of the particles. Moreover, the equilibrium constant prediction models of rare earth and aluminum with magnesium sulfate were constructed using data fitting. From the leaching kinetics experiment, there is a significant relationship between the reaction rate constant of ion exchange and the surface area of the particles: the larger the particle size, the smaller the reaction rate constant. Based on the kinetic test data and the Arrhenius equation, the frequency factors and activation energies of the ion-exchange reactions were inversely analyzed through the Chemistry Reaction Module of COMSOL. The reaction activation energy for rare earth and aluminum leaching is 10,743 J/mol and 10,987 J/mol, respectively. The rate constant prediction model was obtained by fitting the analyzed rate constant data. The rare earth and aluminum leaching results for the full-grade ores are in high agreement with the predictions of the constructed model, which verifies the validity of the proposed model. This study can provide theoretical support for the improvement of the leaching efficiency of rare earths and the optimization of the magnesium sulfate leaching process. Full article

Due to the restrictions of strong acids in some regions, the reuse process of rare earth (RE) precipitation mother liquor is difficult to carry out. To achieve the straightforward and efficient reuse of precipitation mother liquor in such areas, the potential for directly reusing this liquor for rare earth (RE) leaching was explored. The results showed that when the RE concentration in the leachate ranged from 0.1 to 1.5 g/dm³ and the RE precipitation rate exceeded 96%, the residual total carbonate content in precipitation mother liquor was less than 0.01 mol/L, and the solution pH was 7–8. Furthermore, when the total carbonate content in leaching liquor was lower than 0.01 mol/L, the presence of carbonate had a minimal impact on the RE leaching efficiency, which was observed to exceed 93%. Additionally, the process of mother liquor leaching was analyzed using dynamic models and chromatography tray theory. It was found that the leaching results were well fitted with the shrinking core model, and the apparent activation energy of RE was 5.77 kJ/mol, indicating that the reaction was controlled by diffusion, and the reaction order was 0.672 for RE. This confirms that a total carbonate content below 0.01 mol/L in the precipitation mother liquor can be directly used for the RE leaching process. Full article

The development of hydrometallurgical recycling processes for lithium-ion batteries is challenged by the heterogeneity of the electrode powders recovered from end-of-life batteries via physical methods. These electrode materials, known as black mass, vary in composition, containing differing amounts of nickel, manganese, and cobalt (NMC), as well as other chemicals, such as lithium iron phosphate (LFP). This study presents the results of the hydrometallurgical treatment of mixed NMC and LFP black masses aimed at creating flexible recycling processes. This approach leverages the reducing power of LFP to optimize the leach liquor composition for re-synthesizing NMC precursors. In particular, the leaching conditions were optimized based on the LFP content in the solid feed to maximize the extraction of key metals (Ni, Mn, Co, and Li). The leaching solid residue, graphite, was treated and characterized as a secondary raw material for new anode preparation. Iron phosphate was recovered by increasing the pH of the leach liquor, and the NMC precursors were obtained via coprecipitation. This process achieved a recycling rate of 51%, based on the black mass input and the mass of recovered elements in the output products. Additionally, substituting LFP scraps as the reducing agent in place of H₂O₂ reduced the recycling process’s environmental impact by avoiding 1.7 tons of CO₂-equivalent emissions per ton of NMC black mass. Full article

This study introduces a straightforward and effective amorphous ZrP/polyacrylonitrile composite ion exchange method for separating Li from the leachate of spent Li-ion batteries (NMC 111). The cathode materials were leached with a series of optimized experiments. The influence of operating variables, including the H₂SO₄ concentration, temperature, H₂O₂ concentration, and pulp density, on leaching efficiency was examined to determine the optimal conditions for sorption experiments. The leaching efficiencies of Li, Co, Ni, and Mn were found to be 99.9%, 99.5%, 98.8%, and 99.9%, respectively. Subsequently, batch sorption experiments were performed by using am-ZrP/PAN, including the determination of the effect of pH, sorption kinetics, and the sorption isotherm. The effect of pH on adsorption was examined in 1 mmol/L equimolar solutions of Li, Ni, Mn, and Co. Li was separated from Mn, Co, and Ni in the leaching liquor. The adsorbent for Mn, Co, and Ni sorption better fitted pseudo-second-order kinetics. High selectivity for Li was observed, even at the higher solution concentration of 15 mM Li, Ni, Co and Mn. In addition, the column loading process demonstrated selectivity for Li over Co, Ni, and Mn metal ions. The preliminary evaluation of the whole process with mass flow demonstrated that it would be feasible to achieve full separation and metal recovery by integrating a combined hydrometallurgical method in future studies. However, much work is still needed to develop a practical separation flowsheet. Full article

An ironmaking blast furnace slag was prepared and dissolved in lixiviant solutions of known concentrations for the leaching of calcium. A portable laboratory orbital shaking incubator was used for the leaching experiments. In addition, XRF and AAS were utilised for the sample characterization of solid residues and leach liquor, respectively. This study demonstrated that increasing the concentration of the solvent enhances the efficiency of calcium extraction; however, it also causes the leaching of other elements, such as magnesium, which can impede the carbonation stage. The research also revealed that the extraction of calcium from the largest particles is constrained by mass transfer and the accessibility of calcium from the particle. The authors hypothesize that the reaction products build up and hinder the reaction on the surface layer of the particles. However, with the smallest particle size fraction, more calcium can be extracted before the surface is obstructed, thus ensuring maximum extraction efficiency. Based on the activation energy value of 70.51 kJ/mol, it is less likely that the leaching of blast furnace slag in ammonium nitrate is a product-layer-diffusion-controlled process, as the activation energy for this type of process is usually below 20 kJ/mol. Instead, the higher activation energy suggests that the leaching process may be controlled by surface chemical reactions or a mixed mechanism. However, more detailed analysis and experimental data would be required to confirm the reaction mechanism. Full article

Some wastes from the paper pulp production process are still sent to a controlled waste landfill. These materials can constitute alternative resources for constructing road pavements. The study aimed to characterize and explore the sustainable application of two inorganic wastes resulting from the paper pulp process, the dregs (green liquor wastes) and the grits (slaker wastes), in the production of bituminous mixtures by the analysis of samples prepared with 5 and 10% of dregs and 5 and 10% of grits on the baseline reference bituminous mixture AC 14 surf 35/50. Some relevant mechanical properties of the blends were assessed based on Marshall compression, sensitivity to water and wheel-tracking tests. Additionally, water poured on the loose asphalt and compacted slabs’ surface was analysed to determine the portion of harmful chemical compounds leached from the asphalt material. The results show that using dregs presented some technical limitations related to mechanical performance and that the incorporation of grits has an acceptable mechanical behaviour. Moreover, the study shows that the measured leachate resulting from water flow in a reference asphalt mixture and the blends with grits are insignificant. It can be concluded that using grits in asphalt mixtures is a promising technique regarding mechanical behaviour and environmental impacts that need further studies. Full article

The increasing use of rare-earth elements (REEs) in renewable technologies such as electric vehicles and wind turbines is driving a rapid rise in their economic importance. This work investigated the separation of REEs (Nd, Pr, Sm, and Dy) from NdFeB magnets using high-performance solid-phase extraction chromatography. More than 99% of the REEs were extracted from an Fe-rich sulfate-based leach liquor using a three counter-current stage solvent extraction of 34.7 vol.% and O/A 1.5. The REE-loaded H₂SO₄ strip solution was separated into a high-purity Nd and Pr fraction from separate Sm and Dy fractions in a single stage using a D2EHPA-impregnated column and H₂SO₄ gradient elution. Full article

This work focuses on the recovery of rare earth elements (REEs = La, Ce, Nd, Pr) from spent nickel–metal hydride batteries by hydrometallurgical processing. The REEs were precipitated in the form of sodium-lanthanide double sulfate salts by adding Na₂SO₄ to a leach liquor prepared from industrially processed spent batteries. The objectives were to better understand the parameters driving the purity of the product and to identify the phases involved, as well as their crystallographic structure. The methodology included experiments performed in a 2 L reactor, thermodynamic calculations and product characterization. We confirmed that high REE precipitation yields (>95%) can be achieved under a wide range of hydrodynamic conditions. Furthermore, we demonstrated and quantified how appropriately washing the product allows for a significant reduction in nickel losses while maintaining control over REE product purity. Finally, using X-ray Diffraction analyses, it was established that REEs form a solid solution with a chemical formula (Na_0.9K_0.1)(La_0.65Ce_0.24Pr_0.04Nd_0.07)(SO₄)₂·H₂O, which has not been reported so far. Full article

The processing and extraction of critical metals from black mass is important to battery recycling. Separation and recovery of critical metals (Co, Ni, Li, and Mn) from other metal impurities must yield purified metal salts, while avoiding substantial losses of critical metals. Solvent extraction in batch experiments were conducted using mixed metal sulphates obtained from the leach liquor obtained from spent and shredded lithium-ion batteries. Selective extraction of Mn²⁺, Fe³⁺, Al³⁺ and Cu²⁺ from simulated and real leached mixed metals solution was carried out using di-2-ethylhexylphophoric acid (D2EPHA) and Cyanex-272 at varying pH. Further experiments with the preferred extractant (D2EPHA) were performed under different conditions: changing the concentration of extractant, organic to aqueous ratio, and varying the diluents. At optimum conditions (40% v/v D2EPHA in kerosene, pH 2.5, O:A = 1:1, 25 °C, and 20 min), 85% Mn²⁺, 98% Al³⁺, 100% Fe³⁺, and 43% Cu²⁺ were extracted with losses of only trace amounts (<5.0%) of Co²⁺, Ni²⁺, and Li⁺. The order of extraction efficiency for the diluents was found to be kerosene > Exxal-10 >>> dichloromethane (CH₂Cl₂) > toluene. Four stages of stripping of metals loaded on D2EPHA were performed as co-extracted metal impurities were selectively stripped, and a purified MnSO₄ solution was produced. Spent extractant was regenerated after Fe³⁺ and Al³⁺ were completely stripped using 1.0 M oxalic acid (C₂H₂O₄). Full article

Recovery of metals from e-waste forms a major focus of circular economy thinking and aligns well with the Sustainable Development Goals (SDG). While hydrometallurgical extraction from electronic printed circuit boards (PCBs) is well established, the separation of metals from the leach liquors, which are complex mixtures, remains a challenge. To achieve selective separation, ion exchange resins with chelating functional groups were employed in the present study. Batch and column studies for selective recovery of Cu²⁺ from a given mixed metals leach solution were conducted using Dowex M4195 resin, and both the adsorption isotherm and kinetics were studied. The process involves three major steps: selective recovery of Cu²⁺ by M4195 at low pH and elution with H₂SO₄; sorption of Ni²⁺ from the raffinate by Dowex M4195 at pH 2 and removal of Fe³⁺ from raffinate. The batch experimental results showed appreciable and selective recovery of copper (51.1%) at pH 0.7 and 40.0% Ni²⁺ was sorbed from raffinate at pH 2.0 with co-adsorption of Fe³⁺ as impurity. The batch adsorption data could be fitted with both Langmuir and Freundlich isotherms and exhibited pseudo-second-order kinetics. Column studies agreed with the Yoon–Nelson model and indicated that Cu²⁺ break-through time in the column decreased with an increase in flowrate from 3.0 to 10.0 min/mL and decreased in sorption capacity, while it was delayed with increased bed heights from 20 to 30 mm. Complete elution of Ni²⁺ was obtained with 2.0 M H₂SO₄ after selective elution of trace impurities with dilute HCl. Iron in the raffinate was removed via the addition of Ca (OH)₂ at pH 4.0 leaving Zn-Al in the solution. Full article

The complete reaction of chalcopyrite at ≥220 °C under pressure oxidation conditions (10 or 20% w/w pulp density, PO₂ 700 kPa) is a clean, near complete process, yielding high copper extractions (~99%) in an acidic leach liquor composed of dissolved metal sulphates, when high-quality process water is employed. However, when the process water contains chloride ions, here 3–100 g/L, although the copper extraction rate is enhanced, complete oxidation of sulphur under batch processing conditions is delayed. Chloride addition, therefore, appears to favour an oxidation mechanism that liberates cupric ions and preferentially forms elemental sulphur over sulphate. This provides evidence for the decoupling of the copper extraction and sulphate formation reactions. Increasing the reaction temperature, here to 245 °C, increases the rate of sulphuric acid formation and decreases the iron concentration in the leach liquor. The study also examines the effects of various upfront acid and other salt additions upon copper extraction. Added sulphuric acid was shown to slow the reaction, whereas salts such a cupric chloride and sodium sulphate had small effects on the rate and extent of copper extraction. Full article

Lithium is in high demand: this is driven by current trends in e-mobility and results in increased global production and record prices for lithium ores and compounds. Pegmatite ores, in addition to brines, remain of particular interest because of their higher lithium content and lower geopolitical risks. In this work, we investigated lithium extraction via the mechanochemical treatment of the three most common lithium minerals: lepidolite, spodumene, and petalite. Indeed, we determine that the petalite crystal structure was much more suitable due to its less dense packing and the formation of cleavage planes along lithium sites, resulting in substantial lithium extraction of 84.9% and almost complete conversion to hydrosodalite after 120 min of ball milling in alkaline media. Further processing of the leach liquor includes desilication, the precipitation of lithium phosphate, and the conversion and crystallization of pure LiOH·H₂O. Special attention was paid to a holistic approach entailing the generation of by-products, each of which has a specific intended application. The leaching residues were investigated by powder X-ray diffraction, Fourier transform infrared spectroscopy, N₂ adsorption/desorption, and scanning electron microscopy. Moreover, hydrosodalite was found to have a high potential as an adsorbent for heavy metal ions which were studied separately using aqueous solutions containing Cu²⁺, Ni²⁺, Pb²⁺, and Zn²⁺. Full article

Salinity, caused by irrigation with water containing high salt concentrations, excessive fertilization, or the loss of leaching capacity in some soils, is a serious problem on a global scale. Its incidence leads to osmotic and specific effects, as well as an imbalance in nutrient uptake that hinders the growth of most crops. Biostimulants can improve salt tolerance by reducing the uptake and accumulation of toxic ions. Corn steep liquor (CSL) is a byproduct of corn cleaning and maceration. This study investigates whether CSL application induces adaptive responses in pepper (Capsicum annuum L.) plants cultivated under saline conditions. Four treatments were carried out with pepper plants in a culture chamber: irrigation with Hoagland nutrient solution; irrigation with 100 mM NaCl in the Hoagland nutrient solution; irrigation with 100 mM NaCl in the Hoagland nutrient solution and the foliar application of CSL at 5 mL L⁻¹ every 7 days; and irrigation with 100 mM NaCl in the Hoagland nutrient solution and root application of CSL at 5 mL L⁻¹ every 7 days. The beneficial effect of CSL in reducing the phytotoxicity of salt stress was found to be due to an improvement in the photosynthetic efficiency and a reduction in the generation of reactive oxygen species. Thus, the increase in MDA concentration due to saline treatment is less when applying CSL, which is 3.5 times less when it is performed via the foliar route and 4.6 times if the treatment is on the root. The results show that CSL application increased the aerial biomass and leaf area under saline conditions through physiological mechanisms that varied depending on the application method. Full article

The Bayer process is the main method of alumina production worldwide. The use of low-quality bauxites for alumina production results in the formation of a significant amount of technogenic waste—bauxite residue (BR). The Bayer reductive method is one possible way to eliminate BR stockpiling, but it requires high-pressure leaching at temperatures higher than 220 °C. In this research, the possibility of boehmitic bauxite atmospheric pressure leaching at both the first and second stages or high-pressure leaching at the second stage with the simultaneous reduction of hematite to magnetite was investigated. Bauxite and solid residue after NaOH leaching were characterized using XRD, SEM-EDS, and Mössbauer spectroscopy methods. The first stage of leaching under atmospheric pressure with the addition of Fe(II) species in a strong alkali solution (330–400 g L^–1 Na₂O) resulted in a partial reduction of the iron minerals and an extraction of more than 60% of Si and 5–25% of Al (depending on caustic modulus of solution) after 1 h. The obtained desilicated bauxite was subjected to atmospheric leaching at 120 °C in a strong alkali solution (350 g L⁻¹) or high-pressure leaching at 160–220 °C using the Bayer process mother liquor in order to obtain a concentrate with a magnetite content higher than 83 wt. %. Full article