Leaching System Research Articles

Enhancement of weathered crust elution-deposited rare earth ores leaching process with the addition of PQ-10

To solve the problems of the long development period, low mass transfer efficiency and high impurity content in the in-situ leaching process of weathered crust elution-deposited rare earth ores (WCE-DREO), cationic hydroxyethyl cellulose (PQ-10) was composited with conventional leaching agent ammonium sulfate ((NH4)2SO4) to form a novel composite leaching agent. The effects of PQ-10 concentration, leaching temperature and leaching flow rate of the composite leaching agent on the leaching kinetics and mass transfer processes of rare earth (RE) and aluminum (Al) were investigated. Compared to the single leaching agent (NH4)2SO4, the composite leaching agent (2 wt% (NH4)2SO4+0.02 wt% PQ-10) can reduce the RE leaching equilibrium time from 465 to 130 min and increase the RE leaching efficiency and decrease the Al leaching efficiency. It also facilitates the leaching process of WCE-DREO by increasing the peak concentrations of RE and Al, reducing the theoretical tower plate height (HETP) and improving the leaching mass transfer efficiency. It is indicated that PQ-10 can promote the leaching of WCE-DREO. The leaching process of the composite leaching system conforms to the diffusion kinetic control model. When the PQ-10 concentration is in the range of 0.005 wt%–0.020 wt%, the reaction orders of RE and Al are 0.73 and 0.54, respectively, which shows a positive effect on the leaching velocity; when the PQ-10 concentration is in the range of 0.030 wt%–0.060 wt%, the reaction orders of RE and Al are –1.16 and –0.75, respectively, which show a negative effect on the leaching velocity. In the range of 10–50 °C, the apparent activation energies of RE and Al are 15.02 and 17.31 kJ/mol, respectively, and the higher the leaching temperature, the smaller the HETP and the higher the leaching velocity and mass transfer efficiency. The increase in leaching flow rate contributes to the increase in the longitudinal diffusion velocity of the leaching agent within WCE-DREO, causing a shorter time for RE and Al to reach leaching equilibrium. In addition, the flow rate and HETP are consistent with the Van Deemter equation. At a flow rate of 0.8 mL/min, HETP was minimized and the optimal mass transfer efficiencies is achieved for RE and Al.

Copper sulfides agglomeration using a novel lab-scale granulator: Integrated evaluation of bonding, leaching and mechanical behavior

The ore agglomerations could ameliorate intra-particle pore network, homogenize flow paths, and improve leaching efficiency of heap leaching. This paper innovatively develops a novel ore granulator with adjustable inclined angle and rolling speed. To comprehensively evaluate granulation procedure, the effects of physical (crushed feeds particle size distribution, rolling speed, inclined angle), chemical (binder type, curing time) and biological factors (bacterial concentration) on bonding performance of crushed feeds are analyzed. The objective of this paper is to obtain the optimal granulation conditions by studying the influence of various factors on the bonding ability, strength, and stability of granulated ores, in order to improve the pore structure of the heap leaching system, and increase the leaching rate of the ore. The results show that well-shaped agglomeration (WAs) does improve minerals leaching efficiency, and the uniaxial compressive strength of WAs is positively related to curing time, binder concentration, inclined angle, and rolling speed. The excessive lower or higher rolling speed is not suitable to get a higher extraction rate due to undesirable disintegration or compaction. The higher concentration (0.5–10 %) sulfuric acid solution could obviously increase WAs strength from 32.6 KPa to 48.3 KPa. The organic binders such as polyacrylamide are benefit for powders bonding and increase the compressive strength, but does not good for the desirable leaching reaction rate. The bacterial pre-adding has no significant positive influence on bonding and leaching efficiency. Relied on the 3D response surface, the preferred preparing condition is: 78.9 rpm rolling speed, 30° inclined angle, 7-days curing time and 9.3 % H2SO4 solution. Future studies should focus on exploring the intrinsic correlation between the various factors and evaluating the granulating and leaching effects from the perspective of chemical detection and leaching bacteria.

Integrating recycled valuable elements from spent LiFePO4 batteries based on a dimethyl oxalate leaching system

Recycling of spent lithium-ion batteries (LIBs) has great significance in sustainable global development and environmental protection. In this study, a novel strategy is proposed to selectively separate and integrate valuable elements from spent LiFePO4 (SLFP) cathode materials via an eco-friendly leaching process using dimethyl oxalate. By properly regulating and controlling the leaching parameters, 99.19 % Li and 96.28 % P were leached into solution, whereas only 0.2 % Fe was dissolved. Leaching mechanism revealed that the high-efficiency dissolution of the SLFP cathode materials is due to the joint action of methanol and oxalic acid derived from dimethyl oxalate hydrolysis. Furthermore, the lithium-containing leaching solution was used to prepare Li3PO4 products with a purity of 99.62 % through crystallization, and the Fe was retained in leach residue in the form of FeC2O4·2H2O with a purity of 99.54 %. These findings provide a reliable reference for environmental protection, selective recovery, and process design of SLFP LIBs.

Oxidation mechanism of pyrite in a thiosulfate solution: electrochemical impedance (EIS) and in situ Raman spectroscopy

Ammoniacal thiosulfate has been used lately as an alternative lixiviant for leaching gold from sulfides ores which are not amenable for cyanidation. However, the oxidation of the sulfide minerals generates products that inhibit the dissolution of gold and can promote the degradation of the leaching solution. The complexity of the ammoniacal thiosulfate leaching system has prevented the unification and clarification of the mechanisms of oxidation of sulfide ores used for gold extraction.In this study, a method combining polarization curves, Electrochemical impedance spectroscopy (EIS), and in situ Raman spectroscopy was implemented to investigate the oxidation process of high-purity pyrite. Pyrite samples were dispersed in carbon paste electrode (CPE-Py). The polarization curves of CPE-Py exhibited an increase in current values for overpotentials greater than 0.1 V, indicating the initiation of mineral oxidation processes. Subsequently, a maximum current was observed initially, followed by subsequent decrease, indicating the occurrence of passivation processes on the electrode surface. Hydrodynamic polarization curves demonstrated that the overpotential at which the passivation process occurs is independent of mass transport, suggesting that the passivation products were formed through solid-state transformation.Impedance spectra revealed that at overpotentials below 0.1 V, a partially resolved capacitive semicircle was observed, which was associated with the resistance encountered when charge was transferred between the solution and the surface layer interface. This resistance decreased as the polarization overpotential increased, implying a decrease in charge transfer kinetics. At higher overpotentials (0.3 V–0.4 V), a second capacitive semicircle appeared, linked to the oxidation of one or several species present in the mineral.In situ Raman spectroscopy was utilized to identify the oxidation species of pyrite in ammonia-thiosulfate ((NH4)2S2O3) leaching solution at a pH = 10.2. The composition of the species varied depending on the applied anodic potential. At low anodic potentials (0.1 V), Fe(OH)2 and thiosulfate (S2O32−) were formed, while at high anodic potentials (0.4 V), iron products such as Fe3O4 and γ-FeOOH, as well as sulfide species including thiosulfate, tetrathionates and sulfates (S2O32−, S4O6−2 and SO42−) were formed.

The Extraction of Copper from Chalcopyrite Concentrate with Hydrogen Peroxide in Sulfuric Acid Solution

Research on chalcopyrite leaching represents a great challenge, given its importance as one of the most abundant copper minerals and its significant role in global copper extraction. This study aimed to evaluate the effects of different parameters on chalcopyrite leaching by hydrogen peroxide as a strong oxidizing reagent in sulfuric acid solution. A series of leaching tests were carried out to investigate the effect of the solid/liquid ratio, stirring speed, temperature, oxidant and acid concentrations, and lixiviant dosing method on copper extraction from chalcopyrite concentrate. The catalytic decomposition of hydrogen peroxide occurred in the investigated leaching system, as reflected in the obtained metal extraction values. Copper extraction was increased in the first 60 min of the reaction, after which it essentially ceased. The maximum final copper extraction of 64.5% was attained with 3.0 mol/L H2O2 in 3.0 mol/L H2SO4 at a temperature of 40 °C after 120 min of reaction. Due to the catalytic decomposition of hydrogen peroxide in the examined leaching system, the leaching experiment was performed with the periodic addition of lixiviant at specific time intervals as well. The dissolution process was described by the first-order kinetics equation with an apparent activation energy of ~39 kJ/mol. Finally, XRD and SEM-EDS analyses were used to characterize the leached residue, and the results showed that the formation of elemental sulfur on the chalcopyrite surface affected the dissolution process.

Ultrasound-assisted extraction of Sn from tinplate scraps by alkaline leaching: Novel acoustoelectric synergy effect underlying intensifying mechanism

Clean and fast extraction of tin from the surface of tinplate scraps is of great significance for the efficient utilization of waste resources. However, the dense tin layer causes the low efficiency of conventional leaching process. To improve Sn leaching efficiency, the ultrasound technique was adopted to extract Sn from tinplate scraps by alkaline leaching in this study. In the NaOH-H2O2 leaching system, metallic tin and alloyed tin in Fe-Sn alloy located on the surface of tinplate scraps can be oxidized and transferred to soluble Na2SnO3, while the iron in Fe-Sn alloy was oxidized to oxides which were chemically inert in alkaline solution. The differences in chemical solubility of Sn and Fe, and solubleness of stannate and iron oxides gave rise to the selective separation of Sn from the tinplate scraps. The effects of the leaching parameters on the Sn leaching behaviors in conventional and ultrasound-assisted leaching processes were compared. The conventional leaching temperature and time were significantly reduced during the ultrasound-assisted leaching process. Almost all of Sn can be extracted after conventional leaching at 1 mol/L NaOH, temperature of 80 ℃ and time of 60 min, however the same Sn leaching effect can be achieved by ultrasound-assisted leaching at 60 ℃ for 30 min with ultrasound power of 60% (360 W). Sn leaching kinetics based on the plate model demonstrated the reaction rate constant of the ultrasound-assisted leaching was 70% higher than that of the conventional leaching. A novel acoustoelectric synergy effect underlying intensifying mechanism by ultrasound irradiation was proposed in this study. Eventually, this work provided a rapid and clean tin extraction method from tinplate scraps via the ultrasound-assisted alkaline leaching treatment.

SELECTION OF A LEACHING SYSTEM FOR THE EXTRACTION OF MOLYBDENUM-98 FROM USED <sup>99</sup>Mo/<sup>99m</sup>Tс GEL GENERATORS

The production of the radiopharmaceutical “Sodium pertechnetate 99mTc, solution for injection” from the transported 99mTc generator is a complex multi-stage process that includes the collection and disposal of radioactive waste generated at various technological stages of production, as well as after the return of the generator used in clinics. Currently, natural molybdenum oxide is used for the development of the parent isotope 99Mo at the WWR-K reactor, but as the need for 99mTc generators in Kazakhstan increases, the question arises about the use of expensive molybdenum oxide enriched with the isotope 98Mo, therefore, the task of regenerating irradiated molybdenum arises. The paper presents experimental data on the choice of an optimal leaching system for the isolation of molybdenum-98 from spent 99Mo/99mTc generators.

Mechanism of selective lithium extraction from spent LiFePO4 cathodes in oxidizing alkaline leaching system

Lithium-ion batteries (LIBs) usher in an explosive growth, but followed by many spent LIBs processing problems. Recycling the spent LIBs with both economic attributes and environmental benefits is imperative. However, the existing recycling processes have the problem of high cost, low efficiency and environmental pollution. In this study, NaOH is innovatively adopted as leaching agent for the hydrometallurgical recovery of spent LiFePO4 cathodes, realizing the efficiently selective lithium extraction without additional oxidizing agent addition. Meanwhile, Li3PO4 product is obtained by in-situ concentration of the leaching solution without adding precipitant, and Fe2O3 by-product can be obtained by leaching residue. Under the conditions of 2 mol/L NaOH, L/S ratio of 50:1 mL/g, 50 °C and 2 h, the leaching efficiencies of Li and P can reach 98.2 % and 99.9 %, and all of Fe is converted into Fe3O4. The kinetic study reveals that the leaching process is controlled by chemical reaction. Moreover, it is innovatively found that NaOH play the dual role of leaching agent and oxidant, and the Na+ may have intercalation effect on the structure of LiFePO4. Compared with traditional process, this method has the advantages of low cost, high efficiency and environmental friendliness.

Physical effect of ultrasonic on leaching system of zinc oxide dust containing germanium

Abstract Insufficient reaction between dust and sulfuric acid during leaching of zinc oxide dust containing germanium is a major reason for the low leaching efficiency of germanium. This paper makes use of the unique physical effect of ultrasonic wave to play an important role in strengthening the leaching process. Research found that with ultrasonic enhanced leaching, on the one hand, the surface tension and viscosity of the leaching solution decreased by 5.94 and 32.73 %, respectively; on the other hand, for the leached mineral, the contact angle decreases, the surface free energy increases by 9.43 %, the particle size decreases 40.92 %, and the specific surface area and pore volume respectively increase 94.10 and 54.05 %, which reduces the contact resistance between sulfuric acid and dust, making the reaction between them more completely and in-depth. Therefore, the leaching rate is accelerated and the germanium leaching efficiency is increased. Under ultrasonic condition, the leaching efficiency of germanium is enhanced by 3.94 % and the time to reach equilibrium is shortened by about 40.00 %. The above findings can provide theoretical guidance for the extended application of ultrasound in hydrometallurgy and the efficient leaching of germanium-containing zinc oxide dust.

Advanced oxidation using sulfate radicals for the surface oxidation of Cu2O and the separation of copper via acid leaching

The effect of Na2S2O8 on Cu2O surface oxidation and leaching was investigated, and the presence of Na2S2O8 transforms the surface of Cu2O into more easily leachable CuO, resulting in a 35.50% increase in the extraction rate of Cu than that without Na2S2O8. In the acid leaching system, O atoms combined with H+ to form H2O, which was continuously separated from the surface to form vacancies. Cu(I) on the mineral surface formed Cu(0) and Cu(Ⅱ), of which Cu(Ⅱ) separated from the mineral surface and entered the solution, while Cu(0) was reconstructed on the surface, and a Cu-Cu metal bond with a bond length of 2.40 Å was appeared in the DFT calculation, which caused the content of Cu atom on the surface to be higher than that of O atom. After oxidation, high-spin Cu(Ⅱ) contributed by the 3d orbital appeared on the mineral surface. The Cu(Ⅱ) content of the oxidized Cu2O surface was 19.80% higher than that of the pure Cu2O surface, indicating that the copper on the oxidized Cu2O surface was more easily extracted. Moreover, the adsorption energy of chemical adsorption occurring in the presence of oxidant (−1.91 eV) was more negative than that in the absence of oxidant (−0.21 eV).

Comparative of malonic acid aqueous solution and malonic acid-based deep eutectic solvent for LiCoO2 cathode materials recovery: Leaching efficiency and mechanism

Deep eutectic solvents (DESs) and aqueous organic acids are two leaching systems that have achieved remarkable results in hydrometallurgical recovery of spent lithium-ion batteries (LIBs). However, previous studies have only evaluated a single leaching system at a time and thereby failed to compare the differences between DES and organic acids systems in detail. In this study, our purpose was to clarify the differences between the efficiencies of two leaching systems—a malonic acid (MA) aqueous solution and a DES of choline chloride: malonic acid (ChCl:MA) via a systematic investigation of the conditions and mechanisms associated with the leaching of LiCoO2 cathode materials using these two systems. The effects exerted by various process parameters, such as reaction time, temperature, and liquid-to-solid ratio, on the leaching efficiency of these two systems were investigated. The results showed that the Co and Li leaching efficiencies of the DES were higher than those of the MA aqueous solution under identical experimental conditions. The kinetic differences between the two systems were reflected in the fact that the MA aqueous solution was regulated by diffusion, whereas the DES leaching was regulated by chemical reactions. Spectroscopic analysis and density functional theory calculations indicated that MA acts as both a ligand and a reducing agent in aqueous solutions, whereas MA in the DES only acts as a reducing agent. In addition, Co was present in the MA aqueous and DES leaching solutions as octahedral (Co(H2O)2(C3H2O4)2) and tetrahedral ([CoCl4]2-), respectively.

Developing of a Counter-Current Copper Leaching Process Using Response Surface Methodology

ABSTRACT Due to the scarcity of water in many parts of the world, wastewater generated by hydrometallurgical processes has been recognized as a valuable resource for recovery or reuse. A method for reusing hydrometallurgical raffinate in the leaching of low-grade oxide copper ore in a counter-current leaching process was evaluated. In the first stage of the investigation, the influential factors on copper leaching, such as the amount of acid consumed (200–400 g/kg of ore), the initial iron concentration of the raffinate (5–25 g/L), the liquid-to-solid ratio (2–10 mL/g), and the duration of the leaching process (15–75 min), were examined using response surface methodology coupled with central composite design. Two responses, copper recovery and final copper concentration, were selected to determine the optimal conditions for the leaching process. Based on the statistical model, it was found that using 325 g/kg of ore of consumed acid, an initial iron concentration of 10 g/L, a liquid-to-solid ratio of 4 mL/g, and a leaching time of 60 min would result in higher values for both responses. Confirmation runs were conducted to validate the selected conditions and the suitability of the statistical model. Additionally, compositional and morphological characterization of samples before and after the leaching process was conducted using field diffusion scanning electron microscopy and X-ray diffraction analysis, which showed the dissolution of compounds such as tenorite and cuprite. In the second stage, a two-unit counter-current leaching system was adopted, as hydrometallurgical processes are usually carried out in multiple stages on an industrial scale. This leaching system was designed to maximize copper dissolution by considering the information obtained from the response surface methodology. The use of this leaching system increased the overall leaching efficiency by up to 80%. By characterizing the solid samples, it was found that the copper extraction percentage in a counter-current leaching system could be increased by simultaneously precipitating iron-bearing compounds.

Green and efficient recovery of valuable metals from spent lithium-ion batteries using molasses: Parametric optimization and performance evaluation.

In this study, a green and efficient leaching system utilizing methanesulfonic acid (MSA) and sugarcane molasses is investigated, and conditions optimized using response surface methodology (RSM). Results show that molasses is capable of reducing the oxidation state thus facilitating the leaching of the transition metals and lithium. The dissolution rate of the metals in molasses-methanesulfonic acid media is observed to be fast and temperature dependent. >98% of all the metals can be dissolved under the optimized leaching condition of 2 M MSA, reductant dosage of 0.408 g (molasses)/g (cathode material) on a wet molasses (18.5% moisture) and dry cathode material basis, solid-liquid ratio of 50 g/L, 90 °C and 60 min. The proposed system provides an efficient waste-to-wealth approach that utilizes an agro-industrial by-product to recover hazardous metals present in spent LIBs.

Leaching kinetics and permeability of polyethyleneimine added ammonium sulfate on weathered crust elution-deposited rare earth ores

At present, in-situ leaching of weathered crust elution-deposited rare earth ores (WCE-DREOs) encounter with problems such as long leaching cycles, slow infiltration rate and low product purity. In order to solve the above problems, the conventional leaching agent ammonium sulfate ((NH4)2SO4) was compounded with polymeric surfactant polyethyleneimine (PEI) to form a composite leaching agent. The effects of leaching temperature, PEI concentration, flow rate and pH on leaching kinetics and permeability of rare earths (RE) and aluminum (Al) in orebody were studied. It is found that with temperature increasing, the time required to reach leaching equilibrium for both RE and Al is shortened, the apparent activation energies of RE and Al are 14.79 and 13.45 kJ/mol, respectively, and the leaching processes are in accordance with the outer diffusion control. When the concentrations of (NH4)2SO4 and PEI in the composite leaching agent are 2.0 wt% and 0.4 wt%, the time required to reach leaching equilibrium for RE and Al is about 50% shorter than that using (NH4)2SO4 alone, and the leaching efficiencies of RE are slightly higher than that of Al. Properly increasing the temperature and flow rate of the composite leaching agent can improve the leaching efficiencies of RE and Al, but pH has neglected effects on the leaching efficiencies of RE. At PEI concentrations below 0.4 wt%, the addition of PEI promotes the leaching of RE and Al. In column leaching studies of the WCE-DREO, the addition of 0.4 wt% PEI to the traditional leaching agent (NH4)2SO4 has no impact on the leaching efficiencies of RE. However, it can significantly increase the infiltration rate of WCE-DREO, shortening the leaching time per 10 mL effluent from about 30 min for (NH4)2SO4 leaching system to 20 min for the composite leaching system. The leaching time is shortened by one-third, and the leaching cost is reduced, which can provide theoretical guidance for the development and commercial implementation of novel composite leaching agent for WCE-DREO.

Selective leaching of V, W and recycling of TiO2 carrier from waste V2O5-WO3/TiO2 catalysts by mixed alkali liquor

Recovery of selective catalytic reduction (SCR) denitrification catalysts is important to reduce costs and environmental pollution. To recover and reuse the metal resources in the waste V2O5 - WO3/TiO2 catalyst, a mixed alkaline leaching system of NH3·H2O and sodium compounds was used. The method keeps the carrier composition and structure unchanged while achieving the separation of V and W. The effects of three additives, NaOH, Na2CO3 and NaCl, were investigated after determining the optimum leaching concentration of NH3·H2O at 6.0 mol‧L−1. The results showed the most superior leaching efficiency of V and W in NH3·H2O - NaOH solution. Next, the effects of additive concentrations and process parameters on the leaching of V and W were systematically investigated. Under optimum leaching conditions, 77.47%V and 47.7%W were leached without destroying the carrier. Moreover, this method showed similar separation of valuable metals from different components of waste catalysts, demonstrating its versatility. Meanwhile, the TiO2 carriers with undamaged structure can be directly prepared as new denitrification catalysts. Finally, the comprehensive utilization of 92.84%W, 91.94%V and 92.17%Ti resources in the waste denitrification catalyst is realized. Overall, the method may be an environmentally friendly solution for resource recovery of waste SCR catalysts.

Enhancement of copper metal dissolution in sulfuric acid solution with oxygen and ultrasound

A new method for copper metal dissolution by simultaneous use of oxygen and ultrasound was proposed to enhance the copper dissolution rate in sulfuric acid (H2SO4). The influence factors such as ultrasonic power, oxygen flow rate, reaction temperature, initial copper ion (Cu2+) and H2SO4 concentration was studied to study the dissolution behaviour of copper metal. The dissolution rate of Cu could reach 7.52 g h−1 L−1 after the ultrasonic strengthening, which is 1.83 times higher than that without ultrasonic irradiation (4.109 g h−1 L−1). The study of leaching kinetics found that the Cu leaching process with and without ultrasound were both controlled by surface chemical reaction. The ultrasound could significantly reduce the apparent activation energy of the leaching reaction from 43.52 kJ mol−1 to 28.40 kJ mol−1. Characteristics revealed that the cavitation effect of ultrasound could increase the specific surface area of copper metal and oxygen bubble, and enhance the oxidizing capability of this leaching system, which is beneficial for the dissolution of Cu. Therefore, ultrasonic-assisted technology has provided novel insights for the hydrometallurgical recovery of copper.

Alternating Current Electrolytic Extraction of Transition Metals from NMC532 using Rotating Disc Cyclic Voltammetry in Dilute Chloride Solution

The rising application of portable electric devices has led to the rapid accumulation of electronic wastes such as lithium-ion batteries. These wastes pose significant environmental threats when improperly disposed of and contain valuable metals that could supplement the supply chain and reduce the need for certain conflict minerals. Recycling methods that limit the potential for environmental damage and improve separation of transition metals are vital to the sustainability of battery based electrical storage. Conventional aqueous recycling of lithium battery electrode materials utilizes oxidizing acids and a chemical reducing agent. This study investigates if chemical oxidizing and reducing agents may be aided or replaced by the application of an alternating electric field to reduce surface metal oxides and subsequently accelerate reoxidation with a solubilizing anion. The electrolytic leaching mechanics of commercial battery cathode material (NMC532) in dilute hydrochloric acid were investigated using rotating disc cyclic voltammetry (RDE-CV), solution analysis with inductively coupled plasma mass spectrometry (ICP-MS), and residue analysis with scanning electron microscopy and energy dispersive spectroscopy (SEM-EDS). We found evidence that applying an alternating electric field allows for adjustment of leaching rates for different transition metals based on electrochemical cell parameters. By applying up to one volt oscillating between reducing and oxidizing polarity, the relative molar leaching rate of nickel and manganese drastically increased while that of cobalt slightly decreased. Future research will be required to determine how this effect translates to different leaching systems and its applicability to an industrial scale process.The authors acknowledge financial support from the NSF IUCRC program for the “Center for solid-state electric power storage” (#2052631) and support from the South Dakota Board of Regents for the “Governor’s Research Center (GRC) for electrochemical energy storage”.

Selective extraction of Ni and Co from a pyrrhotite-rich flotation slime using an alkaline glycine-based leach system

Ni and Co, mostly produced from sulfide resources, are critical energy metals required for the green energy transition. A significant portion of the Ni and Co in the processed ore, particularly for disseminated mafic/ultramafic ores, is not recovered due to the deportment to fine slimes which has been dumped as tailings during the flotation process. This study applied an alkaline glycine-based leaching method to selectively recover Ni and Co from a pyrrhotite-rich flotation slime and investigated the deportment of impurities. Leaching variables, including dissolved oxygen (DO) level (5–25 ppm), pH modifier (NaOH, KOH and ammonia), particle size and pre-oxidation, were investigated. The highest extractions of 86.2 % for Ni and 79.7 % for Co were achieved by leaching at glycine/(Ni + Cu) molar ratio of 4, DO of 15 ppm, pH of 10.2 (adjusted with ammonia), 10 % solids and 30 °C using a sample size at a grind size P80 of 17 µm within 72 h. Ni that is mineralised in pentlandite can be easily leached by glycine, and oxygen addition is essential for the extraction of Ni and Co when mineralised as sulfides. The study has shown a higher overall metals extraction and faster leaching kinetics, shortening the leaching from 72 to 24–48 h, when ammonia was used as a pH modifier. The alkaline glycine-based leaching achieved both higher Ni and Co extractions and higher rejections of impurities compared with conventional sulfuric acid leaching, with the concentrations of Fe being <250 ppm and Ca and Mg <15 ppm in the leachate. Residue analysis revealed a mechanism of preferable dissolution of pentlandite over pyrrhotite. The Fe and Mg deportment before and after leaching remained similar, which confirmed the high selectivity of the alkaline glycine-based leaching.

Selective leaching of Ni from Cd-depleted spent Ni-Cd batteries by glycine-citrate solution

In the present study, the selective leaching of Ni over Fe from Cd-depleted spent Ni-Cd batteries has been presented using a glycine-citrate solution. These findings can be considered experimental proof of our concept of developing an eco-friendly protocol for the green recycling of both Cd and Ni. In the present study, the pertinent factors affecting Ni leaching, including glycine concentration (0.5–1.5 M), citrate concentration (17–51 mM), temperature (25–55 °C), and time (1–36 h), were investigated. It was found that nearly 95% of Ni can be dissolved when glycine concentration = 1.5 M, citrate concentration = 34 mM, and solid-to-liquid ratio = 2.5% at T = 55 °C after 36 h; noticeably, the amount of Fe entered to solution is only 920 (mg/L). The thermodynamics of the leaching system were comprehensively evaluated and the reactions, responsible for the dissolution of Ni, were predicted. Finally, based on semiempirical kinetic modeling, it was found that the Ni dissolution process is governed by the surface chemical reaction with an activation energy of ∼105 (kJ/mol).

Physical, mechanical, chemical, and durability assessment of water leaching treatment of bamboo

Water leaching is a traditional bamboo treatment method in which fresh bamboo poles are immersed in running water for at least 30 days to leach out water-soluble substances such as starch and carbohydrates. This method is easy to apply and does not require additional chemicals. Although water leaching is widely applied, its influence on the physical, mechanical, and chemical properties of bamboo and its effect on the durability of bamboo against termites has not been fully explored through experimental methods. This paper assesses the effects of water leaching treatment on bamboo and identifies the potential and limitations of this treatment. A 23% reduction in the density of bamboo after water treatment was found, which can be related to the removal of water-soluble extractives from the material. A significant (15%) increase in the modulus of rupture and a 20% increase in the modulus of elasticity were identified using a three-point bending test after water treatment while keeping a similar fibre volume fraction. Water leached bamboo had less dimensional stability and higher water absorption than untreated bamboo. As the density of the bamboo decreased, more space became available in its bundles for water. A darkened surface was observed after treatment, but no chemical modifications were found through FT-IR spectroscopy. Termites can use cellulose as a source of food, and the removal of starch from bamboo did not improve its resistance against this insect. On the contrary, the free space created after treatment favoured the action of the termites, leading to a higher mass loss percentage for treated bamboo. The water leaching system should not be used as the only treatment method in bamboo being utilized for structural purposes, and the reduction of dimensional stability and the darkened surface must be considered when using the bamboo for furniture and handicraft applications.