Fast Leaching Research Articles

Leaching sources and mechanisms of different nitrogen species from bioretention systems

At present, nitrogen (N) leaching from bioretention systems (BRSs) has become a key issue, imposing constraints on their application, a consequence of N dynamics of both inflow and legacy N at different time scales. In this study, the distinct sources (IL: immediate leaching, FL: fast leaching, SL: slow leaching) and the principal transformation processes of different N species (i.e., NH4+, NO3− and DON) leaching originating from inflow and legacy of BRSs were firstly unveiled by various 15N species labeling (i.e., 15N-NH4+, 15N-NO3− and 15N-DON). Results indicate that: NH4+ leaching was primarily caused by FL from influent organic N and SL from influent NH4+, with mineralization being the main transformation process influencing NH4+ leaching; NO3− leaching primarily originated from SL, with the major proportion attributed to the influent organic N in SL, autotrophic and heterotrophic nitrification were the main influencing factors; DON leaching primarily originated from SL, with similar proportions coming from influent organic N, NH4+, and NO3−, inorganic N assimilation was the principal transformation process affecting DON leaching. This study provides an effective framework for apportioning the leaching sources of different N species, providing valuable insights for the implementation of both inflow and legacy N leaching control measures.

Tracking the nitrogen leaching from different sources in bioretention systems with a process-based model

Bioretention systems are a typical stormwater management technology intended to reduce runoff and non-point source pollution. Multiple sources can contribute to nitrogen (N) leaching from bioretention systems, including the current rainfall-runoff (i.e., immediate leaching), recent rainfall-runoffs (i.e., fast leaching) and long-ago legacy N (i.e., slow leaching), however, there is a lack of methods to quantify these contributions. Here, a process-based Bioretention System (BRS) model for N leaching simulations was verified with artificially-labeled 15N data besides N data to reduce predictive uncertainties. The BRS model was then coupled with an Nitrogen Source Apportionment (NSA) module for N leaching tracking to quantify the contributions from different sources. Results from a bioretention system showed that additional 15N data reduced the predictive uncertainty of total N (TN) concentrations by 23 %. Immediate leaching, fast leaching and slow leaching increased, decreased and remained steady during the leaching process and accounted for 79.54 ± 5.08 %, 2.80 ± 1.74 % and 17.66 ± 4.11 % of N leaching, respectively. The dominant immediate leaching can be significantly weakened by a submerged zone, a shorter antecedent dry period (ADP), a lower rainfall intensity or influent concentration. This study provides a framework to quantify N leaching from multiple sources with implications for long-term N leaching management.

Strong Lewis acid-induced self-healing of loose FeOOH for alkaline oxygen evolution

The fast leaching of the Fe catalytic center and low conductivity of FeOOH have hindered the optimal stability and activity of Fe-based electrocatalysts for oxygen evolution reactions (OER). Here, Zn2+ is introduced into FeOOH with a looser nanosheet structure by regulating electric double layer (EDL) repulsion during electrodeposition. Meanwhile, as strong Lewis acids, Zn2+ in ZnxFeOOH could act as an electron acceptor, accepting electrons from FeOOH. The doping of Zn2+ shortens the bond length of Fe-O and enhances the covalency of Fe-O to improve electron transport rate and stability. The faster catalytic kinetics also been obtained by facilitating O* to form OOH* intermediates. At 100 mA cm−2, Zn0.5FeOOH requires overpotential of only 250 mV and maintains initial activity in 1 M KOH after 120 h. Notably, Zn-induced self-healing is achieved when the leaching and redeposition of Fe reach dynamic equilibrium. In 1 M KOH seawater, Zn0.5FeOOH requires overpotentials of 286 mV to produce current density of 100 mA cm−2. At 2.0 V, Zn0.5FeOOH can achieve 1000 mA cm−2 in anion exchange membrane (AEM) water electrolyzer at room temperature. This work provides an effective Zn-induced strategy for designing efficient and stable OER catalysts for industrial development.

In situ anodic leaching of Nd-Fe-B sludge with fast leaching kinetics for selective recovery of rare-earth elements

Neodymium-iron-boron (Nd-Fe-B) sludge is an important secondary resource of rare-earth elements (REEs). However, the state-of-the-art recycling method, i.e., HCl-preferential dissolution faces challenges such as slow leaching kinetics, excessive chemical consumption and wastewater generation. In this work, the in situ anodic leaching of Nd-Fe-B sludge was developed to selectively recover REEs with high efficiency. The leaching rates of the REEs are 2.4–9.0 times higher using the in situ anodic leaching at the current density from 10 to 40 mA/cm2 than using conventional chemical leaching under the maintained pH of 3.7. Mechanism studies reveal that the anode-generated H+ plays the key role during the in situ anodic leaching process that locally increases the H+ concentration at the interface of sludge particles, accelerating the leaching kinetics. By achieving a total leaching efficiency of Nd-Fe-B sludge close to 100% and the Fe deposition efficiency in the range of 70.9%–74.3%, selective leaching of REEs is successfully realized and thus largely reduces chemical consumption. Additionally, a two-step recycling route involving electrolysis-selective precipitation was proposed that enables a stable REEs recovery of 92.2% with recyclable electrolyte. This study provides a novel and environmentally-friendly strategy for the efficient recovery of REEs from secondary resources.

Mechanism and kinetic study of rare earth extraction from allanite by direct acid leaching

Direct acid leaching was conducted to recover rare earth elements (REEs) from an allanite ore assaying 9,861.4 ppm of REEs. The effects of operational variables, such as acid type, sulfuric acid (H2SO4) concentration, temperature, solid/liquid (S/L) ratio, and particle size, on the total REE (TREE) recovery were systematically examined. The REE mineralogy and the involved leaching mechanisms were investigated by electron microscopy characterization and residue re-leaching tests. It was found that approximately 80% of REEs was extracted using 1 M H2SO4 at 75 °C for 2 h. Increasing temperature significantly improved the REE extraction, while changing acid type, H2SO4 concentration, and particle size did not cause noticeable influences on the extraction efficiency. The low fraction of Si leached (<4.0%) suggested that the extraction did not significantly alter the crystal structure of the dominant minerals. The leaching kinetics of REEs was fast within the first 10 min, followed by a much slower stage (i.e., 10–120 min). The kinetic modeling results showed that both stages were likely controlled by both chemical reaction and diffusion, implying a mixed control mechanism. The activation energies for REE leaching using 1 M H2SO4 were determined to be 20.3 kJ/mol for the 0-10 min stage and 10.8 kJ/mol for the 10-120 min stage. The residue re-leaching results suggested that the initial fast leaching kinetics was caused by the preferential dissolution of metamict allanite, while the following slower leaching stage was due to the dissolution of difficult-to-leach REE-bearing minerals, such as well-crystallized allanite.

Recycling of spent LiNixCoyMn1−x-yO2 batteries by a glucose reduction-acid leaching approach: Performance and mechanism

Recycling of valuable elements from spent lithium-ion batteries (LIBs) is of critical significance for both economic benefits and environmental sustainability by preventing potential safety hazards and reducing environmental pollution associated with improper disposal. In this study, a glucose reduction-acid leaching approach was proposed to recover valuable metals from spent LiNixCoyMn1−x-yO2. Under the optimized extraction conditions, 99.54% Li, 99.84% Ni, 99.58% Co, and 99.1% Mn were leached out. The kinetic analysis of the glucose reduction-acid leaching process revealed that the reaction rate was controlled by internal diffusion of valuable metals. The oxidation derivatives of glucose were mainly C6H12O7, C6H10O7, C5H10O6, C4H8O5 and C4H6O6. Through the reductive leaching process, high-valence Ni(III), Co(III), and Mn(IV) metals were reduced to the low-valence state by glucose, allowing for their fast leaching, while glucose was oxidized and decomposed into smaller molecular weight organics. The findings of this study may provide a new strategy for the effective recovery of valuable metals from spent LIBs.

Hydro-physical deterioration of a calcareous clay-rich soil by sodic water in Central Anatolia, Türkiye

The deleterious effects of sodium-induced secondary alkalinization on soil structure and hydraulic properties of calcareous soils can vary widely. This study aims to evaluate the impact of sodicity and leaching velocity on the physical and hydraulic properties of a calcareous clay-rich soil. Two application rates of tap water (TW) and sodic water (SW) are considered: fast leaching, equal to the saturated hydraulic conductivity, Ks, and slow leaching conditions, equal to have 1/2 Ks. For the TW and SW experiments, up to 14 and 26 leaching cycles were performed in duplicates, respectively. After the leaching applications, the PVC columns were cut horizontally, and undisturbed samples were removed from the different depths. It was observed that neither water quality nor water flow rate significantly affected water stable aggregate percentages. TW did not affect soil total porosity and bulk density except at the bottom of the column. On the other hand, there were remarkable reductions in soil porosity and bulk density in the SW leaching experiments ranging from 8.8 to 12.5% and 7.4–13.8%, respectively. High Na concentrations in leaching water caused aggregate swelling and dispersion, leading to reduced Na+ and enhanced Ca2+ transport to the lower portions of the soil column. In the lower layers, the severity of sodium-induced dispersion was restricted by calcium, which was exchanged by the excess amount of Na from the upper layers, maintaining soil particles flocculated. Ca2+, which tightens the soil particles and aggregates together, limited Na-induced disruption of the soil aggregation. Nonetheless, particles that broke away from aggregate did influence the hydraulic properties of the soils. Overall, the experiments revealed that although the physical and hydraulic properties of the soil are affected by the sodic waters and the flow rates, this effect is reduced in calcareous soils due to their strong bonding feature.

Solute transport through undisturbed carbonatic clay soils in dry regions under differing water quality and irrigation patterns

The often-indispensable use of poor-quality irrigation water in drylands instigates diverse physicochemical dynamics leading to soil salinization and sodicity which are recognized as major contributors to land degradation. This study aimed to examine the effects of water quality and irrigation mode on solute transport conditions in terms of ion exchange of colloidal particles. Laboratory studies with undisturbed soil columns were carried out with two water treatments - tap and sodic waters - as well as two water flow velocities: fast leaching which corresponds to Darcy velocity equal to the saturated hydraulic conductivity and slow leaching equal to half the fast-leaching case. Results indicated that the flow velocities did not significantly influence pH, EC and ion concentrations due to the high calcium carbonate and clay contents of the soil which make the soil less permeable. However, flow velocity rapidly decreased in the fast leaching compared to that in slow leaching as the sodic water was applied. This reveals the destructive effect of Na+ in the soil. The EC rapidly dropped at the beginning of leaching for both water qualities opposite to pH, then became steady. All sodic applications caused an increase in Na+ till the end of treatments. This also resulted in variations in measured soluble anions. In general, sharp decreases in highly soluble anions were observed in all treatments, leading to an increase in HCO3–, especially for sodic treatments. Overall, sodicity caused significant changes in flow dynamics and ion concentrations and created favorable conditions for secondary salinization in this low permeable soil system.

Rapid extraction of valuable metals from spent LiNixCoyMn1-x-yO2 cathodes based on synergistic effects between organic acids

The slow rate of organic acid leaching is the main factor hindering the ecological recycling of spent lithium-ion battery (LIB) cathode materials. Here, a mixed green reagent system of ascorbic acid and acetic acid is proposed to leach valuable metal ions from the spent LIBs cathode materials rapidly. In 10 min, 94.93% Li, 95.09% Ni, 97.62% Co, and 96.98% Mn were leached, according to the optimization results. Kinetic studies and material characterization technologies like XRD, SEM, XPS, UV–vis, and FTIR show that the “diffusion” and “stratification” effects of acetic acid contribute to the dual-function leaching agent ascorbic acid quickly extract metal ions from spent LiNi0.5Co0.3Mn0.2O2 (NCM532) materials at a mild temperature. In addition, the density-functional theory (DFT) calculations of spent NCM532 structural surfaces and leaching agents show that the fast leaching of valuable metal ions is due to the synergy between ascorbic acid and acetic acid. These results provided an approachable thinking for developing advanced and environmentally friendly strategies for recycling spent LIB cathode materials.

Source apportionment and controlling mechanisms of nitrogen leaching from bioretention systems

Nitrogen (N) leaching has attracted concerns in bioretention systems (BRSs), while regulation of N leaching in BRSs is a challenge. In this study, N leached from BRSs with three plants (Phragmites australis, Acorus calamus L. and Cana indices L.) has for the first time been apportioned between three types of sources: immediate, fast and slow leaching based on 15N labeling. Results indicated that: fast leaching mainly comes from the previous four rainfall-runoffs, while slow leaching accounts for the largest proportion in total leaching; immediate leaching is mainly as NO3-, fast leaching mainly as NO3- and dissolved organic nitrogen (DON), and slow leaching mainly as DON and NH4+; BRSs with different plants vary in source compositions of N leaching. Meanwhile, N fates, transformation rates, and functional genes were constrained to explain the controlling mechanisms of each source of N leaching: immediate leaching mainly relates to soil characteristics and root morphology (e.g. type, surface area and diameter) that can influence adsorption, preferential flow and plant uptake; fast leaching mainly relates to soil N transformation during the dry periods that can influence the availabilities of NO3- and DON; slow leaching mainly relates to plant uptake and soil retention, soil N transformation and plant-soil interactions can influence the availabilities and stability of DON and NH4+. This study provides insights into the source compositions of N leaching, the long-term N legacy effect and controlling mechanisms of N leaching in BRSs-like engineering systems, which will imply future improvements in design and risk assessment of green infrastructure.

Use of Compost Based on Invasive Algae Rugulopteryx okamurae as a Peat Alternative in Nursery Growing Media

The invasion of the macroalgae Rugulopteryx okamurae is causing several environmental and economic problems along Spanish Mediterranean coasts. The use of composts based on R. okamurae as a peat alternative in nursery production could be a valid alternative for the exploitation of this organic material. The present study evaluated three different composts as peat substitutes in potting media to grow tomato seedlings: compost of R. okamurae, compost of green horticultural residues (two-thirds) and R. okamurae (one-third), compost of garden pruning residues (two-thirds) and R. okamurae (one-third). Each compost was used to formulate two different substrates to reduce the use of peat (40% compost, 40% peat, 20% perlite) or entirely substitute it (80% compost, 20% perlite), using a control treatment with 80% peat and 20% perlite. Only the control treatment received mineral fertigation during the trial. The results showed that the high initial electrical conductivity and ion concentration were remarkably reduced thanks to the fast leaching of salt that occurred with customary irrigation. Generally, compost-based treatments allowed us to obtain tomato seedlings with satisfactory morphological parameters. The substrates that contained 40% compost of R. okamurae or a compost of garden pruning residues and R. okamurae led to the best results in term of seedling parameters. It is therefore concluded that composts based on R. okamuare could be used as a seedling growing medium for the valorization of algae.

Nitrogen dynamics in the Critical Zones of China

Nitrogen dynamics at ecosystem levels profoundly impact the Earth’s surface system due to their environmental and ecological significance. Exploring the sources and transformation of nitrogen in various Critical Zones is vital to understanding biogeochemical cycles and sustainable development. This study summarized nitrogen characteristics in soil profiles and nitrogen dynamics in diverse terrestrial ecosystems based on data from typical Critical Zones of China. The results indicated that nitrogen accumulates in the deep soils of cropland ecosystems due to intensive fertilizer applications, which potentially harms soil functions and water quality. Therefore, it is necessary and meaningful to take adequate measures to alleviate nitrogen accumulation in deep soils. Additionally, surplus nitrogen transported into groundwater and riverine systems from soil has emerged as an important issue for environmental management. There are serious nitrogen pollution issues in many river water and groundwater areas, which could be addressed by reducing the fast leaching and considerable nitrogen accumulation in the vadose zone. Systematic and long-term observational studies are needed to achieve the ultimate goal of ecological conservation and high-quality development. Therefore, future research should consider monitoring and evaluating ecosystems based on the long-term Critical Zone Observatories networks to advance appropriate environmental management strategies that adapt to nature’s rules and strengthen the ecosystem service function for sustainable development.

Assessment of selenium and zinc enriched sludge and duckweed as slow-release micronutrient biofertilizers for Phaseolus vulgaris growth

Selenium (Se) and zinc (Zn) are essential micronutrients that are often lacking in the diet of humans and animals. Application of mineral Se and Zn fertilizers into soils may lead to a waste of Se and Zn due to the fast leaching and low utilization by plants. Slow-release Se and Zn biofertilizer may therefore be beneficial. This study aims to assess the potential of SeZn-enriched duckweed and sludge produced from wastewater as slow-release Se and Zn biofertilizers. Pot experiments with green beans (Phaseolus vulgaris) and sampling of Rhizon soil pore water were conducted to evaluate the bioavailability of Se and Zn in sandy and loamy soils mixed with SeZn-enriched duckweed and sludge. Both the Se and Zn concentrations in the soil pore water increased upon amending the two biomaterials. The concentration of Se released from SeZn-enriched duckweed rapidly decreased in the first 21 days and slowly declined afterwards, while it remained stable during the entire experiment upon application of SeZn-enriched sludge. The Zn content in the soil pore water gradually increased over time. The application of SeZn-enriched duckweed and sludge significantly increased the Se concentrations in plant tissues, in particular in the form of organic Se-methionine in seeds, without a negative impact on plant growth when an appropriate dose was applied (1 mg Se/kg soil). While, it did not increase Zn concentrations in plant seeds. The results indicate that the SeZn-enriched duckweed and sludge could be only used as organic Se biofertilizers for Se-deficient soils. Particularly, the SeZn-enriched sludge dominated with elemental nano-Se was an effective Se source and slow-release Se biofertilizer. These results could offer a theoretical reference to choose an alternative to chemical Se fertilizers for biofortification, avoiding the problem of Se losses by leaching from mineral Se fertilizers while recovering resources from wastewater. This could contribute to the driver for a future circular economy.

Coordination compound-derived Fe4N/Fe3N/Fe/CNT for efficient electrocatalytic oxygen evolution: a facile one-step synthesis in the absence of extra nitrogen source

By annealing an Fe(III)–coordination compound (Fe–CC), [FeCl3(Hbta)2] (Hbta = benzotriazole) in the presence of a carbon nanotube precursor (PCNT) template, an Fe4N/Fe3N/Fe/CNT heterostructure was successfully synthesized without an extra nitrogen source. The decomposition of the Hbta in Fe–CC under high-temperature annealing can produce carbon sheets and reduced graphene oxide (rGO), and the presence of CNTs can alleviate the stacking of the in situ-generated carbon materials. Meanwhile, iron nitride nanoparticles (NPs) can be anchored on the carbon sheets, and the anchoring effect efficiently prevents the agglomeration of NPs and increases the amount of active catalytic sites for the oxygen evolution reaction (OER). Fe4N/Fe3N/Fe/CNT shows an excellent OER activity with a Tafel slope of 63 mV dec−1 as well as overpotentials of 121 (η 10) and 275 mV (η 100) at 10 and 100 mA cm−2, respectively — far exceeding commercial RuO2 and other catalysts. Density functional theory calculations show that the excellent OER performance of Fe4N/Fe3N/Fe/CNT is associated with the Fe4N/Fe3N heterojunction, which can improve the electron conductivity and boost the electron transfer from N to Fe. The Fe4N/Fe3N/Fe/CNT catalyst exhibits long-term OER activity during 100 h of electrolysis at 20 mA cm−2. This is related to the dual coatings of the in situ-generated thin carbon shell and few-layered rGO on the surface of the iron nitride NPs, which can protect the fast leaching of iron nitride during the OER process. Furthermore, the effects of the annealing temperature, the PCNT template and the heating rate on the calcined products were investigated.

Recycling of Lithium-Ion Battery Materials Using Deep Eutectic Solvents

To drive the transition to a climate-neutral economy, industry will need a sustainable and secure supply of key technology metals, which are essential for large-scale renewable energy production and storage as well as the electrification of mobility. Lithium-ion batteries (LIBs) play an increasingly important role for various energy storage systems. The current and future LIB technologies will require materials that are predicted to have a high supply risk in the future. In light of this, recycling has been put forward as a key strategy next to primary mining and critical raw material substitution.Great efforts are currently being made to develop smart and sustainable processes for recycling LIB materials from end-of life batteries and production scrap. Lithium nickel manganese cobalt oxide (NMC) and lithium cobalt oxide (LCO) are two common LIB electrode materials. Deep eutectic solvents (DESs) are considered as green solvents in recycling of LIB materials due to their biodegradability and low toxicity combined with good leachability of metal oxides.In this work, a new process for recycling and direct re-synthesis of NMC111 and LCO is presented. The process is based on leaching using a sustainable DES. Water is used as cosolvent to tune the properties of the DES. Leaching kinetics and mechanisms are determined. The chosen DES shows excellent leaching ability and fast leaching rate at low temperature compared with those DESs reported in the literature. After the leaching step, a new approach is applied to recover the metals from the DES leachate. This approach shows an overall high recovery efficiency and the solid product proves to be a good precursor for direct re-synthesis of new electrode materials. To conclude, this work presents a novel, green, effective and closed-loop metal recovery strategy for recycling LIB materials.

Insights into the coordination enhanced leaching mechanism of spent lithium-ion batteries cathode materials

The ultra-fast leaching of strategic metals from spent lithium-ion batteries cathode materials is achieved by the coordination enhanced leaching with inorganic acids and organic reductants. However, the detailed leaching mechanism that led to the fast leaching kinetics is unclear. This research utilizes the controlled variable method to reveal the coordination enhanced leaching mechanism by a comparison of the thermodynamics and kinetics between sulfate acid coupled with L-ascorbic acid (VC) and hydrochloride acid coupled with VC systems. Thermodynamic calculations, online UV–vis spectroscopy, and in-situ Raman spectroscopy are adopted to interpret the leaching mechanisms in the whole leaching process. The leaching of cobalt is controlled by decomposition of crystal structure and diffusion, respectively, in sulfate acid coupled with VC and hydrochloride acid coupled with VC systems, indicating relatively slow kinetics in the former system. The thermodynamic calculations suggest higher fractions and more stable coordination species, i.e., 26.11% CoCl(H2O)5+ and 8.945% CoCl4(H2O)22- at 363 K, in the latter system, which leads to lower apparent activation energy and might facilitate the rapid leaching kinetics in return. In-situ Raman mapping and depth analysis suggested the formation of coordination species on the crystal structure surfaces, solid-liquid boundaries, and bulk solutions.

Sustainable recovery of surface-deposited oils and valuable metals from uncrushed spent hydroprocessing catalysts

The spent hydroprocessing (HDP) catalysts containing a considerable quantity of oily pollutants and valuable metals including nickel (Ni), molybdenum (Mo), and vanadium (V) are hazardous wastes to be treated urgently. Herein, a sustainable process featuring vacuum pyrolysis and fast acidic elution was proposed to recycling the residual oils and metal values from the uncrushed spent HDP catalysts. The removal efficiency of oils by vacuum pyrolysis reached more than 85% at 400 °C in 60 min. The Ni, Mo, and V deposited on the uncrushed catalysts were fast eluted and recovered by 1 mol/L sulfuric acid solution within 15 min. The ultrasound-assisted leaching could promote metal recovery within 10 min but then has no difference with stirring leaching. The leaching efficiencies of Ni, Mo, and V reached over 95% with few Al being dissolved (7.63%). The obtained uncrushed Al2O3 residue could be potentially recycled as the support for a fresh catalyst. The liquid film diffusion control mechanism was disclosed to represent the fast leaching process of metal values. These results provided a promising and green approach for the sustainable recovery of both residual oils and valuable metals from spent hydroprocessing catalysts.

Active Corrosion Protection by Epoxy Coating on Li2CO3-Pretreated Anodized Aluminum Alloy 2024-T3

The fast leaching and robust barrier property of inhibitors are the basic fundamentals for the formation of active protective coatings to protect aluminum alloys. Herein, an active protective surface was developed based on an epoxy coating and an underlying lithium carbonate (Li2CO3)-treated anodized aluminum alloy 2024-T3. The morphology of the Li-LDH layer was studied to know its formation mechanism. The electrochemical studies revealed that the fast and adequate leaching of lithium led to a substantial increment of corrosion resistance of the scratched coating in 3.5 wt% NaCl from 1 to 8 days. Time of flight secondary ion mass spectroscopy (ToF-SIMS) results indicated that Li was distributed in the lateral direction and covered the scratched area. The 3D images indicated that different lithium compounds were formed and 90% of the scratched area was covered with the lithium protective layer over immersion time. A combined approach of morphology observations, electrochemical measurements, and ToF-SIMS showed the lithium protective layer offered good corrosion resistance. On the contrary, lithium provided fast and adequate leaching from the coating, demonstrating good active protection for aluminum and its alloys.

Rapid Atmospheric Leaching of Chalcopyrite Using a Novel Reagent of Trichloroisocyanuric Acid

With the decrease in high-grade chalcopyrite resources, the copper extraction from low-grade chalcopyrite has attracted more and more attention. However, the kinetic rates of chalcopyrite leaching with traditional oxidants are usually very slow due to the formation of the passivation layer. In this study, a novel reagent of chlorinated oxidant, trichloroisocyanuric acid (TCCA), was used to leach chalcopyrite for the first time. The experimental results showed that when the initial oxidant concentration for TCCA was 0.054 mol·L−1, the leaching temperature was kept at 55 °C, and the pH of the pulp was controlled at 1, the oxidation efficiency of Cu can reach above 90% in less than 30 min. Various analyses of chalcopyrite mineral ore and its oxidized residues, such as chemical composition analysis, X-ray diffraction analysis, scanning electron microscopy analysis and X-ray photoelectron spectroscopy, were conducted, respectively. No obvious passivation layer was found on the chalcopyrite surface, though the sulfur product can also be generated during the leaching. Reaction kinetic analysis results showed that the different influence of surface reaction and diffusion process on the dissolution of chalcopyrite is little due to the fast leaching speed. After calculation, the activation energy of the whole leaching reaction is 9.06 kJ·mol−1, much lower than that in other reports. The mechanism was also proposed that TCCA was hydrolyzed in the solution to form hypochlorous acid, which is the strong oxidant, and cyanuric acid, which prevents the formation of a passivation layer. The processing in this study is expected to be applied as a novel method for atmospheric leaching of chalcopyrite.

Chalcopyrite leaching in ammonium chloride solutions under ambient conditions: Insight into the dissolution mechanism by XANES, Raman spectroscopy and electrochemical studies

Ammoniacal leaching solutions have been considered as an effective lixiviant for the oxidative dissolution of chalcopyrite. However, compared with the extensive studies of acidic chalcopyrite dissolution, the dissolution mechanism of chalcopyrite in ammoniacal solutions needs further understanding. In this study, the oxidative dissolution of chalcopyrite in ammonium chloride solutions under room temperature and pH 8.5 was studied by X-ray absorption near-edge spectroscopy (XANES), Raman spectroscopy and electrochemical impedance spectroscopy (EIS). Both batch leaching experiments and electrochemical studies showed that Cu(II) ions were more efficient than dissolved oxygen for chalcopyrite oxidation in ammonium chloride solutions. Leaching kinetics analysis showed that without the initial addition of Cu(II), chalcopyrite dissolution rate was controlled by two different stoichiometric chemical reactions: the initial and slow leaching stage controlled by dissolved oxygen; then predominated by Cu(II) rather than dissolved oxygen with a fast leaching rate when copper concentration exceeded a certain level (>0.12 g/L). Thiosulfate (S2O32−) rather than sulfate (SO42−) was confirmed as the primary soluble sulfur species produced during chalcopyrite dissolution. Decomposition of S2O32− in the presence of both O2 and Cu(II) resulted in the final stable product SO42− accompanied by the formation of other sulfur intermediate species, including S4O62− and SO32−. No evidence was found for the formation of elemental sulfur. Amorphous hematite (Fe2O3) and six-line ferrihydrite (5Fe2O3·9H2O) were the major components residing on the chalcopyrite surface, which were responsible for the slow dissolution rate at late stage. According to the present work, a model for the chalcopyrite dissolution mechanism in alkaline ammonium chloride solutions under ambient conditions is provided.