Single pretreatment of discarded printed circuit boards for enhanced gold dissolution by bio-lixiviant through an innovative green alkaline sequential strategy.

Eco-friendly two-step leaching of molybdenum and nickel from spent hydrodesulfurization catalysts using glycine and alkaline solutions.

A biogeochemistry ( Picea mariana bark) orientation case study consisting of three transects over two known gold zones was completed in the McFaulds Lake region (“Ring of Fire”) located in the far north of Ontario, Canada. The well known proprietary weak/selective Mobile Metal Ion (MMI TM ) leach with inductively coupled plasma mass spectrometry (ICP-MS) finish was utilized, rather than a conventional technique such as acid digestion and ICP-MS on macerated bark tissue. This approach is based on the need to generate biogeochemical data that more accurately represents the labile phases of elements that may be released from hidden mineral deposits. Extensive peatlands characterize the study area, below which an ∼8 m thick sequence of till covers the underlying Archean bedrock that hosts the Triple J gold zones. The MMI TM results include relevant patterns with respect to the gold zones, in particular for the metals In and Mo. Horizons of massive chromite of the Blackbird deposit also appear to be influencing tree bark biogeochemistry, in particular for Bi, U, and rare earth elements. These biogeochemical signals are possible evidence for the presence of a metal accretion zone in the soil substrate, perhaps due to a redox column developed above the mineralized zones. Peat thickness appears to affect the metals concentrations in bark tissue; I infer that mineral soil substrates provide more metal signal for uptake to the spruce trees compared to thicker peat areas, where significant portions of the root systems are within organic peat. Comparison to a nearby aqua-regia digest (ARD) bark geochemistry dataset helps illustrate that landscape drainage and soil/substrate moisture content present additional variables, which can have significant control on the uptake and translocation of some metals to the outer tissues of Spruce trees. Using a weak or selective leach technique on Black Spruce outer bark may improve the signal-to-noise ratio compared to conventional digestion methods, by targeting any weakly bound, labile phases.

Coal fly ash (FA) is generated in vast quantities, yet remains underutilized. Here, we systematically tuned its surface chemistry and porosity through sequential water washing, HCl digestion (2, 4, and 6 M), and calcination (500, 700, and 900 °C). Water washing followed by acid treatments at higher molarities (4, 6 M) and subsequent calcination at 700 °C proved most effective. The optimized sample (PFA-6M-C700) exhibited a Langmuir maximum adsorption capacity (qmax) of 11.0 mg/g for methylene blue (MB). Furthermore, under identical conditions, PFA-6M-C700 achieved an equilibrium uptake approximately nine times higher than that of as-received FA. This enhancement was attributed to selective leaching of surface carbon, surface enrichment of siliceous phases, removal of Cl-containing residuals, a marked increase in surface area and pore size, and a decreased point of zero charge (PZC) upon modification. In contrast, 2 M HCl was insufficient to enhance porosity and calcination at 900 °C induced sintering. Adsorption followed pseudo-second-order kinetics for all modified samples and fitted the Langmuir model for PFA-6M-C700, which retained 82% of its initial capacity after eight successive uses. Density functional theory calculations revealed that efficient MB binding requires SiO2 surfaces having a balanced ensemble of lattice oxygen, surface -OH groups, and exposed Al centers, a configuration confirmed in the high-performing adsorbents according to characterization results. Beyond highlighting FA as an adsorbent, this work establishes a systematic modification strategy that can be readily transferred to other fields such as catalysis, construction materials, and additional high-value technologies, opening new economic and environmental opportunities.

Abstract Transition metal‐based catalysts typically undergo oxidative reconstruction to form active phases during oxygen evolution reaction (OER), but continuous reconstruction may trigger dissolution of active phases and catalyst deactivation. Synergistically optimizing reconstruction kinetics and structural stability is a key challenge in enhancing practicality of such catalysts. Here, a dynamic self‐reconstruction regulation strategy is proposed, driven by selective Cu leaching, to synthesize CuCo layered double hydroxide (CuCo LDH) pre‐catalyst, where Cu species with low redox potential are preferentially and selectively leached, inducing controllable deep reconstruction. Combined in situ characterizations and theoretical calculations reveal the dual regulatory mechanism of Cu species: its selective preferential leaching induces the formation of CoOOH active phase, while stabilizes the Co oxidation state via electronic interactions, suppressing the over‐oxidation. The reconstructed Act‐CuCo LDH forms crystalline‐amorphous heterostructure, which upshifts the d‐band center and optimizes oxygen intermediates adsorption. As expected, Act‐CuCo LDH exhibits outstanding activity and only 18 mV decay for 550 h stability test at 200 mA cm −2 . Additionally, the anion exchange membrane electrolyzer using Act‐CuCo LDH || Pt/C remains stable for 200 h at 1.0 A cm −2 . This study achieves a balance between deep reconstruction and structural stability, providing a design strategy for highly efficient and stable OER catalysts.

The growing consumption of lithium-ion batteries (LIBs) in electronic devices and electric vehicles has led to a significant increase in waste containing valuable metals such as lithium and cobalt. Recovering these metals is essential to reducing dependence on primary sources and minimizing environmental impact. In this study, the leaching of the cathode active material from discarded LIBs was evaluated using oxaline, a deep eutectic solvent (DES) composed of oxalic acid and choline chloride in a 1:1 molar ratio. The process began with the collection, discharge, washing, drying, and dismantling of the LIBs, followed by the separation of their components. Subsequently, the cathode active material was characterized, revealing a primary composition of cobalt (54.5%) and lithium (6.5%), with the presence of LiCoO2 confirmed by XRD analysis. Leaching experiments were conducted to evaluate the effects of temperature, time, and solid percentage, demonstrating that oxaline is effective for the selective leaching of lithium and cobalt. Under optimal conditions (90 °C, 1–2 wt.% cathode active material, 400 rpm), lithium underwent complete dissolution within the first hour, while cobalt achieved complete leaching by 4 h. Both metals were recovered as oxalates and separated based on differences in solubility. Oxaline proves to be an efficient and environmentally friendly alternative for the selective recovery of lithium and cobalt from LIB waste, supporting a circular economy in the management of critical metals.

Abstract Rare earth elements (REE) are essential in various technologies and are found in Indonesia, especially in monazite minerals from Bangka Island, a by-product of cassiterite processing. Despite efforts, commercial REE extraction from monazite in Indonesia is hindered by technical challenges, particularly from radioactive thorium (Th) and uranium (U). This study focuses on extracting and separating REE from Th and U in a monazite sample from Bangka Island. Experiments involved caustic fusion to remove phosphorus, followed by hydrochloric acid (HCl) leaching under optimal conditions obtained from previous research, selective precipitation, and selective leaching of precipitate. The caustic fusion removed about 92.37% phosphorus from the monazite sample. The leaching process with 6 M HCl at 70 °C for 4 hours dissolved about 60% of REE. The ammonium hydroxide precipitation process selectively precipitated Th and U at pH levels below those for REE. At pH 5, REE, Th, and U precipitation rates were 19.3%, 99.5%, and 99.9%, respectively. Selective leaching at pH 3 separated REE from Th and U, with a leaching efficiency of 90% for REE, 0.55% for Th, and 54% for U.

Selective leaching and solvent extraction of Lithium from spent batteries

Synergistic recycling of spent LiFePO4 batteries with chromium-plating wastewater: a self-sustained approach for selective lithium leaching and dual waste valorization

Selective leaching of arsenic from zinc oxide dust in NaOH-(NH2)2CS solution

A closed-loop strategy for red mud acidic dealkalization: Comparison, reaction behaviors and potential applications.

Transformation mechanism of reduction − selective leaching of Ni and Mo from the residue of soda roasting − water leaching of the spent catalysts

The rise of electric vehicles has led to the increasing use of lithium iron phosphate batteries, and a large number of lithium-ion batteries are facing urgent need for recycling due to close to the end of their service life. This paper reviews the current status of recycling used lithium iron phosphate batteries and introduces the main recycling processes, which are pyrometallurgical recycling, hydrometallurgical recycling, and direct recycling. This paper focuses on the separation and recycling technologies of current cathode materials. This review further explores the latest methods and research advances in the separation and recycling of cathode materials, providing a critical analysis of the core challenges and future development prospects of existing process technologies. Through a comparative assessment of various recycling methods, this review proposes an optimized strategy with potential for industrial-scale application. This strategy shifts away from the conventional “leaching-impurity removal-separation” paradigm, which relies on complex separation steps, and instead emphasizes the most advanced and promising green recycling strategies for spent lithium iron phosphate (LFP) batteries: Namely, “selective leaching” and “direct regeneration.” HIGHLIGHTS An analysis of the current status of lithium iron phosphate recycling was conducted. Provides the latest technical process in the current lithium iron phosphate recovery process. Advances and perspectives in lithium iron phosphate recycling. GRAPHICAL ABSTRACT

Extraction of MgO from Boron Mud by Using Selective Leaching–Chemical Precipitation–Calcination

ABSTRACT Selective leaching of nickel was performed from the nickel laterite ore by the ammonia leaching process coupled with sulfation roasting to increase the recovery rate of nickel from the ore. The influence of leaching temperature, leaching time, and ammonia concentration on the leaching rates of Ni and Fe was analysed and discussed in detail. The shrinking core model (SCM) was used to analyse the reaction kinetics of Ni during the sulfation roasting-ammonia leaching process for the nickel laterite ore. The results showed that the leaching performance was the best when the ammonia concentration was 0.1 N, the leaching temperature was 70C°, and the leaching time was 75 min, with the leaching rate of Ni reaching 91.6%. The kinetic analysis indicated that within the temperature range of 50C°–80C°, the leaching kinetics of Ni by the sulfation roasting-ammonia leaching process was controlled by interface chemical reaction. The activation energy of the reaction was 6.268 KJ/mol, and the kinetic equation was 1-(1-R)1/3 = 0.0986e−753.91/ Tt. XRD, SEM, and EDS revealed the mechanism underlying the sulfation roasting-ammonia leaching process for the nickel laterite ore.

There are many valuable metals hidden inside printed circuit boards (PCBs for short), such as copper, aluminum, lead, iron, tin, and even noble metals like gold, silver, and platinum. To be exact, approximately 49% of all metals in PCBs are copper, 21.8% zinc, 11.6% iron, 6.5% nickel, 5.5% aluminum, 1.9% lead, 1.7% tin, 1.5% silver, 0.5% chromium, 0.1% gold, and less than 0.1% palladium. As technology advances rapidly, old devices are being discarded, yet only about 17.4% of all electronic waste was officially recycled in 2019 [1]. This leads us to believe that roughly 82.6% of all electronic waste was left untreated. This also includes PCBs, which (depending on the production year and manufacturer) can contain approximately 340 g of gold, 3.5 kg of silver, 140 g of palladium, and 130 kg of copper per ton of PCBs [2]. These numbers quickly add up, and many of the lost metals can heavily pollute the environment — including soil and water — if not properly treated. One of the ways to treat and extract these metals is by using hydrometallurgy (metal extraction using aqueous solutions) [3]. It is still widely used to extract various metals, either selectively or broadly. The entire process consists of three main stages: selective leaching, solution purification, and recovery of specific elements (usually via precipitation). In this study, we focus on extracting metals from waste using different acids and reagents. We decided to test traditional methods (such as Aqua Regia and Piranha Solution) and compare them to less commonly used alternatives (such as thiosulfate and salt solutions). Aqua Regia usually consists of 3 parts concentrated HCl and 1 part concentrated HNO₃. It is capable of dissolving noble metals like gold and silver. Piranha solution consists of 3 parts concentrated H₂SO₄ and 1 part H₂O₂. Other less common methods used in this work include: Salt solution, consisting of 10 parts saturated NaCl solution, 1 part concentrated HCl, and 2 parts concentrated H₂O₂.

ABSTRACT The conventional vanadium extraction process generates Cr(VI)-containing byproducts, typically treated through chemical reduction and neutralisation, which results in the formation of hazardous solid wastes and secondary pollutants. To address this environmental concern, a closed-loop recovery strategy was developed involving selective precipitation of Cr(VI) with PbSO₄, followed by leaching using NaHSO₄. Under optimised conditions (pH 9.5, Pb/Cr = 1.4, 30 °C, 240 min), chromium was effectively precipitated as PbCrO₄, reducing residual Cr concentration from 0.86 g/L to 0.002 g/L. Subsequent leaching of the Cr-rich precipitate at 80 °C for 100 min in 0.4 mol/L NaHSO₄ achieved a high Cr recovery efficiency of 97.33%. The regenerated PbSO₄ and leaching solution were reused over multiple cycles. A comparative evaluation demonstrated that this method outperforms conventional Cr(VI) removal technologies in terms of efficiency, waste minimisation, and reagent recyclability. Kinetic studies confirmed pseudo-first-order leaching behaviour (k= 0.0327 min−1) and precipitation governed by a shrinking-core model (kr= 0.00921 min−1), supporting industrial applicability and process robustness. The method eliminates the need for strong reducing agents, minimises waste generation, and enables reagent recycling. This approach outperforms traditional Cr(VI) removal techniques by offering superior selectivity, operational simplicity, and environmental sustainability, establishing a robust framework for green metallurgy and circular economy principles in vanadium slag processing.

Fast and Selective Leaching of Pyrrhotite in the Presence of Pentlandite

Selective leaching and magnetic separation for efficient recovery of lithium and iron phosphate from Aluminum-Contaminated cathode materials of spent LiFePO4 batteries

Manipulation of NiTi-based shape memory alloy nanostructures via a hybrid approach of phase separation and selective leaching