The flotation process for separating anode and cathode materials (blackmass) is a critical step in recycling lithium-ion batteries (LIBs), particularly before the extraction of lithium-bearing materials. Surface electric charge, measured via zeta potential, plays a pivotal role in the flotation separation of these electrode materials. The pH, roasting temperature, thermal treatment duration, and bubbles' presence can significantly influence these materials' surface properties. However, a comprehensive investigation addressing the combined effects of these factors on the zeta potential of electrode active materials is still lacking. This study aims to bridge this gap by systematically exploring the effects of pH (4.5, 7, and 10.5), roasting temperatures (0–500 °C), varied thermal treatment times (1 to 2 h), and the presence or absence of bubbles (nano and microbubbles) on the zeta potential of both anode and cathode materials. The study also examines the impact of conditioning with n-dodecane, a typical flotation collector. While zeta potential is largely pH-dependent, roasting temperature significantly influences surface charge, whereas thermal treatment duration has a minimal effect. Notably, the most considerable zeta potential difference (28.3 mV) between the anode (-18.63 mV) and cathode (9.67 mV) surfaces occurred in the absence of both collector and bubbles, at pH 7, 500 °C, and a thermal treatment time of 2 h. Under conditioning involving bubbles and collector, the highest difference observed was 2.21 mV at pH 7, 250 °C, and 1 h of thermal treatment. These findings contribute to a deeper understanding of surface charge behavior in LIB recycling processes, with implications for improving flotation separation efficiency through surface science and engineering.

As battery technologies evolve and the demand for sustainable energy solutions rises, the request for natural graphite is expected to remain strong. The graphite used in battery anodes is typically a form of high-grade purified flake graphite, which has a layered structure that allows for the intercalation of lithium ions during charging and discharging cycles. Since graphite is naturally hydrophobic, flotation beneficiation is the most utilized enrichment technique for upgrading. Different flotation conditions were investigated for graphite enrichment with various crystal particle sizes. Since the size of the flake directly affects its market price, providing an overview of ‘graphite flotation’ based on the flake size is essential for disseminating the process knowledge and promoting research advancements related to this critical mineral. Thus, as an innovative approach, this work assessed and reviewed published graphite flotation investigations based on flake graphite particle sizes and divided them into fine (<150 μm) and large (>150 μm) groups. The assessments emphasized that large flake graphite particles become irretrievable once their structure is damaged; thus, during their processing, it is essential to minimize the potential damage by separation from fine flakes. On the other hand, several issues are associated with the flotation of fine graphite, including high collector consumption and entrainment. Therefore, this overview focused on four main aspects of graphite flotation (flotation pretreatment, enhancement of the collection process, inhibition entrainment and presented examined solutions for optimizing grinding and flotation beneficiation) and addressed knowledge gaps within these areas.

Froth flotation is the most effective method for separating anode-active materials from cathode ones while recycling spent lithium-ion batteries (LiBs). This separation relies on surface hydrophobicity differences, highlighting the importance of understanding and modifying surface properties to optimize flotation recycling. Although several studies have focused on optimizing flotation conditions and pretreatment methods, research addressing electrode materials' surface interaction and modification still needs to be completed. This study comprehensively reviewed the surface properties of LiBs’ electrode materials under various modification scenarios. Key surface characteristics such as wettability, electric surface charge (zeta potential), and surface chemistry were explored using analytical tools, including zeta potential measurements, FTIR, XPS, ToF-SIMS, and SEM-EDS. Notable findings include the challenges posed by polymer binders like PVDF and CMC, which make flotation separation less efficient by homogenizing surface properties. Thermal pretreatment, particularly pyrolysis at 400 °C, improved flotation performance, as reflected by contact angle differences of 35° (cathode) vs. 75° (anode). The isoelectric point (IEP) shifted significantly after pyrolysis, with cathode materials moving from pH < 2 to 3–5, while anode materials displayed an IEP at pH 1.6. FTIR analyses revealed the breakdown of PVDF binders at 175 °C, while XPS highlighted a 52 % reduction in fluorine content after pyrolysis at 400 °C. Despite these improvements, SEM-EDS indicated that complete binder removal remains challenging, and temperatures above 500 °C may reduce anode hydrophobicity. The findings underscore the need for detailed studies on surface properties under consistent conditions to enhance the flotation recycling of LiBs.

Starch is a traditional depressant for hematite beneficiation by cationic reverse flotation separation from silicates. Alkali or thermal gelatinization must be used to prepare starch and promote its dissolution in water. In industry, gelatinization is typically carried out using sodium hydroxide at room temperature at different starch/NaOH mass ratios (SNMR). Surprisingly, no investigation has systematically studied the optimum SNMR for boosting hematite depression. This work examined the influence of starch gelatinization under various SNMR (3:1, 5:1, 7:1, and 9:1) on hematite depression (at pH = 10.5, 22 °C) by exploring flotation response (R), contact angle (θ), induction time (τ), hydrodynamic diameter (dH) of starch macromolecules, total energy of interaction starch/hematite (GTOT), based on its two components: the attractive Lifshitz-van der Waals energy (GLW) and attractive/repulsive electrostatic energy (GEL). Flotation test results indicated that SNMR = 5:1 promoted the lowest hematite recovery (14.8 %), coupled with the highest induction time (τ = 55 ms) and the lowest contact angle (θ = 11°). The hydrodynamic diameter (dH) of macromolecules in solutions prepared under different SNMR was determined by Dynamic Light Scattering, showing three peaks: amylopectin (350 < dH < 420 nm), amylose (50 < dH < 100 nm) and debris from gelatinization (dH ∼ 5000 nm). Since the latter only occurred in solutions prepared under SNMR of 7:1 and 9:1, deficient hematite depression might be caused by incomplete gelatinization. As amylopectin is the starch component that is responsible for its depressant ability, larger amylopectin macromolecules (dH = 411 nm) found in solutions prepared at SNMR = 5:1 contrast with smaller macromolecules (dH = 353 nm) produced at SNMR = 3:1. Considering starch macromolecules as a sphere, and hematite&apos;s surface as a plane; GLW, GEL, and GTOT were calculated in function of the sphere/plane separation distance (2 nm < H < 20 nm). GLW was determined based on the assessment of the Hamaker constant of the starch/water/hematite system (2.9 × 10−20J < A132 < 3.3 × 10−20J), whereas GEL was determined based on the zeta potential of starch (−2mV < ζ1 < −4mV) and hematite (ζ2 = −29 mV). GTOT for starch gelatinized at SNMR = 5:1 (−502.9 × 10−21 J) is greater than GTOT for starch prepared at SNMR = 3:1 (−468.8 × 10−21 J) and SNMR = 7:1 (−469.0 × 10−21 J), at a confidence level of 95 %. These results corroborate the more intensive hematite depression by starch prepared at SNMR = 5:1 compared to the other values explored by this study.

Vickers microhardness (MH) of coal is known to be strongly correlated with coal rank. To examine coal rank and other coal quality parameters, such as organic sulfur, that might influence MH, a suite of more than 300 samples from the Penn State Coal Quality database with vitrinite Rmax < 1.1 % were examined. The data set was narrowed down to 296 coals with moisture (as-received basis) < 20 %. As MH is a parameter measured on vitrinite, vitrinite Rmax was used as the rank parameter. The Eocene Big Dirty coal (Washington state) stood out as a high MH/high-moisture coal while Hanna and Green River basin coals (Wyoming) had low atomic H/C values and K Unita Basin (Utah) coals had high H/C. Organic S did not show a correlation with MH within discrete rank ranges. With respect to vitrinite Rmax vs. MH, the Big Dirty coal and some Illinois and Iowa coals lie on the high-MH/low-Rmax side and the Pennsylvanian Tioga (West Virginia) and the Indiana Brazil Formation coals, all dominated by dull lithotypes, lie on the low-MH/high-Rmax side of the main data trend. Overall, the quadratic regression of vitrinite Rmax vs. MH yields an R2 of 0.55, indicating a significant correlation at the 95 % level.

Exponential increasing demands for base metals have made meaningful processing of their quite low-grade (>1%) resources. Froth flotation is the most important physicochemical pretreatment technique for processing low-grade sulfide ores. In other words, flotation separation can effectively upgrade finely liberated base metal sulfides based on their surface properties. Various sulfide surface characters can be modified by flotation surfactants (collectors, activators, depressants, pH regulators, frothers, etc.). However, these reagents are mostly toxic. Therefore, using biodegradable flotation reagents would be essential for a green transition of ore treatment plants, while flotation circuits deal with massive volumes of water and materials. Pyrite, the most abundant sulfide mineral, is frequently associated with valuable minerals as a troublesome gangue. It causes severe technical and environmental difficulties. Thus, pyrite should be removed early in the beneficiation process to minimize its problematic issues. Recently, conventional inorganic pyrite depressants (such as cyanide, lime, and sulfur-oxy compounds) have been successfully assisted or even replaced with eco-friendly and green reagents (including polysaccharide-based substances and biodegradable acids). Yet, no comprehensive review is specified on the biodegradable acid depression reagents (such as tannic, lactic, humic acids, etc.) for pyrite removal through flotation separation. This study has comprehensively reviewed the previously conducted investigations in this area and provides suggestions for future assessments and developments. This robust review has systematically explored depression performance, various adsorption mechanisms, and aspects of these reagents on pyrite surfaces. Furthermore, factors affecting their efficiency were analyzed, and gaps within each area were highlighted.

Flotation separation is the most important upgrading critical raw material technique. Measuring interactions within flotation variables and modeling their metallurgical responses (grade and recovery) is quite challenging on the industrial scale. These challenges are because flotation separation includes several sub-micron processes, and their monitoring won&apos;t be possible for the processing plants. Since many flotation plants are still manually operating and maintaining, understanding interactions within operational variables and their effect on the metallurgical responses would be crucial. As a unique approach, this study used the “Conscious Lab” concept for modeling flotation responses of an industrial copper upgrading plant when Potassium Amyl Xanthate substituted the secondary collector (Sodium Ethyl Xanthate) in the process. The main aim is to understand and compare interactions before and after the collector substitution. For the first time, the conscious lab was constructed based on the most advanced explainable artificial intelligence model, Shapley Additive Explanations, and Catboost. Catboost- Shapley Additive Explanations could accurately model flotation responses (less than 2% error between actual and predicted values) and illustrate variations of complex interactions through the substitution. Through a comparative study, Catboost could generate more precise outcomes than other known artificial intelligence models (Random Forest, Support Vector Regression, Extreme Gradient Boosting, and Convolutional Neural Network). In general, substituting Sodium Ethyl Xanthate by Potassium Amyl Xanthate reduced process predictability, although Potassium Amyl Xanthate could slightly increase the copper recovery.

Processing fine and ultrafine coal particles from primary resources is essential for sustainable development. As one of the most recently developed enrichment equipment, cyclonic microbubble flotation columns (FCMC) showed high efficiency in upgrading various fine minerals. However, understanding the effect of FCMC operating variables on coal upgrading process responses remains a black box and needs fundamental assessments. To fill the gap, this study examined the influence of circulating pump pressure and froth height on the recovery of different coal particle size ranges to assess and explore fundamental FCMC performance. The experimental results established that increased froth height would simultaneously reduce the collection and froth recovery. Coarse particles in the high froth height were detached due to bubble coalescence or rupture, while the liquid drainage reduced fine particle pollution of froth products. Increasing circulating pump pressure would increase the collection zone’s turbulence, lead to coarse particle detachment, and reduce collection recovery. Meanwhile, increasing circulating pump pressure could promote froth stability and decrease froth detachment in the froth zone. The calculated first-order rate constant (k c) confirmed that the flotation rate constants of coarse (−0.5 + 0.25 mm) and fine (−0.074 mm) particles were low, while the intermediate particles (−0.125 + 0.074 mm) had faster flotation kinetics.

Gelatinization of starch by NaOH is an essential stage for this depressant preparation to enhance its water solubility through the reverse cationic flotation. No investigation has explored the rheology of the starch gelatinization to demonstrate the hematite depression completeness. To fill the gap, this study examined the influence of a wide range of SNMRs (3:1, 5:1, 7:1, 9:1) to explore the efficiency of the gelatinization process. The main aim was to highlight how starch gel preparation can influence hematite depression in cationic reverse flotation. The steady and dynamic shear rheological measurements plus optical micrographs were assessed for the starch gel gelatinization process for different SNMR conditions. Various experiment outcomes indicated that through the starch gelatinization by SNMR>6:1, the solubilization did not occur completely (due to the presence of some pristine granules) and the gels exhibited solid-like behavior, as evidenced by K' > K'', tan <1, ≥ 94.3s, and 0 ≥ 32.0 Pas. The incomplete release of AP macromolecules into the solution was the cause of the poor hematite depression efficiency. Pretreating starch by SNMR ≤5:1 indicated a full release of both AM and AP species to the solution since the gels showed fluid-like behavior with K' < K'', tan >1, ≤ 0.7s, and 0 ≤ 2.4 Pas. However, the excessive alkalinity promoted a reduction in the hydrodynamic size of macromolecules. These findings explain the better efficiency of SNMR = 5:1 to depress hematite compared to SNMR = 3:1. In general, starch preparation with SNMR = 6:1 marked the onset of the sol-gel transition, and the gels exhibited a balance between fluid-like behavior and solid-like behavior.