Mineral Recovery Research Articles

Considering the development levels of countries, contributions of mineral recovery from mining tailings and urban mining wastes to sustainability criteria – A review

The need for a sustainable mining waste management/legislation and mineral recovery from tailings is increasing day by day in the world. There is a need to draw a perspective for mining companies and public authorities & Sustainable Development Organizations (SDOs) on the sustainable recovery of mine waste from both mining operations and urban mining. Although there are many publications in the literature on mineral recovery from mine wastes, there is a lack of a study that will respond to the information needs of public authorities & SDOs in terms of both mining enterprises and urban mining sector on sustainable mineral recovery by covering the latest developments in the world and making the distinction between waste and tailing. Considering this deficiency in the literature, this study firstly emphasizes the on-site mitigation of mine wastes and their environmental impacts, and briefly discusses mine wastes & tailings dams in the mining process. Then, the mitigation of negative environmental impacts in landfills and the feasibility of mineral recovery from mining tailings and urban mining wastes are evaluated. Finally, the objective of mineral recovery in the context of sustainable development and legislative efforts are discussed. The results of the study are as follows: The wastes generated as a result of mining operations have increased worldwide. These mine wastes are used to recycle mines. The necessity and nature of the recovery of minerals from wastes necessitates the efficient management of these wastes. At this point, there is a need for effective and up-to-date mining waste legislation, incentives and practices to ensure an sustainable mining waste management and optimum mineral recovery from mining tailings. The categories of "mineral recovery from mining tailings" and "mineral recycling from urban mining waste" were compared by assigning an estimated score out of ten, considering the level of development of the countries and the characteristics of the categories. In this comparison, the contribution/relationships of the activities in these categories to different sustainability criteria are shown and in-text citations are considered in the scoring. By considering these contribution levels or lack thereof, countries with different levels of development in different geographies around the world can develop their mineral waste management and mineral recovery policies in much more detail, considering their mineral requirements and waste inventories. This study may contribute to less mineral waste generation and cleaner, more efficient, and sustainable mineral recovery in mining operations, thanks to the awareness it will create for mining companies and public authorities & SDOs. This study serves as a guide for SDOs and countries’ policymakers & mining sector on mineral recovery from waste in countries.

Application of pre-magnetic separation to address grinding classification density effects and enhance iron-copper separation in deep polymetallic magnetite ores

This study investigates the challenges faced in the grinding and classification process of a polymetallic magnetite ore from Anhui, particularly focusing on low classification efficiency, significant over-grinding, and decreased metal recovery rates. By analyzing the mineralogical properties of the ore, specifically mineral composition, intergrowth relationships, intergrowth particle size, and liberation degree, with an emphasis on magnetite, chalcopyrite, cobalt minerals, and precious metal minerals, this research aims to identify the underlying causes of these issues. Subsequent single-factor experiments were conducted to assess the effects of magnetic field strength and grinding parameters on the enrichment of magnetite and chalcopyrite. Under optimal processing conditions, with a magnetizing current of 0.25 A and a grinding fineness of 65% passing through a 200-mesh sieve, the application of butyl xanthate as a collector during mixed rough flotation achieved a copper recovery rate of 89.54%. Building on these findings, the study further discusses the impact of various process flow optimizations on grinding, classification operations, and the recovery of target minerals. Additionally, it evaluates the advantages and disadvantages of different processing methods in practical applications and ultimately proposes a suitable mineral processing flow for intermediate to deep ore deposits.

The Mineral Recovery Enhanced Desalination (MRED) process for improved brackish water desalination

The Mineral Recovery Enhanced Desalination (MRED) process for improved brackish water desalination

Recovery and Size-Tuning of Amorphous Silica from Geothermal Scales in Batangas, Philippines

Scale deposits in geothermal power plants are well-known potential sources of minerals. Extensive research in mineral recovery is crucial due to the considerable variability in scale composition and geochemistry based on location. Geothermal scales from Batangas, Philippines, were used to synthesize size-modified amorphous silica (SiO2) via sol-gel method. Initial analyses employing x-ray fluorescence spectroscopy (XRF), total dissolved solids (TDS), electrical conductivity (EC), and pH measurements confirmed that the scale is rich in silica and salts at neutral pH. Then, the effect of varying scale concentration, precipitation pH, and aging time on the particle size distribution of recovered amorphous silica were investigated. Dynamic light scattering (DLS) for particle size analysis (PSA) revealed that the sample with 2.5% (w/v) scale precursor in NaOH and precipitated until pH 10 had the lowest average cumulant diameter (1.66 μm). Moreover, the synergy of precipitation pH and aging time was found to significantly affect the polydispersity index and cumulative diameter of precipitated SiO2 based on 23 factorial ANOVA at 0.05 significance level. X-ray diffractometry (XRD), Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM) confirmed that the precipitates were amorphous SiO2 with spherical morphology. This study proves the viability of utilizing geothermal scales from Batangas, Philippines for the synthesis of amorphous SiO2 with controlled particle size, which is a potential filler for composite materials.

Atomized Reagent Addition with Synchronized Jet Pre-Mineralization to Enhance the Flotation Process: Study on Atomization Parameters and Mechanisms of Enhancement

The atomized reagent and synchronous jet pre-mineralization technology, as a novel method to enhance the flotation process, increases the solubility of fatty acid collectors in pulp through atomized reagent application and improves the mineralization effect and flotation rate via synchronous jet pre-mineralization technology, thereby laying a theoretical foundation for the flotation of minerals with fatty acid collectors. Systematic studies on the atomization method, atomization particle size, and flotation experiments revealed that, compared with conventional stirring methods, the atomized reagent method increases the solubility of sodium oleate in pulp from 82.5 mg/L to 142.9 mg/L at 288.15 K. The induction time for quartz particles treated with atomized reagents and bubbles is significantly lower than that of the conventional stirring method. Semi-industrial test results of the atomized reagent and synchronous jet pre-mineralization show that, compared to traditional roughing, the TFe grade increased by 0.87 percentage points, iron recovery increased by 3.95 percentage points, and reagent consumption decreased by 7.5 percentage points. Experimental and test results demonstrate that the atomized reagent and synchronous jet pre-mineralization technology can effectively enhance mineralization, accelerate the flotation rate, improve flotation indices, and reduce reagent consumption to a certain extent, providing significant guidance for the efficient recovery of fine-grained minerals.

Deep insight into the effect of smithsonite particle size on surface heterogeneity and adsorption behavior: A case of fatty acid system

The studies for microfine mineral flotation have focused on the two main directions of increasing the apparent mineral particle size and reducing the bubble size, while little research has been reported on the special surface properties and adsorption mechanisms of mineral particles of different sizes. In this study, sodium oleate was chosen as a typical surfactant. The mechanism of the effect of smithsonite particle size on the heterogeneity and adsorption behavior of the mineral surface was explored in depth. Through microflotation experiments, BET area tests, Washburn contact angle tests, particle agglomeration tests, adsorption tests and inorganic carbon analysis, it was pointed out that the smaller the size of the particles, the greater the surface wettability, and the smaller the density and thickness of adsorbed oleate on the surface. The difficulty of encapsulating the mineral surface with a hydrophobic layer of oleate hydrocarbon chains, as well as suboptimal particle aggregation sizes, are key reasons for the poor flotation behavior of fine smithsonite. Furthermore, the inhomogeneity of active sites and charge distribution of surface components of smithsonite with different sizes was revealed from a microscopic point of view by DRIFT spectroscopic analysis, XPS analysis and zeta potential measurements. As the particle size of smithsonite decreases, the positive charge density on the surface is higher and the hydration tendency is more intense, hindering the adsorption of oleate. This work is expected to guide the full particle size recovery of minerals in the flotation from a novel microscopic point of view.

Soluble mineral flotation paradox: Improved recovery with no sign of collector adsorption on minerals signifies colloidal attraction between bubble-bound collector colloids and mineral particles

Froth flotation uses air bubbles to separate mineral particles based on the difference in mineral surface hydrophobicity. Collectors are needed to selectively hydrophobize the surface of targeted minerals to augment the difference in surface hydrophobicity between wanted minerals and unwanted ones. Here, we showed that this classical (well-established) principle fails to describe the flotation of water-soluble minerals. Our systematic micro-flotation tests using soluble minerals (NaCl and KCl crystals) in brines and three popular collectors (dodecylamine hydrochloride, sodium dodecylsulfate, and sodium laurate) showed a substantial flotation recovery of the salt minerals without detected collector adsorption at the mineral surfaces by X-ray photoelectron spectroscopy (XPS). Complementary particle size distribution measurement indicated the occurrence of sub-micron collector colloids in saturated brines. Moreover, the flotation recovery agreed well with the measured contact angle, suggesting the attraction between bubble-bound collector colloids and salt crystal surfaces. These paradoxical results signify a new principle underlying the flotation of soluble minerals, i.e., the selective colloidal attraction between bubble-bound collector colloids and salt particles enables the flotation separation of soluble minerals.

Flotation of Li Pegmatite with a Soybean Oil-Based Collector: Fundamental Studies

ABSTRACT In this work, the effect of a soybean oil-based collector on the surface properties of spodumene, feldspar, quartz, and muscovite was characterized and evaluated. By means of gas chromatography, it was determined that the reagent was composed of a mixture of carboxylic acids: linoleic (48%), oleic (28%), palmitic (13.3%), stearic (3.6%), α-linolenic (3.4%), and elaidic (3.2%). The reagent contained ~14 ppm Ca (determined by inductively coupled plasma optical emission spectroscopy – ICP-OES) and a critical micellar concentration (CMC) of 100 mg/L. At pH 6, the spodumene recovery was 50–60% higher than the other mineral recoveries, ascribed to chemical adsorption of the collector ionic-molecular species, which has high hydrophobicity power, on Al3+ sites on the spodumene surface. For pH values >10, the recoveries of feldspar and quartz were higher than spodumene, due to their activation by hydroxyl and hydroxide of Ca and subsequent adsorption of ionic specimen of the collector. The electrokinetic potential curves of spodumene, feldspar, and muscovite with collector were shifted toward more negative values compared to their electrokinetic potential curves without reagent. Fourier transform infrared spectroscopy (FT-IR) showed chemical adsorption of the anionic species of the collector at pH 6 with the Al3+, Fe3+, and Ca sites on the surface of aluminosilicates and Ca for quartz.

Investigation of the effect of mineral composition and size on particle separation in Wet low and high intensities magnetic separators: An industrial case

Magnetic separation is used in ore processing to separate the minerals according to their magnetic susceptibility. Particle size also plays a role in the separation although few industrial results are presented in the literature to discuss this matter. Results from sampling industrial Wet Low Intensity Magnetic Separators (WLIMS) and Wet High Intensity Magnetic Separators (WHIMS) for processing an iron ore show that except for the strongly paramagnetic magnetite (Fe3O4), the recovery of minerals decreases with increasing particle size for both WLIMS and WHIMS. The examination of polished sections of the coarse size fractions from the reject streams of the WHIMS does not provide ground to suspect liberation to be responsible for the reduced recovery of coarse particles. Results also show that it is difficult to establish clear relationships between the mineral recoveries and their reported magnetic susceptibilities for WLIMS while for WHIMS a weak trend is observable.

Ultrasonic Enhancement for Mineral Flotation: Technology, Device, and Engineering Applications

In the past five years, the number of articles related to ultrasonic mineral flotation has increased by about 50 per year, and the overall trend is on the rise. The most recent developments in ultrasonics for flotation process intensification are reviewed herein, including effects of ultrasound treatment on an aqueous slurry, improvement in flotation methods and technological processes, device development tracking, and application effects in mineral process engineering. At this point in time, there are pilot-scale flotation tests to evaluate the feasibility of ultrasonic pretreatment technology for industrial use to enhance residue flotation separation, and the results showed that the recovery rate of concentrate is increased by about 10%. Four aspects of ultrasonic flotation process improvement are summarized, namely, changing the ultrasonic parameters, the synergistic effect of ultrasound and reagents, the ultrasonic effect of particles with different-sized fractions, and application to new systems. In addition, the effect of ultrasonic flotation mechanisms is explored through a quadratic model and numerical simulation. The combination of ultrasonic flotation with other fields, such as magnetic fields, to enhance the separation efficiency and recovery of minerals is also a future trend. It is also proposed that ultrasonic flotation technology will be used with big data, industrial Internet of Things, and automatic control technology to achieve deep bundling, optimizing the flotation process by implementing remote monitoring and control of the flotation process.

Fast pyrolysis of paper sludge in a continuous stirred-tank reactor and liquid-liquid extraction of benzenoid aromatics from fast pyrolysis bio-liquid

Paper sludge is a solid waste in paper mills and is conventionally treated by, e.g., landfill, composting, and incineration. Paper sludge contains paper production fillers and lignocellulosic biomass, both of which can be recycled to recover circular minerals and produce bio-based fuels and chemicals by, e.g., thermochemical recycling technology namely fast pyrolysis, for circular bioeconomy. In this paper, three different paper sludge samples collected in The Netherlands and Spain were analyzed by thermogravimetric analysis, moisture analysis, ash analysis, CHNS elemental analysis, powder X-ray diffraction, and X-ray fluorescence spectrometry. Fast pyrolysis of paper sludge was carried out in a lab-scale continuous stirred tank reactor at 500 ± 10 °C with a paper sludge feeding rate of 1 kg h−1. The recovery of circular minerals, which are mainly calcium carbonate, is 87.1 ± 2.2 % (on mineral basis). The yields of fast pyrolysis bio-liquid and biochar are 49.2 ± 6.7 wt% (on biomass basis, equivalent to 23.7 ± 2.2 wt% on paper sludge basis) and 23.8 ± 8.3 wt% (on biomass basis). Fast pyrolysis bio-liquid is a diluted aqueous containing various oxygenates (major, including alcohols, acids, benzenoid aromatics, aldehydes, ketones, ethers, and esters) and hydrocarbons. Liquid-liquid extraction of the fast pyrolysis bio-liquid using CH3OH/H2O and SO2/H2O was further performed to obtain an improved bio-liquid with relatively high concentration of the desired bio-based chemicals (namely benzenoid aromatics with the concentration of 53.1–65.9 area%). Both SO2/H2O and CH3OH/H2O show high liquid-liquid extraction efficiency to concentrate the benzenoid aromatics for 3.4–11.0 times. This work shows the fast pyrolysis followed by liquid-liquid extraction for the valorization of paper sludge, of which the former has been recently demonstrated on a pilot-scale unit in industry. However, the latter still needs to be further developed by, e.g., focusing on the extraction solvent and continuous liquid-liquid extraction process integrated to fast pyrolysis.

INOVASI TEKNOLOGI UNTUK KONSERVASI SUMBERDAYA MINERAL: TANTANGAN DAN PELUANG

Technological innovation has become the key to improving mineral resource conservation worldwide. In this paper, we discuss the challenges and opportunities faced in developing technology for mineral resource conservation. One of the main challenges is the ever-increasing demand for mineral resources, which requires extraction technologies that are not environmentally friendly and can generate waste and pollution. However, efficient processing technology, mineral recovery and recycling technology, as well as the use of renewable energy in the mining industry, digital sensors and monitoring, and geographic information technology (GIS) have shown great benefits in reducing environmental impact and increasing resource use efficiency. In addition, appropriate policies and regulations, human resource skills enhancement, community awareness and acceptance, as well as mineral resource diversification and local community empowerment are also important factors in mineral resource conservation.

Hierarchical Approach to the Management of Drinking Water Sludge Generated from Alum-Based Treatment Processes

The management of drinking water treatment plant (DWTP) sludge is challenging for water treatment facilities. Previous studies reported mainly on handling sludge through landfilling, release into water bodies, discharge into wastewater treatment plants, onsite disposal, and incineration methods for the treatment of sludge. The limitations of these sludge-handling methods are well documented. This article focuses on the hierarchical approach as an alternative and comprehensive method for handling DWTP sludge. The core of hierarchical management streamlines the minimization of the generated DWTP sludge; treatment of DWTP sludge to reduce toxicity; changing of the physicochemical form of DWTP sludge; and finally, the reuse, recycling, and recovery of DWTP sludge. The premise is to achieve zero landfilling of DWTP sludge, establish a circular economy, generate job opportunities, and preserve the environment. Thus, this study also proposes two main technologies, which are gravity-based sludge separators for fractionating the sludge and photocatalytic membrane reactors (PMRs) as a technology for the treating and/or recovery of nutrients and minerals from DWTP sludge. Until the chemical deductive or minus approach becomes a reality in water treatment, the use of PMRs and gravity-based sludge separators will enhance the management of DWTP sludge when incorporated into the hierarchical approach.

A Study on the efficiency of organic activator application to process refractory hard-to-beneficiate raw materials

Polymetallic ores with complex mineralogical compositions pose significant challenges in flotation beneficiation, often resulting in suboptimal separation and recovery of valuable minerals. This study aims to analyse the effectiveness of alkyl benzene sulfonic acid (ABSA) as a frothing activator in improving the flotation performance and mineral recovery of polymetallic ore. It presents the results of flotation beneficiation experiments for polymetallic ore of complex mineralogical composition. Experiments were conducted on polymetallic ore samples using ABSA as the frothing activator in the flotation process. The performance was evaluated based on recovery rates and separation efficiency, comparing the results with standard floating frothing agents. The findings showed the highest efficiency of ABSA application for samples of mixed-type ores in increasing the recovery of gold, copper, zinc and lead in the collective concentrates of flotation beneficiation. ABSA activator promotes additional cleaning of fragments containing valuable metals from oxide films and coatings and the transfer of valuable metals' microparticles due to the organics' adsorption properties and the formation of metal-carbon bonds. Another effect of using this reagent is there was an increase in concentrate mass yield while maintaining the quality parameters. A similar effect was observed for beneficiation of copper ore with complex composition - copper recovery in the main concentrate increased. Selective flotation with the development of gold concentrate from hard-to-beneficiate polymetallic ore also showed a significant increase in gold recovery with ABSA pretreatment.

The depressant-free flotation separation of Cu/Zn sulfide minerals with an environmentally friendly triazine-thiol collector

The depressant-free flotation separation of chalcopyrite from sphalerite in the lower alkaline (pH<10) environment will contribute to reduce carbon emission and benefit the recovery of precious metal minerals. However, it is almost impossible for traditional collectors such as xanthates due to their weak selectivity for chalcopyrite against sphalerite. In this paper, a novel triazine-thiol collector, 2-diethylamine-4-hydroxy-1,3,5-triazine-6-thiol (DEHTT), was first introduced in flotation separation of chalcopyrite from sphalerite. The micro-flotation results elucidated that in the absence of depressants, the recoveries of chalcopyrite and sphalerite from their mixture with 2.0 × 10−6 mol/L DEHTT at pH 9.45 (Na2CO3 as regulator) were 91.83 % and 28.84 %, respectively, while those with sodium isobutyl xanthate (SIBX) were 96.11 % and 78.00 % under the same conditions. In situ AFM and contact angle exhibited that DEHTT assembled on chalcopyrite surface to form lots of aggregates which increased its hydrophobicity, while an insignificant change of sphalerite surface was observed. FTIR, zeta-potential and XPS explored that DEHTT chemisorbed the Cu sites of chalcopyrite surface through its S or O atoms. The specific flotation affinity of DEHTT to chalcopyrite might contribute the cleaner recovery of copper sulfide ores with the lower carbon emission.

Is Pulsed Electric Field (PEF) a Useful Tool for the Valorization of Solid and Liquid Sea Bass Side Streams?: Evaluation of Nutrients and Contaminants

AbstractIn this study, fresh sea bass’s (Dicentrarchus labrax) heads, skin, viscera, and muscle were evaluated for their potential valorization as a source of nutrients and bioactive compounds. For this purpose, a pulsed electric field (PEF) treatment (1.0 kV/cm field strength and 220.5 kJ/kg specific energy for head, 3.0 kV/cm and 299.4 kJ/kg for skin, 3.0 kV/cm and 123.7 kJ/kg for viscera and muscle) was used. Subsequently, extraction processes were carried out using either 100% water or 50% ethanol. Protein assessment (protein content and bioactive peptides’ identification), as well as ICP-MS analysis of minerals and heavy metals, was conducted on both the solid matrices and liquid extracts. The findings indicate that the choice of solvent (100% water or 50% ethanol) and PEF treatment significantly (p &lt; 0.05) affected protein recovery in the sea bass side streams liquid extracts, while a considerable protein amount was retained in the solid matrices. Furthermore, the ICP-MS analysis of minerals revealed that PEF treatment significantly (p &lt; 0.05) improved mineral recovery in the head and muscle liquid extracts. However, a considerable amount of minerals remained in the solid matrices. Lower contents of heavy metals were found in the liquid extracts compared to the solid matrices, being anyway the quantities of the five heavy metals analyzed within edible and safe limits. Additionally, the total antioxidant capacity (TAC) of sea bass side stream extracts was assessed to measure the potential antioxidant bioactive compounds in the liquid extracts. PEF treatments significantly (p &lt; 0.05) increased the TAC of the liquid extracts from sea bass viscera, as opposed to other side streams. Both 100% water and 50% ethanol were effective as extraction solvents, promoting the recovery of high-added-value compounds not only from the liquid extracts but also from solid matrices. Thus, PEF pre-treatment can be considered a valuable technique to enhance fish side stream valorization.

Sulfidation of Smithsonite via Microwave Roasting under Low-Temperature Conditions

This study employs microwave roasting to decompose smithsonite mineral (zinc carbonate) into zinc oxide, which then reacts with pyrite to sulfurize its surface, forming zinc sulfide. This process is beneficial for the flotation recovery of zinc oxide minerals. The surface sulfidation behavior of smithsonite under low-temperature microwave roasting conditions is examined through X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and thermodynamic calculations. XRD and thermodynamic analysis indicate that smithsonite completely decomposes into zinc oxide at 400 °C. Introducing a small amount of pyrite as a sulfidizing reagent leads to the formation of sulfides on the surface of decomposed smithsonite. XPS analysis confirms that the sulfide formed on the surface is zinc sulfide. SEM analysis reveals that sulfides are distributed on the surface of smithsonite, and the average sulfur concentration increases with the pyrite dosage. Microwave-assisted sulfurization of smithsonite (ZnCO3) was found to significantly enhance its floatability compared to conventional sulfurization methods. The optimal mass ratio of ZnCO3 to FeS2 is approximately 1:1.5, with the best temperature being 400 °C. These findings provide a technical solution for the application of microwave roasting in the efficient recovery of smithsonite through flotation.

Selective aggregation of hematite from quartz using charged polyacrylamides: In-situ sizing

Recovering fine valuable material has been a significant challenge in minerals processing. This primarily stems from insufficient collision opportunities between fine particles and bubbles, specifically when utilising traditional recovery methods such as froth flotation. This research endeavours to address this challenge by exploring the use of various commercially available, high molecular weight polymers- specifically polyacrylamide (PAM)- to selectively aggregate hematite from quartz. Investigation of the conditions in which selective aggregation of hematite over quartz occurs, with the goal to achieve aggregate sizes of between 20 and 150 μm, were undertaken. Targeting this size range ensure that conditions are optimised for future use in conventional mechanical flotation cells as an efficient mineral recovery method. The study investigates the selectivity of charged PAM towards hematite and quartz at pH 10, using adsorption studies. Anionic PAM demonstrates a preference for hematite, with a range of charge density studies, highlighting stronger adsorption capacity with lower charge density polymers. Using BlazeMetrics probe technology for in-situ sizing and imaging, it was observed that conditioning 50–300 g APAM per t of hematite resulted in aggregates in the range of 30–230 μm after 5 min. Interestingly, the charge density of APAM does not markedly affect the size of the hematite aggregates, although altering the charge density of the polymer impacts the selectivity towards quartz. Additionally, cationic PAM results in the simultaneous aggregation of both hematite and quartz, not demonstrating selectivity. To mitigate heterocoagulation between minerals, a common dispersant, sodium hexametaphosphate (SHMP), was employed, which notably prevents quartz aggregation. Separation of aggregated hematite from quartz by sedimentation was only slightly effective with the majority of quartz settling with the hematite. Adding up to 1000 g of dispersant per t of hematite reduced the amount of quartz in the sediment bed by 23 %. The dispersant increased the magnitude of the negative zeta potential of the two minerals, particularly hematite, lowering heterocoagulation and improving effectiveness of hematite flocculation.

(Invited) Energy-Efficient and Impurity-Tolerant Electrochemical Co-Generation of Acid and Base Solutions

The sequential application of acid and base solutions can be used to perform chemical transformations that are of interest for carbon management and sustainable resource utilization, including CO2 capture, CO2 removal, production of slaked lime, and recovery of critical minerals. Electrochemical co-generation of acid and base from salt solutions enables their use in closed-loop processes that could be powered by renewable electricity, wherein acid and base are regenerated from the salt byproduct of their application. To be viable at scale, acid-base co-generating systems need to be energy-efficient and tolerant to impurities that are inevitably released into recycle loops. Conventional electrochemical methods for co-generating acid and base, such as bipolar membrane electrodialysis (BPMED), rely on the use of ion exchange membranes (IEMs) to inhibit H+ and OH– recombination, but IEMs cause large resistive losses that severely limit the energy efficiency and current density of these systems. In addition, cation exchange membranes (CEMs) do not tolerate polyvalent cations (e.g., Ca2+, Mg2+) in the presence of base, yet polyvalent cations are intrinsic to all high-impact applications. In this talk, I will describe our development of acid-base co-generating systems in which H+ and OH– recombination is inhibited by competitive transport of supporting electrolyte and H+ masking, which enables the use of a simple porous diaphragm separator instead of IEMs. We developed an ion transport model to predict the current efficiency for acid-base co-generation as a function of the electrolyte composition and operating parameters. Instead of a bipolar membrane, our systems use the H2 oxidation reaction (HOR) and H2 evolution reaction for H+ and OH– generation, respectively. We demonstrate IEM-free production of acid and base at useful concentrations in the presence of polyvalent cations with much higher energy efficiency and current density than state of the art BPMED systems. Individual cells can be stacked by combining HOR and HER electrodes into bipolar gas diffusion electrodes that recirculate H2 with near-unity efficiency. To demonstrate the utility of the acid and base solutions generated by this system, I will describe their use to extract Mg(OH)2 from ultramafic rocks for application in CO2 removal.

Deep Ensemble Learning-Based Sensor for Flotation Froth Image Recognition.

Froth flotation is a widespread and important method for mineral separation, significantly influencing the purity and quality of extracted minerals. Traditionally, workers need to control chemical dosages by observing the visual characteristics of flotation froth, but this requires considerable experience and operational skills. This paper designs a deep ensemble learning-based sensor for flotation froth image recognition to monitor actual flotation froth working conditions, so as to assist operators in facilitating chemical dosage adjustments and achieve the industrial goals of promoting concentrate grade and mineral recovery. In our approach, training and validation data on flotation froth images are partitioned in K-fold cross validation, and deep neural network (DNN) based learners are generated through pre-trained DNN models in image-enhanced training data, in order to improve their generalization and robustness. Then, a membership function utilizing the performance information of the DNN-based learners during the validation is proposed to improve the recognition accuracy of the DNN-based learners. Subsequently, a technique for order preference by similarity to an ideal solution (TOPSIS) based on the F1 score is proposed to select the most probable working condition of flotation froth images through a decision matrix composed of the DNN-based learners' predictions via a membership function, which is adopted to optimize the combination process of deep ensemble learning. The effectiveness and superiority of the designed sensor are verified in a real industrial gold-antimony froth flotation application.