Visual MINTEQ Research Articles

Iron Separation from Iron-Rich Manganese Ore Leachate: Comprehensive Optimization of Operating Parameters and Economic Viability

In the current electrolytic manganese industry, iron separation and reuse from iron-rich manganese ore leachate (IRMOL) has become one of the most pressing challenges. This study aimed to investigate the optimal conditions for iron separation from IRMOL and to assess the economic and practical advantages of iron separation or removal in industrial manufacturing. To identify more cost-effective and technologically advanced production circumstances, we examined five key elements that weaken Fe(OH)3 colloidal production conditions in enterprises: reaction temperature, pH, crystal species, aging, and reaction time. The screening results showed that when the conditions were optimized, the efficiency of reducing manganese loss decreased from 6.15% to 4.69%. Additionally, the generation of iron-rich electrolytic manganese residue (IREMR) was decreased by 44.32%, and the filtration velocity of IREMR increased from 0.0030 to 0.0220 mL/(s·cm2) compared to the production conditions before optimization at the enterprise. Through multiphase equilibria modeling with Visual MINTEQ, we have determined that raising the temperature and pH levels increases the expenses associated with chemicals and energy usage and results in an elevation of Fe(OH)2+ concentration. This can lead to the creation of Fe(OH)3 colloidal, causing a high water content in IREMR, inefficient filtration, and significant loss of manganese. This strategy is highly significant for the production of electrolytic manganese and the reduction of electrolytic manganese residue.

Enhanced leaching control of chromium, antimony, and chlorine utilizing CO2-curing slag-fly ash-based agent

This study strives to address the technical bottleneck posed by leaching risks associated with Cr, Sb, and soluble Cl in low-carbon slag-fly ash-based cementitious materials (BFCM) according to our previous research. The introduction of CO2 activation significantly enhances the dissociation of BFS, leading to superior mechanical performance and environmental safety of BFCM. LT3 matrix of BFCM (BFS: MSWI fly ash: FGDG: cement= 42: 20: 10: 28) showed excellent compressive strength (46.79Mpa at 7d). The LT3 matrix enables effective solidification/stabilization (S/S) of Cr, Sb, and Cl with CO2-curing (7d). Furthermore, the leaching concentrations of Sb and Cl within LT system, exhibit a positive correlation, while they demonstrate a negative correlation with Cr. Sb primarily relies on the levels of Ca2+ and OH- in the leaching solution, critical for the formation and stability of Ca-Sb precipitation based Visual MINTEQ fitting. CO2-curing enhances the S/S efficiency of Cl by accelerating the ion exchange of Cl- with OH- in C-A-H and SO42- in the AFm phase, leading to the formation of functional Friedel’s salt. This process is characterized by OH- dissolution and subsequent CaSO4 crystallization. The LT system activated by CO2 exhibited accelerated reaction kinetics relative to traditional hydration (LH), characterized by rapid BFS dissociation and the formation of functional hydration products such as ettringite, C-(A)-S-H, and Friedel's salt. This process also reduced macropores and capillary pores of BFCM, a positive correlation exists between the relative macropore content and Cl leaching levels, whereas the decrease in both macropores and capillary pores is associated with ettringite crystallization.

Chemical elements migration in underground waters of mining territory

Relevance. The need to study the forms of migration of chemical elements in the groundwater of flooded copper pyrite mines in order to correctly understand and predict their transfer and distribution in hydrogeochemical fields. Ground and surface waters are a complex mixture of substances in which, depending on pH, Eh and t °С, phase transitions are formed with subsequent dissolution or precipitation of minerals. To solve these problems, numerical hydrogeomigration modeling is used, including physicochemical, which allows drawing conclusions about the scale of pollution and the localization of such areas for subsequent development of measures to improve the state of the hydrosphere. Aim. To determine the forms of metal migration in groundwater and to calculate water saturation indices in relation to minerals. Objects. Groundwater in the territory of the closed Levikha copper pyrite mine. Methods. Laboratory studies of groundwater were carried out using flame emission spectrometry, flame atomic absorption, photometric method with Nessler's reagent, titrimetric, mercumetric and potentiometric methods; mass spectrometry with ionization in inductively coupled plasma and gravimetric method. Physical and chemical modeling using the software product Visual MINTEQ 3.1. Results. According to the results of processing chemical analyzes and physical and chemical modeling, all tested wells are divided into groups: 1) wells no. 1, 2, 3 and 6, located within the former mining allotment (near the Levikha XIV mine, a man-made reservoir, the Levikha II mine and a neutralization station); 2) represented by water in wells no. 4 near the shaft of the mine Tsentralnaya and no. 5 near the dump Yuzhny; 3) well no. 7, located near the mouth of the Levikha river. Saturation indices and forms of migration of components in the aquatic environment make it possible to identify the scale of pollution and the localization of such areas. Thus, with the current pumping system, there is no large-scale pollution of groundwater at the Levikha mine. It is localized in the area of the Tsentralny mine shaft (well no. 4) and the Yuzhny dump (well no. 5).

Simultaneous rare earth sulfate transformation and carbon dioxide mineralization

The wet metallurgical process route for recovering rare earth elements usually uses sulfuric acid. To obtain marketable individual rare earth products, converting rare earth sulfates to chlorides is essential. Conventional chemical precipitation and solvent extraction methods result in significant amounts of ammonia wastewater and greenhouse gas emissions. Therefore, we propose a novel process that integrates CO2 mineralization with rare earth sulfates transformation. By utilizing a base-catalyzed mechanism with trioctylamine (TOA), CO2 is effectively employed for selective precipitation of more than 95 % of rare earths from magnesium and calcium under optimized conditions. Subsequently, dissolution in hydrochloric acid allows for enrichment of the concentration of rare earths up to 188.3 g/L. The reaction mechanism is examined through Visual MINTEQ simulations and various analytical techniques. This process not only offers a sustainable approach to rare earth sulfates transformation but also contributes to carbon capture, utilization, and sequestration efforts.

Treatment and nutrient recovery from landfill leachate by sequential persulfate oxidation and struvite precipitation: An evaluation of technical feasibility.

The technical feasibility of advanced oxidation process, in particular persulfate (PS) oxidation followed by struvite precipitation for landfill leachate treatment and nutrient recovery has been depicted in the current study. Furthermore, the impact of activation of PS with thermal and ultraviolet (UV) irradiation techniques on COD removal efficiency is also investigated. A maximum COD removal efficiency of 96% is accomplished at 65°C together with supply of UV irradiation. The impact of persulfate dose, pH, and PS/65°C/UV system on COD and biodegradability is also illustrated in the current study. Additionally, decomposition rate constant values are also ascertained in the present study. Afterwards, nutrient recovery using struvite precipitation is carried out for sustainable utilization of resources. Preliminary treatment of leachate with PS/65°C/UV system is greatly conducive to recovering high quality struvite crystals. Besides, 94.9%, 83.5%, and 91.3% of PO43- -P, NH4+ -N, and Mg2+ recovery efficiency attained respectively at pH 9.5 and 1.2:1:1 molar ratio of Mg2+: NH4+-N: PO43--P. Additionally, all the nutrient recovery studies are validated using chemical equilibrium model Visual MINTEQ. Later, bioavailable fraction of PO43--P in the recovered struvite is also investigated for utilization as fertilizer. The presence of Cu and Zn in the recovered struvite precipitate enhanced its economic value as a fertilizer. Since Cu and Zn are vital micronutrients for growth of plants. The low soluble values of recovered struvite precipitate confirmed its utilization as slow releasing fertilizer.

Highly efficient recovery of phosphate and fluoride from phosphogypsum leachate: Selective precipitation and adsorption

Phosphogypsum, a typical by-product in the phosphorus chemical industry, could generate a large amount of leachate containing phosphate and fluoride in the process of rainfall and long-term stacking, which not only causes serious environmental pollution, but also leads to a waste of resources. In this study, a united treatment of calcium hydroxide precipitation and lanthanum zeolite (La-ZFA) adsorption was proposed to achieve the recovery of phosphate and fluoride from phosphogypsum leachate. In phosphogypsum, most phosphorus could be leached except P in the residual occurrence form, while for fluoride, only water-soluble F could be effectively leached. The optimum leaching amounts of phosphate and fluoride were 22.59 and 4.64 mg/g, respectively, at liquid-solid ratio of 400:1, leaching time of 120 min, pH of 6.0, particle size of >200 mesh (<0.075 mm), and leaching temperature of 25°C. Using Ca(OH)2 as the precipitant, the phosphate could be precipitated selectively from phosphogypsum leachate by controlling pH and time, and the concentrations of it decreased significantly to 0.29 mg/L at pH 10.0, with a removal efficiency of 99.48%. XRD, SEM and Visual MINTEQ software analysis proved that the main component of the precipitate was hydroxyapatite (Ca5(PO4)3(OH)). After P precipitation, a series of sorbents for fluoride were investigated, and La-ZFA sorbent was chosen and utilized to recover the fluoride from the leachate through a cyclic fixed-bed column. The efficiency of La-ZFA was basically not affected by the high concentration sulfate, and it can selectively adsorb fluoride from phosphogypsum leachate, leading to a final fluoride concentration of 0.29 mg/L in the effluent. The characterization demonstrated that fluoride might be adsorbed onto the La-ZFA via ligand exchange with hydroxy groups. The proposed method in this study is expected to sequentially recover phosphate and fluorine from the leachate of phosphogypsum, and it has great guiding significance for resource utilization and management of phosphogypsum.

Trace metal speciation trends in Mazowe dam, Zimbabwe, a typical sub-tropical dam ecosystem impacted by gold mining and agriculture.

The present study aimed to assess trace metal speciation trends in the water and sediments of Mazowe Dam, a typical sub-tropical dam ecosystem impacted by gold mining and agriculture in Zimbabwe. The elements studied include Al, As, Cd, Co, Cr, Cu, Hg, Fe, Mn, Ni, Pb, and Zn. Elemental speciation in the water column was determined using Visual MINTEQ version 3.1 geochemical computer modelling, while speciation in the sediment phase was determined using sequential extraction techniques. For each element, the data obtained were subjected to extensive correlation analysis to identify intra- and inter-metal species interactions in the water column and the sediment phase, as well as across the water-sediment interface. Possible mechanisms to account for the observed species interactions are proposed. In the water column, Co was predicted to have the highest number of chemical species (9), Cd and Zn (8), Mn and Fe (7), Ni (6), Pb (5), Al and Cu (3), Cr, Hg, and As have the least (2). In the sediment, Al, As, Co, Cr, Cu, Fe, Ni and Fe mainly exist in the residual fraction, while Zn and Mn concentrations in fractions vary per sampling site, with no fraction that is dominant across the sampling sites. Equilibrium exchange reactions across the water-sediment interface were observed e.g., for Cd species /FA2Cd (aq) and Co species /FACo+2G (aq), and /FA2Co (aq). This study is valuable in highlighting trace metal speciation in a tropical dam ecosystem in Africa and adds to the growing knowledge about the behaviour of trace metals in aquatic ecosystems in the region and globally.

Nitrogen modified graphene nanowalls for retrieval of trace level cerium from aqueous medium

Removal of cerium from environmental and aqueous streams is essential in waste water rejuvenation processes. Nitrogen modified graphene nano walls (N-GNWs) have shown ultra-high sorption efficiency of trivalent cerium from aqueous medium (Kd > 2 × 107) and a large sorption capacity of ∼ 2500 mg/g is achieved. N-GNWs were deposited on carbon paper substrate using PECVD technique. The three-dimensional nature of N-GNWs are revealed from high resolution FESEM images. Raman spectroscopic studies have shown that GNWs are defective and possess a few layer graphene like structure. Secondary Ion Mass Spectroscopic studies of the Ce sorbed N-GNWs and optical emission spectroscopy of the residual solution confirm the sorptive retrieval of cerium. Visual Minteq based ionization model is introduced to explain high (>90 %) sorption of Ce at pH≥7 and the mechanistic aspects of sorption for standard Cerium solution is discussed. The sorption involves attachment of cerium hydroxyl ions to the active cites on the sorbent surface.

An unconventional approach for the efficient recovery of iron, cobalt, copper and silicon from copper slag

High-grade heavy metal elements in copper slag (CS) are worth recovering. Unfortunately, the high viscosity of leaching solution, low leaching efficiency, difficult filtration and low separation efficiency of valuable components exist in the traditional sulfuric acid leaching process. In this study, the above problems are solved by sulfuric acid pretreatment + curing + water leaching. Moreover, iron, cobalt and copper ions in solution are separated by stepwise precipitation. The final iron, cobalt, copper and silicon recoveries are 99.01 %, 98.45 %, 93.13 % and 99.52 %, respectively. Thermodynamic calculations show that H4SiO4 can be converted to insoluble SiO2 to improve filtration properties under curing conditions of sulfur dioxide partial pressures of 10−20∼0 atm, oxygen partial pressures of 10−20∼0 atm and 400–600k. Simulation studies of the phase equilibria of the components of the leach solution by Visual MINTEQ showed that the oxidation of Fe2+ to Fe3+ is necessary for the removal of Fe2+ from the solution by precipitation. This study provides a new idea for the efficient utilization of CS.

Challenges in geochemical modelling of metal(loid) solubility and binding mechanisms along a soil profile at a multi-contaminated site

Recognising the need for robust models in predicting groundwater contamination risks from metal(loid)s in contaminated topsoil, this study focuses on the geochemical behaviour of As, Cd, Cu, Pb, Sb and Zn in one of Sweden's most heavily contaminated areas. Samples were collected from the waste zone and underlying subsoil down to 5 m and batch experiments were carried out to assess pH-dependent solubility. The results indicate that Cd, Cu, Pb and Zn are efficiently immobilized in the waste zone, while As(V) and Sb(V) are more easily leached. With the exception of Pb and Cu at high pH, the mobilized metals appear to be predominantly in a truly dissolved state, as confirmed by ultrafiltration at 10 kDa.Speciation modelling using Visual MINTEQ did not suggest a significant role of precipitates such as Zn or Pb arsenates and phosphates, although their involvement could not be ruled out. To better understand sorption/desorption patterns, a multi-surface geochemical model was established, drawing on the Stockholm Humic and CD-MUSIC models for organic matter and Fe/Al (hydr)oxide sorption. However, when default parameters were used, the model consistently overestimated the solubility of Cd, Cu, Pb and Zn in both the waste zone and the uncontaminated subsoil. In contrast, As(V) solubility was generally underestimated, also when the reactive surface area of the Fe- and Al (hydr)oxides was decreased in the model. The model's performance was better for Sb(V), though not without imperfections. When the parameters for organic matter were adjusted such that 100% of the solid-phase organic matter was active with respect to ion binding, but only 25% of the dissolved organic matter, the model description improved considerably for Pb and Cu in the upper soil layers. The model revealed distinct differences in the adsorption behaviour of the metal cations, with Pb being sorbed mostly to Fe/Al (hydroxides), whereas a considerable part of Cu was sorbed to organic matter, particularly in the waste zone.Possibly, the dissolution of easily weatherable metal-containing mineral phases may have contributed to the poor model performance for Cd, Zn and for Cu in the deeper soil layers, although other factors, such as a contribution of hydrous SiO2 or Mn oxides to metal binding, could not be ruled out. Metal sorption to carbonate phases may also have been a contributing factor in the waste zone. Lastly, the reactivity of Fe- and Al (hydr)oxides may have been overestimated by oxalate extraction when default parameters for high-surface-area ferrihydrite were applied.These findings provide valuable insights for environmental management and underscore the need for a more detailed characterization of metal(loid) sorption in contaminated soils, as well as the development of improved modelling strategies to enhance solubility predictions.

Waste-treating-waste: Effective heavy metals removal from electroplating wastewater by ladle slag

Ladle slag, a by-product of steelmaking, presents a valuable strategy for waste reduction and valorization in wastewater treatment. This work demonstrates the successful simultaneous removal of Al(III), B(III), Ba(II), Cr(III), Mg(II), Sr(II), Pb(II), and Zn(II), from electroplating wastewater by ladle slag. First, Cr(III) and Pb(II) removals were evaluated in single synthetic systems by analyzing the influence of pH, temperature, and ladle slag dosage. Competitive removal was observed in binary batch experiments of Cr(III) – Pb(II), achieving 88% and 96% removal, respectively, with fast kinetics following a pseudo-second-order model. The findings of XRD, SEM, EDX, and FTIR of the slag after removal helped to elucidate the synergic removal mechanism involving ladle slag dissolution, precipitation, ion exchange, and adsorption in a tight relationship with the solution pH. Lastly, ladle slag was tested in real electroplating wastewater with the aforementioned ions at concentrations ranging from <1 to 1700 mg/L. The removal was performed in two steps, the first attained the following efficiencies: 73% for Al(III), 88% for B(III), 98% for Ba(II), 80% for Cr(III), 82% for Mg(II), 99% for Pb(II), 88% for Sr(II), and 88% for Zn(II). Visual MINTEQ simulation was utilized to identify the different species of ions present during the removal process. Furthermore, the leaching tests indicated a minimal environmental risk of secondary pollution in its application. The results promote an effective and sustainable approach to wastewater treatment within the circular economy.

Improving nutrients ratio in class A biosolids through vivianite recovery: Insights from a wastewater resource recovery facility

Class A biosolids from water resource recovery facilities (WRRFs) are increasingly used as sustainable alternatives to synthetic fertilizers. However, the high phosphorus to nitrogen ratio in biosolids leads to a potential accumulation of phosphorus after repeated land applications. Extracting vivianite, an FeP mineral, prior to the final dewatering step in the biosolids treatment can reduce the P content in the resulting class A biosolids and achieve a P:N ratio closer to the 1:2 of synthetic fertilizers. Using ICP-MS, IC, UV–Vis colorimetric methods, Mössbauer spectroscopy, and SEM-EDX, a full-scale characterization of vivianite at the Blue Plains Advanced Wastewater Treatment Plant (AWTTP) was surveyed throughout the biosolids treatment train. Results showed that the vivianite-bound phosphorus in primary sludge thickening, before pre-dewatering, after thermal hydrolysis, and after anaerobic digestion corresponded to 8 %, 52 %, 40 %, and 49 % of the total phosphorus in the treatment influent. Similarly, the vivianite-bound iron concentration also corresponded to 8 %, 52 %, 40 %, and 49 % of the total iron present (from FeCl3 dosing), because the molar ratio between total iron and total incoming phosphorus was 1.5:1, which is the same stoichiometry of vivianite. Based on current P:N levels in the Class A biosolids at Blue Plains, a vivianite recovery target of 40 % to ideally 70 % is required in locations with high vivianite content to reach a P:N ratio in the resulting class A biosolid that matches synthetic fertilizers of 1:1.3 to 1:2, respectively. A financial analysis on recycling iron from the recovered vivianite had estimated that 14–25 % of Blue Plain's annual FeCl3 demand can potentially be met. Additionally, model simulations with Visual Minteq were used to evaluate the pre-treatment options that maximize vivianite recovery at different solids treatment train locations.

Assessment of the impact of irrigating with treated wastewater on soil and crop trace metal accumulation

ABSTRACT Water scarcity is growing quickly, especially in the arid and semi-arid regions along with the growing population. So, using treated wastewater in agricultural irrigation presents a sustainable approach, enhancing soil quality, increasing organic carbon levels, and improving crop productivity are achieved through this approach, concurrently reducing the need for chemical fertilizers. Yet, escalating industrial effluent discharge raises concerns regarding trace metals in wastewater and associated health risks. Our study in the Tenth of Ramadan City focused on employing secondary treated mixed industrial and municipal wastewater for olives, mandarins, and guavas. Sampling wastewater, soil, and plant parts, we analyzed their properties and trace element concentrations, employing Visual MINTEQ for geochemical speciation. Adhering to the international guidelines, the wastewater exhibited acceptable pH and alkalinity but showed concerning trace element levels for irrigation. Differences in soil composition and trace element concentrations suggest potential contamination in soils irrigated with wastewater, raising concerns about health risks associated with elevated metal levels in plants. Variations in trace element concentrations in guavas, olives, and mandarins’ leaves and fruits were observed, with efficient translocation in olives, while mandarin and guava displayed reduced efficiency. Bioaccumulation Factor trends indicated species-specific metal uptake differences. Waste “Minimization Prioritization Tool categorized” trace element levels as of low concern. Daily Intake of Trace Metals and Health Risk Index highlighted the need for health risk assessment, especially for elevated Ni in mandarins and guavas. Regression findings emphasized soil factors influencing metal uptake in plants, highlighting the need for vigilant soil management to curb trace element contamination in agriculture, ensuring both food safety and environmental health. Therefore, water reuse adds contributes to sustainable development, which is three dimensions; Economic, Social and Environmental. It improves economics to utilize water that would be otherwise wasted, and by making water more productive. It improves the social dimension by addressing water scarcity and satisfying the increasing water demand for sustainable livelihoods. It also improves the environment by increasing wastewater treatment levels and reducing pollution.

Overlooked effects of chlorides and bicarbonates on the intensity of peroxydisulfate activation in Fe(II)/citric acid-S2O82− process

The influence of chlorides (Cl−) and bicarbonates (HCO3−) on the Fe(II)/citric acid peroxydisulfate based (Fe(II)/CA-S2O82−) process has been commonly attributed to the formation of secondary reactive species, such as Cl• and CO3•, and their different reactivity with the target pollutant compared to primary reactive species (e.g., SO4•−). However, this conclusion has been entirely based only on analyzing target pollutants removal without the context of S2O82− consumption and dissolved Fe concentration throughout the process. To address this knowledge gap, we conducted a series of batch experiments to investigate the influence of Cl− (2 mmol∙L-1) and HCO3− (1 mmol∙L-1) on the intensity of S2O82− activation within the Fe(II)/CA-S2O82− process with tetrachloroethene (PCE) as the target pollutant. Throughout the experiments, PCE removal efficiency, S2O82− consumption, pH, redox potential, and dissolved Fe were analyzed. Equilibrium hydrochemical modelling (Visual MINTEQ 4) and high-resolution transmission electron microscopy (TEM) were employed to analyze and interpret the data obtained. We found that both Cl− and HCO3− significantly affected the intensity of S2O82− activation. While Cl− influenced the steady-state dissolved Fe(II) concentration, HCO3− primarily increased solution pH, which led to the formation of CA-stabilized ferrihydrite nanoparticles. This resulted in the inaccessibility of dissolved Fe(III) to the Fe(III)/Fe(II) regeneration cycle, consequently suppressing S2O82− activation intensity and PCE removal. Overall, the findings in this study have deepened the fundamental knowledge of how Cl− and HCO3− influence the Fe(II)/CA-S2O82− process, which may help improve the design and operation of S2O82−-based advanced oxidation processes using the Fe(II)/CA activation method.

Efficient sequestration of plutonium from aqueous medium using nitrogen doped graphene nano walls

Nitrogen doped graphene nanowall(s) deposited on carbon paper is employed in sequestration of trace-level plutonium from aqueous solution using batch adsorption technique. Surface and structural characteristics of the sorbent are studied using SEM and Raman spectroscopy, respectively. Radiometric α-counting of the supernatant solution showed > 90% sorption at pH > 7. Visual Minteq modelling revealed that Pu(OH)4 species is responsible for high sorption. Freundlich model evolved as the best fit, implying multilayer deposition on a heterogeneous surface as the mechanism of sorption. The combination of 10 M HNO3 and EDTA resulted in 75% desorption. The results are promising for the sequestration of trace-level plutonium.

A simulation-based approach for understanding CO2 capture and mineralization dynamics in desalination brine

In the pursuit of sustainability, it is crucial to repurpose waste resources into valuable chemicals. One promising avenue is sequential CO2 mineralization using natural seawater or desalination brine solution, which concurrently removes CO2 from the atmosphere while recovering valuable minerals. To realize this approach, it is paramount to grasp the factors influencing the process efficiency and product composition. Here, we present a simulation approach using the visual MINTEQ v3.1 and PHREEQC v3.7.0 models to investigate the impact of CO2 concentration and OH− (as an alkaline source) on the mineral recovery process. The findings reveal that both CO2 concentration and OH− significantly influence the mineral phase composition. Specifically, higher CO2 flow rates or elevated OH− levels promote calcite formation while suppressing the brucite phase, with limited hydromagnesite formation. Moreover, an interactive effect between OH− and CO2 is observed, with OH− essential for carbonate formation. We further validated these insights through preliminary experiments employing electrochemical methods as a source of OH−, wherein aqueous CO2 and applied current density (proportional to OH− concentration) regulated mineral phase composition. Notably, the weight percentage of the brucite phase in the precipitates ranged from 67 % to 73 %, while the calcite phase varied from 20 % to 26 % with alterations to the applied electric currents. The present study not only provides valuable insights into the recovery of potential elements and efficient capture of CO2 in non-synthesized brine solution with a combined theoretical and experimental approach but also demonstrates the viability of employing electrochemical-driven methods as a greener alkaline source for CO2 capture and mineral recovery.

Lead species formation on pure hemimorphite surface and its performance for subsequent sulfidization

Hemimorphite is important-supplementary resource for the commercial zinc production, but it easy loses into tailings due to extreme difficulty for its surface sulfidization. Adding active metal ions after sulfidization have been widely proposed for enhancing hemimorphite floatability, but its desired efficiency in flotation practice has not yet been completely achieved caused by the instability of sulfide layer. Whereas pre-adsorption of active metal ions to modify the hemimorphite surface has strong potential to make up for this shortcoming. Herein, the feasibility and appropriate environment of free Pb&lt;sup&gt;2+&lt;/sup&gt; for modifying the pure hemimorphite surface was evaluated. Subsequently, the performance of Pb&lt;sup&gt;2+&lt;/sup&gt; adsorption for enhancing sulfidization stability and floatability of hemimorphite were investigated. The X-ray photoelectron spectroscopy results indicated that the Pb&lt;sup&gt;2+&lt;/sup&gt; adsorption on hemimorphite surface was achieved through the Pb ions displacement for Zn ions, and it was bond to oxygen-containing groups on hemimorphite surface. Such adsorption was strengthened with the increasing of solution pH, owing to the abundant Pb hydroxyl species precipitated on mineral under alkaline conditions, in term of the results of visual MINTEQ modeling and time-of-flight secondary-ion mass spectrometry. In addition, the X-ray photoelectron spectroscopy results showed dominant Pb hydroxyl species further reacted with sulfur during subsequent sulfidization to generate much more S species than that of without Pb&lt;sup&gt;2+&lt;/sup&gt; pre-modification. Meanwhile, such sulfide layer composed by Pb&lt;sup&gt;2+&lt;/sup&gt; on the mineral surface presented much higher stability than Zn-S species, which was verified via adsorption and desorption tests. As a result, the sulfidization and flotation recovery of hemimorphite increased after Pb&lt;sup&gt;2+&lt;/sup&gt; pre-adsorption.

Pressure-resistant and portable array gas membrane device for rapid Escherichia coli detection in infant milk powder via smartphone colorimetry with all-in-one preparation strategy

This study presents a novel Pressure-Resistant and Portable Array Gas Membrane Separation (PAGMS) device for the rapid, smartphone-based detection of Escherichia coli (E. coli) in infant milk powder. The PAGMS device efficiently separates acetic acid, a byproduct of E. coli growth, enhancing detection sensitivity. Utilizing bromocresol violet as an indicator, this method quantifies E. coli based on colorimetric changes, with UV spectrum absorbance shifts indicating a linear correlation (R2 = 0.9864) within 5.0–120 μmol/L acetic acid concentration. Visual MINTEQ simulations validate the mechanism behind the indicator’s response. The approach surpasses traditional plate culture methods in terms of sample preparation time, achieving detection within a comparable timeframe of 15 min, and can concurrently process up to 48 samples, thereby substantially enhancing analytical throughput while detecting E. coli with a limit of detection of 5 cfu/g. This method demonstrates enhanced sensitivity, speed, and high-throughput capabilities, offering significant advantages in food safety monitoring.

Dissolved Iron and Organic Matter in Boreal Rivers across a South–North Transect

Iron (Fe) is one of the main nutrients present in dissolved, suspended, and colloidal states in river water. Predicting the composition and size of dissolved Fe compounds is crucial for assessing water quality. In this stud, we used a combination of physical methods (filtration), chemical techniques (ion exchange chromatography), and thermodynamic modeling (Visual MINTEQ) to characterize dissolved Fe speciation in boreal organic-rich rivers across a sizable south–north transect. We chose contrasting rivers with a predominance of either allochthonous or autochthonous organic compounds. We found that the dissolved organic matter (DOM) in the studied rivers varies in molecular weights and the degree of humification. Regardless of the climate parameters of the river watershed, the dominant status of dissolved Fe during the summer low-water period was essentially colloidal and dominated by anionic complexes of the type [MeL]n−.

An integrated process incorporating pH-controlled biomineralization and sulfate bioreduction to facilitate recovery of schwertmannite and sulfated polysaccharides from acid mine drainage

Acid mine drainage (AMD) poses an environmental challenge to the global mining industry. However, it is also a potential source of iron and sulfate for recovery. In this work, we proposed an integrated process of pH-controlled biomineralization of iron and biological sulfate reduction to facilitate the concurrent purification of AMD and selective recovery of iron and sulfate as valuable products. Compared with the biomineralization controlling pH at 2.8, the modified biomineralization controlling pH at 3.2 improved the iron precipitation efficiency from 9.7 % to 95.3 %, leading to a 53–fold increase in pure-grade schwertmannite Fe8O8(OH)4.08(SO4)1.96 production in AMD. This improvement may be related to the relatively low Gibbs free energy value of the Fe3+ mineralization reaction at pH 3.2. The solution equilibrium calculation using Visual MINTEQ indicated that keeping the system pH at an appropriate level is crucial for the spontaneous and effective biomineralization of Fe to schwertmannite at room temperature. The specific pH required for Fe biomineralization is slightly affected by the content of metal cations (e.g., Al3+, Ca2+, Mg2+, Cu2+, and Mn2+) and oxoanion (AsO33−/AsO43−) in AMD but greatly affected by sulfate content (mM) (pH = 0.149 ln c(SO42−) + 2.551). For the effluent resulting from AMD biomineralization, sulfate reduction at pH 5.0 removed residual Zn2+ (99.9 %), Mn2+ (97 %), Cu2+ (100 %), and sulfate (87.1 %) while recovering sulfated polysaccharides with antiangiogenic bioactivity (as confirmed by the chorioallantoic membrane tests). The pilot-scale continuous flow operation experiments demonstrated that this integrated method has the potential to recover valuable iron/sulfate products from AMD.