Flotation separation of wolframite from calcite using a new trisiloxane surfactant as collector

Li M., Yang C., Wu Z., Gao X., Tong X., Yu X., Long H.

Chlorite, as the most representative gangue mineral associated with specularite, of which the separation of these two minerals is difficult. This paper investigated the depression effect of taurine on specularite/chlorite separation via flotation experiments, adsorption tests, contact angle measurements, Zeta potential detection, FT-IR measurements, and XPS analyses. The results of single mineral flotation indicated that chlorite could be depressed selectively by taurine with the recovery of less than 30%, but the floatability of specularite remains high with recovery rate of 81.77% at pH 10. The artificial mixed mineral flotation results confirmed the effectiveness of taurine as a depressant. Surface adsorption, contact angle, and Zeta potential detection revealed taurine primarily adsorbs on the chlorite surface, which hampered the DDA’s subsequent adsorption and results in the chlorite’s poor floatability. The FT-IR spectra and XPS analyses provided further proof that taurine adsorbed on chlorite surface as an electron donor, and part of the electrons transferred from the sulfonic acid group of taurine to metal ions during the adsorption process. In addition, the hydrogen bond between amino-group of taurine and O ions in chlorite surface was also formed in the adsorption process. Finally, optimized adsorption configurations of taurine on chlorite surfaces were proposed.

Cao S., Yin W., Yang B., Zhu Z., Sun H., Sheng Q., Chen K.

Temperature affects the flotation of quartz in the calcium/sodium oleate (NaOL) system, while there is a lack of understanding of its potential mechanism. Therefore, in this work, the flotation response of quartz to temperature was investigated via micro-flotation experiments, interface property analyses, and theoretical calculations. Flotation results demonstrated that increasing temperature contributed to higher flotation recovery of quartz, which enhanced the removal of quartz from hematite. Surface tension results revealed that higher temperatures lowered the critical micelle concentration (CMC) and surface tension of the NaOL solution, and thus enhanced its surface activity. Solution chemistry calculations and X-ray photoelectron spectroscopy (XPS) measurements confirmed that the increased content of Ca(OH) + achieved by increasing temperatures enhanced the adsorption amounts of calcium species (acting as activation sites) on the quartz surface. Dynamic light scattering (DLS) measurements verified that the association degree of RCOO − to form (RCOO) 2 2− was strengthened. Furthermore, adsorption density measurements and molecular dynamics (MD) simulations confirmed that increasing the temperature facilitated NaOL adsorption toward the surface of the quartz, which was attributed to the stronger interaction between NaOL and the calcium-activated quartz surface at higher temperatures. As a result, quartz flotation was improved by increasing temperatures. Accordingly, a possible adsorption model was proposed.

Huang Z., Shuai S., Wang H., Liu R., Zhang S., Cheng C., Hu Y., Yu X., He G., Fu W.

Comparison diagram of flotation behavior of lepidolite by new Gemini collector HBDB and traditional monomolecular collector DA. • A novel amine-based Gemini surfactant HBDB was synthesized in our lab. • HBDB was introduced as an efficient collector of lepidolite flotation. • HBDB has better collecting ability and selectivity than traditional collector DA. • Using less dosage HBDB obtained a higher quality lepidolite concentrate. The global lithium supply and demand in this century is accelerated by the energy transition from carbon-based fossil fuels to renewable energy where electrical energy storage and electric vehicles heavily depend on the lithium-ion battery. The lepidolite is one of the main resources for extracting lithium, and it is usually enriched by froth flotation separation technology. However, the traditional lepidolite collector is monomer surfactant with only a single hydrophobic group and hydrophilic group, which usually leads to the low flotation separation efficiency. Therefore, to achieve the flotation separation of lepidolite ore more efficiently, in this work, an amine-based Gemini surfactant, hexanediyl-α, ω-bis (Dimethyldodecylammonium bromide) (HBDB), was synthesized, and compared with the conventional single molecule collector dodecylamine (DA). The experimental results show that the optimum pH value of flotation is 3, and the optimum dosage of HBDB and DA are 150 g/t and 300 g/t respectively. In bench-scale flotation experiments, compared with the conventional monomer DA collector (350 g/t), the Gemini HBDB with only 1/2 dosage of DA (175 g/t) increased the recovery of lepidolite by 16.18%. Economic calculation for a lepidolite ore plant, 1500 t/d, demonstrating that using Gemini HBDB can gain more about $ 8.2 million USD per year than using traditional unimolecular DA. Accordingly, this study provides a new and highly efficient collector for the flotation separation of lepidolite ore.

Zhang S., Huang Z., Wang H., Liu R., Cheng C., Guo Z., Yu X., He G., Fu W.

In this study, a new hydroxamic-acid molecule - sebacoyl hydroxamic acid (SHA) was synthesized and characterized. It was the first time that SHA with dual hydroxamic acid groups of “crab” structure was used as a collector for wolframite flotation, and its collecting ability was compared with the traditional collector benzohydroxamic acid (BAH) in the presence or absence of lead ions. In micro-flotation experiments, the wolframite recovery using 4 × 10 −4 mol/L SHA collector alone was 30% higher than that using 4 × 10 −4 mol/L BHA collector and 1 × 10 −4 mol/L Pb(NO 3 ) 2 activator. The results of bench-scale flotation experiments showed that the WO 3 recovery of wolframite concentrate with 180 g/t SHA was 10.05% higher than that with 360 g/t BHA and 300 g/t Pb(NO 3 ) 2 . Therefore, using SHA collector with “crab” structure for wolframite flotation can not only improve the separation index at a low dosage, but also eliminate the use of Pb(NO 3 ) 2 . The schematic illustration of the flotation separation process. • A novel surfactant sebacoyl hydroxamic acid (SHA) was synthesized. • SHA with a “crab” structure was first used as a collector for wolframite flotation. • SHA without Pb(II) ions had a stronger collecting ability than benzohydroxamic acid. • Using SHA collector improved the separation index and increased the economic benefit.

Lu Y., Wang S., Zhong H.

Wolframite is often associated with calcium bearing minerals, leading to low grade, while conventional anionic collectors are hard to realize their efficient flotation separation, thus the effective structural modification of cationic collectors provides a new insight into enhancing the comprehensive development of wolframite resources. In this study, a surfactant 3-dodecyloxy propyl amidoxime (DOPA) was designed and first used as the collector in flotation separation of wolframite from fluorite and calcite. Computational calculations basically proved the correctness of predictions about the performances of DOPA. Micro-flotation tests indicated that compared to DDA and conventional anionic collector benzohydroxamic acid (BHA), DOPA possessed superior collecting ability to wolframite and excellent selectivity against fluorite and calcite at low concentration, with no frother or activator employed, which is supposed to be an efficient collector for separating wolframite from calcium bearing minerals. The separation mechanisms of DOPA between wolframite and fluorite/calcite were further probed, revealing that besides the electrostatic attraction between DOPA and wolframite, DOPA could chemisorb onto wolframite surfaces by forming five-membered ring toward the surface cation site Fe or Mn, with no significant interaction observed on fluorite/calcite surfaces, resulting to the excellent separation performance.

Zhang M., Ning B., Bai Y., Tai X., Wang G.

Foam control of polyether trisiloxane (PTS) superspreader solutions with a traditional defoamer, such as silica-filled polydimethylsiloxane, is weak or even ineffective, which represents a problem that needs to be solved. In this paper, we describe a new foam control method for PTS by blending this superspreader with low foaming butynediol alkoxylate trisiloxane (TBEO). TBEO can be dissolved in PTS, acting as a foam control agent. The two components were pre-blended in different proportions (10–90% PTS-TBEO) before dilution. Performance tests of PTS-TBEO were conducted by measuring the equilibrium surface tension, dynamic surface tension, wettability, foam morphology, and foam stability. It was found that the addition of TBEO had an insignificant effect on the equilibrium and dynamic surface tension of the PTS foaming system. In addition, with an increase in the proportion of TBEO, the spreading speed of the mixture aqueous solution at different hydrophobic interfaces slows down, but the change at a low proportion of TBEO (10–40%) is negligible. However, the introduction of TBEO with different proportions will cause the originally stable foam to show different degrees of “cliff-like” decline, and with the increase of TBEO proportion, the relative antifoam efficiency also increases. And from the perspective of the interaction between TBEO molecules and the foam liquid film, the mechanism of TBEO in suppressing foam height of PTS superspreader solution was further explored. • The foam performance of polyether trisiloxane (PTS) can be effectively controlled by introducing TBEO. • A TBEO/PTS mixture still has high surface activity and strong surface wettability. • TBEO can enter the liquid film through bridging, thereby reducing foam stability.

Huang H., Qiu T., Ren S., Qiu X.

Hydration models of wolframite, lead ions, benzo hydroxamic acid ions (BHA), and their co-adsorption models were created to simulate the adsorption processes using the density functional theory (DFT). Pure minerals flotation tests, analysis of reagent adsorption capacity and infrared spectrum of products were carried out. The results indicate that the mechanism of Pb(II) activation in BHA flotation of wolframite in a neutral solution environment was probably due to the traction from Pb(II) on the H2Os around the site of the manganese on the wolframite surface reduced the hydration, making them more easily adsorbed by BHA. Therefore, the activation of Pb(II) on BHA adsorption is indirect.

Ren H., Li J., Tang Z., Zhao Z., Chen X., Liu X., He L.

The separation and extration of tin and tungsten from wolframite – scheelite mixed ore with high tin content is urgently needed given the increasingly exhaustion of the high-grade tungsten ore. However, current tungsten hydrometallurgy technologies suffer from considerably drawbacks, such as low recovery of tin, high consumption of chemicals, and large sodium salt waste water discharge. In this study, a novel reduction melting pretreatment method was used for the thorough separation of tin in the purification process and to improve the recovery of tin and tungsten. In this process, tin was first separated from tungsten and recovered in the form of SnS. Approximately 99% of tin was volatilized under the optimized conditions of the [WO3]/[CaSO4]/[C] molar ratio of 1:2:4 after blowing nitrogen at a flow rate of 3 L/min for 15 min, and the tin content in the reduction melting products was less than 0.05%. Meanwhile, wolframite was converted to scheelite and ferric calcium tungstate that then were easily digested by the mixed sulphuric-phosphoric acid solution, and the leaching ratio of tungsten reached 99%. The leaching residue of calcium sulfate was reused as the sulfurizing reagent in the reduction melting process. The efficient separation and extraction of tin and tungsten of this technology indicated its potential for industrial application.

Huang Z., Zhang S., Zhang F., Wang H., Zhou J., Yu X., Liu R., Cheng C., Liu Z., Guo Z., He G., Ai G., Fu W.

In froth flotation separation process, the collector molecular design has a crucial effect on potash processing to ensure sustainable production of potassium fertilizer (KCl) that is important to secure food supply in human society. Carnallite is an important source of KCl fertilizer production in industry. Reverse flotation has been used to separate halite (NaCl) impurities from carnallite (KCl·MgCl2·6H2O) for carnallite resources. However, progress in the carnallite resource reverse froth flotation has been constrained by the inherent limitation of traditional collector molecules with a single hydrophilic head and single hydrophobic chain per molecule. Herein, a novel morpholine-based Gemini molecule with double hydrophilic heads and hydrophobic chains, butanediyl-α, ω-bis (morpholino tetradecylammonium bromide) (BMTB) was synthesized and applied as the flotation collector in the reverse flotation separation for carnallite mineral. The better flotation performance of Gemini BMTB was achieved, compared to the traditional monomeric surfactant N-(n-Tetradecyl) morpholine (TDM). The bench-scale froth flotation separation results revealed that BMTB exhibited outstanding affinity and selectivity for NaCl crystals from carnallite at natural pH, resulting in less collector dosages – only 1/3 of TDM molecules. In contrast with traditional monomeric surfactant TDM (120 g/t), less amount of Gemini BMTB (40 g/t) – only one third of TDM molecules, was needed to obtain higher KCl recovery (KCl recovery raised by 4.69%). Meanwhile, the grade of NaCl with 40 g/t BMTB collector (2.19%) was lower than that with 120 g/t TDM collector (3.91%), and the grade of KCl with BMTB collector (22.59%) was higher than that with TDM collector (22.12%). Therefore, this work demonstrated the next-generation of flotation collector for the reverse froth flotation separation of the carnallite resources.

Zhong W., Yin W., Wang Y., Yao J.

In this paper, α-chloro-oleate acid (α-COA) and sodium hexametaphosphate (SHMP) were employed as collector and depressant in the flotation separation of magnesite from dolomite respectively. Properties of these two reagents were investigated through micro-flotation tests, zeta potential measurements, contact angle measurements and theoretical computation of adsorption energy based on conceptual density functional theory (DFT). Zeta potential measurements results revealed that SHMP was selectively adsorbed on the surface of dolomite, which leads to an exclusively depressing effect on dolomite. Results of contact angle measurements and theoretical computation indicated that α-COA had a stronger collecting ability to magnesite because of a stronger adsorption occurred on the surface of magnesite. In micro-flotation of artificially mixed minerals, separation of magnesite from dolomite with Gaudin's selectivity index up to 6.42 was succeeded using α-COA as collector and SHMP as depressant.

Sun Q., Lu Y., Wang S., Zhong H.

In order to improve the floatability of cassiterite, a novel surfactant 2-(benzylthio)-acetohydroxamic acid (BTHA) was synthesized and first used as flotation collector to selectively separate cassiterite from calcite and quartz. The flotation performance and adsorption mechanism of BTHA to cassiterite were studied by micro-flotation tests, zeta potential measurements, solution chemistry analysis, XPS and DFT calculations. The results of micro-flotation tests showed that BTHA possessed not only stronger collecting ability than either octanohydroxamic acid (OHA) or benzohydroxamic acid (BHA) under weak alkaline conditions, but also better selectivity to cassiterite against calcite and quartz. The results of zeta potential and solution chemistry analysis suggested that BTHA could produce co-adsorption between molecules and ions on the surface of cassiterite. The results of XPS spectra demonstrated that Sn-BTHA complexes were formed on cassiterite surfaces while no chemical bond or new chemical state emerged on calcite or quartz surfaces after BTHA treatment. DFT calculations provided further evidence that the BTHA interacted with cassiterite mainly through C O and OH in hydroxamate groups and S atoms in BTHA had certain electronic supply abilities which would promote the flotation of cassiterite.

Foucaud Y., Filippov L., Filippova I., Badawi M.

Recently, tungsten has drawn worldwide attention considering its high supply risk and economic importance in the modern society. Skarns represent one of the most important types of tungsten deposits in terms of reserves. They contain fine-grained scheelite (CaWO4) associated with complex gangue minerals, i.e. minerals that display similar properties, particularly surface properties, compared to scheelite. Consistently, the froth flotation of scheelite still remains, in the 21st century, a strong scientific, industrial, and technical challenge. Various reagents suitable for scheelite flotation (collectors and depressants, mostly) are reviewed in the present work, with a strong focus on the separation of scheelite from calcium salts, namely fluorite, apatite, and calcite, which generally represent significant amounts in tungsten skarns. Albeit some reagents allow increasing significantly the selectivity regarding a mineral, most reagents fail in providing a good global selectivity in favour of scheelite. Overall, the greenest, most efficient, and cheapest method for scheelite flotation is to use fatty acids as collectors with sodium silicate as depressant, although this solution suffers from a crucial lack of selectivity regarding the calcium salts, namely fluorite, calcite, and apatite. Therefore, the use of reagents combinations, commonly inducing synergistic effects, is highly recommended to achieve a selective flotation of scheelite from the calcium salts as well as from calcium silicates.

Meng Q., Yuan Z., Li L., Lu J., Yang J.

The surface modification of wolframite by Pb2+ ions and its influence on the flotation of wolframite using a salicylhydroxamic acid (SHA) collector were investigated through microflotation experiments, contact-angle tests, zeta-potential measurements, atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS). The results indicated that the addition of Pb2+ ions increased the SHA adsorption onto wolframite surfaces and contributed to the concomitant increases in the hydrophobicity and floatability of wolframite. Results of zeta-potential and XPS analyses confirmed that Pb2+ modification occurred via ion exchange, dehydration reaction, and precipitation reaction, generating Pb-containing complexes on wolframite surfaces. As expected, the Pb2+-modified wolframite exhibited increased interaction with SHA. The results of zeta-potential, FT-IR and XPS analyses indicated that SHA species reacted with Pb-containing complexes adsorbed on the wolframite surfaces, forming the hydrophobic Pb–SHA complexes. These findings verify the great potential of surface modification for strengthening wolframite flotation.

Foucaud Y., Filippova I., Dehaine Q., Hubert P., Filippov L.

The Tabuaco tungsten project, located in Northern Portugal, consists of two skarn layers, namely “Main” and “Lower” skarns, which display significantly different mineralogical and geochemical features. Both skarns contain fine-grained disseminated scheelite, but the Lower-skarn gangue is dominated by silicates whereas the Main-skarn gangue contains calcium-bearing minerals including fluorite, apatite, and vesuvianite, in close association with scheelite. Preliminary feasibility studies showed that direct separation of calcium-bearing minerals by flotation with fatty acids, which are environmentally benign, was unsuccessful due to their similar surface properties. Several routes for each skarn type were proposed with a strong focus on the Main skarn that displays the most complex mineralogical associations. Enhanced gravity separation (Falcon concentrator), high intensity magnetic separation, and flotation with fatty acids were investigated for the Main Skarn level with the objective of producing a marketable scheelite concentrate. Flotation was thoroughly investigated in terms of depressants, producing optimally a concentrate assaying 9.2% WO3 at 87.9% WO3 recovery from a ~1.1% WO3 feed, by means of a 1:1 ratio of sodium carbonate and sodium silicate. Fluorite is the most problematic mineral in flotation with fatty acids and, consequently, new fatty-acids-based collector formulations have been developed to improve the separation contrast between scheelite and fluorite, producing a concentrate assaying 14.1% WO3 with 77.1% WO3 recovery for the fully-optimised conditions. Furthermore, the performance of two types of Falcon bowls (SB and UF) were investigated and optimised for gangue minerals rejection. The Falcon concentrator was used as a desliming and pre-concentrating apparatus: one stage of Falcon SB allowed rejection of 84% of the total amount of fluorite, more than 95% of the slimes, and 85 wt% of the mass. Consequently, it improved significantly the performance of the fully-optimised scheelite flotation as the final concentrate, after one Falcon SB stage and 4 flotation stages, assayed 62.9% WO3 with 59.4% WO3 recovery, which constituted a marketable scheelite concentrate. Both the Falcon SB parameters and the number of fully-optimised flotation stages can be optimised to maximise either the WO3 grade or the WO3 recovery, regarding the product specifications. Finally, the high intensity magnetic separation allowed rejection of around 45 wt% of the total yield prior to the milling stage with only 6.0% WO3 losses, which would decrease significantly the energy consumed during the milling stage.

Barim E., Akman F.

In this study, a novel acrylamide monomer was synthesized and characterized by UV-Vis, FT-IR and 1H NMR measurements. The acrylamide monomer namely, N-(2-acetyl-benzofuran-3-yl)acrylamide (NABA), was prepared in two steps. In the first step, 1-(3-aminobenzofuran-2-yl)ethan-1-one was synthesized by the reaction of 1-chloroacetone with 2-hydroxy-benzonitrile under basic conditions. In the second step, the obtained 1-(3-aminobenzofuran-2-yl)ethan-1-one was reacted with acryloyl chloride and triethylamine at 0–5 °C temperature for obtaining NABA monomer. Then, the structural, vibrational, nuclear magnetic resonance and electronic properties for the synthesized monomer were determined by quantum chemical calculations of DFT method. The results were compared with experimental FT-IR, 1H NMR and UV–Vis spectral data. The band gap of HOMO and LUMO show that the NABA monomer is chemically active and has charge transfer within the monomer. Moreover, molecular electrostatic potential (MEP) maps were drawn to identify reactive regions of NABA monomer.

Cheng C., Zeng G., Huang Z.

Ridho M.Z., Pertiwi R., Bagaskara E.D., Rambani R.R., Pitaloka C.S., Wahyuni F.M., Rahmawati I., Reza M.

Pan Y., Feng Y., Li Y., Chen J., Li Y.

Cheng C., Zeng G., Huang Z.

Liu P., Zhou Y., Tian M., Sun W.

Ren Q., Liu P., Yu C., Liu S., Zhang W., Kang J., Sun W., Tian M.

Zhang X., Li C., He L., Zhang Y., Yuan F., Zheng S., Sun Z.

Tahooni Bonab S., Abdollahi H., Abbaspour A.

Tahooni Bonab S., Abdollahi H., Abbaspour A.

Tao L., Wang J., Liao D., Jia W., Zhao Z., Che W., Qi Z., Sun W., Gao Z.

Flotation is the most common method to obtain concentrate through the selective adsorption of collectors on target minerals to make them hydrophobic and floatable. In the hydrometallurgy of concentrate, collectors adsorbed on concentrate can damage ion-exchange resin and increase the chemical oxygen demand (COD) value of wastewater. In this work, we proposed a new scheme, i.e., desorbing the collectors from concentrate in ore dressing plant and reusing them in flotation flowsheet. Lead nitrate and benzohydroxamic acid (Pb-BHA) complex is a common collector in scheelite flotation. In this study, different physical (stirring or ultrasonic waves) and chemical (strong acid or alkali environment) methods for facilitating the desorption of Pb-BHA collector from scheelite concentrate were explored. Single-mineral desorption tests showed that under the condition of pulp pH 13 and ultrasonic treatment for 15 min, the highest desorption rates of Pb and BHA from the scheelite concentrate were 90.48% and 63.75%, respectively. Run-of-mine ore flotation tests revealed that the reuse of desorbed Pb and BHA reduced the collector dosage by 30% for BHA and 25% for Pb. The strong alkali environment broke the chemical bonds between Pb and BHA. The cavitation effect of ultrasonic waves effectively reduced the interaction intensity between Pb-BHA collector and scheelite surfaces. This method combining ultrasonic waves and strong alkali environment can effectively desorb the collectors from concentrate and provide “clean” scheelite concentrate for metallurgic plants; the reuse of desorbed collector in flotation flowsheet can reduce reagent cost for ore dressing plants.

Yu J., Gong X., Yao J., Yin W., Xue F., Tian D., Wang Y.

Herein, polyaspartic acid (PASP) was used as an environmentally friendly and efficient inhibitor to achieve the effective flotation separation of magnesite and calcite in a sodium oleate (NaOL) system. Microflotation experiments indicated that using NaOL as a collector allowed PASP to considerably reduce the flotation recovery of calcite while showing a slight impact on that of magnesite. Among them, a PASP dosage of 6 mg/L achieved a maximum flotation difference of 71.88% between magnesite and calcite. An adsorption capacity test showed that the presence of PASP significantly decreased NaOL adsorption on calcite and slightly decreased that on magnesite. Zeta potential and infrared spectroscopy analyses indicated that PASP strongly affected the surface charge of calcite and introduced corresponding characteristic functional groups on its surface; however, the effect of PASP on that of magnesite was weak. X-ray photoelectron spectroscopy indicated that PASP exhibited strong selectivity for calcite and a weak one for magnesite, which was in good agreement with the shift in the Ca and Mg peak positions and the change in their relative contents. The contact angle measurements demonstrated that PASP considerably reduced the contact angle of calcite and slightly reduced that of magnesite. Extended Derjaguin–Landau–Verwey–Overbeek theoretical calculations indicated that using NaOL alone resulted in an attraction between the magnesite/calcite particles and bubbles. After PASP addition, the attraction force was retained for magnesite, while a repulsive force was observed for calcite due to PASP selectivity, thereby hindering the adhesion between calcite particles and bubbles.

Gong X., Yao J., Yang B., Yin W., Fu Y., Wang Y.

Sodium polyphosphate (SP) is a representative phosphate that can integrate metal ions. Herein, the inhibition effect and mechanism of SP on the flotation of dolomite in the flotation separation of brucite and dolomite were studied in a sodium dodecyl sulfonate (SDS) flotation system. In the flotation test, SP exhibited a strong inhibition effect on dolomite flotation but had little effect on brucite. In the contact angle test, SP had a stable inhibition effect on two types of minerals and strongly inhibited dolomite flotation. In the zeta potential test, the effect of SP under negative charge on dolomite potential was significantly higher than that of brucite, and the stronger adsorption capacity reflected the affinity of SP to dolomite. Infrared spectrum analysis revealed that SDS displayed strong collecting ability toward both types of minerals; however, it lost its collecting effect because of the selective adsorption of SP on the dolomite surface. In X-ray photoelectron spectroscopy analysis, the changes in the characteristic elements of the two minerals and the change characteristics of the P element belonging to SP again indicated that the strong interaction between SP and the dolomite surface was the key factor inhibiting dolomite in flotation.

Azeez N.R., Salih S.S., Kadhom M., Mohammed H.N., Ghosh T.K.

Zinc and cadmium pollutants cause a significant environmental effect that cannot be ignored. Due to their considerable amount in an aqueous environment, industries are seeking suitable adsorbents that are environmentally friendly and inexpensive for removing metals from wastewater before disposing of them in surface waters. This research employed original MXene (MX) and chitosan-modified MXene (CSMX) to extract zinc (Zn(II)) and cadmium (Cd(II)) metal ions from water-based solutions. The composite material produced was analyzed using techniques such as X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy (FTIR), and Brunauer-Emmett-Teller (BET). The effects of contact duration, pH of the solution, and initial concentration of metal ions on the adsorption process of zinc and cadmium onto both MX and CSMX composites were investigated. MXene and prepared CSMX composite presented a high adsorption capacity for both studied heavy metals, which were 91.55 and 73.82 mg/g for Zn(II) and Cd(II) onto MX, 106.84 and 93.07 mg/g for Cd(II) and Zn(II) onto CSMX composite, respectively. Furthermore, the maximum competitive adsorption capacities for Zn(II) onto MX and CSMX composites are 77.29 and 93.47 mg/g, and for Cd(II) 60.30 and 79.66 mg/g, respectively. Hence, the removal capacities for both single and competitive metal ions were superior to CSMX composite. However, the adsorption capacities after five successive regeneration sequences were only dropped by 13.2% for Zn(II) and 17.4% for Cd(II) onto the CSMX composite compared to the first cycle. These results confirm that both metals could be efficiently terminated from wastewater, which makes the prepared CSMX composite a favorable candidate adsorbent in practical applications.

Wang J., Lu W., Cao Z., Wu X., Wang P., Wang X., Liu W.

The surface properties of bastnaesite and parisite are similar to their associated gangue mineral, fluorite, which makes the flotation separation of these two rare earth minerals from fluorite one of the industry’s most significant challenges. This study systematically investigates the inhibitory effects and mechanisms of sodium silicate (SS) on bastnaesite, parisite, and fluorite in an octyl hydroxamic acid (OHA) collector system through flotation experiments, various modern analytical methods, and DFT simulations. The flotation test results indicate that the inhibition effects of SS on the three minerals are in the order: fluorite > parisite > bastnaesite. Detection and analysis results indicate that SS forms hydrophilic complexes with Ca atoms on the surfaces of fluorite and parisite, enhancing surface hydrophilicity and inhibiting OHA adsorption, but its impact on bastnaesite is relatively minor. DFT simulation results show that OHA forms covalent bonds with metal ions on mineral surfaces, favoring five-membered hydroxamic-(O-O)-Ce/Ca complexes, and reacts more strongly with Ce atoms than Ca atoms. SS primarily forms covalent bonds with metal atoms on mineral surfaces via the SiO(OH)3− component, and OHA and SS compete for adsorption on the mineral surfaces. OHA has a stronger affinity for bastnaesite, whereas SS shows the highest affinity for fluorite, followed by parisite, and the weakest affinity for bastnaesite.

Wang L., Li Z., Zhang H., Huang L., Zhu Y., Li F.

Flotation technology is an effective way to separate magnesite from dolomite. However, the efficient separation of magnesite from dolomite in sodium oleate (NaOL) system is rather challenging without depressants due to their highly similar physicochemical surface properties. Herein, gellan gum (GG) was employed as a new flotation inhibitor in separating magnesite from dolomite. The depression performance and inhibitory mechanism were systematically studied by flotation experiments, and a number of surface testing technologies. Flotation experiments indicated that GG greatly affected the floatability of dolomite, whereas it had little impact on the magnesite flotation. The artificial mixed mineral experiments confirmed that effective separation of magnesite and dolomite was fulfilled with GG as flotation inhibitor. Zeta potential analyses, surface wettability measurements, and Fourier transform infrared (FTIR) spectroscopy tests indicated that GG strongly prevented the NaOL adhesion on the dolomite, while it scarcely impeded the NaOL adhesion onto magnesite. X-ray photoelectron spectroscopy (XPS) detections demonstrated that GG adhered stronger towards dolomite than magnesite, which was mainly due to its higher affinity towards Ca2+. AFM images intuitively identified that much stronger interaction and thicker adsorption layer occurred on the dolomite than magnesite. Additionally, higher adsorption concentration, closer adsorption distance and hither adsorption strength of GG on the dolomite was further confirmed by molecular dynamics (MD) simulations. Therefore, GG was a promising flotation depressant to separate magnesite from dolomite and achieve the efficient exploitation of magnesite resources.