The influences of tetraborate anions on manganese electrodeposition in an anion-exchange membrane electrolysis reactor were investigated. The experimental results of manganese electrodeposition indicate that a certain amount of tetraborate anions can increase cathode current efficiency and initial pH 7.0–8.0 is suitable for high cathode current efficiency. X-ray diffraction (XRD) and scanning electron microscope (SEM) analysis show the nanocrystalline structure and impact morphology of electrodeposited manganese. The purity of electrodeposited manganese is above 99.88 %. The tests of tetraborate anions on buffer capacity (β) and pH value of the electrolyte near the cathode surface confirm that tetraborate anions facilitate manganese electrodeposition. Tetraborate anions can improve concentration polarization of Mn2+ ions and then increase the overpotential of hydrogen evolution reaction. Therefore, ammonium tetraborate can reduce the hydrogen embrittlement, pore, and pitting negative effect on electrodeposit surface, to improve the corrosion resistance of electrodeposited manganese. After tetraborate anions being added in electrolyte, weight loss measurement indicates that the corrosion resistance of electrodeposited manganese is improved. Electrochemical measurements testify that corrosion resistance of electrodeposited manganese containing tetraborate anions in electrolyte is reflected by less negative corrosion potential and higher impedance.

Mn3O4 hollow microspheres have been facilely prepared via a green synthesis of 2,3,5,6-tetrachloropyridine reduced from pentachloropyridine by manganese. The specific hollow microspheres were made by a H2 gas bubble-templating method presenting a high specific surface area (87.1 m2 g−1) and a big total pore volume (0.2030 cm3 g−1). The Mn3O4 hollow microspheres as an anode material demonstrate a good electrochemical performance, with a high reversible capacity of 646.9 mA h g−1 after 240 cycles at a current density of 200 mA g−1. The good cycling performance is attributed to numerous mesopores, high specific surface area and big total pore volume, which can offer good electrical contact and conductivity as well as accommodate the mechanism strains. In addition, the yield and selectivity of 2,3,5,6-tetrachloropyridine achieved up to 99.2% and 99.5%, respectively.

Mn3O4 hollow microspheres have been facilely prepared via a green synthesis of 2,3,5,6-tetrachloropyridine reduced from pentachloropyridine by manganese. The specific hollow microspheres were made by a H2 gas bubble-templating method presenting a high specific surface area (87.1 m2 g−1) and a big total pore volume (0.2030 cm3 g−1). The Mn3O4 hollow microspheres as an anode material demonstrate a good electrochemical performance, with a high reversible capacity of 646.9 mA h g−1 after 240 cycles at a current density of 200 mA g−1. The good cycling performance is attributed to numerous mesopores, high specific surface area and big total pore volume, which can offer good electrical contact and conductivity as well as accommodate the mechanism strains. In addition, the yield and selectivity of 2,3,5,6-tetrachloropyridine achieved up to 99.2% and 99.5%, respectively.

•Phase compositions of iron were varied with microwave roasting conditions.•5% alkali lignin was favorable for improving the magnetic properties of roasted ore.•Better magnetic properties of roasted ore were achieved at 200 °C, 600 W for 30 min.•Magnetic properties of roasted ores were associated with phase compositions of iron.•The iron concentrate with Fe recovery of 82.92% was obtained by magnetic separation.Phase transformation and magnetic properties of limonite ore with 40.10% Fe via microwave roasting with addition of alkali lignin were investigated by chemical phase analysis and vibrating sample magnetometer (VSM) analysis, respectively. The results of chemical phase analysis indicated that phase compositions and contents of iron in microwave roasted limonite ore were varied with the dosage of alkali lignin, the roasting temperature, the roasting time and the microwave power, and among them the dosage of alkali lignin exerted more significant influence. Iron oxides in limonite ore could be reduced to magnetic iron oxides including γ-Fe2O3 and Fe3O4 in the following sequence during microwave roasting process by evenly distribution of alkali lignin below 5%: FeOOH/α-Fe2O3→γ-Fe2O3→Fe3O4, accompanied with small amount of FeO, and as the dosage was over 5%, γ-Fe2O3 and Fe3O4 could be in turn successively transformed into α-Fe2O3. Magnetic property studies demonstrated that an iron concentrate containing 88.72% magnetic iron oxides with a maximum saturation magnetization of 41.393 emu/g could be produced from roasted ore which was obtained by microwave roasting at 200 °C and 600 W with 5% alkali lignin for 30 min. In addition, the roasted ore was further used for magnetic separation, and the results showed that combining microwave roasting with addition of 5% alkali lignin could improve the iron recovery from the roasted ore distinctively. It was concluded that the microwave roasting process in the presence of alkali lignin could be a promising approach to effective utilization of limonite ore resources.Download high-res image (818KB)Download full-size image

•S-[(2-hydroxyamino)-2-oxoethyl]-N,N-dibutyl-dithiocarbamate surfactant.•HABTC hydrophobilized copper mineral particles at pH 6–10.•Chalcopyrite adsorbing HABTC is an endothermic chemisorption.•Both dithiocarbamate and hydroxamate of HABTC anchored on chalcopyrite.•Cu(II)-hydroxamate and Cu(I)-dithiocarbamate exist in Cu-HABTC species.In this paper, S-[(2-hydroxyamino)-2-oxoethyl]-N,N-dibutyl-dithiocarbamate (HABTC) was first synthesized and characterized by 1H NMR, 13C NMR and FTIR. The role of HABTC’s hydroxamate and dithiocarbamate groups in chalcopyrite flotation was evaluated by micro-flotation, bench-scale flotation, adsorption experiments, zeta potential and X-ray photoelectron spectroscopy (XPS). HABTC exhibited excellent affinity to chalcopyrite particles under pH 6–10 and achieved superior flotation recovery of copper minerals in comparison with sodium isobutyl xanthate (SIBX). The adsorption thermodynamics and kinetics elucidated that HABTC adsorption on to chalcopyrite surfaces was a spontaneously endothermic chemisorption process. Zeta potential demonstrated that HABTC might chemisorb on to the positive sites of chalcopyrite surfaces. XPS spectra further revealed that both dithiocarbamate and hydroxamate groups of HABTC anchored on chalcopyrite surfaces through Cu(II)-hydroxamate and Cu(I)-dithiocarbamate configurations, resulting in an enhanced collecting power of HABTC to chalcopyrite particles.The adsorption mechanism and flotation performance of S-[(2-hydroxyamino)-2-oxoethyl]-N,N-dibutyl-dithiocarbamate (HABTC) to chalcopyrite (CuFeS2) particles.Download high-res image (92KB)Download full-size image

The flotation of diaspore and three kinds of silicate minerals, including kaolinite, illite and pyrophyllite, using an organosilicon cationic surfactant (TAS101) as collector and starch as depressant was investigated. The results show that both diaspore and aluminosilicate minerals float readily with organosilicon cationic collector TAS101 at pH values of 4 to 10. Starch has a strong depression effect for diaspore in the alkaline pH region but has little influence on the flotation of aluminosilicate minerals. It is possible to separate diaspore from aluminosilicate minerals using the organosilicon cationic collector and starch depressant. Further studies of bauxite ore flotation were also conducted, and the reverse flotation separation process was adopted. The concentrates with the mass ratio of Al2O3 to SiO2 of 9.58 and Al2O3 recovery of 83.34% are obtained from natural bauxite ore with the mass ratio of Al2O3 to SiO2 of 6.1 at pH value of 11 using the organosilicon cationic collector and starch depressant.

The influences of sodium silicate on manganese electrodeposition in sulfate solution were investigated. Manganese electrodeposition experiments indicate that a certain amount of sodium silicate can improve cathode current efficiency and initial pH 7.0–8.0 is the optimized pH for high cathode current efficiency. The analyses of scanning electron microscopy (SEM) and X-ray diffraction (XRD) indicate the compact morphology and nanocrystalline structure of electrodeposits. X-ray photoelectron spectrometry (XPS) analysis shows that the elements of Mn, Si and O exist in the deposit. The solution chemistry calculations of sulfate electrolyte and sodium silicate solution indicate that species of Mn2+, MnSO4, Mn(SO4)2–2, Mn2+, MnSiO3, Mn(NH3)2+, SiO32– and HSiO3− are the main active species during the process of manganese electrodeposition. The reaction trend between Mn2+ and Si-containing ions is confirmed by the thermodynamic analysis. In addition, polarization curve tests confirm that sodium silicate can increase the overpotential of hydrogen evolution reaction, and then indirectly improve the cathode current efficiency.

•Molybdenite was depressed in sea water flotation at pH above 9.5.•SEM-AES, XPS and ToF-SIMS were used to study the depression mechanism.•Mg(OH)2 and CaCO3 deposited on the surface of molybdenite in sea water at pH 11.•Colloidal precipitates Mg(OH)2 depressed molybdenite more than crystallized CaCO3.De-ionized water (DI water) and simulated sea water were applied to float molybdenite in this study. Results showed that the flotation recovery of molybdnite was sharply reduced in simulated sea water at pH above 9.5. To find out the exact mechanisms of depression, several advanced apparatuses were applied for surface characterization. Based on the measurements by the scanning electron microscopy (SEM), two kinds of precipitates (colloidal precipitates and crystallized precipitates) were observed on the molybdenite surface which was immersed in the simulated sea water during flotation. It was found that the colloidal precipitates overspread on the surface while the crystallized precipitates randomly scatted on the surface. With the detection by auger electron spectrum (AES), it was found that magnesium and calcium were the main components in the colloidal precipitates and crystallized precipitates, respectively. According to the X-ray photoelectron spectrum (XPS) tests, it was testified that the colloidal precipitates were Mg(OH)2 and the crystallized precipitates were CaCO3, which was confirmed by ToF-SIMS results. These precipitated Mg(OH)2 and CaCO3 particles on the molybdenite surfaces play an important role in inhibiting the flotation of molybdenite in the simulated sea water.Molybdenite is depressed by the colloidal precipitates Mg(OH)2 deposited on the surfaces at pH above 9.5 in sea water flotation.

The influences of oxalate anions on manganese electrodeposition in sulfate solution were investigated on the basis of cathode current efficiency, characterization of SEM-EDX and XRD, solution chemistry calculation, thermodynamics and electrochemical test. The experimental results show that the range of (NH4)2C2O4 was adjusted from 0 mol/L to 4.8 × 10−3 mol/L. And 1.5 × 10−3 mol/L (NH4) 2C2O4 was suitably used with initial pH 7.0. The characterization of SEM indicates that oxalate anions can improve the morphology of electrodeposited films. The electrodeposited films containing manganese were characterized and determined by EDX and XRD. The solution chemistry calculation of catholyte and oxalate anions shows that the main active species are MnSO4, Mn(SO4)2− 2, Mn2+, Mn(SO4)C2O2− 4, MnC2O 4, Mn(NH3)2+, and C2O2− 4. The reaction trend between C2O2− 4 and Mn2+ ions is confirmed by computation of reaction energy. Electrochemical test analysis indicates oxalate anions increase the overpotentials of hydrogen evolution reaction and manganese electrodeposition.

•A novel surfactant NHOO was first introduced as wolframite flotation collector.•NHOO exhibited a stronger affinity to wolframite than BHA and OHA.•NHOO has two active centers to mineral surfaces and two hydrophobic groups.•NHOO showed self-adapting adsorption forces and hydrophobicity to pH values.•A more hydrophobic and stable surfaces improved wolframite flotation recovery.In this paper, a novel surfactant N-(6-(hydroxyamino)-6-oxohexyl)octanamide (NHOO) was prepared and its flotation performances and adsorption mechanism for wolframite were first investigated by FTIR spectra, flotation tests, zeta potential and adsorption quantity measurements. The flotation results showed that NHOO was a stronger collector than the conventional hydroxamic acid collectors such as benzoyl hydroxamic acid (BHA) and octyl hydroxamic acid (OHA). The adsorption data demonstrated that the adsorption affinity of NHOO to wolframite was far stronger than that of BHA or OHA, and the preferable pH ranges for NHOO adsorption on wolframite surfaces were below 6.69 or above 9.35. The results of FTIR spectra and zeta potential illustrated that NHOO might adsorb on wolframite mainly through hydrogen bonding and electrostatic attraction by its amide C(O)H2N+ group at pH < 6.69 or coordination bonding by its hydroxamic C(O)NHO− group at pH > 9.35. In the pH range between 6.69 and 9.35, NHOO might exist in zwitterion species which was formed through intramolecular electrostatic attraction between its positive amide and negative hydroxamic groups, resulting in mildly weakening interaction force and collecting power to wolframite. NHOO’s unique properties, such as double reactive centers to mineral surfaces, double hydrophobic groups, and self-adapting adsorption manner and hydrophobic geometry to pulp pH values, made it a superior collector for wolframite flotation.The flotation mechanism of NHOO, OHA, or BHA to wolframite.

One-pot synthesis of cyclic aldol tetramer and α, β-unsaturated aldol from C3-C8 linear aldehydes using phase-transfer catalyst (PTC), quaternary ammonium, combined with sodium hydroxide as catalysts was investigated. Butanal was subjected for detail investigations to study the effect of parameters. It was found that the selectivity of cyclic aldol tetramer depends greatly on the operating conditions of the reaction, especially the PTC/butanal molar ratio. The average selectivity of 2-hydroxy-6-propyl-l, 3, 5-triethyl-3-cyclohexene-1-carboxaldehyde (HPTECHCA) was 54.41% using tetrabutylammonium chloride combined with 14% (mass fraction) NaOH as catalysts at 60 °C for 2 h with a PTC-to-butanal molar ratio of 0.09:1. Pentanal was more likely to generate cyclic aldol tetramer compared with other aldehydes under the optimum experimental conditions. Recovery of the PTC through water washing followed by adding enough sodium hydroxide from the washings was also demonstrated.

The kinetics of reductive leaching of manganese from a low-grade manganese oxide ore were studied using cellulose as reductant in dilute sulfuric acid medium. It was found that when the stirring speed was higher than 200 r/min, the effect of gas film diffusion on manganese extraction efficiency could be neglected, and the kinetic behavior was investigated under the condition of elimination of external diffusion influence on the leaching process. Effects of leaching temperature, mass ratio of cellulose and ore, and the sulfuric acid concentration on manganese extraction efficiency were discussed. The kinetic data were analyzed based on the shrinking core model, which indicated that the leaching process was dominated by both ash layer diffusion and chemical reaction at the initial stage, with the progress of leaching reaction, the rate-controlling step switched to the ash layer diffusion. It was also concluded that the sulfuric acid concentration had the most significant influence on the leaching rate, the reaction orders with respect to the sulfuric acid concentration were 2.102 in the first 60 min, and 3.642 in the later 90 min, while the reaction orders for mass ratio of cellulose and ore were 0.660 and 0.724, respectively. An Arrhenius relationship was used to relate the temperature to the rate of leaching, from which apparent activation energies were calculated to be 46.487 kJ/mol and 62.290 kJ/mol at the two stages, respectively. Finally, the overall leaching rate equations for the manganese dissolution reaction with cellulose in sulphuric acid solution were developed. The morphological changes and mineralogical forms of the ore before and after the chemical treatment were discussed with the support of SEM and XRD analyses.

The separation of rhenium from molybdenum in aqueous solution has always been a problem in hydrometallurgy. The separation of rhenium from the electro-oxidation leachate of molybdenite and its mechanism were investigated. The results show that pH of the leachate significantly affects adsorption rate compared with other experimental parameters. When temperature is 30 °C, pH=8, and adsorbing time is 1 h, adsorption rates of rhenium and molybdenum are 93.46% and 3.57%, respectively, and separation factor of D301 resin for rhenium and molybdenum is 169.56. In addition, the separation factor is higher when the initial molybdenum concentration in model solution is increased. The saturated adsorption capacity of D301 resin for molybdenum and rhenium calculated based on simulated results are 4.263 3 mmol/g and 4.235 5 mmol/g, respectively. D301 resin is an effective separation material of rhenium from electric-oxidation leachate of molybdenite. The adsorption kinetics results also show that the adsorption of rhenium is easier than that of molybdenum, and the adsorption process of D301 for rhenium and molybdenum may be controlled by liquid film diffusion.

In this paper, three flotation approaches, bulk flotation followed by separation, selective Cu flotation followed by bulk flotation and then separation, and preferential Mo flotation followed by Cu flotation, were investigated to concentrate molybdenite from Dexing (Jiangxi Province, China) porphyry Cu–Mo ores. The bench-scale flotation results demonstrated that compared to other two flotation approaches, the preferential Mo flotation approach using a new non-thiol collector obtained a high recovery of molybdenite in a molybdenum circuit, while the tailing of molybdenum circuit was treated by a copper flotation circuit to obtain a high recovery of other co-present metal values. The industrial flotation tests indicated that compared to the bulk flotation approach, the preferential Mo flotation approach achieved an excellent cleaner concentrate containing 0.655% Mo with 88.49% Mo recovery, and increased Mo recovery and grade over 34.0% and 0.4% in the molybdenum circuit, respectively. For being uncontaminated with thiol collectors, this cleaner concentrate was readily treated to perform the Mo/Cu flotation separation which returned a superior Mo concentrate containing 48.83% Mo with 90.60% Mo operation recovery as well as saved about 1/2 Na2S consumption.Graphical abstractThe principal flowsheet of preferential Mo flotation followed by Cu flotation for recovery of Mo and Cu from a porphyry Cu–Mo ore.Download full-size imageHighlights► Lime impairs the floatability of molybdenite in flotation of a porphyry Cu–Mo ore. ► A novel approach is introduced to reduce the effect of lime on Mo recovery. ► The preferential Mo flotation approach is evaluated and optimized by flotation tests. ► The novel approach achieves a high Mo recovery without the effect of lime.

The leaching kinetics of reductive leaching of manganese from manganese dioxide ores (MDO) in dilute sulfuric acid in the presence of Phytolacca americana powder (PAP) was investigated. The effects of stirring speed, leaching temperature and leaching time, particle size, weight ratio of PAP to MDO (CW) and sulfuric acid concentration (CH) on the leaching efficiency of manganese were studied. The leaching efficiency of manganese based on the shrinking core model was found to be controlled by diffusion through the ash/inert layer composed of the associated minerals. The apparent activation energy is 15.18 kJ mol−1. The experimental results indicate reaction order of 0.797 for CH and 1.25 for CW. The overall leaching efficiency equations for MDO dissolution reaction with PAP in dilute sulfuric acid were proposed by a semi-empirical model.

•2-Amino-6-decanamidohexanoic acid was first introduced as collector.•AHA-10 exhibited superior affinity to diaspore against aluminosilicate.•AHA-10 owned unique bond patterns and double hydrophobic groups.•AHA-10 formed intermolecular hydrogen bonds on diaspore surfaces.In this paper, a novel surfactant, 2-amino-6-decanamidohexanoic acid (AHA-10) was synthesized and used as a collector for flotation separation of diaspore and aluminosilicate minerals. The adsorption mechanism of AHA-10 onto diaspore was also evaluated by FTIR spectra, zeta potential, XPS and solution chemistry. The flotation results demonstrated that AHA-10 exhibited superior collecting power to diaspore and good selectivity against kaolinite and illite, and could effectively recover diaspore from bauxite ores contained aluminosilicate minerals at pH around 10. The analyses of FTIR spectra, zeta potential and solution chemistry inferred that at pH around 10, AHA-10 might chemisorb on diaspore surfaces by formation of AlO and AlN bonds. AHA-10’s unique properties, such as characteristic bond model to Al atoms on diaspore surfaces, double hydrophobic groups and intermolecular hydrogen bonds between neighboring AHA-10 molecules coated on diaspore surfaces, rendering a weakening surface energy and enhancing hydrophobicity of diaspore particles.The potential absorption model of a layer of AHA-10 coated on diaspore.Download high-res image (137KB)Download full-size image

•iPOPECTU exhibits excellent selectivity towards chalcopyrite against pyrite.•Pyrite can be separated from pyrite-including Cu-Mo ore with iPOPECTU in sea water.•ToF-SIMS analysis revealed Cu-iPOPECTU complexes improve chalcopyrite floatability.•iPOPECTU does not impact the floatability of molybdenite.Single mineral flotation of chalcopyrite, molybdenite and pyrite with a regular collector (potassium amyl xanthate) and a selective collector (N-isopropoxypropyl-N′-ethoxycarbonyl thiourea) for chalcopyrite in both de-ionized water and synthetic sea water were investigated in this study. The results indicated a wider effective pH range for separation of pyrite from chalcopyrite and molybdenite with N-isopropoxypropyl-N′-ethoxycarbonyl thiourea than with potassium amyl xanthate in de-ionized water flotation. The separation can be achieved in low alkaline conditions only with the selective thiourea collector in synthetic sea water flotation in this study. The results of the mixed minerals flotation in synthetic sea water confirmed the successful separation of pyrite from chalcopyrite and molybdenite by N-isopropoxypropyl-N′-ethoxycarbonyl thiourea at pH 9. In addition, time-of-flight secondary ion mass spectrometry (ToF-SIMS) analysis revealed the mechanism of separation.iPOPECTU can use as selective collector to separate pyrite from chalcopyrite without depressing molybdenite at pH 9 in sea water flotation.Download high-res image (195KB)Download full-size image

•HPA was first introduced in malachite flotation.•HPA was a powerful collector for malachite without Na2S and MIBC.•HPA was mainly absorbed on surface of malachite in chemical bond.The flotation behavior and adsorption mechanism of α-hydroxyoctyl phosphinic acid (HPA) to malachite were investigated by micro-flotation tests, zeta potential measurements, and FTIR and XPS analysis. The micro-flotation results demonstrated that compared with sodium isobutyl xanthate (SIBX) and styrene phosphonic acid (SPA), HPA exhibited superior collecting performances to direct flotation recovery of malachite and floated out above 80% malachite at pH 5–10. The results of zeta potential measurement inferred that there might be covalent bonds between HPA and copper on the malachite surface. The FTIR analysis confirm that HPA might react with copper species of malachite surfaces to form Cu–HPA complex adsorption layers, with a release of H+ ions (from PH group). The XPS analysis provided very clear evidence that the Cu(II) species was partly reduced to Cu (I) species during HPA chemisorption on malachite surfaces, accompanying P(III) oxidation to P(V) species of HPA.Absorption model of HPA on the surface of malachite.Download full-size image

•A novel bifunctional catalyst for MIBK synthesis was proposed.•It exhibited 75% MIBK selectivity and 60% acetone conversion.•A high stability of bifunctional catalyst was observed.We report here an efficient bifunctional catalyst of TiO2 coating and supported Pd on cordierite (T500/Cor&Pd/Cor) for one-pot synthesis of MIBK from acetone. The obtained 75% MIBK selectivity at 60% acetone conversion was the best performance ever reported for metal oxide based catalyst, without obvious deactivation for at least 12 h on stream. The superior performance of T500/Cor&Pd/Cor could be attributed to the dominant base sites and moderate acid sites on TiO2 coating caused by the nanoscale anatase crystallite, and its combination style of being physically mixed with Pd.

In order to get close-packed hydrophobic molecular monolayer, surface modification of ilmenite was carried out with cupric ions. As it was found by zeta potential and XPS measurement, the cupric ions modification occurs via ion exchange, metal hydroxides adsorption, and redox processes. After modifying by cupric ions, ilmenite surface properties became more active and the adsorption amount of α-hydroxyoctyl phosphinic acid (HPA) increased. As expected, the flotation behaviour of ilmenite improved. XPS measurements verified the ability to establish a covalently attached HPA on the surfaces of ilmenite after Cu(II) activation. The findings of this study will provide a fundamental basis for strengthening flotation.Two-step sequential method depicting modification of ilmenite surfaces with Cu(II) and HPA. The method is analogous to formation of more intensive HPA monlayers on ilmenite.Download full-size image

•Amide hydroxamate was first introduced as a collector for Ca minerals flotation.•Amide hydroxamates exhibited superior affinity to scheelite against calcite.•Amide hydroxamates owned unique bond patterns and double hydrophobic groups.•Amide hydroxamates formed intermolecular hydrogen bonds on scheelite surfaces.In this paper, novel amide-hydroxamic acid surfactants, such as (N-(6-(hydroxyamino)-6-oxohexyl) benzamide (NHOB), N-(6-(hydroxyamino)-6-oxohexyl) octanamide (NHOO), N-(6-(hydroxyamino)-6-oxohexyl) decanamide (NHOD) and N-(4-(hydroxyamino)-4-oxobutyl) octanamide (NOBO), were introduced as flotation collectors for selective separation of scheelite from calicite. The micro-flotation results demonstrated that compared to NHOO, NOBO and NHOB, NHOD exhibited superior collecting power to scheelite and enabled the separation of scheelite and calcite under pH around 10. The calculation results of density functional theory (DFT) and C log P (octanol–water partition coefficient) indicated that NHOD owned excellent hydrophobicity and affinity to scheelite surfaces. The analyses of FTIR spectra, zeta potential and XPS illustrated that besides the electrostatic attraction with Ca cationic species on scheelite surfaces, NHOD might chemisorb onto scheelite by formation of NHOD-W surface complexes, resulting in a superior selectivity to scheelite compared with calcite. NHOD's unique properties, such as characteristic bond patterns on scheelite surfaces, double hydrophobic groups, and intermolecular hydrogen bonds between neighboring molecules coated on scheelite surfaces, rendered it to be a superior collector for scheelite/calcite flotation separation.Download full-size image