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The recovery of scheelite from calcium-bearing carbonate ores by foam flotation is challenging due to its low separation efficiency. This study investigated the effect of pentasodium diethylenetriaminepentaacetate (PD) on the surface properties of scheelite and fluorite. For this purpose, we performed micro-flotation tests and carried out zeta potential measurements, as well as Fourier transform infrared (FT-IR) and X-ray photoelectron (XPS) spectroscopic measurements, in order to analyze the surface properties of these minerals. The addition of PD as a novel depressor significantly improved the effect of fluorite and sodium oleate (NaOl) on the flotation-based scheelite recovery and separation from fluorite. PD was spontaneously adsorbed onto fluorite through electrostatic and chemical adsorption. By contrast, PD did not appear on the scheelite because of the reaction conditions, surface site, and steric hindrance. X-ray photoelectron spectroscopy measurements and a solution chemistry analysis were used for the determination of the PD-selective adsorption mechanism and key factors derived from multi-layer adsorption onto fluorite, which completely hindered that of NaOl. [ABSTRACT FROM AUTHOR]

In this study, the effect of phytic acid (PA) on the surface properties of scheelite and fluorite was systematically investigated. PA was spontaneously adsorbed onto fluorite through electrostatic and chemical adsorption. By contrast, PA did not appear on the scheelite due to the reaction conditions, surface site, and steric hindrance. XPS measurements were utilized together with a solution chemistry analysis to understand better both the PA selective adsorption mechanism and the key factors derived from multi-layer adsorption onto fluorite, which was found to hinder completely that of NaOl. [ABSTRACT FROM AUTHOR]

In previous studies, by regulating the Pb/BHA ratio and pH, lead complexes of benzohydroxamic acid (Pb-BHA) have been proven to be selective for the separation of scheelite from calcium minerals. In this study, sodium silicate (Na 2 SiO 3 ) and Al-Na 2 SiO 3 polymer were used as depressants for the further separation of scheelite from calcite. Flotation results indicated that both scheelite and calcite were depressed by Na 2 SiO 3 , while Al-Na 2 SiO 3 polymer gave good selectivity. The depressing ability of Na 2 SiO 3 for calcite was significantly improved due to the formation of some Al-Na 2 SiO 3 species with aluminum ions, while the reverse was true for scheelite. Zeta potential results indicated that both colloidal Na 2 SiO 3 and Al-Na 2 SiO 3 particles were negatively charged and difficult to adsorb on the negative scheelite surface through electrostatic attraction, especially for Al-Na 2 SiO 3. X-ray photoelectron spectroscopy analysis results showed that the Al-Na 2 SiO 3 adsorbed amount on the scheelite surface was less than the Na 2 SiO 3 adsorbed amount, while the reverse was true on the calcite surface. Binding energy analysis results indicated that calcium cations of scheelite and calcite surfaces could bond to oxygen atoms of Na 2 SiO 3 /Al-Na 2 SiO 3 through chemisorption. However, compared with Na 2 SiO 3 , Al-Na 2 SiO 3 showed weaker chemisorption on the scheelite surface, but adsorbed more powerfully onto the calcite surface. Therefore, Al-Na 2 SiO 3 showed excellent selectivity for scheelite and calcite, which has been successfully applied at the Shizhuyuan mine. [ABSTRACT FROM AUTHOR]

This research demonstrates an effective application of etidronic acid to improve the scheelite flotation efficiency and reduce the consumptions of energy and reagents. The cleaning recovery is significantly increased by 7%, and the cleaning cost is reduced by 17% accompanied with the efficient improvement of roughing grade from 1.22% to 1.68% compared with that in previous month. The depression abilities of etidronic acid, normal water glass, and acidified water glass for the scheelite roughing flotation are studied using laboratory-scale experiments. Etidronic acid shows an improved selective performance in improving the roughing grade. This performance is further verified by industrial test. The use of etidronic acid in the roughing circuit improves the product grade from 24.66% to 28.26%. The daily product output is also increases by 1.54 t. Economic evaluation results indicate that the heating cost is reduced by 28%, and the water glass consumption is decreased by 14%. An increased product profit of $1,248,000 and a reduced cost of $20,841 are also obtained. [ABSTRACT FROM AUTHOR]

To improve the floatability of tungsten minerals, lead ions (lead nitrate) were used to modify the surface properties of the minerals and benzohydroxamic acid (BHA) was used as a collector in the flotation system. Pb 2+ -BHA complexes are inevitably present in this process and the role of it is unclear. This investigation is going to describe a new approach and the mechanism of catalyzing BHA adsorption onto scheelite by lead ions. Chemical speciation, zeta potential, FTIR, and XPS studies were conducted to establish the important role of lead ions. Indeed, Pb 2+ -BHA complexes were shown to be the active species responsible for flotation. The speciation and zeta potential results showed the presence of the adsorbed Pb 2+ -BHA complexes on the scheelite. The XPS results for atomic composition and binding energies confirmed Pb 2+ -BHA species adsorbed on the scheelite surface, which contributed to more adsorption of BHA. The new method would increase the recovery of scheelite, simplify the flowsheet and reduce the processing cost. [ABSTRACT FROM AUTHOR]

The similar flotability of scheelite, fluorite, and calcite resulted in the difficult separation by flotation. This work revealed the effect of water glass on the flotation of scheelite by FTIR and the wettability change of the usual cleavage plane, and proved that water glass inevitably influenced the flotation of tungsten minerals to a large extent in traditional fatty acid flotation process. A new collector, lead complexes of benzohydroxamic acid, was found to be selective for the separation of scheelite and calcium minerals with little water glass. Hence a novel flotation process was developed for the recovery of tungsten minerals in Shizhuyuan Mine in China. Normal temperature flotation of tungsten minerals was developed to instead of the classical “Petrov's process” for scheelite-calcite-fluorite type ores. Compared with the traditional process, the recovery was improved by almost 10% and the grade of scheelite concentrate was above 55%. The disappearance or decreasing of water glass contributed to improving the recovery of tungsten and the circulation of water and reagents. [ABSTRACT FROM AUTHOR]

Abstract: Anisotropic surface broken bond densities and surface energies of six surfaces of scheelite were calculated with density functional theory (DFT). The calculation results show that its surface energy is directly proportional to its surface broken bond density. {112} and {001} surfaces are the two predominant cleavage or exposed planes. The prediction of morphology is well consistent with our experimental observations based on XRD. Anisotropic adsorption behaviors and wettability of these two surfaces after being immersed in sodium oleate and DDA solutions were studied by means of contact angle measurement, AFM and flotation test. The contact angle values at a given NaOl concentration decreased in the order {112}>{001}. As for DDA, similar wettability for the two surfaces was observed. The results were interpreted by AFM and interaction energies for the adsorption of surfactants on each surface calculated in accordance with molecular dynamics (MD) simulation. [Copyright &y& Elsevier]

This study presents a highly selective reagent system that utilizes sodium hexametaphosphate (SHMP) to improve the separation of scheelite from calcite and fluorite using an anionic–nonionic collector. The recoveries of calcite and fluorite decreased to 20% as the SHMP dose exceeded 6 × 10−6 mol/L, whereas that of scheelite remained at 85%. The interaction mechanisms of minerals with SHMP were investigated through equilibrium speciation, Zeta potential, Fourier transform infrared spectrometry, and X-ray photoelectron spectroscopy analyses. SHMP exists as hydrogen phosphate anion in the aqueous solution with a pH of 7–12. Moreover, it may be adsorbed intensively on the positively charged surfaces of calcite and fluorite via electrostatic force or chelation with calcium ion to impede further adsorption of the assembled collector. By comparison, the adsorption of SHMP is feeble on the scheelite surface because of its negative charge. The roughing grade of low-grade scheelite ore is substantially improved from 0.74% to 1.65% compared with that in the contrast test in the absence of SHMP. [ABSTRACT FROM AUTHOR]

The flotation separation of scheelite from calcite is problematic, where sodium silicate modified by polyvalent metal ions has shown some advantages for selective depression. In this study, an Al-Na2SiO3 polymer was used as the depressant for the flotation separation of scheelite from calcite using a lead complex of benzohydroxamic acid (Pb-BHA) as the collector. Furthermore, a number of measurements were conducted to investigate the structure of the Al-Na2SiO3 polymer and its adsorption behavior with Pb-BHA complexes on the mineral surface. Flotation experiments indicated that the Al-Na2SiO3 polymer shows good selectivity for the flotation separation of scheelite from calcite at pH 8, where the optimum ratio of sodium silicate to aluminum sulfate was 2:1. Fourier-Transform Infrared (FTIR) and solution chemical analyses revealed that aluminum hydroxide complexes and the hydroxy moiety of silicic acid are able to self-assemble via condensation affording an Al-Na2SiO3 polymer, i.e., a composite aluminosilicate polymer. The zeta potential measurements and adsorption capacity measurements indicated that, upon adsorption of the Al-Na2SiO3 polymer and Pb-BHA complexes on the mineral surface, the Al-Na2SiO3 polymer had less influence on the adsorption of Pb-BHA complexes on the scheelite surface, while the opposite was true for calcite. Therefore, more Pb-BHA complexes and fewer Al-Na2SiO3 polymers were deposited on the scheelite surface, while fewer Pb-BHA complexes and more Al-Na2SiO3 polymers were adsorbed on the calcite surface. The selective separation of scheelite from calcite was attributed to the cooperative selectivity of the Pb-BHA complexes and Al-Na2SiO3 polymer. [ABSTRACT FROM AUTHOR]

An efficiently optimized reagent regime was investigated to improve scheelite heating flotation. The scheelite grade and recovery in the plant were significantly improved by 5% and 6%, respectively, which remarkably augmented the economic profit by $260,000 per month. The interaction mechanisms of sodium sulfide and sodium oleate with scheelite, calcite and fluorite were evaluated by adsorption amount and Fourier transform infrared (FTIR) analyses. Sodium sulfide exhibited an excellent ability to promote the adsorption and desorption of sodium oleate on the scheelite surface and from the calcite and fluorite surfaces, thus facilitating the separation of scheelite from fluorite and calcite. [ABSTRACT FROM AUTHOR]

Pb–BHA complexes have been shown to be selective for the separation of tungsten and cassiterite minerals from calcium minerals. These minerals could be enriched synchronously to some extent using Pb–BHA complexes flotation. However, it is difficult to further improve the quality and recovery of the scheelite, wolframite, and cassiterite concentrate due to their different behavior in flotation, such as flotation rate and sensitivities to depressants. Moreover, the super fine particles create some challenges for the cleaning flotation process. In this study, advanced gravity separators for super fine particles were introduced for the cleaning process based on the slight difference in the specific gravity of scheelite, wolframite, and cassiterite. The new process featured pre-enrichment using Pb–BHA flotation, and upgrading using gravity separation, taking into account both the similarities and differences in floatability and density of the different minerals. The grades of WO3 and Sn in the concentrate of the new process reached to 61% and 2.89%, respectively, and the recovery of Sn was significantly improved. In addition, gravity separation is highly efficient, cost effective, and chemical-free, which is environmentally friendly. This study has proven that physical separation can be used for the purification of flotation products and provide some solutions for separation problems of complex refractory ores, which has, up until now, been rarely reported in the literature and/or applied in mineral processing. [ABSTRACT FROM AUTHOR]

This study investigates the effects of silicate removal from recycled wastewater on scheelite flotation performance. Systematic experiments were conducted to identify and evaluate the mechanisms underlying the influence of sodium silicate on scheelite flotation and silicate removal. When the sodium silicate concentration exceeds 1 × 10 −2  mol/L, scheelite recoveries decrease from 80% to 20% because excess sodium silicate strongly competes with sodium oleate for adsorption sites on the scheelite surface. Under treatment with 5 g/L calcium chloride, silicate removal can reach 90%, and system pH decreases from 12.5 to 11. The reduction of system pH to the range of 11–9 is conducive to promote silicate polymerization and improve silicate removal. The micromorphology and crystal structure of the precipitates that formed under different reaction pH levels were analyzed through scanning electron microscopy coupled with energy dispersive spectrometry, X-ray diffraction, and Fourier transform infrared. The results of these analytical tests confirm that calcium chloride removes silicate through the formation of amorphous calcium silicate hydrate precipitates with low crystallinity. Continuous pilot-scale tests on recycled wastewater treatment and reuse further demonstrate the feasibility and stability of silicate removal. Silicate removal can reach 90%, and system pH can decrease from 11 to 9.5. The use of treated water increases scheelite roughing grade from 0.47% to 0.63% and improves scheelite recovery by 5%. [ABSTRACT FROM AUTHOR]

Cationic flotation is a promising method for separating scheelite from calcite at room temperature, because of the significant difference between their surface charges. Three quaternary ammonium salts, i.e., didecyldimethylammonium chloride (DDAC), trioctylmethylammonium chloride (TOAC), and dodecyltrimethylammonium chloride (DTAC), were investigated as cationic collectors in the flotation of scheelite from calcite. The flotation behaviors of scheelite and calcite with the three quaternary ammonium salts were studied using single-mineral and mixed-mineral flotations; flotation with oleate was used for comparison. The results show that flotation of scheelite from calcite was possible around pH 8 with DDAC and TOAC as collectors. The collecting powers and selectivities of these compounds for scheelite were higher than those of oleate. The molecular structures, Fourier-transform infrared spectra, and zeta potentials indicated that when quaternary ammonium salts are used as collectors, electrostatic interactions play a primary role in the flotation of scheelite from calcite. The adsorptions of the three quaternary ammonium salts fitted a general adsorption isotherm well, but the Langmuir isotherm only fitted the adsorption of DDAC well. It can be concluded from the adsorption isotherm parameters that the role of van der Waals forces is as significant as that of electrostatic forces in the interactions of quaternary ammonium salts with the two minerals, and that the selectivities of the quaternary ammonium salts for scheelite result from their large van der Waals forces, as well as the opposite charges on scheelite and calcite. The van der Waals forces of quaternary ammonium salts significantly affect the adsorption processes and consequently the isotherm plots. [ABSTRACT FROM AUTHOR]

In this work, the adsorption behavior of dodecylamine (DDA) on scheelite and calcite mineral surfaces were investigated by molecular dynamics (MD) simulation, zeta potential measurement, AFM observation, contact angle measurement, and flotation test. The results implied that, the different adsorption behavior of DDA on scheelite and calcite surfaces was mainly attributed to cationic species RNH 3 + of DDA. The adsorption of neutral species RNH 2 and complex precipitates produced by the reactions between RNH 3 + and anionic species released by both mineral surfaces, also played important roles. In a DDA solution (1 × 10 −4 mol/L, pH 7.5–8.0), a handful of RNH 2 of DDA adsorbed on both scheelite and calcite surfaces through N–Ca bonding and hydrogen bonding between hydrogens of –NH 2 group and mineral surface oxygens. On positively charged calcite surface, RNH 3 + adsorbed on a moderate number of CO 3 2 − sites through electrostatic attraction and hydrogen bonding, which caused a moderate zeta potential increase for calcite. On negatively charged scheelite surface, a large number of cationic species RNH 3 + could easily adsorb on abundant WO 4 2 − sites, which caused a significant increase of zeta potential for scheelite. The different adsorption behavior led to a heavier monolayer coverage of DDA species on scheelite surface, and thus a more hydrophobic surface and a better flotation recovery of scheelite. The present work helps propose a new adsorption model of DDA on scheelite and calcite. [ABSTRACT FROM AUTHOR]

• Petrov's process is complex, costly and difficult to control. • Scheelite was selectively separated from fluorite using Pb-BHA complexes. • Adsorption mechanism of Pb-BHA complexes was studied. • A simplified flotation process was developed. • New process is beneficial to improving the recovery and water treatment. It is difficult to separate scheelite especially from fluorite with fatty acid collectors because the adsorption mechanism of these collectors occurs through chemisorption of the oleate ion onto the mineral surface. A simplified flotation process using Pb-BHA complexes was developed to replace the energy-inefficient Petrov's process of using a fatty acid, increasing the recovery of scheelite and reducing the cost. The relationship between surface chemical properties (crystal chemistry, solubility, and Zeta potential) of minerals and flotation by using a fatty acid or Pb-BHA complexes was studied in detail to provide new insights into the selective separation mechanism. The results indicate that the scheelite surface exposes more O atoms than Ca and that they are negatively charged due to the anisometric dissolution of Ca and WO 4 , which provides the possibility for separation using selective interfacial reaction. The Fourier Transform infrared spectroscopy (FTIR) and Zeta potential results indicate that both chemical and electrostatic adsorption play an important role in the adsorption of Pb-BHA complexes on the scheelite surface. The X-ray photoelectron spectroscopy (XPS) results of the atomic composition and binding energies confirmed the presence of the adsorbed Pb-BHA complexes and that Pb, O and Ca may be the active adsorption sites. Therefore, scheelite was able to be collected by forming either a Ca-O-Pb-collector or W-O-Pb-collector (BHA). However, fluorite was only able to be collected by a fatty acid collector and colloidal [H 2 SiO 3 ] n −, and a high temperature was needed improve the selective desorption of the adsorbed fatty acid collector by forming Ca-[H 2 SiO 3 ] n − on the fluorite surface, resulting in serious problems in industry. However, the Pb-BHA complexes significantly contribute to improving the recovery of scheelite minerals, simplifying the flotation process, and circulation of the residual reagents and water. [ABSTRACT FROM AUTHOR]

A selective organic depressant was investigated to promote the separation of scheelite from calcite and fluorite. 1-Hydroxyethylidene-1, 1-diphosphonicacid (HEDP) could efficiently reduce the recoveries of calcite and fluorite to less than 20%, while that of scheelite remained above 85%. The selective interaction mechanism was demonstrated via Zeta potential and X-ray photoelectron spectroscopy (XPS) analyses. The conceivable adsorption models of reagents on mineral surfaces were constructed to explain their adsorption mechanism. HEDP exhibited an excellent ability to selectively depress calcite and fluorite attributed to the intense adsorption on their surfaces, whereas its adsorption on scheelite surface was feeble. The technology feasibility of using HEDP to improve the scheelite flotation performance was verified through laboratory and industrial tests. The roughing grade was dramatically improved from 1.22% to 1.68%, and the product grade was enhanced from 24.66% to 28.26% with a noteworthy improvement of cleaning recovery by 6.93%, which would produce a considerable economic benefit. [ABSTRACT FROM AUTHOR]

Highlights • Surface transformation occurred on calcite and fluorite surface. • Surface transformation may be beneficial to the flotation separation. • A fluorite film formed on calcite surface in presence of fluorite particles. • Fine fluorite particles are better than fluoride ion. • Fluorite film prevents the adsorption of Pb-BHA complexes. Abstract Lead complexes of benzohydroxamic acid (Pb-BHA complexes) have been successfully applied to the industrial separation of scheelite from calcite and fluorite minerals. However, the separation of scheelite from calcite using Pb-BHA complexes in the absence of fluorite is difficult. In flotation tests, both sodium fluoride and fluorite particles have been shown to depress calcite but not scheelite. Therefore, fluoride ions from the dissolved fluorite particles play an important role in the flotation separation of scheelite from calcite. In the current study, the results of zeta potential analysis confirmed that fluoride ions are strongly adsorbed on calcite surfaces and that the point of zero charge for calcite shifts to that of fluorite. X-ray photoelectron spectroscopy and atomic force microscopy analyses clearly indicated that the fluoride ions are adsorbed on the calcite surface to form a fluorite film. Thus, this type of surface transformation shows promise as a strategy for the flotation separation of semi-soluble minerals. [ABSTRACT FROM AUTHOR]

Metal ions are widely used as activators in the flotation of oxidised minerals. At the same dosage of collector, the recovery of target minerals (cassiterite, scheelite, wolframite and ilmenite) can be evidently improved with the addition of metal ion activator. Adsorption of metal ions and their hydroxides can provide attractive sites for collector attachment, contrary to bare minerals that exhibit considerably low affinity towards the collector. Iron complexes of benzohydroxamic acid (BHA) are formed during the reaction of ferric chloride with BHA in the solution. These complexes also exhibit strong collecting ability towards cassiterite in the flotation, which contradicted the classical theory that the activator must be added before the collector. However, the major active component and the underlying adsorption mechanism of the Fe-BHA complexes are still unknown. In this study, the solution chemistry calculation has been used to identify the major active components of the Fe-BHA complexes. Accordingly, a preferred adsorption model of the Fe-BHA complexes onto the cassiterite surface has been proposed and proven effective, through first-principles calculations based on density functional theory, flotation experiments and adsorption tests. Our results might shed new light on the activation mechanism of metal ions in mineral flotation. [ABSTRACT FROM AUTHOR]

The efficient separation of scheelite from calcium-bearing minerals, especially calcite, remains a challenge in practice. In this work, a novel reagent scheme incorporating a depressant of sodium hexametaphosphate (SHMP) and a collector mixture of octyl hydroxamic acid (HXMA-8) and sodium oleate (NaOl) was employed in both single and mixed binary mineral flotation, and it proved to be highly effective for the separation. Furthermore, the role of the pH value in the separation was evaluated. Additionally, the mechanism of the selective separation was investigated systemically via zeta potential measurements, fourier transform infrared (FTIR) spectroscopy analysis, X-ray photoelectron (XPS) spectroscopy analysis and crystal chemistry calculations. It turns out that the selective chemisorption of SHMP on calcite (in the form of complexation between H 2 PO 4 − /HPO 4 2− and Ca 2+ ) over scheelite is ascribed to the stronger reactivity and higher density of Ca ions on the commonly exposed surfaces of calcite minerals. The intense adsorption of HXMA-8 on scheelite over calcite due to the match of the O O distances in WO 4 2− of scheelite and CONHOH of HXMA-8 holds the key to the successful separation. We were also interested in warranting the previous claim that NaOl is readily adsorbed on both minerals via chemisorption. Our results provided valuable insights into the application of mixed collectors and an effective depressant for flotation separation. [ABSTRACT FROM AUTHOR]

Sodium oleate (NaOl) has been widely used as a collector for the scheelite flotation. However, low selectivity of NaOl and large amount of sodium silicate (SS) needed remain tough problems. In this study, octyl hydroxamic acid (HXMA-8) was used as an associate collector with NaOl in scheelite flotation. The flotation tests showed that a novel reagent scheme, i.e., a lower dosage of SS (300 mg/L) and mixed collectors of HXMA-8 + NaOl (total concentration 4.5 × 10 − 4 mol/L, preferred mass ratio of 1:2) achieved the selective separation of scheelite from calcite. Zeta potential measurements indicated that the depressant, SS, adsorbed more strongly on calcite surface than on scheelite surface. HXMA-8 adsorbed significantly on scheelite surface either in the absence or presence of SS by chemical bonding between oxygens of HXMA-8 and surface metal ions. NaOl also adsorbed on both mineral surfaces by chemisorption, but the adsorption on calcite surface was influenced adversely by the presence of SS. [ABSTRACT FROM AUTHOR]

Collector 733, a sodium soap (C 12 – 16 COONa) is widely used industrially for scheelite flotation. Low selectivity of 733 collector is always observed. In this study, a collector mixture of 733 and MES (sodium fatty acid methyl ester sulfonate) demonstrated a high selectivity for the flotation of scheelite from calcite and fluorite. An optimal mass ratio 4:1 of 733:MES was found, producing a 65.76% WO 3 concentrate grade with a recovery of 66.04% from a feed material containing only 0.57% WO 3 . In addition, the effect of water hardness and water glass addition were studied. The results indicated that the presence of Ca 2+ or Mg 2+ had little effect on the adsorption of the collector mixture at the scheelite surface. Addition of water glass for depressing calcite and fluorite had no significant effect on the adsorption of the collector mixture on the scheelite surface. The advantages of this new collector mixture (733+MES) include lower cost, low dosage, high tolerance against water hardness and high selectivity, and this collector mixture has great potential for industrial application. [ABSTRACT FROM AUTHOR]

In this study, flotation behavior of scheelite and calcite was investigated using mixed cationic/anionic collectors of dodecylamine (DDA) and sodium oleate (NaOL). Individual NaOL or DDA was also tested for comparison. The flotation results of single mineral and mixed binary minerals demonstrated a high selectivity and recovery for the flotation of scheelite from calcite at pH 7 using mixed DDA/NaOL collectors. The adsorption mechanism of the selective separation was analyzed through zeta potential measurement. [ABSTRACT FROM AUTHOR]