Sustainable and efficient extracting of tin and tungsten from wolframite – scheelite mixed ore with high tin content

Lin S., Liu R., Li W., Sun W., Hu Y.

Sulfur removal from mineral concentrates is urgently needed given the increasingly stringent environmental regulations and low−sulfur feedstocks required by smelters. However, current desulfurization technologies suffer from considerably drawbacks, such as high costs and harmful byproducts. In this study, we investigated the potential use and feasibility of reverse flotation to desulfurize sulfur−rich tungsten concentrates. Several important factors were evaluated by batch flotation tests. Results proved that sulfur could be effectively removed from sulfur−rich tungsten concentrates by carefully adjusting pH and reagent dosages. Industrial−scale tests conducted in Shizhuyuan Polymetallic Dressing Plant showed that reverse flotation was a feasible and reliable desulfurization method to remove sulfur and increase the grade of tungsten concentrates simultaneously. The average sulfur content in tungsten concentrates decreased from 4.53% to 1.77%. The average WO3 grade of tungsten concentrates increased from 37.50% to 41.14%. The low cost and environmental friendliness of this reverse flotation desulfurization technology indicated its potential for commercialization and widespread industrial application.

Soloviev S.G., Kryazhev S.G., Dvurechenskaya S.S.

The Maikhura W-Sn skarn deposit is situated in the Gissar Segment of the Southern Tien Shan. It associates with a Late Carboniferous-Early Permian composite granitoid pluton, which includes earlier ilmenite-series, transitional metaluminous to peraluminous, I-type granodiorite, and later magnetite-series, biotite to biotite-tourmaline granite/leucogranite. The oxidized granitic intrusions exhibit A-type granite affinity and define a geochemically and genetically distinct group of W-Sn deposits. The deposit incorporates both pyroxene- and garnet-dominant prograde and retrograde skarns with scheelite and locally magnetite, overprinted by highly reduced (pyrrhotite-stable) post-skarn mineral assemblages of hydrosilicate and phyllic alteration stages, containing scheelite, cassiterite and sulfides. The fluid inclusions data indicate the involvement of carbonic-free aqueous, moderately-saline (9.9–16 wt% NaCl-eq.), high-pressure (2.1 ± 0.5 kbar), hot fluid, which was sourced from crystallizing magma and formed prograde calcic skarn. This fluid evolved into a sodic-chloride, slightly less saline (8.6–11 wt% NaCl-eq.), lower-pressure (1.7 ± 0.5 kbar), cooler fluids toward the retrograde skarn stage; this stage was characterized by deposition of scheelite in association with magnetite. The hydrosilicate (propylitic) alteration was formed from a low salinity, Ca-enriched, homogenous aqueous-carbonic (methane-rich) fluid at lower temperatures (∼350–400 °C), with precipitation of scheelite and cassiterite, particularly in phlogopite-chlorite-oligoclase-quartz assemblage. Corresponding pH decrease explains the trend toward overlapping fields of insoluble cassiterite and scheelite. The phyllic alteration assemblages were formed from a boiling aqueous-carbonic (CO2-dominated), low-salinity fluid at temperatures of ∼310–250 °C and pressure of 1.85 ± 0.1 kbar. The alteration evolving from chlorite- through muscovite- to albite-dominant paragenesis indicates a trend toward higher pH (less acidic) conditions and was accompanied by precipitation of scheelite and cassiterite, with further deposition of sulfides. A homogeneity of δ34S values suggests sulfur isotope homogenization in a magmatic chamber, whereas their proximity to the meteorite standard supports a magmatic source of sulfur. The depletion in heavy sulfur isotope of sulfides from hydrosilicate (propylitic) alteration (δ34S = +1.8 to +0.7‰) to sulfides from phyllic alteration (δ34S = −0.1 to −0.8‰) is consistent with the evolution from ilmenite-series to magnetite-series magmatic source.

Shen L., Li X., Zhou Q., Peng Z., Liu G., Qi T., Taskinen P.

To directly obtain solution of (NH4)2WO4 instead of Na2WO4 is the key for developing a cleaner technology of ammonium paratungstate production. In this paper, ammoniacal ammonium carbonate solution was adopted for leaching tungsten from the converted product, a mixture of H2WO4 and CaSO4 obtained by treating scheelite with sulfuric acid. The research indicates that tungsten can be efficiently extracted in form of ammonium tungstate solution with WO3 leaching yield of >99.5% under moderate leaching conditions. The WO3 leaching yield is influenced by the transformation of calcium sulfate to calcium carbonate due to forming CaWO4 through the secondary reaction between CaSO4 and (NH4)2WO4, whereas an excess (NH4)2CO3 (≥0.64 mol/L) can suppress the secondary reaction by facilitating the transformation. Additionally, the consumed ammonium carbonate can be recovered by treating the leaching residue with ammonium sulfate solution at above 70 °C. This work presents a cleaner and sustainable technique for producing ammonium paratungstate, with circulating the leaching reagents and bypassing the conversion of Na2WO4 to (NH4)2WO4.

Zulhan Z., Ryanta I.G.

Pyrite is very commonly used as a source of sulfur for converting tin oxide from tin smelting slag or low-grade tin ore/concentrate into tin sulfide by means of a tin fuming process to increase the overall tin recovery in a tin smelting plant. The conversion of tin sulfide into tin oxide as final product of a tin fuming process produces sulfur dioxide, which is captured by spraying of calcium hydroxide, producing gypsum as the byproduct. To reduce the footprint of pyrite mining activity and to reduce the environmental impact, the recycling of sulfur from gypsum byproduct as a fuming agent to substitute pyrite was studied in this research. The FactSage™ thermodynamic software was applied to simulate the performance of tin fuming by addition of gypsum. The experiments were conducted in a muffle furnace for 1 h at 1100, 1200, and 1300 °C. The experimental results showed that a gypsum addition of 20% into tin smelting slag containing 10.44% Sn (S/Sn ratio = 1.3) yields a tin volatilization of 81.2% at 1200 °C. The addition of more gypsum lowers the degree of tin volatilization.

Zhang R., Lehmann B., Seltmann R., Sun W., Li C.

Li Y., Yang J., Zhao Z.

With most high-quality tungsten ores being exhausted, the enhancement of low-grade scheelite concentrates processing has attracted a great deal of attention. The objective of this study is to develop a method to maximize the recovery tungsten and molybdenum from a low-grade scheelite via a new acid leaching process followed by solvent extraction. Under optimal conditions (350 g/L H2SO4, 95°C, and 2 h), approximately 99.8% of tungsten and 98% of molybdenum were leached out. In the subsequent solvent extraction process, more than 99% of the tungsten and molybdenum were extracted with a co-extraction system (50% TBP, 30% HDEHP, and 10% 2-octanol in kerosene) using a three-stage cross-flow extraction. The raffinate can be recycled for the next leaching process after replenishing the H2SO4 to the initial value (approximately 350 g/L). Based on these results, a conceptual flowsheet is presented to recover tungsten and molybdenum from the low-grade scheelite.

Zhang R., Lu J., Lehmann B., Li C., Li G., Zhang L., Guo J., Sun W.

The large low-grade Piaotang W–Sn deposit in the southern Jiangxi tungsten district of the eastern Nanling Range, South China, is related to a hidden granite pluton of Jurassic age. The magmatic-hydrothermal system displays a zonation from an inner greisen zone to quartz veins and to peripheral veinlets/stringers (Five-floor zonation model). Most mineralization is in quartz veins with wolframite > cassiterite. The hidden granite pluton in underground exposures comprises three intrusive units, i.e. biotite granite, two-mica granite and muscovite granite. The latter unit is spatially associated with the W–Sn deposit. Combined LA-MC-ICP-MS U–Pb dating of igneous zircon and LA-ICP-MS U–Pb dating of hydrothermal cassiterite are used to constrain the timing of granitic magmatism and hydrothermal mineralization. Zircon from the three granite units has a weighted average 206Pb/238U age of 159.8 ± 0.3 Ma (2 σ, MSWD = 0.3). The cathodoluminescence (CL) textures indicate that some of the cassiterite crystals from the wolframite-cassiterite quartz vein system have growth zonations, i.e. zone I in the core and zone II in the rim. Dating on cassiterite (zone II) yields a weighted average 206Pb/238U age of 159.5 ± 1.5 Ma (2 σ, MSWD = 0.4), i.e. the magmatic and hydrothermal systems are synchronous. This confirms the classical model of granite-related tin–tungsten mineralization, and is against the view of a broader time gap of >6 Myr between granite magmatism and W–Sn mineralization which has been previously proposed for the southern Jiangxi tungsten district. The elevated trace element concentrations of Zr, U, Nb, Ta, W and Ti suggest that cassiterite (zone II) formed in a high-temperature quartz vein system related to the Piaotang granite pluton.

Li J., Zhao Z.

Considering the strict environmental requirements and cost of energy consumption, a cheap and non-volatile agent (H 2 SO 4 ) was used to digest scheelite concentrate in the presence of phosphoric acid. In the digestion process, tungsten was completely leached in the form of a highly soluble 12-tungstophosphoric heteropoly acid (H 3 PW 12 O 40 ), and calcium remained in the residue as CaSO 4 •nH 2 O, which can be later used as cement raw materials. The effects of the leaching parameters, the concentrations of H 2 SO 4 and H 3 PO 4 , the temperature and the particle size, were analysed to model the kinetics of scheelite decomposition. The kinetics data were consistent with the shrinking-core model, and the apparent activation energy of 63.8 kJ/mol shows that the system was under chemical reaction control.

Li X., Xu X., Xu W., Zhou Q., Qi T., Liu G., Peng Z., Cui Y., Li J.

The conversion of tungsten-containing materials to a readily soluble substance in ammoniacal solution is significant in the development of a cleaning process for manufacturing ammonium paratungstate. In this work, Ca 3 −  x (Fe, Mn) x WO 6 (0  x  ≤ 1) was prepared by roasting a mixture of tungsten-containing materials and calcium carbonate. The leachability of the roasted products in aqueous ammonium carbonate solution was then tested. Thermodynamic analyses and experimental results showed that Ca 2 FeWO 6 and Ca 2 MnWO 6 can be obtained by roasting the mixture with appropriate ingredients in neutral or weakly reducing atmosphere, and Fe(II) in Ca 2 FeWO 6 can be substituted by Ca to form Ca 3 −  x Fe x WO 6 (0  x 3 W 3 C and Mn 3 W 3 C can be generated. Additionally, leaching results showed that Ca 3 −  x (Fe, Mn) x WO 6 had excellent leachability in aqueous ammonium carbonate solution with 99% WO 3 recovery. The results presented can be used to exploit a novel technique with recycling solutions for ammonium paratungstate production.

Bai X., Wang M., Jiang Y., Qiu H.

Dating ore minerals is the most direct method to determine the mineralization age of a deposit, but only a few ore minerals can be directly dated by traditional isotopic geochronometers. The aim of this study is to investigate the possibility of direct dating of the ore minerals cassiterite and wolframite from the Piaotang tungsten deposit using the 40Ar/39Ar stepwise crushing technique, comparing the age to coexisting K-rich muscovite dated by 40Ar/39Ar laser stepwise heating. The cassiterite, wolframite and muscovite samples were separated from four pieces of ore hand-specimens. The 40Ar/39Ar isochron ages of cassiterite and wolframite are concordant with ages of their coexisting muscovite, indicating that cassiterite and wolframite are suitable ore minerals for directly dating the ore-forming event by 40Ar/39Ar stepwise crushing.

Martins J.I.

A linear correlation between free energy and enthalpy for crystalline and soluble oxocompounds based in the Sverjensky–Molling equation is used to calculate the Gibbs free energies of formation of MnWO4 (−1172.48 ± 12.76 kJ mol−1), H2WO4 (−1006.91 ± 10.36 kJ mol−1), and Na2WO4 (−1455.39 ± 12.81 kJ mol−1). Using these data with the known thermodynamic data, the equilibrium constants for reactions of leaching of scheelite and wolframite in acidic and basic media were determined. The results show that the acid route based in relatively cheap inorganic acids is desirable for scheelite digestion, despite the diffusion problems concerned with tungstic acid developed on the solid particles. Meanwhile, wolframite may be operated under favorable thermodynamics conditions by alkaline and acid processes.

Zhang X., Song X., Sun Z., Li P., Yu J.

The reductive decomposition of calcium sulfate (CaSO4) to calcium sulfide (CaS) was one of the most important methods for anhydrite resource utilization. When CaSO4 was decomposed reductively by carbon monoxide (CO), usually there were CaS and/or calcium oxide (CaO) in the decomposition products of CaSO4 depending on the reaction temperature and reactant concentrations. In this paper, the mechanism of CaSO4 reductive decomposition by CO was studied in the framework of density functional theory (DFT). In the calculation, the exchange-correlation term was approximated by Perdew–Wang (PW91), a functional within the generalized gradient approximation (GGA) family. To study the interaction of CO and CaSO4, the transition states of CaSO4 decomposition and the minimum energy path (MEP) were analyzed. The results showed that the CaS product could be obtained when CaSO4 was reduced by CO with the 4:1 stoichiometric ratio of CO and CaSO4, and the decomposition of CaSO4 to CaSO3 was the rate-determining step, and ac...

Ma L., Niu X., Hou J., Zheng S., Xu W.

FactSage6.1 software simulation and experiments had been used to analysis the reaction mechanism and influence factors for CaS generation during the process of phosphogypsum decomposition. Thermodynamic calculation showed that the reaction for CaS generation was very complex and CaS was generated mainly through solid–solid reaction and gas–solid reaction. The proper CO and CO2 have benefit for improving the decomposition effects of phosphogypsum and reducing the generation of CaS at 1100 °C. Using high sulfur concentration coal as reducer, the proper reaction conditions to control the generation of CaS were: the coal particle size was between 60 mesh and 100 mesh, reaction temperature was above 1100 °C and the heating rate was 5 °C/min. Experimental and theoretical calculation indicated that the concentration of CaS was only ten percents in the solid product at 1100 °C, which is favorable for the further cement producing using solid production.

Lu H.-., Liu Y., Wang C., Xu Y., Li H.

The Shizhuyuan deposit, China, is a world-class W-Sn-Bi-Mo-F skarn deposit hosted by Devonian limestone in the thermal aureole of the Qianlishan granite complex. The Qianlishan complex comprises five separate intrusions, including fine-grained porphyritic biotite granite (182–187 Ma, granite 1), medium-grained biotite-K feldspar granite (158–163 Ma, granite 2), fine-grained biotite and K feldspar granite (granite 3), granitic porphyry (144–146 Ma, granite 4), and diabase (142 Ma). The upper part of the granite complex is characterized by extensive greisen alteration. Skarn zones distributed around the intrusions are mainly calcic, consisting of garnet, garnet-pyroxene, vesuvianite-garnet, and wollastonite-vesuvianite, progressively outward from the intrusion. Following the primary skarn formation, some of the skarn zones underwent retrograde alteration. The high garnet/pyroxene ratio and the diopside-rich and andradite-rich compositions of the pyroxene and garnet indicate that the skarn belongs to the oxidized type. Mineralization consists of Sn-Be veinlet ore (type I) in marble and porphyry, massive W-Bi-Mo-Sn skarn ore (type II), stockwork W-Sn-Bi-Mo-F ore (type III), and W-Sn-Mo-Bi greisen ore (type IV), mainly associated with granite 2. Emplacement of granite 2 was accompanied by late, intense fracturing characterized by stockwork mineralization (type III), which was superimposed on massive skarn and greisen zones. The stockwork ore consists mainly of greisen and skarn veins and veinlets with scheelite, wolframite, molybdenite, cassiterite, bismuthinite, and fluorite. The Sm-Nd method has been used to analyze the Sm-Nd concentration, and data for pyroxene and garnet in the massive skarn (type II ore) associated with granite 2 yields an isochron age of 157 Ma. This age corresponds closely to the age of granite 2. Fluid inclusion studies of four types of ore samples reveal four types of inclusions: aqueous two-phase inclusions, H2O-CO2 inclusions, gas-rich inclusions, and daughter mineral-bearing inclusions containing halite or calcite. Homogenization temperatures of fluid inclusions in skarn minerals range from 350° to 535°C. The homogenization temperatures of fluid inclusions in greisen and stockwork are lower than that in skarn, and range from 200° to 360°C. The fluid inclusion data indicate that there are two types of fluids associated with the massive skarn and greisen, having salinities from 26 to 41 wt percent NaCl equiv, and from 1 to 21 wt percent NaCl equiv, respectively. The high-salinity inclusions are daughter mineral bearing, whereas the low-salinity inclusions are dominantly aqueous with a few gas-rich inclusions. The results suggest the evolution of the ore-forming fluids either by immiscibility or by mixing between a high-temperature, high-salinity magmatic water and a low-temperature, low-salinity fluid such as meteoric water, consistent with previously published isotopic studies. The Shizhuyuan deposit is a multi-element skarn, highly enriched in W, Sn, Bi, Mo, and F. This is interpreted to reflect multiple sources and stages of mineralization, which, in turn, may account for the large size of the Shizhuyuan deposit.

Wood S.A., Samson I.M.

The characteristics of granitoid-related tungsten deposits hosted in siliceous (carbonate-free) rocks (e.g., Panasqueira, Cligga Head, Pasto Bueno) are reviewed and the ranges of physicochemical parameters of the ore-forming fluids are summarized. The two important tungsten minerals in these deposits are wolframite and scheelite, which were deposited mostly between 200° and 500°C and 200 and 1,500 bars. The salinities of the mineralizing fluids were typically less than 15 wt percent but commonly were significantly higher (up to 55 wt %). The two predominant dissolved components are Na+ and Cl– with subordinate Ca2+, K+, and carbonate species (\batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(CO_{3}^{2{\mbox{--}}}\) \end{document}/HCO3–). The contents of CO2 are highly variable, but XCO2 values typically range from 0 to 0.1. Limited pH and f O2 estimates indicate a moderately acidic fluid with oxygen fugacities between those of the QFM and HM buffers. These parameters were used to guide solubility and speciation modeling of W in hydrothermal fluids in granitoid environments. Experimentally derived thermodynamic data for scheelite, ferberite, aqueous Ca, Fe, and W species, and other required aqueous species were critically evaluated and the most reliable data were adopted. Where necessary, missing data were estimated. The resultant thermodynamic database provides a basis for solubility and speciation calculations in the system Ca-Fe-W-Cl-O-H. The simultaneous solubilities of scheelite and ferberite in NaCl-HCl-H2O solutions were calculated at temperatures from 200° to 600°C, pressures from 500 to 1,000 bars, pH from 3 to 6, and m NaCl from to 0.1 to 5.0 moles/kg H2O. The solubility model takes account of the species H+, OH–, Na+, Cl–, NaCl, HCl, NaOH, H2\batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(WO_{4}^{0}\) \end{document}, \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(HWO_{4}^{{\mbox{--}}}\) \end{document}, \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(WO_{4}^{2{\mbox{--}}}\) \end{document}, Fe2+, FeCl+, \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(FeCl_{2}^{0}\) \end{document}, FeOH+, FeO, \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(HFeO_{2}^{{\mbox{--}}}\) \end{document}, Ca2+, CaCl+, \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(CaCl_{2}^{0}\) \end{document}, CaOH+, \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(NaHWO_{4}^{0}\) \end{document}, and \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(NaWO_{4}^{{\mbox{--}}}\) \end{document}. The calculations indicate the following: (1) solubilities of scheelite and/or ferberite can attain values as high as hundreds to thousands of parts per million as the tungstate species H2\batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(WO_{4}^{0}\) \end{document}, \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(HWO_{4}^{{\mbox{--}}}\) \end{document}, \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(WO_{4}^{2{\mbox{--}}}\) \end{document}, \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(NaHWO_{4}^{0}\) \end{document}, and \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(NaWO_{4}^{{\mbox{--}}}\) \end{document}; thus, tungsten-chloride, -fluoride, or -carbonate complexes, or more exotic species are not required to transport sufficient W to form an ore deposit; (2) the tungsten concentration in equilibrium with scheelite and ferberite increases strongly with increasing temperature, increasing NaCl concentration and decreasing pH, but is only weakly dependent on pressure; (3) the Ca/Fe ratio of a solution in equilibrium with both scheelite and ferberite decreases strongly with increasing temperature, i.e., the field of stability of scheelite expands with increasing temperature; the implication, therefore, is that simple cooling of a solution with a constant Ca/Fe ratio cannot result in the replacement of ferberite by scheelite, and that field observations of the late-stage replacement of ferberite by scheelite require an increase in the Ca/Fe ratio concomitant with cooling; (4) the Ca/Fe ratio is relatively independent of pH; and (5) the effect of NaCl concentration on this ratio changes as a function of temperature and pressure. At less than 400°C the ratio is independent of, or decreases with, increasing NaCl concentration; at higher temperatures the ratio first decreases and then increases with increasing NaCl concentration. Experimental data on the solubility of scheelite and the Ca/Fe ratio of fluids in equilibrium with scheelite + ferberite, and which are not used in parameterizing our model, generally agree with the results of calculations performed using our thermodynamic database within an order of magnitude. However, our critical examination of available thermodynamic data reveals that significant uncertainty remains in several parameters (e.g., the solubility products of scheelite and ferberite and the association constants for alkali tungstate ion pairs). This uncertainty can only be reduced via carefully conceived, executed, controlled, and interpreted experiments, taking into account the various experimental pitfalls identified in this paper.

Chen Y., Huo G., Guo X., Chen J.

Kanari N., Diot F., Korbel C., Fosu A.Y., Allain E., Diliberto S., Serris E., Favergeon L., Foucaud Y.

Tungsten (W), a rare metal, is categorized as a Critical and Strategic Raw Material (CRM) by the European Union (EU), with the highest economic importance of all selected CRMs since 2014. Tungsten and its derivatives are extracted from their commercial raw materials, mainly wolframite [(Fe,Mn)WO4] and scheelite (CaWO4) ores. Subsequently to mining and mineral processing, the W ore is submitted to thermal treatment and hydrometallurgy under aggressive conditions (high pressure and temperature), which are usually applied for the extraction of tungsten compounds. This paper aims to investigate a thermal route for scheelite processing using various selected chemical agents, resulting in a W-bearing material that is capable of being leached under softer conditions. In this context, a thermodynamic study of the interaction between FeWO4, MnWO4 and CaWO4 and various chemical reagents is described. The thermochemical calculations and data modeling show that, among other considerations, the reaction of CaWO4 with magnesium chloride (MgCl2) can lead to the formation of magnesium tungsten oxide (MgWO4), which appears to be more easily leachable than CaWO4. Experimental tests of the reaction of scheelite with MgCl2 appear to validate the thermodynamic predictions with satisfactory process kinetics at temperatures from 725 to 775 °C.

Ali H.H., Dessouky O.K., Khoziem H.A., Nasir S., Hassan M.M.

Hu Y.

Zheng Q., Dong L., Shen P., Zhang T., Liu D.

Scheelite and cassiterite are common tungsten and tin oxide minerals that often coexist in nature. However, the similar oxidation degrees and solution and surface chemical properties of scheelite and cassiterite pose challenges to their flotation separation. Moreover, research in this area is currently limited. This study investigated the selective depression mechanism of gallic acid (GA) in the flotation separation of scheelite and cassiterite and successfully achieved the effective separation of the two minerals. Single mineral and artificially mixed mineral experiments were performed to analyze the flotation separation behavior of scheelite and cassiterite. The results revealed that in the absence of a depressant, scheelite and cassiterite exhibited recovery of 93.43 % and 89.72 %, respectively. After the addition of 5 × 10−4 mol/L GA to the mineral slurry, the grades of WO3 and Sn in the flotation concentrates were 48.93 % and 18.13 %, with recovery of 82.50 % and 31.62 %, respectively. Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, zeta potential, adsorption amount, contact angle, and atomic force microscopy imaging analyses were conducted to examine the selective depression mechanism of GA in the flotation separation of scheelite and cassiterite. In the slurry, the cassiterite surface provided active Sn sites for the chemical adsorption of GA. Moreover, the phenolate O- donor atoms of the deprotonated polar groups of GA will undergo coordination with metal ions and then adsorb on the mineral surface. GA forms metal gallate through adsorption of its –COOH and –OH groups on mineral surface and produces textured oxide layer rich in OH groups, thus reducing the surface hydrophobicity of cassiterite and then depressing cassiterite. The selective adsorption of GA on the cassiterite surface hindered the further adsorption of NaOL, thereby reducing its surface hydrophobicity. Therefore, GA finally realized the flotation separation of the two minerals.

Hutabarat I., Maryono, Rudiyansah, Ramadan D.F., Wigyantoro K.

Tungsten minerals which are major as Wolframite and Scheelite mineral are by-product minerals of Tin mineral known as Cassiterite. Tin minerals are mostly found in Bangka Island which is one of the islands in the Southeast Asian tin belt that makes Indonesia the largest Tin (Sn) producer in the world. This research aims to characterize the mineralogy of Tungsten and associated minerals for potential mineral processing to gain the Tungsten concentrates. The Tungsten minerals were collected from the eastern edge of Klabat Granite in Toboali District, South Bangka. The Tungsten minerals were magnetically separated up to 14000 Gauss. The magnetic and non-magnetic fractions were identified to analyze the associated mineral of Tungsten with SEM analysis. The associated minerals in the Tungsten mineralization system in Toboali were found along with Silicates, Oxides, Sulphides, and Carbonates where Silicates dominated up to 91.8% of the non-magnetic minerals while Wolframite presence up to 0.9% in the non-magnetic fraction. At magnetic fraction found that Silicates dominates also up to 84.6% while Wolframite existed at 1.1%. The results of element deportment in the non-magnetic fraction show that Tungsten is associated with iron minerals and also in liberated form. The potential Tungsten mineral is Wolframite (Fe,Mn) WO4 in the magnetic and non-magnetic fraction. Mineral locking at P100 size 18.8 μ. shows that 84.4% Wolframite was locking with 3 (three) other minerals, 10.4% locking with 2 (two) other minerals, and only 4.8% Wolframite was 100% free in the magnetic fraction while in non-magnetic fraction P100 size 31.5 μ 77.5% Wolframite was locking with 3 (three) other minerals 18.3% locking with 2 (two) other minerals and only 4.2% Wolframite was 100% free. The processing concept is to liberate Tungsten from the associated minerals either with comminution or a combination of roasting alkali and leaching process and concentrate it up to marketable Tungsten concentrates.

Zhao G., Liu S., Qi J., Yang L., Liu G.

To improve the flotation recovery of tungsten minerals, 4-alkoxy benzohydroxamic acids containing C3 alkyl (C3OBs), namely 4-propoxy benzohydroxamic acid (POB), 4-iso-propoxy benzohydroxamic acid (IPOB) and 4-allyloxy hydroxamic acid (AOB), were designed as scheelite and wolframite collectors. The micro-flotation results uncovered that C3OBs exhibited stronger collecting ability towards Pb(Ⅱ)-activated scheelite and wolframite than benzohydroxamic acid (BHA) and the collecting ability of C3OBs was in sequence of POB > IPOB > AOB. The density functional theory (DFT) calculation indicated that the alkoxy oxygen atom of C3OBs contributed to their highest occupied molecular orbital (HOMO), and the HOMO energy followed the order as IPOB > POB > AOB > BHA. The higher HOMO energy, the stronger electron-donating activity. Nevertheless, IPOB didn’t return the highest flotation recovery of tungsten minerals. On the other hand, the hydrophobicity of these four hydroxamate collectors was in sequence of POB > IPOB > AOB > BHA, corresponding to the results of contact angle, micro-flotation and adsorption capacity. Therefore, the hydrophobization of the four hydroxamate collectors played a key role in their flotation performance to the Pb(II)-activated scheelite and wolframite. Moreover, this work offered a new approach for developing superior collectors.

Zhang L., Shen L., Zhou Q., Qi T., Peng Z., Liu G., Li X.

Due to the existence of large auxiliary material consumption, huge wastewater discharge, and high production cost in present tungsten extractive metallurgy practice, a novel technology featuring sulfuric acid conversion-ammonium salts leaching was proposed. Based on the complete conversion of tungsten minerals in sulfuric acid solution, this paper studied the leaching of WO3 from sulfuric acid converted product of scheelite in NH3·H2O–(NH4)2C2O4 solution. The effect of leaching conditions on WO3 leaching efficiency and solid phase transformation was systemically investigated. The WO3 leaching efficiency was > 98% under optimized conditions of 1 mol/L (NH4)2C2O4, 3 mol/L NH3·H2O, 350 rpm, 5 min, and 25 °C. The formed flaky CaC2O4·H2O densely covered on the surface of banding or rodlike shaped CaSO4, which prevented the further transformation of CaSO4. The morphology of leaching residue was more irregular for converted product of scheelite concentrate than that for synthetic scheelite. Minor secondary reaction between CaSO4 and (NH4)2WO4 might occur with increased (NH4)2WO4 concentration, which could be restrained by the existence of (NH4)2C2O4 in solution due to the larger Ksp value of CaC2O4·H2O than CaWO4. The leaching process could be explained by acid–base neutralization of H2WO4 and phase transformation of CaSO4 in NH3·H2O–(NH4)2C2O4 solution.

Zhang L., Shen L., Zhou Q., Qi T., Peng Z., Liu G., Li X.

Since the current industrial method for ammonium paratungstate (APT) production from ammonium tungstate solutions involves evaporative crystallization to remove the excess ammonium, which discharges large amounts of wastewater and consumes considerable energy, a novel method for preparing APT from ammonium metatungstate (AMT) solutions by adding ammonia was developed and investigated systemically in this study. Thermodynamic calculations indicated that the dominant tungsten-containing anions depending upon the solution pH were: metatungstate [H2W12O406−] at pH 2–4, paratungstate [H2W12O4210−] and [W7O246−] at pH 5–8, and tungstate WO42− at pH > 8. The experimental results showed that the temperature, ammonia dosage, stirring speed, reaction time and different ammonium salts added affected the crystallization efficiency and crystalline morphology. The APT crystallization efficiency reached 91.4% with an average particle size of 492.2 μm under the following conditions: a temperature of 85 °C, a 1.6-fold stoichiometric ammonia dosage, a reaction time 5 h, a stirring speed 150 rpm and a C(NH4)2SO4 1 mol/L. The crystallization mechanism involved the transformations of isopolytungstate ion from H2W12O406− to the intermediate H6W12O426− and then to the final H2W12O4210−, which resulted in APT precipitation due to accumulation and combination of the H2W12O4210− and NH4+ ions in solution. The crystallized product exhibited the two primary phases (NH4)6[H6W12O42]·10H2O and (NH4)10[H2W12O42]·10H2O at 40 °C and 55 °C, respectively, while (NH4)10[H2W12O42]·4H2O was formed at temperatures ≥70 °C. Results showed that (NH4)6[H6W12O42] acted as an intermediate in APT crystallization from the AMT solution, which has not been previously reported. Compared with evaporative crystallization, this method for preparing APT product from AMT solutions by adding ammonia exhibits the advantages of (i) less chemical consumption, (ii) minor amounts of discharged wastewater, (iii) low production costs, and (iv) environmental friendliness.

Wang F., Liu H., Yan L.

Tungsten tailing is a great deal of solid waste produced in the production process of tungsten metal, for which there is no simple and effective treatment method in the world. The success synthesis of layered double hydroxide composites (TTF-LDH) by co-precipitation method from tungsten tailing is a feasible way to solve this problem. The structure and properties of TTF-LDH were confirmed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). The obtained TTF-LDH was in combination with intumescent flame retardants (IFR) to achieve a series of intumescent fire resistance coatings. The effects of TTF-LDH on the fire protection, smoke suppression and anti-ageing performances of coatings were evaluated by fire resistance test, smoke density test, cone calorimeter test and accelerated ageing test, while the flame-retardant mechanism of TTF-LDH in coatings was revealed. The results illustrate that an appropriate amount of TTF-LDH can remarkably enhance smoke suppression and fire-resistant abilities of coatings, among which the coating containing 3 wt % TTF-LDH (IFRC-LDH3) exhibits the optimal synergistic effect, revealing a smoke density rating value of 17.3%, a total heat release of 7.0 MJ/m2 and an equilibrium backside temperature of 146.2 °C at 900 s. Meanwhile, the addition of TTF-LDH can strengthen the char formation and thermal stability abilities of the coatings, and the residual weight of IFRC-LDH3 rises to 35.7% at 800 °C, as supported by thermogravimetric (TG) analysis. The results of accelerated ageing test demonstrate that the presence of TTF-LDH can strengthen structural stability of coating, decrease migration and decomposition of IFR, thus giving the coating better integrity and durability of fire-resistant and smoke suppression properties.

Liu P., Wang H., Yin C., Chen X., Liu X., Chen A., Li J., He L., Sun F., Zhao Z.

The discharge of ammonium-containing wastewater and saline wastewater, which are among the main sources of water pollution in China, is difficult to avoid in traditional tungsten extraction processes. Sulfuric acid decomposition of scheelite can address the issue of saline wastewater discharge, but effectively dissolving tungsten from the sulfuric acid decomposition product without causing ammonia pollution remains a challenge. To tackle these problems, this work proposes a novel process of selectively extracting tungsten from sulfuric acid decomposition products using hydrogen peroxide coordination. Under the optimum preparation conditions, 99.0% of tungsten in scheelite was transformed into tungstic acid. The extraction efficiency of tungsten from the product by hydrogen peroxide reached 99.4%, while tungsten content in residue is

Chen Y., Huo G., Guo X., Zhang L.

Acid leaching is considered an appropriate method for the tungsten concentrate treatment. However, it is difficult to leach wolframite efficiently. To reveal the origin of this behavior, the leaching behaviors of scheelite and wolframite in treating a mixed scheelite–wolframite concentrate by hydrochloric acid and the leaching mechanism of the two minerals were studied. The results indicated that the leaching efficiency of scheelite was much higher than that of wolframite, and wolframite was difficult to be completely leached. It was found that the preferential leaching order of tungsten minerals by hydrochloric acid is CaWO4 > MnWO4 > FeWO4. The interaction between Ca, Mn, Fe, and O in tungsten mineral crystals increases in order, indicating that the difficulty of ions being dissolved from mineral crystals is Fe2+ > Mn2+ > Ca2+. In addition, the stronger force between Fe/Mn and O makes the crystals of FeWO4 and MnWO4 form a tighter structure than that of CaWO4, which leads to the worse digestibility of wolframite than scheelite. Wolframite could be converted into scheelite by adding Ca(OH)2 in the mechanical activation, significantly improving the leaching efficiency of wolframite. This work provides an effective countermeasure for expanding the applicability of acid leaching process.

Lyu S., Li J., Liu X., Chen X., He L., Sun F., Zhao Z.

The caustic soda autoclaving process for digesting scheelite (CaWO4) is a unique and widely used tungsten (W) metallurgy technology in China. However, some experimental phenomena still need a proper theoretical explanation. In this work, some operational details and the theoretical basis of the technology are reported. During the digestion, some impurities, such as P, As, and Si are also digested. The P impurity was taken as an example. Based on the analysis of thermodynamic equilibrium phase diagram analysis, low levels of P impurities in the leaching solution were obtained. However, during the next dilution of the residue, P was supplemented as an inhibitor to reduce W loss. The inhibition of the reverse reaction mechanism is explained. The washed Na2WO4 solution containing excess NaOH can be reused in the evaporation–crystallization process; meanwhile, the supplemented P should be removed by adding Ca(OH)2. A theoretical analysis of the thermodynamic equilibrium phase diagram shows that there is an area where Ca5(PO4)3OH is stable, but CaWO4 is not. The experimental results show that over 90% of P can be removed by adding the theoretical Ca(OH)2 amount at the beginning of the evaporation-crystallization step. The W loss ratio can be controlled below 0.2%.

Dong L., Qiao L., Zheng Q., Shen P., Qin W., Jiao F., Liu D.

In this study, in light of the poor selectivity of single copper ions (Cu2+) and poor inhibition ability of citric acid (CA), the flotation separation effect of mixed depressant Cu2+/CA on scheelite and calcite was explored. The microflotation experiment showed that the mixed depressant had better separation effects on the two minerals than the single depressant, and the laboratory-scale experiment verified the efficient separation effect of the mixed depressant. The solution chemical analysis demonstrated the dominate components in the slurry environment. Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) analysis demonstrated the selective chemical co-adsorption of the mixed depressant in the form of copper species complexes on the calcite surface. The thermodynamic calculation of the complex formation and the conditional stability constant calculation prove that the copper species complex (CuL-) is more easily formed and more stable than the calcium species complex. The mixed depressant Cu2+/CA can efficiently separate scheelite and calcite, and scheelite can be efficiently enriched.

Shuai S., Huang Z., Burov V.E., Poilov V.Z., Li F., Wang H., Liu R., Zhang S., Cheng C., Li W., Yu X., He G., Fu W.

Since wolframite is usually associated with calcite, the separation and enrichment of wolframite by froth flotation remains a great challenge. Herein, a novel trisiloxane surfactant N-(2-aminoethyl)-3-aminopropyltrisiloxane (AATS) was successful synthesized, which was used for the separation of wolframite from calcite for the first time. The flotation separation performance of AATS was studied by flotation test, and its adsorption mechanism was explored based on contact angle, infrared spectrum analysis (FTIR), zeta potential and density functional theory (DFT) calculation. The results of micro-flotation test and binary mixed ore flotation test binary mixed ore flotation test pointed that AATS had excellent selectivity and more prominent collection capacity for the flotation of wolframite when compared with industrial reagent sodium oleate (NaOL). The measurement results of contact angle proved that AATS improved the hydrophobicity of the wolframite surface. The highly selective adsorption mechanism of AATS surfactant on mineral surfaces were further researched and analyzed by FTIR and zeta potential. The results revealed that AATS surfactant had significant adsorption effect on wolframite, yet almost no adsorption on calcite. DFT calculation indicated that AATS produced electrostatic adsorption with wolframite surface through —N+H3 group.