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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]

Highlights • Calcite is more difficult to be depressed in the mixed concentrate of fluorite and calcite. • Depressing effect of depressant on calcite was significantly enhance by acid. • The mixture of acid and depressants can depress calcite better. • Surface dissolution is the key factor in depressing of calcite by acidizing depressants. Abstract In this study, the effects of reagent addition order on the flotation behavior of calcite and fluorite, as well as the influence of acid on the floatation behavior of the calcite, were investigated. Results showed that when the calcite surface had adsorbed the collector, the depression of calcite became increasingly difficult. The presence of acid significantly enhanced the selective depressing effect of depressants on calcite. Actual ore flotation and artificial mixed ore flotation experiments demonstrated that the addition of acid can significantly reduce the calcite content in the concentrate. This phenomenon can be explained by the exposure of the new calcite surface due to the surface dissolution, which facilitated the reaction of calcite with the depressor. [ABSTRACT FROM AUTHOR]

Fluorite is a nonrenewable mineral used to produce anhydrous hydrofluoric acid (AHF) and aluminum fluoride. The demand for low-grade fluorite powder (CaF2 < 97%) has fallen sharply owing to the current market conditions. Therefore, a large number of fluorite concentrates have been improved by acid leaching. While this approach can efficiently remove CaCO3 from fluorite concentrate, the SiO2 content, which significantly affects AHF consumption during the production of HF or aluminum fluoride, cannot be completely removed. To solve this problem, in this study, we used reverse flotation before leaching the fluorite concentrates. Subsequently, the feasibility of reverse flotation desilication was determined. The obtained results of the ZP (zeta potential) measurements, solution chemistry analysis, FTIR (Fourier transform infrared spectroscopy) analysis, and micro-flotation tests indicated that employing dodecylamine as the collector and citric acid as the depressor could effectively separate sericite from fluorite. The batch flotation experiment and the pilot test were conducted in Chenzhou (Hunan, China) followed by their operation in Xinyuan Mining Co. Ltd., which produces monolithic fluorite ore on the large scale in Asia. Notably, we found that the contents of both SiO2 and Al2O3 were from 2.82%, 1.17% reduced to 1.28%, 0.74% in the batch flotation experiment. The results of the pilot test showed that the new reverse flotation + leaching technology could dramatically reduce the potential environmental impact and costs, thereby significantly improving the economic benefits by satisfying the requirements of the market. [ABSTRACT FROM AUTHOR]

• TA prefers to adsorb onto the calcite surface rather than the fluorite surface, but pyGA/GA are the opposite. • The balance of the chemical force and VdW force is responsible for the interaction difference. • Precisely predicating the performance of flotation reagents needs to consider spatial structures of big molecules and mineral surface structures. Interaction mechanisms of flotation reagents including pyrogallic acid (pyGA), GA and tannic acid (TA) adsorption onto fluorite (1 0 0) and calcite (1 0 4) surfaces were investigated by first-principles calculations, molecular mechanics (MM) and molecular dynamics (MD) approaches under vacuum phases to understand the spatial effects of molecules. First-principles calculations indicated that GA/pyGA could more strongly adsorb onto the fluorite surface than onto the calcite surface, but MM and MD results indicated TA tended to adsorb onto the calcite surface rather than the fluorite surface. These results were consistent with reported flotation results. Further analysis showed that the interaction difference was ascribed to the different balance of the corresponding chemical and van der Waals forces on different mineral surfaces. [ABSTRACT FROM AUTHOR]

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 influences of long-term static interaction between flotation reagents and minerals on mineral surface properties and their flotation behaviors were investigated in this work. Single mineral results showed that when the static interaction time between flotation reagents and minerals increased from 0 to 8 days, there were no significant differences in the recovery of fluorite (ranging from 77.50% to 74.50%), while the recovery of calcite dramatically decreased from 97.17% to 41.13%. The collector adsorption results indicated that after the long-term static interaction between the collector and minerals, adsorption and desorption of collector on the minerals occurred, and the adsorption amount of collector on fluorite and calcite varied from 0.396 mg/g to 0.421 mg/g, and from 0.444 mg/g to 0.404 mg/g, respectively. The contact angles of fluorite and calcite decreased from 134.3° and 105.0° for 0 days to 109.7° and 52.5° for 8 days, respectively, which demonstrated that the fluorite had a higher hydrophobicity than that of calcite after 8 days of static interaction between the minerals and collector. The Fourier transform infrared spectroscopy (FTIR) analysis showed that there were chemisorptions between the collector and the surfaces of the fluorite and calcite. Meanwhile, the X-ray photoelectron spectroscopy (XPS) results further elucidated that the amount of C=O from the oleic acid (OA) molecule for calcite treated for 8 days was less than for that treated for 0 days. In addition, the flotation results of the tailings from Jiangxi containing fluorite and calcite, indicated that the grade and recovery of fluorite increased from 87.18% and 40.99% for 0 days to 93.00% and 46.01% for 8 days, respectively, indicating that the separation of fluorite from calcite could be achieved via increasing the long-term static interaction between the flotation reagents and minerals. [ABSTRACT FROM AUTHOR]

F-containing wastewater does great harm to human health and the ecological environment and thus needs to be treated efficiently. In this paper, the new calcium-containing precipitant calcite and aided precipitant fluorite were adopted to purify F-containing wastewater. Relevant reaction conditions, such as reaction time, oscillation rate, dosage of hydrochloric acid, calcite dosage and the assisting sedimentation performance of fluorite, and action mechanism are analyzed. The experiment showed that the removal rate of fluoride in simulated wastewater reached 96.20%, when the reaction time, the dosage of calcite, the dosage of 5% dilute hydrochloric acid, and the oscillation rate was 30 min, 2 g/L, 21.76 g/L, and 160 r/min, respectively. Moreover, the removal rate of fluoride in the actual F-containing smelting wastewater reaches approximately 95% under the optimum condition of calcite dosage of 12 g/L, reaction time of 30 min, and oscillation rate of 160 r/min. The addition of fluorite significantly improves the sedimentation performance of the reactive precipitates. The experimental results showed that calcite and fluorite can effectively reduce the concentration of fluoride ions in F-containing wastewater and solve the problem of slow sedimentation of reactive precipitates. [ABSTRACT FROM AUTHOR]

• SFG provides molecular details about the adsorption of sodium silicate (SS). • SFG signal shows the change in surface charge and adsorption. • SS physically adsorbs at CaF 2 surface at pH < 7 and is removed by water flow. • SS chemically adsorbs at CaF 2 surface at pH > 7 and is unremoved by water flow. • SS penetrates the innermost water layer at SiO 2 surface and adsorbs on it chemically. Sodium silicate (SS) is often used as a depressant or a dispersant to improve the selectivity of froth flotation. The depressing ability of SS changes with its concentration and the solution pH. However, the depressing mechanism is unclear. In this paper, sum frequency generation spectroscopy was used to investigate the water structure at the mineral-water interface to provide a molecular understanding of SS adsorption and its role in flotation. Our study shows that a significant amount of silicate species adsorbs at the fluorite-water and silica-water interfaces in a wide range of pH, independently of the surface potential. The adsorption layer of silicate species on the fluorite surface can be removed at low pH (acidic condition), but its removal becomes difficult at high pH (basic condition). On the contrary, the adsorption of silicate species at the silica surface is so strong that the adsorbed species cannot be removed at the whole pH range. This finding agrees with flotation results showing that SS can be used as a dispersant for fluorite at pH = 6–8, but it behaves like a depressant at higher pH. Also, SS effectively depresses the silica floatability at the whole range of pH due to its strong interaction with the mineral surface. This work provides the molecular details about the SS adsorption onto the mineral surface which is complementary to the previous macroscopic studies such as FTIR, zeta potential, and XPS measurements. [ABSTRACT FROM AUTHOR]

Highlights • Propyl gallate was used as a excellent flotation collector for fluorite. • Separation of fluorite from calcite without using any depressant can be achieved. • The flotation mechanism of fluorite from calcite was studied. • Adsorption of PG onto the surfaces of fluorite and calcite was studied. Abstract In real flotation systems, the flotation separation of fluorite from calcite is a challenge due to the similar surface properties of these two minerals. The purpose of this paper is to develop a highly selective flotation collector for the separation. Propyl gallate (PG) was introduced as a collector for selective flotation separation of fluorite from calcite. The separation of fluorite from calcite without using any depressant can be achieved by using PG as the collector. The flotation mechanism of fluorite and calcite was studied by zeta potential measurements, adsorption, FT-IR and XPS analysis. The results indicated that phenolic hydroxyls were the functional groups of PG which can selectively adsorb on fluorite, and the adsorption amount of PG on the surface of fluorite was larger than on calcite. [ABSTRACT FROM AUTHOR]

Fluorite is a non-renewable mineral that is used for anhydrous hydrofluoric acid and aluminum fluoride purposes. In China, along with the excellent fluorite resource, which is over-exploited, many off-specification fluorites (CaF 2  > 93, under 97%; SiO 2  > 1.5%) are produced. Improving the grade of fluorite instead of costly technologies of the Buss and CHEMCO are conducted. To improve the grade of fluorite, an excessive amount of sodium silicate is commonly used. However, this approach cannot stably produce high-quality fluorite and result in excessive reagent consumption, poor selectivity and high-water content of the fluorite concentrate. To solve these problems, suitable hydrophilic polymer depressants, which are highly stable, safe, non-toxic, hydrophilic, biodegradable and low processing cost because of abundant in nature, are selected to replace sodium silicate. To make the study practical, the testing location chosen was in Chenzhou (Hunan, China) and was operated by Xinyuan mining Co. Ltd., the largest monolithic fluorite ore producer in Asia. Meanwhile, to prevent the above problems from occurring, the focus throughout this study was achieving separation in the flotation process through the successful occurrence of two sub-processes. The first process was desilicication using dextrin, and the second process was decalcification using tannin. A tech-economic assessment based on the pilot program showed that compared with sodium silicate, the new technology (dextrin + tannin) improved fluorite recovery by 19.23%, removal rate of CaCO 3 by 13.43% and SiO 2 by 8.93% and reduced production costs by $2914.8 per day. The technology (dextrin + tannin) produced an excellent result, simplifying the flow during fluorite flotation, which can led to a reduction in power consumption as well as reduction in production costs for each ton of 105% sulfuric acid of $3.24 (t/t) for the entire production chain lifecycle. The new technology was an efficient, economic and environmentally friendly and has widespread applications and promising market prospects. [ABSTRACT FROM AUTHOR]

Selective adsorption of tannic acid (TA) on calcite surfaces and the implications of this process for the separation of fluorite ore were studied by microflotation tests, surface adsorption experiments, zeta potential measurements, UV–vis analysis, and X-ray photoelectron spectroscopy (XPS) analysis. The microflotation tests indicated that TA, when added before sodium oleate (NaOl), could selectively depress calcite from fluorite at pH 7. Surface adsorption experiments revealed that TA hinders the interaction of NaOl with calcite. The zeta potential of calcite became more negative with TA than with NaOl. However, the characteristic features of TA adsorption were not observed on fluorite, suggesting that the dominant adsorption sites are dissimilar on the fluorite and calcite surfaces in the pulp. UV–vis spectroscopy, XPS, and solution chemistry analysis were utilized to obtain a better understanding of the mechanism for selective adsorption of TA as well as the key factors determined by the Ca 2+ and Ca(OH) + components on the mineral surfaces. A possible adsorption mechanism along with an adsorption mode is proposed for the surface interaction between TA 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]

The dissolved components of calcium-bearing gangue minerals will adsorb onto the celestite surface, which increases the difficulty of the flotation separation of celestite from fluorite and calcite. Single mineral and artificial mineral flotation experiments show that EDTA exhibits an excellent selective inhibition effect towards celestite and calcium-bearing minerals. Surface dissolution experiments reveal that EDTA can strongly inhibit the dissolution of calcium ions on the fluorite surface, thus reducing the influence of dissolved calcium ions on celestite flotation. Zeta potential experiments and adsorption experiments demonstrate that the amount of depressant EDTA adsorbed on the fluorite surface is greater than that on the celestite surface, which is contrary to the adsorption amount of collector sodium dodecyl sulfate (SDS) on the fluorite and celestite surfaces. Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) analyses further reveal that, through chelating with calcium ions, EDTA can change the chemical surroundings of elements on the fluorite surface, while the chelation is not evident on the celestite surface. Based on the experimental and analytical results above, a possible model for the flotation separation process is created. Unlabelled Image • EDTA can selective inhibit the flotation of celestite and calcium bearing minerals. • EDTA can strongly inhibit the dissolution of calcium ions on the fluorite surface. • The adsorption of EDTA on the fluorite surface is greater than that of celestite. • EDTA can be adsorbed by chelating with calcium ions on the fluorite surface. [ABSTRACT FROM AUTHOR]

• The flotation separation of fluorite from calcite and celestite was realized. • The optimum conditions for flotation separation were found. • The selective depression mechanism of the mixed depressant Al 2 (SO 4) 3 -AWG was discussed. To cope with the increase of sulfate gangue minerals in fluorite ores, flotation separation of fluorite from calcite and celestite using Al 2 (SO 4) 3 and acidified water glass (AWG) as mixture depressants was studied in this paper. The flotation separation performance and underlying mechanism were studied by flotation experiments, zeta potential measurements, microcalorimetric analysis, adsorption measurements, and X-ray photoelectron spectroscopy (XPS). The flotation results show that under optimum conditions, the inhibition effect of AWG on celestite is more remarkable with the assistance of Al 2 (SO 4) 3 , but has no obvious effect on the flotation of fluorite. Zeta potential measurements show that both positively charged Al species and negatively charged Si species are adsorbed on the surface of the minerals. Microcalorimetric analysis confirms that the interaction between Al 2 (SO 4) 3 and celestite is more intense than that of calcite and fluorite, while AWG is more likely to be adsorbed on the calcite surface. Adsorption measurements reVeal that there is competitive adsorption between the depressant and collector and that the adsorption of the depressant AWG prevents the collector NaOL from adsorbing on the surface of the minerals. The XPS results show that Al species and Si species are chemically adsorbed on the surface of the minerals and change the chemical surroundings of the elements on the mineral surface. Moreover, compared with fluorite, Al species can more clearly enhance the adsorption of Si species on the celestite surface. [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]

Abstract Fluorite, one of the major raw materials for fluoride in China, is mainly associated with sulfide and calcite minerals. The presence of these sulfide and calcite minerals cause the pipe blockage and efficiency loss during the production of anhydrous hydrofluoric acid (AHF). Worldwide, direct flotation techniques are utilized to beneficiate the fluorite into the chemical grades, but their separation efficiency remained limited due to similar flotability behaviors of fluorite, sulfide and calcite in fatty acid. In the present study, a novel method based on the acid leaching and reverse flotation has been envisaged for the purification and desulfurization of fluorite concentrates containing higher concentrations of sulfur and calcium. Leaching tests were performed by using hydrochloric acid, whereas the reverse flotation experiments were performed by using butyl xanthate as the collector and terpenic oil as the foaming agent. Leaching results showed that, calcite mineral dissolved and the fatty acid lost its collecting and foaming activities under the action of hydrochloric acid. The reverse flotation tests demonstrated that weight percent of sulfides, which are the main causes of blockage in AHF production, was substantially reduced from the fluorite concentrate. Interestingly, this method has been successfully implemented in Shizhuyuan fluorite dressing plant in China for the upgradation of fluorite concentrate. Calcite and sulfur contents of the concentrate were reduced from 4% to 0.01% and 0.5%–0.01%, respectively, and the grade of fluorite concentrate improved from 93.2% to more than 97% with a slight loss of fluorite. Furthermore, the safety in production of AHF was ensured with increased profit from the concentrator. [ABSTRACT FROM AUTHOR]

Highlights • Surface broken bonds can be used to assess surface properties of fluorite. • A surface with lower broken bond density shows a high exposure in particles. • A surface with higher broken bond density exhibits a faster dissolution. • The broken bond method is helpful for mineral/material chemistry research. Abstract Crushing and grinding, the prerequisite processes in many industries, are employed in areas such as minerals processing and powder technology. During these processes, minerals will cleave or fracture along specific crystal directions, where there are weak inter-planar bonds, generating exposed surfaces. On an exposed mineral surface, different ions can possess different numbers of broken bonds. The total number of broken bonds of all ions on the exposed surface can be considered as the number of broken bonds of the exposed surface. The broken bonds on the exposed surface make the latter more active and determine its reactivity. The broken bond density on the exposed surfaces of fluorite was calculated, enabling the anisotropic surface reactivity of fluorite such as surface energy, surface relaxation, dissolution, wettability, surface charge and adsorbability to be revisited. The results show that the surface broken bond density, which is related to the specific surface energy, could be used to predict the cleavage nature, surface relaxation degree, dissolution rate and surface stability of fluorite crystal. The distribution feature and the number of broken bonds of exposed active ions (such as Ca2+ for fluorite) can be used to predict and explain the anisotropic surface wettability and surface charge, as well as the adsorption mode and strength of organic molecule binding to different exposed surfaces. The calculation of surface broken bonds can serve as useful method to assess mineral surface chemical behavior. This approach is helpful for mineral/material chemistry research in general. [ABSTRACT FROM AUTHOR]

Fluorite, a chief source of fluorine in the nature, usually coexists with calcite mineral in ore deposits. Worldwide, flotation techniques with a selective collector and/or a selective depressant are commonly preferred for the separation of fluorite from calcite. In the present study, an attempt was made to use benzhydroxamic acid (BHA) as a collector for the selective separation of fluorite from calcite without using any depressant. Results obtained from the flotation experiments for single mineral and mixed binary minerals revealed that the BHA has a good selective collecting ability for the fluorite when 50 mg/L of BHA was used at pH of 9. The results from the zeta potential and X-ray photoelectron spectroscopy (XPS) indicated that the BHA easily chemisorbs onto the fluorite as compared to calcite. Crystal chemistry calculations showed the larger Ca density and the higher Ca activity on fluorite surface mainly account for the selective adsorption of BHA on fluorite, leading to the selective separation of fluorite from calcite. Moreover, a stronger hydrogen bonding with BHA and the weaker electrostatic repulsion with BHA − also contribute to the stronger interaction of BHA species with fluorite surface. [ABSTRACT FROM AUTHOR]

[Display omitted] • Trisodium nitrilotriacetate (TN) was a novel depressant during fluorite separation from calcite. • TN showed excellent depressing performance on calcite at pH 7.9. • The multi-dentate neutralization reaction between TN and calcite surface occurred. • An adsorption model is finally obtained. The recovery of fluorite from calcium-bearing carbonate ores by foam flotation is challenging due to low separation efficiency. Herein, we studied the effect of trisodium nitrilotriacetate (TN) addition on the surface properties of calcite 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 to analyze the surface properties of these minerals. The addition of TN as a novel depressor significantly improved the effect of calcite and sodium oleate (NaOl) on the flotation-based fluorite recovery and separation from calcite. TN interacted with fluorite via an electrostatic interaction according to the zeta-potential and XPS analyses. The interaction of TN with calcite was via electrostatic attraction and chemical adsorption. Preferential chemical adsorption of NaOl replaces TN from the fluorite surface. However, calcite preferentially adsorbs TN due to the chemical bonding between carboxyl of TN and the hydrated calcite surface layer, which chemically modifies the original calcite surface. This work also suggests interaction and adsorption mechanisms between TN and calcite. [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]

• HEDP used as pH-dependent switch to depress and activate fluorite flotation. • Over 85% of calcite removed from mixed binary minerals at pH 6 using HEDP and NaOL. • HEDP has a stronger chemical and hydrogen bonding interaction with fluorite. Fluorite is usually separated from calcite by froth flotation method using large amounts of sodium silicate depressant, which can cause trouble in the loss of fluorite and wastewater treatment. In this study, green and low-cost 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP or H 4 L) was used as pH-dependent switch to initially depress fluorite for calcite pre-removal at pH 6.0, and then activate fluorite for further upgrading fluorite concentrate at pH 8.0. The depressing behavior and mechanism were reported in this work. H 2 L2− was the dominant form of HEDP, and a stronger chemical adsorption of H 2 L2− on fluorite hindered the subsequent adsorption of sodium oleate (NaOL), while that of the calcite showed the opposite result. Two active O atoms in H 2 L2− could well match in interatom distance with two Ca sites on fluorite to form Ca-H 2 L complexes. The pH-dependent switch reagent reported here may open a new avenue for more selective separation among mixed mineral systems. [ABSTRACT FROM AUTHOR]