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Apatite (Ca10(PO4)6F2) is the most important phosphate mineral, and flotation is the main beneficiation method to separate apatite from its major gangue mineral calcite (CaCO3). Till date, fatty acids and their salts have been widely used as collectors in the apatite/calcite flotation separation due to their low cost and strong collecting ability, but their selectivity is limited. Therefore, screening or designing a selective collector becomes the key to the efficient separation. In this work, an attempt was made to utilize benzohydroxamic acid (BHA) as the collector for the selective separation of apatite from calcite without any depressant. The single and mixed binary mineral flotation experimental results prove the excellent selectivity of BHA in the apatite/calcite flotation separation. Zeta potential measurement results indicate a greater affinity of BHA on the apatite surface than calcite, which is also confirmed by the higher adsorption energy of BHA on the apatite surface based on the first-principle density functional theory calculations. The X-ray photoelectron spectroscopy analysis shows that the selective chemisorption of BHA on apatite over calcite is due to the stronger reactivity and the higher density of Ca2+ ion on the apatite surface than calcite. This work shows that surfactants of hydroxamic acid type can be an ideal collector for phosphate mineral flotation. [ABSTRACT FROM AUTHOR]

Highlights • The three polycarboxylic acids effectively inhibit calcite flotation. • The inhibition abilities decrease in the order of PASP > HPMA > PESA. • The depressant prevents the adsorption of sodium oleate on calcite surface. • PASP exhibits best selectivity in the flotation separation of fluorite from calcite. Abstract As a common gangue mineral, the inhibition of calcite is very important to enrich the valuable minerals by flotation. With the increasing complexity of mineral properties and higher requirements for environmental protection, developing a newly eco-friendly depressant for calcite flotation is necessary. In this study, the effects of polyaspartic acid (PASP), polyepoxysuccinic acid (PESA), and hydrolytic polymaleic anhydride (HPMA) on the flotation performance of calcite using sodium oleate as the collector were investigated through flotation experiments. The results showed that all the three depressants exhibited strong inhibition to calcite, and the inhibition capabilities decreased in the order of PASP > HPMA > PESA. The results of zeta potential measurement, contact angle measurement and X-ray photoelectron spectroscopy indicated that the adsorption of sodium oleate on calcite surface was greatly decreased as the addition of the depressant. To investigate the inhibition selectivity, three depressants were used in fluorite flotation, and the results suggested that sodium oleate could still adsorb on fluorite surface in the presence of PASP. The flotation separation of fluorite from calcite could be therefore realized with PASP on the basis of the best selectivity among the three depressants. [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]

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]

• 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]

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]

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]

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]

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]

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]

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]

The anisotropic physicochemical properties of calcite, including cleavage nature, surface (free) energy, surface relaxation degree, wettability and adsorption behaviour, were revisited in this paper based on the surface structures and surface broken bonds reported previously. The relationships between these surface properties were also discussed. The analysis indicated that the positive relationship between the density of surface broken bonds and the surface energy of calcite was established, and the former could be used to predict the cleavage nature, commonly exposed surfaces and the degree of surface relaxation. The distribution characteristic and the number of broken (or unsaturated) bonds of surface Ca atoms can be used to explain the anisotropic surface wetting and adsorption behaviour of calcite. This review demonstrated that surface broken bonds could be a fast way to study the surface properties of minerals and materials. [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]

Tin and its compounds have a variety of applications. It is recovered as cassiterite from ore deposit by flotation. Traditionally, the use of fatty acids and their derivatives with limited selectivity of cassiterite over calcite (the main gangue mineral) has been replaced by benzohydroxamic acid (BHA). BHA shows poor collecting ability to cassiterite, even when lead nitrate (LN) is added as the activator. In this work, the flotation results show that cassiterite can be separated efficiently from cassiterite-calcite binary mixed minerals using a mixture of LN/BHA as collector and carboxymethyl cellulose (CMC) as depressant. The separation performance of the mixture of LN/BHA is much better compared with adding LN and BHA in sequence at the same dosage. Zeta potential measurements indicate that the mixture of LN/BHA exhibits much stronger ability to adsorb on cassiterite compared with adding LN and BHA in sequence even in the presence of CMC. [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]

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]

• 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]