Collector Chemistry for Bastnaesite Flotation – Recent Developments

ABSTRACT

One of the most important aspects in any flotation separation is the choice of the flotation collector. For this reason, based on both our recent research developments and the results from other researchers, this detailed review focuses on fundamental surface chemistry features of fatty acid, hydroxamate, phosphonate, and phosphate as collectors for the flotation recovery of the rare earth (RE) mineral, bastnaesite, including selectivity considerations with respect to separation from calcite, barite, and quartz.     

Investigating the use of an ionic liquid for rare earth mineral flotation

Common collectors for rare earth mineral(REM) flotation,which include carboxylates and hydroxamates,face problems such as being non-selective and sensitive to impurity ions.A type of ionic liquid(IL),tetraethylammonium mono-(2-ethylhexyl)2-ethylhexyl phosphonate([N_(222)][EHEHP]),has been investigated previously for rare earth elements(REE) solvent extraction,and was proven to be selective and effective.In this work,[N_(222)][EHEHP] was evaluated as a collector in bastnasite(a primary REM source for REE production) flotation for the first time.The results were compared with quartz and hematite,two common gangue minerals in REM deposits.Zeta potential measurements and Fouriertransform infrared spectroscopy(FT-IR) were completed to investigate the surface chemical properties involved in the flotation of these minerals using this collector.The findings were compared with microflotation results.FT-IR and zeta potential measurements suggest adsorption of the collector's phosphonate group onto bastn(a|")site and hematite,likely through chemisorption;whereas for quartz,the minimum micro flotation recovery is likely due to no adsorption of IL on its surface.Micro flotation re sults show higher collectability of [N2222] [EHEHP] for hematite than bastnasite,the latter only shows appreciable recovery at pH 5 with elevated dosage of IL(500 g/t).To achieve better separation,a two-stage flotation scheme was designed and evaluated by bench scale flotation on a synthetic mineral mixture.The concentrates and tails were analyzed by magnetic separation,and it is found that bastnasite recovery over 90% with maximum upgrade ratio 1.7 can be achieved with elevated collector dosage.     

A novel method for synthesis of styryl phosphonate monoester and its application in La(III) extraction

Herein, styryl phosphonate monoester (SPE) was synthesized and first introduced as rare earth extractant. The solvent extraction of lanthanum (III) from nitrate solution using styryl phosphonate mono-iso-octyl ester (SPE108), di-2-ethylhexyl phosphoric acid (D2EHPA) and 2-ethylhexyl phosphonic acid-mono-2-ethylhexyl ester (EHEHPA) as extractants was investigated. The effects of experimental parameters including equilibrium time, extractant concentration, aqueous pH, phase ratio and salt concentration on the extraction process were studied. The results indicate that the extraction ability and capacity of the extractants follow the order: SPE108 > D2EHPA > EHEHPA. What's more, the extraction process is less affected by ammonium sulfate in the aqueous phase with SPE108. The results of the separation between lanthanum and adjacent lanthanides (Ce, Pr, Nd, Sm) show that SPE108 can separate lanthanides efficiently at low pH. The extraction mechanism of SPE108 is proved to be similar to D2EHPA, and the density functional theory (DFT) calculation results infer that SPE108 exhibits superior extraction ability due to its strong electron-accepting ability.     

Structural and electronic properties of bastnaesite and implications for surface reactions in flotation

The structural and electronic properties of bastnaesite were studied by using the first-principles method based on the density functional theory(DFT).The geometry structure of bastnaesite was first optimized,and then the Mulliken populations,electron density and density of states were calculated and further analyzed in detail.The calculation results reveal that it mainly ruptures along the ionic Ce-O and Ce-F bonds during the cleavage of bastnaesite,leaving≡Ce~+,≡F~-and≡CO_3~-dangling bonds exposed on the cleavage surface of bastnaesite.Combined with contact angle measurement,surface complexation theory and XPS analysis,the implications of structural and electronic properties on bastnaesite flotation reactions were studied.The hydration of exposed strong ionic bond on cleavage surface results in hydrophilic surface.According to surface complexation theory,the formed surface groups are≡CeOH~0,≡CO_3 H~0 and≡FH~0 groups.The investigated metal ions and flotation reagents complex with surface≡CeOH~0 groups,while≡CO_3 H~0 and≡FH~0 groups are not involved in the complexation.The high activity of Ce atoms facilitates these surface reactions.     

Synergistic depression mechanism of Ca2+ ions and sodium silicate on bastnaesite flotation

Bastnaesite is an important rare earth mineral and is usually beneficiated by flotation. Sodium silicate is commonly used to depress calcium-bearing gangue minerals, however it can also depress bastnaesite when Ca²⁺ ions exist in the pulp. In this study, the effect of Ca²⁺ ions and sodium silicate individually or in combination on bastnaesite flotation was studied through micro-flotation, zeta potential, fluorescence spectroscopy and X-ray photoelectron spectroscopy (XPS) measurements. Micro-flotation results show that the combination of Ca²⁺ ions and sodium silicate depresses bastnaesite more severely due to their synergistic effect. Zeta potential results show that the combination renders the surface potential of bastnaesite negatively shifted more significantly. Fluorescence spectroscopy shows that the combination decreases the surface hydrophobicity of bastnaesite more severely. XPS shows that the combination increases the adsorption of sodium silicate on bastnaesite by forming hydrophilic Ca-SiO₃ precipitate, which causes more serious depression on bastnaesite flotation.     

Separation and recovery of rare earth from waste nickel-metal hydride batteries by phosphate based extraction-precipitation

A novel type of extraction-precipitation strategy based on phosphate was developed to recover rare earth (RE, i.e., La, Ce, Nd, and Pr) from waste nickel-metal hydride (NiMH) batteries. This method does not require saponification and organic solvents. The novel phosphates, i.e., dibenzyl phosphate (DBP), diphenyl phosphate (DPP), triphenyl phosphate (TPP) were studied as extraction-precipitants. DBP has high precipitation efficiencies for RE³⁺, which can reach 97.84%, 100%, 100% and 99.77%, respectively. In addition, the precipitation efficiencies of Mn²⁺, Co²⁺ and Ni²⁺ are less than 1.75%. DBP-RE has the largest particle size (D10 = 52.6 μm, D50 = 135.35 μm, D90 = 296.08 μm), which is much larger than the precipitations formed by NH₄HCO₃, H₂C₂O₄, CaO and MgO. The larger precipitation particle sizes contribute to improving the solid-liquid separation efficiency. With 3 mol/L hydrochloric acid, the stripping efficiency of DBP-RE reaches 98.60%, and the purity of recovered RE is 99.85%. The regenerated DBP can be directly used for the recycling extraction. Therefore, the novel extraction-precipitation strategy is a green and sustainable separation method.     

Behavior of phase transformation of Baotou mixed rare earth concentrate during oxidation roasting

Based on the new process named “Combination Method” for metallurgy and separation of Baotou mixed rare earth concentrate (BMREC), the aim of this paper is to clearly elucidate the phase change behavior of BMREC without additives during oxidative roasting at 450–800 °C. The results indicate that the bastnaesite in BMREC is decomposed at 450–550 °C, the weight loss is about 10.3 wt%, and the activation energy (E) is 144 kJ/mol. The bastnaesite in BMREC is decomposed into rare earth fluoride, rare earth oxides (La₂O₃, Ce₇O₁₂, Pr₆O₁₁ and Nd₂O₃), and CO₂, particularly, with the increase of roasting temperature, bastnaesite in BMREC is more completely decomposed into LaF₃, which causes a decrease in leaching rate of La during the HCl leaching process. Additionally, the maximum cerium oxidation efficiency reaches about 60 wt% when the roasting temperature is equal to or above 500 °C, and the oxidation reaction rate of cerium increases with the increasing roasting temperature.     

Study on separation of rare earth elements in complex system

The effect of the feed acidity,acetic acid concentration and rare earth concentration on the distribution ratio,separation coefficient and extraction capacity of light rare earth elements were studied in the P204(DEHPA)-HCl system and P507(HEH/EHP)-HCl system both containing acetic acid,respectively. The results showed that the distribution ratio and separation coefficient decreased with increasing of acidity,and increased with increasing of acetic acid concentration and rare earths concentration,and the extraction capacity increased with increasing of acetic acid concentration. When pH value of feed was 2.0,[RE]/[acetic acid] was 1:1 and rare earth concentration 0.35 mol/L,in P204(DEHPA) -HCl system with acetic acid,the maximum separation coefficient(β) reached to βCe /La=4.09,βPr/Ce=1.96 and βNd/Pr=1.53,and the separation ability of this extraction system was better than P507(DEHPA)-HCl system.     

Recovery of High Purity Y2O3 by Solvent Extraction Route Using Organo-Phosphorus Extractants

A rare earth concentrate assaying about 60% Y₂O₃, is generally obtained directly from Y rich minerals like xenotime or from monazite after preliminary fractionation of rare earths chloride as is practised currently at Indian Rare Earths Ltd.. Alwaye. Using this intermediate concentrate. SX process has been developed in our laboratory to purify Y (>99.9%) in presence of NH₄SCN. The process parameters for DEHPA and PC 88A systems have been optimised using a computer program in BASIC. The DEHPA flowsheet has been tested at bench-scale to produce several kilograms of 93% Y₂O₃. During these trials certain problems were faced due to high acidities. With PC 88A there were no problems and the flowsheet based on the solvent was confirmed at pilot-plant level. The solution containing 93% pure Y₂O₃, is purified further by another cycle of SX with 50% TBP in kerosene in presence of 1.0 M NH₄ SCN. The impurities are extracted leaving >99.9% pure Y₂O₃ in the aqueous phase. The process parameters optimised for obtaining >90% recovery of Y₂O₃ are described.     

Energy transfer from Ce~(3+) to Tb~(3+) and Eu~(3+) in zinc phosphate glasses

Ce3+,Eu3+ and Tb3+ singly doped and Ce3+/Eu3+ and Ce3+/Tb3+ co-doped zinc phosphate glasses were prepared by sintering P2O5,ZnO,Ce2(C2O4)3·10H2O and Eu2O3/Tb4O7 mixtures at 1200 °C in the air for 2 h and then annealing at 450 °C for 10 h.The obtained glasses were homogeneous and transparent.The glasses without Ce3+ were colorless and those with Ce3+ showed slightly yellow.The singly doped glasses showed strong emissions and excitations from doped trivalent rare earth ions.Strong energy transfer from Ce3+ to Tb3+ was observed for Ce3+/Tb3+ coped samples.There were also some very weak evidences for the energy transfer from Ce3+ to Eu3+.     

A novel extractant bis(2-ethylhexyl) ((2-ethylhexylamino)methyl) phosphine oxide for cerium(IV) extraction and separation from sulfate medium

By introducing the amine group into phosphorus extractant, a novel aminophosphine compound bis(2-ethylhexyl) ((2-ethylhexylamino)methyl) phosphine oxide (DEHAPO, abbreviated as A) was synthesized for the extraction of cerium (IV) (Ce(IV)) from sulfate medium (H₂SO₄). The influence factors including extractant concentration, H₂SO₄ concentration and temperature on the Ce(IV) extraction were investigated and discussed. It is found that the extraction ability of Ce(IV), thorium (IV) (Th(IV)) and rare earths (REs(III)) (La, Gd, Yb) decreases in sulphate medium in the following order: Ce(IV) > Th(IV) > REs(III). The extraction process is an exothermic reaction and the thermodynamic parameters were calculated. The extracted complex of Ce(HSO₄)₂SO₄·A in loaded organic solution was identified by the slope methods and further proved by FT-IR spectral analysis. Stripping studies indicate that Ce(IV) can be effectively stripped from the organic phase. The results of separation factors (β) and saturation loading capacity demonstrate that DEHAPO could be used to selectively extract Ce(IV) from sulphate medium with high separation efficiency and good extraction ability.     

New Environment-Friendly Approach for Bastnasite Metallurgic Treatment (I): Extraction of Tetravalent Cerium from Sulphuric Acid Medium with Di(2-ethylhexyl) Phosphoric Acid

Bastnasiteisamainsourceofrareearthproducts inwhichCeO2/REOisabout50%.Atpresent,a cidity leachingcombinedwithalkali conversion method[1]iscommonlyusedinthebastnasitetreat ment.Thismethodisunfriendlytotheenvironment becausetheradioactiveelementofthoriuman…     

Mechanism of phthalic acid collector in flotation separation of fluorite and rare earth

The mechanism of phthalic acid,a dicarboxylic acid collector,in flotation separation of fluorite and rare earth(RE)was studied in this paper.The experimental data of flotation show that phthalic acid,as the collector,can realize highly efficient separation of fluorite and rare earth under weakly acidic conditions.The adsorption mechanism of phthalic acid on the surface of fluorite and bastnaesite was analyzed in this paper by means of the zeta potential measurement,the Fourier transform infrared(FT-IR),the X-ray photoelectron spectroscopy(XPS)and the stability constant measurement of active metal ion and phthalic acid coo rdination complex.According to the zeta potential testing results,the surfaces of fluorite adsorb the collector phthalate ion with negative charge under weakly acidic conditions which,in turn,increases its electronegativity and results in the motion of its potential.After the reaction between phthalic acid and fluorite ores under weakly acidic conditions,the peak of the fluorite ores is found to have significant changes in the FT-IR results,indicating strong chemical adsorption on the surfaces of phthalic acid and fluorite ores.According to the XPS analysis,the peak of benzene ring of phthalic acid is as high as 2%on the surface of fluorite,while no obvious characteristic peak of benzene ring is found on the surface of bastnaesite.According to the pH potentiometric titration results,the stability constant Ktotal of calcium phthalate complex within the acid range is higher than the stability constant K’total of cerium phthalate complex,indicating that the complex generated between phthalic acid and Ca²⁺is more stable than the complex generated between phthalic acid and Ce³⁺.The possible reason is that Ca²⁺,with the highest reticular density,plays a prevailing role in the octahedron structure of fluorite amidst the acidic media.As the active point of flotation,Ca²⁺works with the carboxyl groups of the collector phthalic acid(-C=O-)to form polycyclic calcium phthalate complex.     

Study on separation of rare earth elements in complex system

The effect of the feed acidity, acetic acid concentration and rare earth concentration on the distribution ratio, separation coefficient and extraction capacity of light rare earth elements were studied in the P204(DEHPA)-HCl system and P507(HEH/EHP)-HCl system both containing acetic acid, respectively. The results showed that the distribution ratio and separation coefficient decreased with increasing of acidity, and increased with increasing of acetic acid concentration and rare earths concentration, and the extraction capacity increased with increasing of acetic acid concentration. When pH value of feed was 2.0, [RE]/[acetic acid] was 1:1 and rare earth concentration 0.35 mol/L, in P204(DEHPA)- HCl system with acetic acid, the maximum separation coefficient(β) reached to β_{Ce /La}=4.09, β_Pr/Ce=1.96 and β_Nd/Pr=1.53, and the separation ability of this extraction system was better than P507(DEHPA)-HCl system.     

某氟碳铈稀土矿混合浮选捕收剂优化试验研究

四川省牦牛坪稀土矿是我国第二大轻稀土矿,主要矿藏有氟碳铈稀土矿、伴生萤石和重晶石等。为提高微细粒级稀土回收率,采用混合浮选工艺替代原稀土浮选工艺,并研发了新型捕收剂CXS-211,优化试验提高了新药剂对矿石性质的适应性。闭路试验结果表明：新药剂可获得稀土REO回收率92%以上、萤石回收率88%以上的混浮精矿。     

The extraction of zinc(II) from sulphate and perchlorate solutions by di(2-ethylhexyl)phosphoric acid dissolved in Isopar-H

The extraction of zinc from sulphate and perchlorate solutions at constant ionic strength, by di(2-ethylhexyl)phosphoric acid, DEHPA, in Isopar-H has been studied at 25°C as a function of metal and DEHPA concentrations. The distribution data have been analyzed both graphically and numerically, using the computer program LETAGROPDISTR [33]. The results showed that the species extracted into the organic phase have the composition ZnA₂HA and ZnA₂H₂A₂ for both perchlorate and sulphate systems. The formation constants for each system are given in Table 2. An estimate of the formation constant of ZnSO₄ in aqueous phase was obtained from the extraction data in sulphate solutions.     

The extraction of iron(III) from aqueous acid solutions by di(2-ethylhexyl)phosphoric acid

The extraction of iron(III) from aqueous solutions containing sulphuric, hydrochloric and nitric acids by di(2-ethylhexyl)phosphoric acid (DEHPA) in kerosene has been investigated under different conditions. As a result, it is found that although extraction is dominated by an ion-exchange reaction, the rate of iron(III) extraction from sulphuric acid solutions to reach equilibrium is relatively slow in comparison with that from hydrochloric or nitric acid solutions. In the extraction from aqueous solutions containing hydrochloric or nitric acid, however, the DEHPA combines with iron(III) according to the solvating reaction at higher aqueous acidity. From studies on the rate of the extraction from sulphuric acid solutions, examined under non-equilibrium, it is confirmed that dependencies of extraction rate on hydrogen ion and DEHPA concentrations are in the first and inverse first orders, respectively. The hydrolyzed species is considered to interpret the extraction mechanism in this system.     

Study on Anticorrosive Cerium Conversion Coating of Cf/6061Al Composite Surface

The optimum chemical passivation process of the rare earth metal (REM) conversion coating on the Cf/6061Al composite surface was introduced in this paper and its polarization curves properties were investigated. Ridge-like coatings were found by scanning electro microscope (SEM) observations, and the Al matrix and carbon fibre reinforcement were both coated with Ce conversion coatings, with some minor cracks. The energy dispersive spectroscopy (EDS) plane scan analysis indicates that the major elements in the coating are Ce, O, Si, Al and the Ce content reaches 47.48%(mass fraction). The Ce conversion coatings increase the corrosion resisting properties of Cf/6061Al composite, with a higher free corrosion potential (Ecorr) and a lower free corrosion current density (icorr) for the coated composite than those of the bare composite. And the Boehmite-treatment would enhance the corrosion resistance of the REM conversion coating. The cathodic polarization and anodic polarization were retarded by REM conversion coating, resulting in an improved corrosion resistance.     

织金含稀土磷矿酸法浸出性能及预处理优化工艺试验

硫酸、盐酸、磷酸和硝酸对原生织金磷矿的稀土组分浸出效率不理想,总稀土浸出效率不到36%。采用焙烧活化—硝酸氨水混合预浸出处理织金磷矿,最适宜条件下,CaO和MgO的浸出率分别为24.55%和19.75%,相应的P_2O_5和稀土元素(Y、La、Nd、Ce)损失率为11.25%和3.61%。所得精矿中,Y、La、Nd、Ce和P_2O_5实现了不同程度的富集。预处理精矿的浸出性能较原矿显著改善,硝酸体系下P_2O_5和稀土元素(Y、La、Nd、Ce)浸出效率提高了近40个百分点。     

A comparative study on extraction of Fe(III) from chloride leach liquor using TBP, Cyanex 921 and Cyanex 923

A comparative study on extraction of Fe(III) from the HCl leach liquor of low grade iron ore tailings has been carried out using Tri-n-butyl phosphate (TBP), Cyanex 921 and Cyanex 923 in distilled kerosene. The percentage extraction of iron increased with increasing HCl and extractant concentrations. The extracted species in each case was found to be HFeCl₄·S. The extraction isotherms for the above extractants indicated quantitative extraction of Fe(III) in 3-stages at O:A ratio of 3:2 with TBP, and in 2-stages at O:A ratio of 1:1 with Cyanex 921 and Cyanex 923. The stripping studies of the loaded organic phases were carried out with 0.4 M HCl. The stripping isotherms indicated 2-stages at O:A ratio of 5:2 for TBP, and 3-stages at O:A ratio of 2:3 for Cyanex 921 and Cyanex 923. From the extraction studies, the extraction efficiency of the extractants for Fe(III) was in the order TBP < Cyanex 921 < Cyanex 923. Although Cyanex 923 was found to be the best extractant, the percentage stripping of Fe from the loaded Cyanex 923 was the least. The stripping of Cyanex 923 was 94.9%, but with TBP and Cyanex 921, it was 99.8% and > 99.9%, respectively.