Liping Luo ,Houqin Wu,b, *,Longhu Xu,c ,Jinping Meng ,Jihui Lu ,Hun Zhou ,Xiomei Huo,Lingyun Hung

a Key Laboratory of Solid Waste Treatment and Resource Recycle Ministry of Education,Southwest University of Science and Technology,Mianyang 621010,China

b School of Civil Engineering and Architecture,Southwest University of Science and Technology,Mianyang 621010,China

c State Key Laboratory for Environment-friendly Energy Materials,Southwest University of Science and Technology,Mianyang 621010,China

d State Key Laboratory of Complex Nonferrous Metal Resources Clean Utilization,Kunming University of Science and Technology,Kunming 650093,China

Keywords:Ilmenite Titanaugite Mixed collector Flotation Adsorption

ABSTRACT This paper researched the enhanced flotation separation performance of ilmenite and titanaugite using the mixed collector benzhydroxamic acid/dodecylamine(BHA/DDA).The interface assembly mechanism was mainly investigated through in situ attenuated total reflectance Fourier transform infrared (ATRFTIR) spectroscopy combined with the two-dimensional correlation spectroscopy (2D-COS) and X-ray photoelectron spectroscopy(XPS).It has been found that BHA/DDA mixed collectors successfully separate ilmenite from titanaugite at a molar ratio of 8:1.Zeta potential experiments suggested that,in the presence of mixed collector system,the BHA-DDA complex adsorbed on the ilmenite surface via the chemically adsorbed BHA and the electrostatically adsorbed DDA,however,the complex adsorbed on the surface of titanaugite unstably.According to in situ ATR-FTIR combined with 2D-COS and XPS results,the interface assembly mechanism of BHA/DDA is summarized as:the function group of BHA molecules first binds to the metal sites on minerals to form bidentate ligand,then DDA co-adsorbed with BHA on the surface of minerals through hydrogen bonding.DDA may change the adsorption modes of some BHA on the ilmenite surface from four-membered ring to five-membered ring,while the modes on the titanaugite surface is true opposite.Finally,recommended adsorption configurations of the BHA/DDA complex on the two mineral surfaces are proposed.

1.Introduction

Hydroxamic acid,an anion collector,exhibits excellent chelate ability to certain transition metal or rare earth metal ions on the surface of minerals.Moreover,it could be considered as an environmentally friendly reagent because it is difficult to hydrolyze,oxidize,or decompose into other chemical species [17].Therefore,many researchers have paid attention to its advantages and considered using it as one of the components of mixed collectors to improve selectivity performances [18–21].In hydroxamic acidcontaining mixed collectors,there are two combinations.One is the combination of hydroxamic acid and another type of anionic collector.For example,it is found that co-adsorbed of mixed collector octanohydroxamic acid/sodium oleate(OHA/NaOL)on bastnaesite surface is more superior hydrophobicity than the single OHA or NaOL with combination of OHA/NaOL at the molar ratio of 2:1.Another mode is a mixture of hydroxamic acid and cationic collector.For instance,the mixture of BHA/DDA at the molar ratio of 6:1 showed a very obvious synergistic interactions and selectivity,realized the flotation separation of spodumene from feldspar[22].However,the latter one has not yet been involved in the ilmenite-titanaugite flotation system,especially the mixed collector BHA/DDA.The adsorption of hydroxamic acid on the mineral surfaces is presumably divided into monodentate and bidentate forms.The bidentate forms of hydroxamic acid and metal ions refers to four-membered ring adsorption or five-membered ring adsorption [22–24].In previous studies,due to the limitation of experimental conditions and analytical techniques,the adsorption mechanism of hydroxamic acid on ilmenite-titanaugite system remains controversial,not to mention the adsorption mechanism of combined collector containing hydroxamic acid on the ilmenite and titanaugite surfaces.

Recently,in situ ATR-FTIR technology has the powerful capability of real-time monitoring,which is widely used to study both the interaction between reagents and the adsorption of reagent on solid during separation processes [25,26].Moreover,2D-COS can enhance resolution by resolving overlapping peaks in the in situ infrared spectrum in two dimensions,and analyze the adsorption process at the sub-molecular level [27].Thus,in situ ATR-FTIR combined with 2D-COS is a greatly promising way for detailed understanding the adsorption configuration of collectors and assembly behaviors at liquid/solid interfaces [27,28].

In this work,in order to really reveal the adsorption mechanism of BHA/DDA on the surfaces of ilmenite/titanaugite,different experimental techniques such as micro-flotation,in situ ATR-FTIR spectroscopy,2D-COS,and XPS are conducted.This is the refinement of hydroxamic acid and its mixed collector flotation theory,hoping to provide theoretical guidance for industrial flotation of ilmenite.

2.Materials and methods

2.1.Materials and reagents

The mineral samples used in this study were taken from Panzhihua,Sichuan province,China,which were same as the previous study [29,30].The chemical composition and X-ray diffraction(XRD) spectra of the two minerals are shown in Table 1 and Fig.1,which shows both the ilmenite and the titanaugite are of high purity.After being hand-selected,crushed,ground,and screened,the ilmenite and titanaugite powders with size of-75 μm fractions were prepared.Some of the sample were further ground to-2 μm for in situ ATR-FTIR and zeta potential measurements.Analytical grade sulfuric acid (H2SO4,97%) and sodium hydroxide (NaOH) were used as pH regulators.Before each flotation experiment,the mixed BHA/DDA collectors were freshly prepared.The structural formulas of BHA and DDA are depicted in Fig.2.Additionally,deionized water was used in all tests.

Fig.1.X-ray diffraction pattern of minerals.

2.2.Micro-flotation experiments

Micro-flotation was performed in an XFG Ⅱtype (Changchun,China) flotation device with a 40 mL flotation cell at an impeller speed of 1700 r/min.The final result of each experiment was the average of at least three times tests.

2.3.Zeta potential measurements

All zeta potential measurements were proceeded via Zeta Potential Analyze (Zetasizer Nano ZS90,Malvern Instrument Co.,UK).In each test,30 mg of ground mineral (～3 μm) was added to 50 mL deionized water containing 1 mM NaCl.Next,collectors with same concentration as the flotation process were added for 15-min stirring,during which pH was adjusted with H2SO4or NaOH.Followed by 30 min settlement,the supernatant of the solution was taken for zeta measurements,and the final result was the average of at least three times measurements.

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2.4.Infrared (IR) spectroscopy and 2D-COS

The ATR-FTIR spectra were recorded by a single-beam FTIR spectrometer (Perkin Elmer,U.S.) equipped with a deuteratedtriglycine-sulphate (DTGS) detector and a variable-angle ATR accessory.To analyze in situ adsorption of collectors on the ilmenite and titanaugite surfaces in a real time,30 μL of mineral slurry with a concentration of 8 mg/mL was dropped on the ATR crystal,and then the crystal was dried under vacuum at 40 ℃to form a mineral film.100 mL NaCl background electrolyte aqueous solution with a concentration of 0.1 M,at pH 8–9,was flowed through the mineral film at a rate of 8.688 mL/min,and was recirculated until there was no further change in the spectrum.Then NaCl solution was changed to a collector solution with the same pH condition.Spectra were collected with an average of 100 scans in the 450–4000 cm-1range at a resolution of 4 cm-1.The interval for spectrum collection is 10 min.The software 2DShige was applied for 2D analysis of ATR-FTIR spectra to obtain synchronous and asynchronous spectra.

Fig.2.Structural formulas of BHA and DDA.

2.5.X-ray photoelectron spectroscopy (XPS)

XPS tests were conducted by the Thermo Fisher Scientific KAlpha 1063 System.Survey spectra were recorded in a single sweep from 1350 to 0 eV at a step size of 1.0 eV,and highresolution scans were performed at a step size of 0.1 eV.The samples were prepared as same reagent addition process as flotation.Next,the samples were rinsed three times with same pH distilled water,and dried at a temperature below 50 °C.

3.Results and discussion

3.1.Flotation tests

Fig.3 shows the flotation recovery of ilmenite and titanaugite as a function of pH using the individuality collector BHA or DDA(0.2 mM).Clearly,when single BHA is added,both ilmenite and titanaugite exhibit poor floatability,since the maximum recovery of ilmenite and titanaugite are just 25.2% and 13.6%,respectively.Hence,BHA has a slight selectivity for ilmenite and titanaugite flotation in the whole pH range,and it has a poor collecting capacity for these two minerals.Unlike BHA,when DDA alone is used as collector,both ilmenite and titanaugite show extremely high floatability.Specially,the flotation recoveries of both ilmenite and titanaugite exceed 95% at pH 8.From these results,it is obviously revealing that the single BHA or DDA collectors can hardly separate ilmenite from titanaugite.

Fig.3.Effect of pH on the flotation of ilmenite and titanaugite treated with different reagents (concentration:0.2 mM).

Considering their mixture,the flotation separation of ilmenite and titanaugite becomes possible.Fig.4 depicts the flotation behavior of ilmenite and titanaugite as the molar ratio of BHA to DDA changing from 2:1 to 14:1 at pH range of 8–9.Within the proportion studied,mixed collectors exhibit diverse degrees of selectivity.For titanaugite,the recovery gradually decreases from around 36% to 4% at the ratio of 12:1 and then increases slightly with the ratio increasing.Meanwhile,the ilmenite recovery maintains at a high level in the range of ratio 2:1 to 8:1,then the recovery begins to decline when the ratio changed from 8:1 to 12:1.Obviously,the biggest difference between ilmenite and titanaugite flotation recoveries is 74% at molar ratios of 8:1 (ilmenite 92.5%and titanaugite 18.5%).Therefore,the optimal ratio condition of 8:1 is chosen to continue the follow-up experiments.

Fig.5 represents the floatability of ilmenite and titanaugite with the mixed BHA/DDA collector(0.2 mM)at different pH.As seen in Fig.5,the recovery of ilmenite increases sharply to 99% as the pH increases from 2.3 to 8.5,and then drops slightly after that.The recovery of titanaugite shows a similar trend to that of ilmenite.However,the titanaugite recovery is always <20% within the pH range explored.Fig.5 clearly exhibits that,in a wide pH range(6

3.2.Zeta potential analysis

To explicate the dynamic potential changes of mineral surfaces with different treatments,the zeta potentials are measured at different pH values[31].Fig.6 presents the zeta-potentials of ilmenite and titanaugite under different pH when treated with 0.2 mM different flotation reagents (single DDA,single BHA,and the mixed BHA/DDA).As seen in Fig.6,the zeta potentials of the minerals decrease with the increase of pH,which is attribute to adsorption/dissociation reactions of H+and OH ions in solution with broken metal-O bonds at the crystal edges[32].The isoelectric point(IEP) of ilmenite conditioned in water is at pH 3.25,whereas the zeta potential of titanaugite is always negative,agreeing well with previous study [30].

Fig.4.Relationship between the recovery of ilmenite/titanaugite and the ratio of BHA to DDA at pH of 8–9 (concentration:0.2 mM).

Fig.5.Floatability of ilmenite and titanaugite with the mixed BHA/DDA collector at different pH (concentration:0.2 mM).

As seen in Fig.6,distinct positive shifts of the zeta potentials of both ilmenite and titanaugite are observed after adding DDA,which demonstrates that the adsorption of DDA on mineral surfaces by electrostatic force occur.Compared with the situation at pH <10,the zeta-potential values increase significantly at pH >10,indicating that DDA has a greater adsorption capacity on the mineral surface under such conditions.However,there is a reduction of hydrophobicity at pH 10(see flotation results in Section 3.1).According to the species distribution of DDA [33],at pH below 10,the RNH3+and(RNH3)22+species predominate in the solution.With the pH increasing from 6 to 10,the concentration of the neutral molecular species RNH2(aq) becomes dominant.At pH above 10,the neutral molecule precipitates RNH2(s).Pugh et al.[34] indicated that when the critical pH value is approximately 8,the cascading adsorption of DDA on the surface occurs.At pH above 10,the precipitation RNH2(s)of the less hydrophobic amines in a multilayer adsorbed outer layer turns the polar groups toward the solution,thus reducing hydrophobicity.Therefore,in the presence of DDA alone,the floatability of the two minerals decreases despite the increasing adsorption of DDA in alkaline environment.

Compared to those of minerals conditioned in water,the zeta potential of ilmenite and titanaugite changes slightly after adding single BHA.Presumably,the amount of BHA adsorbed on the mineral surfaces is not enough to cause the change of the mineral surface potentials or the adsorption of BHA on the mineral surfaces cannot exist stably.This will be discussed in the next sections(Sections 3.3 and 3.4).

Treated with the same concentration of BHA/DDA mixed collector,it is interestingly found that the zeta-potentials of ilmenite is more positive than that with single BHA but more negative than that with DDA alone.Apparently,both the chemically adsorbed BHA and the electrostatically adsorbed DDA act on the surface of ilmenite.However,there is no significant difference between the surface zeta potential of titanaugite treated with BHA/DDA mixture and that treated with single BHA and water.This indicates that the combined addition of BHA and DDA do not change the hydrophobicity of titanaugite,or that the BHA/DDA complex still cannot stably adsorb on the surface of titanaugite.For ilmenite,what needs to be noticed is that the zeta potential differences caused by adding mixed collector BHA/DDA and water decrease significantly with the pH changing from 2 to 10.This can be explained by the dissolution logarithm diagram of BHA[35].The dissociation equilibrium of BHA in aqueous solution occurs at pH 8.BHA mainly exists in its anionic form at pH >8,thus,the adsorption of more BHAdecreases the surface potential of ilmenite.In fact,when the positively charged DDA and the negatively charged BHA are mixed together in the solution,they may interact first and the resulting complex will adsorb on the mineral surface [36].Therefore,it can be speculated the differences in adsorption methods of the BHA/DDA complex on the ilmenite and titanaugite surfaces may be the reason for their prominent separation.

Fig.6.Zeta potential of ilmenite and titanaugite.

Fig.7.Chelate products of hydroximic acid with metal cations (after [38]).

3.3.Infrared (IR) spectroscopy

3.3.1.In situ ATR-FTIR analysis

It has been reported[37]that when hydroxamic acid bond with metal ions,the ‘‘O,O”five-membered ring and the ‘‘N,O”fourmembered ring structures appear,with the former more stable than the latter,and the two adsorption configurations are shown in Fig.7[38].Therefore,in order to study the adsorption difference of the BHA/DDA complex on ilmenite and titanaugite,spectra of the pure reagent BHA/DDA and adsorption of BHA/DDA onto these minerals are measured at several pH (Fig.8).In this work,since-NH3+,C=O,C=N,and the benzene rings are the main function groups,1200–2600 cm-1range is the area of interest in this section.Peak assignments from previous research [22,24,39,40],are used to aid in the interpretation.For the pure reagent BHA/DDA,four prominent peaks are observed at 1491,1630,1722,and 2360 cm-1in Fig.8a.For ilmenite,the corresponding four peaks are observed at 1542,1685,1775,and 2394 cm-1in Fig.8b.It is found that they shift for 51,55,53,and 34 cm-1,respectively.The appearance and shifts of these bands on the surface of ilmenite provide evidence for the chemical adsorption of the BHA/DDA complex on the ilmenite surface.As visibly presented in Fig.8b,at pH<8,two C=O stretch peaks of the hydroxamate appear,a distinct peak at 1685 cm-1and a weaker peak at 1775 cm-1.With the pH increasing,especially at pH>8,the peak at 1775 cm-1is blue shifted,suggesting deprotonation of the terminal oxygen[24].Moreover,the peaks of C=O imply that BHA maybe adsorb to the ilmenite surface by ‘‘O,O”coordination of the carbonyl oxygen with deprotonated OH(the five-membered ring) [41–43].On the other hand,these remaining peaksat1542and2345cm-1areassignedtothe-NH3+twistofdodecylamineand the-CN of dodecylamine,respectively.For titanaugite(Fig.8c),the displacements of the four peaks of interest are 26,15,2,and 15 cm-1,indicating that less chemisorbed BHA/DDA collectors adsorb onto the surface of titanaugite.Moreover,the peak intense of protonated BHA is weaker than that of ilmenite,that is,less physisorbed hydroxamate ion adsorbs onto the surface of titanaugite.Moreover,it should be mentioned that,compared to titanaugite,there is an obvious new peak at 1610 cm-1in the spectrum of ilmenite,which is assigned to the functional groups of C=N[22],indicating that the adsorption of BHA on titanaugite surface is mainly through the‘‘N,O”four-membered ring forms.Similarly,the peaks of the -NH3+twist of dodecylamine and the -CN of dodecylamine (1473 and 2394 cm-1)are weaker than that of ilmenite,indicating less adsorption of DDA on the titanaugite surface.As mentioned in Section 3.2,the adsorption of the complex,formed by the reaction of BHA and DDA,on the ilmenite surface results in higher recovery.Therefore,it can be speculated that it may be due to the inability of BHA to stably adsorb to the titanaugite surface,resulting in a decrease of the amount of DDA,which will be confirmed in subsequent research.

3.3.2.2D-COS analysis

To provide details about the reaction between BHA and DDA and difference in adsorption behavior on the surfaces of ilmenite and titanaugite,2DShige is applied to perform 2D correlation analysis.Fig.9 shows the synchronous correlation spectra and asynchronous correlation spectra in the range of 1000–2600 cm-1,respectively.Peak locations and assignments for mixed collectors are also derived from previous research[22,24,44–49]and summarized in Table 2.

Table 2 Peak positions and assignments related to the BHA/DDA complex adsorption process at pH of 8–9.

In synchronous spectra,the peaks at 1430,1585,1670,and 2350 cm-1are recognized as autopeaks in the synchronous plot of ilmenite (Fig.9a),while the other auto-peaks of titanaugite appeared at 1095,1470,1540,1625,1685,and 2360 cm-1(Fig.9b).This indicates the substantial changes of the related groups of BHA and DDA during the adsorption process.In asynchronous correlation spectra of ilmenite,both the positive crosspeaks at 1430/1585,1585/1670 cm-1are absent(red circle),which shows that strong interactions occur and new bonds may even appear between the C-H on benzene ring/C=O and -NH3+groups.Furthermore,off-diagonal cross-peaks at 1350/2350,1430/2350,1585/2350,and 1670/2350 cm-1appeared in the upper left triangle of in Fig.9a.In accordance with the well-established Noda’s rules [48],the orders of these peaks in the upper left triangle in Fig.9c can be summarized as:1350 →2350,1430 →2350,and 1670 →2350 cm-1(δHON/ωC-H/νC=O→δCN,where δHONrepresents the hydroxamate HON-bend),where‘‘→”means‘‘prior to”.Thus,the adsorption process of the BHA/DDA complex can be described as:‘‘the function groups HON and C=O of BHA preferentially interact with the metal sites to form a five-membered ring adsorption configuration.DDA is co-adsorbed with BHA on the surface of minerals by forming hydrogen bonds between the C-H on benzene ring/C=O and -NH3+groups.For titanaugite,apart from the peaks appearing on ilmenite,two obvious peaks at 1095 and 1625 cm-1are observed,which are assigned to C-O and C=N,indicating the existence of the four-membered ring structure of BHA on titanaugite.According to the same judgment method,the sequences of functional groups on titanaugite should be:1095 → 2360,1540 → 2360,1625 → 2360,and 1685 →2360 cm-1(νC-O/ωC-H/νC=N/νC=O→δCN,where νC-Orepresents the hydroxamate C-O stretch).Similarly,the positive cross-peak pairs at 1095/1540,1470/1540,and 1540/1690 cm-1disappear in the asynchronous spectra (red circle,Fig.9d),manifesting that the C=C/C-H on benzene ring and C-O/C=O of BHA interact with NH3+of DDA to form hydrogen bonds.

In conclusion,the possible adsorption process of the mixed collector BHA/DDA on ilmenite and titanaugite is summarized as follows:the functional groups of BHA first chelate with metal ions on the mineral surface to form bidentate adsorption,referring to fivemembered rings structure on the ilmenite surface and fourmembered rings structure on the titanaugite surface.DDA and BHA form complexes by hydrogen bonds,subsequently adsorbing onto the surface of ilmenite and titanaugite.Thus,the difference in adsorption configurations causes a lower adsorption density of DDA on titanaugite than ilmenite.Lastly,based on the above discussion,possible adsorption configurations for the adsorption BHA/DDA complex on the ilmenite and titanaugite surfaces are proposed in Fig.10,respectively.

Fig.8.ATR-FTIR difference spectra of the pure agent BHA/DDA,and the adsorption of BHA/DDA onto ilmenite and titanaugite at different pH (concentration:0.2 mM).

Fig.9.Synchronous and asynchronous of BHA/DDA adsorbed on ilmenite and titanaugite.Numbers in the first and second rows indicate auto peaks φ(v1,ν2)and cross-peaks ψ(v1,ν2) respectively, v1=ν2 in auto peaks.

3.4.X-ray photoelectron spectroscopy (XPS) analysis

XPS is an effective surface detection technology [50–52].Here,XPS measurements are carried out to provide additional details of the adsorption difference about ilmenite and titanaugite in different reagent systems.Fig.11 depicts the survey spectra of ilmenite and titanaugite treated with single and mixed collectors.Major peaks appear at 711.08 eV for Fe(2p),529.08 eV for O(1s),458.08 eV for Ti(2p),351.06 eV for Ca(2p),and 284.8 eV for C(1s)[53].After conditioning of ilmenite with BHA alone or BHA/DDA mixture,a weak peak is observed at 399.08 eV,corresponding to N(1s),which can be attributed to the chelation between BHA and metal ions on the mineral surfaces,the adsorption of DDA as well,for both BHA and DDA contain element N.

Fig.10.Main adsorption configuration of single-layer BHA/DDA on ilmenite and titanaugite.

Fig.11.XPS survey spectra of minirals with different collector.

The chemical states of the N element can directly reflect the adsorption configurations of single BHA or the mixed BHA/DDA on the minerals surfaces [54].Fig.12 shows the high-resolution XPS spectrum of N(1s) of the ilmenite and titanaugite surfaces treated with different collectors.Tian et al.[55] reported that two peaks of N(1s) at about 400.64 and 398.99 eV are attributed to (-C(OH)=N-O)and (-C(=O)-NH-O),respectively.As shown in Fig.12,for ilmenite (Fig.12a and c),two peaks at about 401.28 and 401.93 eV are attributed to (-C(OH)=N-O),while peaks at 399.68 and 399.93 eV correlate to (-C(=O)-NH-O).The main active sites on the ilmenite surface are Fe and Mg [6].The adsorption behavior of BHA or BHA/DDA on ilmenite can be summarized as Fe and Mg on the surface of ilmenite combine with two oxygens to form a five-membered ring,or with one nitrogen and one oxygen to form a four-membered ring,and the former is dominant.Moreover,for titanaugite (Fig.12b and d),the peaks at 402.58/401.08 eV and 399.83/399.48 eV are assigned to (-C(OH)=N-O)and (-C(=O)-NH-O),respectively.Fe,Mg,and Ca are the main active sites on the titanaugite surface[6].The adsorption behavior of BHA or BHA/DDA on titanaugite can be summarized as Fe,Mg and Ca on the surface of titanaugite combine with two oxygens to form a five-membered ring,or with one nitrogen and one oxygen to form a four-membered ring,and the latter is dominant.The above results prove the existence of both the stable five-membered-ring structure and four-membered-ring structure of BHA-metal or BHA/DDA-metal complexes on the ilmenite and titanaugite surfaces.What should be mentioned is that the content of the two bonds (five-membered-ring structure and fourmembered-ring)on the surface of ilmenite and titanaugite are significantly different.The relative contents of (-C(OH)=N-O) and(-C(=O)-NH-O) are listed in Table 3.When ilmenite is treated with single BHA,the relative content of five-membered-ring structure and four-membered-ring are 54.51%and 45.49%,respectively.In the presence of the mixed BHA/DDA,the relative contents of five-membered-ring structure and four-membered-ring changed as 79.52% and 20.48%,respectively.Therefore,the addition of DDA may change the adsorption mode of some BHA on ilmenite surface from four-membered ring to five-membered ring.While on the surface of titanaugite,the addition of DDA decreases the relative amount of five-membered-ring structure from 39.82% to 18.3%.BHA adsorbs on mineral surface in the form of fourmembered ring,which is more easily desorbed than that of fivemembered rings [22].

Fig.12.N(1s) XPS spectra of ilmenite and titanaugite treated with single BHA and the BHA/DDA complex at pH 8–9.

Table 3 Relative contents of -C(OH)=N-O and -C(=O)-NH-O.

4.Conclusions

In this work,this work researched the enhanced flotation separation performance of ilmenite and titanaugite using the mixed collector BHA/DDA,and the interface assembly mechanism of BHA/DDA was systematically investigated.The several important conclusions obtained from the above analyses are shown below.

(1) Single mineral flotation results suggest that mixed collector BHA/DDA (0.2 mM,at a molar ratio of 8:1) can effectively separate ilmenite from titanaugite with an ilmenite recovery of around 99.8% and that of titanaugite is <20% at pH 8–9.

(2) The adsorption process is described as:the function groups of BHA molecules first interact with the metal sites on minerals to form bidentate ligand,then DDA co-adsorbs with BHA on the surfaces of minerals through hydrogen bonding.

(3) XPS data provide further evidence that the existence of DDA may change the adsorption mode of some BHA on ilmenite surface from four-membered ring to five-membered ring,while the modes on the titanaugite surface is true opposite.Moreover,the difference in adsorption configurations results in a lower adsorption density of DDA on titanaugite than ilmenite,which might be the main reason for the poor flotation performance of titanaugite.

(4) Based on the above results,the adsorption configurations of the BHA/DDA complex on the surfaces of ilmenite and titanaugite are obtained.

Acknowledgements

This work was supported by the National Natural Science Foundation of China (Nos.51904249 and 51922091),the Sichuan Science and Technology Program (No.SYZ202074) and the Open Research Fund of State Key Laboratory of Complex Nonferrous Metal Resources Clean Utilization (No.CNMRCUKF2001).