Synthesis of S-Allyl-O, O ′ -Dibutyl Phosphorodithioate and Its Adsorption Mechanism on Chalcopyrite Surface

: The demand for non-ferrous copper metals has increased dramatically with the development of the global economy; accordingly, some refractory copper sulfide ores with low grade and their associated minerals are beginning to be utilized, making the flotation separation of copper concentrates exceptionally difficult, especially the separation of chalcopyrite and pyrite. In this paper, S-allyl-O, O ′ -dibutyl phosphorodithioate (ADTP) was synthesized by a one-pot method and used as a chalcopyrite collector in the flotation separation of chalcopyrite and pyrite. Flotation experiments results have shown that ADTP exhibits better selectivity and greater collecting power for chalcopyrite under neutral or weak base conditions. The 95% recovery of chalcopyrite can be achieved at pH 8.0 and 8.0 mg/L ADTP. From the analysis results of the contact angle, the SEM-EDS spectrogram, and elemental mapping, it was found that ADTP adsorbed uniformly on a chalcopyrite surface and made a significant contribution to the hydrophobicity of the surface. Confirmed by FTIR and XPS analysis, ADTP was able to form P–S–Cu bonds on a chalcopyrite surface, proving that it was adsorbed on the chalcopyrite surface in the form of chemisorption.


Introduction
With the rapid development of the global economy, the demand for non-ferrous metal minerals has increased dramatically.Among them, copper metal is a very important basic material and strategic resource, which has been widely used in such important fields as electric power, electronics, machinery manufacturing, and national defense engineering, with large consumption [1][2][3][4][5].Chalcopyrite (CuFeS 2 ) is the main source mineral of copper metal, but chalcopyrite often coexists with other sulfide ores, for example, pyrite [6][7][8].Traditionally, chalcopyrite/pyrite separation is achieved under high alkalinity conditions by using inexpensive lime to depress pyrite flotation.In addition to lime, other inorganic inhibitors can also be used to depress pyrite, such as NaClO, Ca(ClO) 2 , CaCl 2 , Na 2 S 2 O 3 , and (NH 4 ) 2 S 2 O 8 .Moreover, organic inhibitors, including tannic acid, carboxymethyl cellulose (CMC), ethylenediaminetetraacetic acid (EDTA), and some organic polymers, are also used.Lime is widely used in industry; its overuse can cause irreversible damage to the operating environment, flotation equipment, and water resources [9][10][11][12][13].Therefore, the effective separation of chalcopyrite from pyrite under neutral or weakly alkaline (low lime) conditions has always been a research hotspot.
In recent years, scholars have carried out a lot of research on the flotation separation of chalcopyrite and pyrite concentrates.There have been many studies on sulfhydryl surfactants, including xanthate, dithiocarbamate, dithiophosphate, and thiocarbamate, which are common flotation collectors for sulfide minerals.Qiu et al. [14] synthesized a new type of thiocarbamate compound with good selectivity under low alkali conditions, with a strong Minerals 2024, 14, 528 2 of 14 ability to combine chalcopyrite and a weak ability to collect pyrite.Sheridan et al. [15] prepared a derivative of a xanthate analogue, named N-allyl-O-alkyl thiocarbamate, which has been used worldwide in industrial flotation for the separation of chalcopyrite and pyrite ores due to its excellent selectivity for chalcopyrite.Liu et al. [16] investigated in detail the adsorption mechanism of the allyl isobutyl urethane collector on the surface of copper sulphide minerals, showing superior selectivity for chalcopyrite compared to pyrite and confirming the advantages of the structure of allyl-based urethane collectors.Thiocarbamate collectors have a good flotation capacity for chalcopyrite with excellent selectivity, and there is considerable research on these types of collectors [17,18].However, studies on phosphorodithioate collectors are rarely reported [19][20][21], and it would be of high research value to introduce allyl groups into their structure to improve the flotation performance.
In this paper, a novel surfactant, S-allyl-O, O ′ -dibutyl phosphorodithioate (ADTP), was designed and synthesized for the first time by introducing allyl groups into the molecular structure of ammonium dibutyl dithiophosphate (DTP), which was used in the flotation separation of chalcopyrite and pyrite.The flotation performance of the ADTP collector on chalcopyrite and pyrite was investigated by single-mineral flotation tests.The adsorption mechanism of ADTP on the chalcopyrite surface was systematically investigated by contact angle measurements, SEM-EDS energy spectroscopy and elemental mapping analyses, and FTIR and XPS spectroscopic analyses.

Materials and Reagents
The main raw materials used were ammonium dibutyl dithiophosphate (DTP), an industrial product obtained from Qingdao Jiahua Chemical Co., Ltd.(Qingdao, China Pure chalcopyrite and pure pyrite samples were both produced in Daye City, Hubei Province.They were hand crushed, ground, and dry sieved to obtain −200 +400 mesh samples, viz.38~74 µm (D80: 67.05 µm for chalcopyrite; 71.85 µm for pyrite), which were then cleaned and dried, and analyzed by X-ray diffraction (XRD: Figure 1), and their chemical element content (XRF: Table 1) showed that the diffraction peaks of the mineral crystal surfaces corresponded to each other with the standard minerals and that the purities of chalcopyrite and pyrite were 98.7% and 95.0%, respectively.These two pure mineral samples both have high purity; therefore, these mineral samples are suitable for pure mineral flotation experiments.
of chalcopyrite and pyrite ores due to its excellent selectivity for chalcopyrite.Liu [16] investigated in detail the adsorption mechanism of the allyl isobutyl uret collector on the surface of copper sulphide minerals, showing superior selectivit chalcopyrite compared to pyrite and confirming the advantages of the structure of based urethane collectors.Thiocarbamate collectors have a good flotation capacit chalcopyrite with excellent selectivity, and there is considerable research on these of collectors [17,18].However, studies on phosphorodithioate collectors are r reported [19][20][21], and it would be of high research value to introduce allyl groups their structure to improve the flotation performance.
In this paper, a novel surfactant, S-allyl-O, O′-dibutyl phosphorodithioate (AD was designed and synthesized for the first time by introducing allyl groups int molecular structure of ammonium dibutyl dithiophosphate (DTP), which was used i flotation separation of chalcopyrite and pyrite.The flotation performance of the A collector on chalcopyrite and pyrite was investigated by single-mineral flotation tests adsorption mechanism of ADTP on the chalcopyrite surface was systemat investigated by contact angle measurements, SEM-EDS energy spectroscopy elemental mapping analyses, and FTIR and XPS spectroscopic analyses.

Materials and Reagents
The main raw materials used were ammonium dibutyl dithiophosphate (DTP industrial product obtained from Qingdao Jiahua Chemical Co., Ltd.Pure chalcopyrite and pure pyrite samples were both produced in Daye City, H Province.They were hand crushed, ground, and dry sieved to obtain −200 +400 samples, viz.38~74 µm (D80: 67.05 µm for chalcopyrite; 71.85 µm for pyrite), which then cleaned and dried, and analyzed by X-ray diffraction (XRD: Figure 1), and chemical element content (XRF: Table 1) showed that the diffraction peaks of the mi crystal surfaces corresponded to each other with the standard minerals and tha purities of chalcopyrite and pyrite were 98.7% and 95.0%, respectively.These two mineral samples both have high purity; therefore, these mineral samples are suitab pure mineral flotation experiments.

Synthesis Experiment
Synthesis of ADTP: ADTP was synthesized by one-pot reaction by using DTP and chloropropene as the initial raw materials and water as the solvent; the product appeared as a light-yellow oily liquid, the yield was about 95.2%, the purity of the purified product was about 99.0%.Synthesis conditions: the molar ratio of DTP and chloropropene was around 1.05, the reaction temperature was set at 45 • C, and the reaction time was 3.0 h; after that, a crude product of ADTP with light yellow color was obtained.Purification step: The crude product ADTP was transferred to a separating funnel, and then a small amount of ethyl acetate was added to extract the ADTP product.The upper layer was an organic layer, and the sublayer was an aqueous phase.The aqueous phase was removed from below.After washing with water three times, a small amount of anhydrous MgSO 4 was added to the obtained oil phase to remove the residual water in the organic phase.Thereafter, the MgSO 4 solid with crystal water was filtered and the ethyl acetate solvent was removed, and the high-purity ADTP collector was finally obtained by rotary distillation of the filtrate.The synthetic route of the ADTP product is shown in Figure 2.

Synthesis Experiment
Synthesis of ADTP: ADTP was synthesized by one-pot reaction by using DTP and chloropropene as the initial raw materials and water as the solvent; the product appeared as a light-yellow oily liquid, the yield was about 95.2%, the purity of the purified product was about 99.0%.Synthesis conditions: the molar ratio of DTP and chloropropene was around 1.05, the reaction temperature was set at 45 °C, and the reaction time was 3.0 h; after that, a crude product of ADTP with light yellow color was obtained.Purification step: The crude product ADTP was transferred to a separating funnel, and then a small amount of ethyl acetate was added to extract the ADTP product.The upper layer was an organic layer, and the sublayer was an aqueous phase.The aqueous phase was removed from below.After washing with water three times, a small amount of anhydrous MgSO4 was added to the obtained oil phase to remove the residual water in the organic phase.Thereafter, the MgSO4 solid with crystal water was filtered and the ethyl acetate solvent was removed, and the high-purity ADTP collector was finally obtained by rotary distillation of the filtrate.The synthetic route of the ADTP product is shown in Figure 2.

Micro-Flotation Test
Micro-flotation tests were carried out by using an XFGC (5~35 g) flotation machine (Jilin Prospecting Machinery Factory, Jilin, China).Firstly, 2.0 g single mineral or artificially mixed mineral samples (38~74 µm) were dispersed with deionized water and then ultrasonic cleaned for 1 min.After that, the upper water was poured off, and another new 25 mL of water was added.Next, the pH was adjusted to a desired value, and then the pulp was transferred into the flotation cell, stirring for 2 min at 1758 rpm.Thereafter, the collector was introduced, stirring occurred for another 2 min, and then the foaming agent MIBC was added and stirred for another 1 min.When finished, the froth flotation was conducted for 4 min with an air flowrate of 0.2 m 3 /h.Finally, the froth product and the tailings were dried and weighed and the recoveries were calculated.The flowsheet for micro-flotation tests is shown in Figure 3.

Micro-Flotation Test
Micro-flotation tests were carried out by using an XFGC (5~35 g) flotation machine (Jilin Prospecting Machinery Factory, Jilin, China).Firstly, 2.0 g single mineral or artificially mixed mineral samples (38~74 µm) were dispersed with deionized water and then ultrasonic cleaned for 1 min.After that, the upper water was poured off, and another new 25 mL of water was added.Next, the pH was adjusted to a desired value, and then the pulp was transferred into the flotation cell, stirring for 2 min at 1758 rpm.Thereafter, the collector was introduced, stirring occurred for another 2 min, and then the foaming agent MIBC was added and stirred for another 1 min.When finished, the froth flotation was conducted for 4 min with an air flowrate of 0.2 m 3 /h.Finally, the froth product and the tailings were dried and weighed and the recoveries were calculated.The flowsheet for micro-flotation tests is shown in Figure 3.

Contact Angle Measurements
The wettability of the surface of chalcopyrite or pyrite is closely related to their floatability [4], and its contact angle was measured on the SDC-100 contact angle meter equipment.During the preparation of the samples, chalcopyrite and pyrite were processed using the optimum conditions for flotation, and the processed mineral samples

Contact Angle Measurements
The wettability of the surface of chalcopyrite or pyrite is closely related to their floatability [4], and its contact angle was measured on the SDC-100 contact angle meter equipment.During the preparation of the samples, chalcopyrite and pyrite were processed using the optimum conditions for flotation, and the processed mineral samples were pressed into flakes to determine their contact angles, which were compared with those of the original pure chalcopyrite and pyrite samples.

SEM-EDS Measurements
An appropriate amount of chalcopyrite (38~74 µm) was taken, cleaned by ultrasonic, dried under vacuum, and treated with the ADTP collector for chalcopyrite and untreated blank chalcopyrite as a comparison.The samples were tested using Scanning Electron Microscope and Energy Dispersive X-ray Spectroscopy (SEM-EDS) mapping tests to observe the surface of the minerals as well as the distribution of elemental variations.

FTIR Measurements
The tested samples were obtained by the fine grinding of pure chalcopyrite (1.0 g) to −2 µm in an agate mortar and stored under vacuum firstly.After that, these ground samples were placed into a beaker, 25 mL water was added, and the pulp pH was adjusted.Next, the ADTP collector was introduced and stirred magnetically for 30 min.After washing, the ore samples were dried at 60 • C under vacuum.FTIR measurements were carried out on a Nicolet IS-10 (Thermo Fisher USA, Waltham, MA, USA) FTIR spectrometer.Herein, the FTIR spectra of ADTP, chalcopyrite, and treated chalcopyrite with ADTP were recorded in the range of 4000 cm −1 and 400 cm −1 using the KBr disc technique.

XPS Measurements
XPS measurements of untreated and treated chalcopyrite samples with ADTP were carried out with an ESCALAB Xi+ (Thermo Fisher Scientific, USA), respectively, under the testing conditions of a monochromatic Al-Kα X-ray source with power of 150 W, energy of 30 eV, and an analytical chamber with pressure of about 10 −9 Torr.The binding energy of each element was obtained by calibrating against C 1s (284.80 eV).

Characterization of ADTP
The chemical structure of ADTP was confirmed by FTIR (Figure 4) and 1 H NMR (Figure 5).The analysis results are presented in Table 2.

Characterization of ADTP
The chemical structure of ADTP was confirmed by FTIR (Figure 4) and 1 H NMR (Figure 5).The analysis results are presented in Table 2.

Micro-Flotation Test
The flotation performance of ADTP on chalcopyrite and pyrite was investigated through single-mineral micro-flotation tests.Figure 6a shows the variation rule of the flotation recoveries of chalcopyrite and pyrite with pH changes under the condition of 10.0 mg/L ADTP.The results show that the recovery of chalcopyrite firstly increases and then decreases in the interval of pH 5.0~12.0,and its flotation recovery reaches a maximum value of 95.5% at pH around 8.0, while for pyrite, its recovery is kept below 20% within the tested pH range and decreases with the increase of pH.According to the above analysis, the separation of chalcopyrite and pyrite in the presence of ADTP will be achieved at pH 8.0. Figure 6b shows the change rule of the flotation recovery of chalcopyrite and pyrite when changing ADTP dosages at pH 8.0.The recovery of chalcopyrite increases significantly as the ADTP dosage increases from 2.0 to 12.0 mg/L.When the ADTP dosage was 8.0 mg/L, the chalcopyrite recovery was 95.2%, and then it levelled off.However, pyrite's recovery does not change significantly.In summary, it can be seen that the recovery difference in the flotation performance of ADTP for chalcopyrite and pyrite favors the separation in the chalcopyrite/pyrite mineral system.rite when changing ADTP dosages at pH 8.0.The recovery of chalcopyrite increases significantly as the ADTP dosage increases from 2.0 to 12.0 mg/L.When the ADTP dosage was 8.0 mg/L, the chalcopyrite recovery was 95.2%, and then it levelled off.However, pyrite's recovery does not change significantly.In summary, it can be seen that the recovery difference in the flotation performance of ADTP for chalcopyrite and pyrite favors the separation in the chalcopyrite/pyrite mineral system.As observed in Figure 6, ADTP would be an excellent collector for chalcopyrite with good selectivity.In order to evaluate its separation efficacy in the flotation separation of chalcopyrite/pyrite, artificial mixed minerals (chalcopyrite and pyrite, mass ratio = 1:1) were subjected to flotation at pH around 8.0.Herein, as a comparison, two traditional collectors, O-isopropyl-N-ethyl thiocarbamate (Z200) and DTP, were employed with a same dosage of 8.0 mg/L as ATDP.The amount of foaming agent MIBC was fixed at 8.0 mg/L.The flotation separation results for artificially mixed minerals are shown in Table 3.As noted in Table 3, when using ADTP as the collector, the copper recovery in the concentrate is 95.74%, which is higher than 83.03% and 92.52% when using Z200 and DTP.Meanwhile, the copper grade in the concentrate in the presence of ADTP is 23.38%, which is also higher than Z200 (16.93%) and DTP (20.60%).Therefore, ADTP shows better selective flotation performance for chalcopyrite in the flotation separation of chalcopyrite/pyrite.As observed in Figure 6, ADTP would be an excellent collector for chalcopyrite with good selectivity.In order to evaluate its separation efficacy in the flotation separation of chalcopyrite/pyrite, artificial mixed minerals (chalcopyrite and pyrite, mass ratio = 1:1) were subjected to flotation at pH around 8.0.Herein, as a comparison, two traditional collectors, O-isopropyl-N-ethyl thiocarbamate (Z200) and DTP, were employed with a same dosage of 8.0 mg/L as ATDP.The amount of foaming agent MIBC was fixed at 8.0 mg/L.The flotation separation results for artificially mixed minerals are shown in Table 3.As noted in Table 3, when using ADTP as the collector, the copper recovery in the concentrate is 95.74%, which is higher than 83.03% and 92.52% when using Z200 and DTP.Meanwhile, the copper grade in the concentrate in the presence of ADTP is 23.38%, which is also higher than Z200 (16.93%) and DTP (20.60%).Therefore, ADTP shows better selective flotation performance for chalcopyrite in the flotation separation of chalcopyrite/pyrite.

Contact Angle Analyses
The effect of the ADTP collector on the surface wettability of chalcopyrite and pyrite can be reflected by the contact angle [26], as shown in Figure 7, which was 64.5 • and 24.6 • for the original chalcopyrite and pyrite, respectively.The contact angles of treated chalcopyrite and pyrite were measured under the optimal flotation conditions, i.e., pH 8.0 and 8.0 mg/L ADTP.As shown in Figure 7, the contact angle of chalcopyrite after ADTP adsorption was 101.3 • , which was 36.8 • higher than that before treatment, and the hydrophobicity of its surface was greatly improved.However, the contact angle of pyrite after treatment was only 36.5 • , with a slight change, just because a small amount of ADTP can adsorb on the pyrite surface, only resulting in a small enhancement of hydrophobicity.This finding suggests that ADTP has a greater ability to adsorb on the chalcopyrite surface than on pyrite, creating favorable conditions for chalcopyrite/pyrite separation.In order to further illustrate the advantages of ADTP, a comparative analysis was conducted with the initial DTP collector and the traditional Z200 collector.Under the same conditions, the contact angles between chalcopyrite treated with Z200 and DTP are 112.2• and 88.6 • , respectively, and the contact angles with pyrite are 58.5 • and 39.3 • , respectively.Compared with chalcopyrite and pyrite treated with ADTP, their contact angles are both improved.Compared with chalcopyrite/ADTP, the surface contact angle of chalcopyrite treated with ADTP is significantly higher than that of DTP but lower than that of Z200, showing better selectivity for chalcopyrite by introducing allyl groups into the DTP molecular structure, while for pyrite, ADTP exhibits a weak adsorption on its surface with a lower contact angle of 36.5 • than those of Z200 (58.5 • ) and DTP (39.3 • ).From these results, it can be inferred that ADTP can significantly improve the hydrophobicity of the chalcopyrite surface and promote weak adsorption on pyrite, creating a great separation environment from pyrite.
This finding suggests that ADTP has a greater ability to adsorb on the chalcopyrite s than on pyrite, creating favorable conditions for chalcopyrite/pyrite separation.In to further illustrate the advantages of ADTP, a comparative analysis was conducted the initial DTP collector and the traditional Z200 collector.Under the same conditio contact angles between chalcopyrite treated with Z200 and DTP are 112.2°and 88. spectively, and the contact angles with pyrite are 58.5° and 39.3°, respectively.Com with chalcopyrite and pyrite treated with ADTP, their contact angles are both imp Compared with chalcopyrite/ADTP, the surface contact angle of chalcopyrite treate ADTP is significantly higher than that of DTP but lower than that of Z200, showing selectivity for chalcopyrite by introducing allyl groups into the DTP molecular stru while for pyrite, ADTP exhibits a weak adsorption on its surface with a lower conta gle of 36.5°than those of Z200 (58.5°) and DTP (39.3°).From these results, it can be in that ADTP can significantly improve the hydrophobicity of the chalcopyrite surfac promote weak adsorption on pyrite, creating a great separation environment from p

SEM-EDS Analyses
The microscopic morphology of the chalcopyrite surface was characterized by scanning electron microscopy and Energy Dispersive X-ray Spectroscopy (SEM-EDS).SEM-EDS analysis can clearly show the adsorption of regents on a mineral surface [27].Figure 8a-f shows the SEM images of the original chalcopyrite and treated chalcopyrite with ADTP at different magnifications.From the differences of the morphology before and after treatment, it can be observed that the treated chalcopyrite surface becomes rougher after the adsorption of the ADTP collector, inferring the successful adsorption of the collector on the chalcopyrite surface [28,29].By analyzing the surface-scanning energy dispersive X-ray spectra (EDS) [30] of the chalcopyrite before and after ADTP treatment, as shown in Figure 9a-d, the comparison results reveal that there are relatively significant changes observed in the content of each element, among which the content of the P element has been greatly enhanced.In addition, scanning electron microscope (SEM) images (Figure 10a) and EDS elemental mapping results (Figure 10b-f) show that these O, C, Cu, P, and S elements are observed in the treated chalcopyrite surface with ADTP and are evenly distributed on the surface [31].In summary, these findings provide the visual evidence that the ADTP collector had been uniformly adsorbed on the chalcopyrite surface successfully.
ment has been greatly enhanced.In addition, scanning electron microscope (SEM) images (Figure 10a) and EDS elemental mapping results (Figure 10b-f) show that these O, C, Cu, P, and S elements are observed in the treated chalcopyrite surface with ADTP and are evenly distributed on the surface [31].In summary, these findings provide the visual evidence that the ADTP collector had been uniformly adsorbed on the chalcopyrite surface successfully.changes observed in the content of each element, among which the content of the P element has been greatly enhanced.In addition, scanning electron microscope (SEM) images (Figure 10a) and EDS elemental mapping results (Figure 10b-f) show that these O, C, Cu, P, and S elements are observed in the treated chalcopyrite surface with ADTP and are evenly distributed on the surface [31].In summary, these findings provide the visual evidence that the ADTP collector had been uniformly adsorbed on the chalcopyrite surface successfully.

FTIR Analyses
The structure and chemical bonding of the molecules on the chalcopyrite surface before and after treatment with ADTP were analyzed by FTIR spectroscopy, as well as its reaction mechanism on the surface.The FTIR spectra of ADTP, untreated chalcopyrite, and treated chalcopyrite with ADTP are shown in Figure 11.The FTIR spectra show that -P=S stretching vibration at 687 cm −1 and -C-S-characteristic absorption bands at 1028

FTIR Analyses
The structure and chemical bonding of the molecules on the chalcopyrite surface before and after treatment with ADTP were analyzed by FTIR spectroscopy, as well as its reaction mechanism on the surface.The FTIR spectra of ADTP, untreated chalcopyrite, and treated chalcopyrite with ADTP are shown in Figure 11.The FTIR spectra show that -P=S stretching vibration at 687 cm −1 and -C-S-characteristic absorption bands at 1028 cm −1 appear on the surface of chalcopyrite.The asymmetric bending vibration of -CH 3 and the scissor rocking vibration of -CH 2 -appeared on chalcopyrite at 2956 cm −1 and 2884 cm −1 , respectively [32,33], and the peaks on chalcopyrite/ADTP were very similar to the two peaks on ADTP at 2962 cm −1 and 2878 cm −1 [34]; the position of the characteristic peaks on chalcopyrite/ADTP does not change much, indicating that the ADTP collector has adsorbed on chalcopyrite [35].After the adsorption of ADTP on pristine chalcopyrite, a new obvious characteristic absorption peak at 1424 cm −1 was noted, which may be the ligand bond formed between chalcopyrite and ADTP as Cu-ADTP, indicating chemisorption between the surface of chalcopyrite and ADTP.

FTIR Analyses
The structure and chemical bonding of the molecules on the chalcopyrite surface before and after treatment with ADTP were analyzed by FTIR spectroscopy, as well as its reaction mechanism on the surface.The FTIR spectra of ADTP, untreated chalcopyrite, and treated chalcopyrite with ADTP are shown in Figure 11.The FTIR spectra show that -P=S stretching vibration at 687 cm −1 and -C-S-characteristic absorption bands at 1028 cm −1 appear on the surface of chalcopyrite.The asymmetric bending vibration of -CH3 and the scissor rocking vibration of -CH2appeared on chalcopyrite at 2956 cm −1 and 2884 cm −1 , respectively [32,33], and the peaks on chalcopyrite/ADTP were very similar to the two peaks on ADTP at 2962 cm −1 and 2878 cm −1 [34]; the position of the characteristic peaks on chalcopyrite/ADTP does not change much, indicating that the ADTP collector has adsorbed on chalcopyrite [35].After the adsorption of ADTP on pristine chalcopyrite, a new obvious characteristic absorption peak at 1424 cm −1 was noted, which may be the ligand bond formed between chalcopyrite and ADTP as Cu-ADTP, indicating chemisorption between the surface of chalcopyrite and ADTP.

XPS Analyses
The adsorption mechanism of ADTP on the chalcopyrite surface was analyzed by XPS, and the high-resolution XPS spectra of chalcopyrite before and after ADTP treatment were also investigated and fitted.The survey XPS spectra of chalcopyrite (a) and chalcopyrite/ADTP (b) are shown in Figure 12.The results show that the XPS spectrum of chalcopyrite/ADTP contains Cu, Fe, O, C, S, and P, which indicates that ADTP has adsorbed on the chalcopyrite surface [36], maintaining good agreement with the EDS test and elemental mapping test results.To further explore the valence states of elements on the chalcopyrite surface, the high-resolution XPS spectra of Cu 2p, S 2p, O 1s, and P 2p [37] on the chalcopyrite surface before and after ADTP adsorption are fitted and shown in Figure 13.
Figure 13a shows the fitted Cu 2p XPS spectra.The Cu 2p 3/2 XPS spectra of pristine chalcopyrite were fitted with two peaks at 931.93 eV and 933.08 eV, belonging to Cu-S (CuFeS 2 ) and Cu-O (CuO or Cu(OH) 2 ), respectively [38,39], which indicated that a small portion of the chalcopyrite surface was oxidized.After ADTP treatment, three Cu 2p 3/2 peaks appearing at 931.83 eV, 932.94 eV, and 934.28 eV are noted.The binding energies of Cu-S and Cu-O from pristine chalcopyrite were shifted down to 931.83 eV and 932.94 eV, respectively.The reason is that the adsorption of ADTP leads to an increase in the density of the outer electrons and an increase in the shielding effect, thereby resulting in a decrease in the binding energy.The new peak at 934.28 eV may belong to the Cu-ADTP complex, formed by the reaction of the Cu site on the chalcopyrite surface with the P=S group in the ADTP structure (the P-S-Cu bond).
The adsorption mechanism of ADTP on the chalcopyrite surface was analyzed by XPS, and the high-resolution XPS spectra of chalcopyrite before and after ADTP treatment were also investigated and fitted.The survey XPS spectra of chalcopyrite (a) and chalcopyrite/ADTP (b) are shown in Figure 12.The results show that the XPS spectrum of chalcopyrite/ADTP contains Cu, Fe, O, C, S, and P, which indicates that ADTP has adsorbed on the chalcopyrite surface [36], maintaining good agreement with the EDS test and elemental mapping test results.To further explore the valence states of elements on the chalcopyrite surface, the high-resolution XPS spectra of Cu 2p, S 2p, O 1s, and P 2p [37] on the chalcopyrite surface before and after ADTP adsorption are fitted and shown in Figure 13.XPS, and the high-resolution XPS spectra of chalcopyrite before and after ADTP treatment were also investigated and fitted.The survey XPS spectra of chalcopyrite (a) and chalcopyrite/ADTP (b) are shown in Figure 12.The results show that the XPS spectrum of chalcopyrite/ADTP contains Cu, Fe, O, C, S, and P, which indicates that ADTP has adsorbed on the chalcopyrite surface [36], maintaining good agreement with the EDS test and elemental mapping test results.To further explore the valence states of elements on the chalcopyrite surface, the high-resolution XPS spectra of Cu 2p, S 2p, O 1s, and P 2p [37] on the chalcopyrite surface before and after ADTP adsorption are fitted and shown in Figure 13.  Figure 13b shows the fitted S 2p XPS spectra.The results show that the S 2p XPS spectrum consists of S 2p 3/2 and S 2p 1/2 , and the intensity of S 2p 3/2 is two times higher than that of S 2p 1/2 [40].The S 2p 3/2 XPS peaks of untreated pristine chalcopyrite can be fitted into three peaks located at 161.06 eV, 162.05 eV, and 163.67 eV, which belong to sulphide (S 2− ), disulphide (S 2 2− ), and polysulphide (S n 2− ), respectively [14,39], while the peak area accounts for 47.4%, 37.4%, and 15.2%, respectively.After ADTP adsorption, the S 2p 3/2 XPS spectrum on the chalcopyrite surface shows three different peaks at approximately 160.95 eV, 161.97 eV, and 163.64 eV, with peak area ratios of 43.9%, 35.1%, and 21.0%, respectively.The peak area increased at 163.64 eV, indicating that these peaks are attributed to the S species (S 2− ) on the chalcopyrite surface and the Cu-S and P-S-C groups of the Cu-ADTP surface species.This study indicates that the S atom in the P=S group contributes its electrons to the copper ion, P=S bond breakage of ADTP and forms a P-S-Cu bond with Cu sites on the chalcopyrite surface.
Figure 13c shows the fitted O 1s XPS spectra.Clearly, the O 1s XPS spectrum of the pristine chalcopyrite sample consists of three peaks at 530.0 eV, 531.50 eV, and 532.76 eV, which are common characteristics of O 2− from Fe 2 O 3 , OH − of FeOOH, and adsorbed H 2 O, respectively [38,41].After treatment with ADTP, the spectrum of O 1s was split into four peaks.The peaks of O 2− of Fe 2 O 3 and OH − of FeOOH did not change much, indicating that there was no reaction between the Fe atoms on the chalcopyrite surface and the ADTP molecules [39].The peak of O from water was reduced relative to the original chalcopyrite, indicating that the adsorption of ADTP increased the hydrophobicity of chalcopyrite, thereby reducing the adsorption of water.In addition, a new peak appeared at 529.27 eV, which was supposed to be the O 1s peak of the C-O-P group in ADTP structure, further indicating that the ADTP collector had adsorbed on the surface of chalcopyrite and had no significant effect on Fe, which laterally reflects the excellent selectivity of ADTP to chalcopyrite.
Figure 13d shows the fitted P 2p XPS spectra.The analysis result shows that for untreated chalcopyrite with the ADTP collector, the P 2p peaks are hardly detected in its XPS spectrum.After the adsorption of ADTP on the chalcopyrite surface, a very distinct P 2p peak appeared at 133.44 eV, which is due to the P element in the -(P=S)-S group in the ADTP structure.This finding further suggests that ADTP is very likely to chemisorb onto the chalcopyrite surface.
It can be inferred from these FTIR and XPS analysis results that the introduction of an allyl group in the structure of the DTP molecule improves the collecting ability and the selectivity, and the newly synthesized ADTP collector can adsorb on the surface of chalcopyrite in the form of chemical bonding, viz. the P-S-Cu bond between the P=S group in ADTP and Cu sites on the surface of chalcopyrite [42,43].Based on these above findings, the adsorption model of the ADTP collector on the surface of chalcopyrite can be proposed as shown in Figure 14.

Conclusions
In present study, the ADTP collector was synthesized by a simple one-pot method and used as a selective collector for chalcopyrite, and its flotation performance on chalcopyrite and pyrite and its adsorption mechanism were well investigated.The main findings can be drawn as follows.
The micro-flotation test results showed that ADTP had better selectivity on chalcopyrite than on pyrite, with a 95% recovery on chalcopyrite and a weaker flotation performance on pyrite under neutral and weak alkaline conditions.The difference in the floatability between these two minerals was more obvious when the pulp pH was around 8.0.The contact angle showed that the adsorption of ADTP greatly enhanced the hydrophobicity of the chalcopyrite surface rather than that of pyrite surface, compared with the

Conclusions
In present study, the ADTP collector was synthesized by a simple one-pot method and used as a selective collector for chalcopyrite, and its flotation performance on chalcopyrite and pyrite and its adsorption mechanism were well investigated.The main findings can be drawn as follows.
), and chloropropene (98%), a chlorohydrocarbon reagent obtained from Shanghai McLean Biochemical Science and Technology Co., Ltd.(Shanghai, China), which were used to synthesize the ADTP collector.The methyl isobutyl methanol (MIBC 99%) frother and sodium hydroxide (NaOH) modifier were obtained from Shanghai McLean Biochemical Science and Technology Co. Ltd., and hydrochloric acid (HCl) was supplied by Sinopharm Chemical Reagent Co., Ltd.(Shanghai, China) and used for single mineral flotation tests.Deionized water was used for all of the experiments.
(Qingdao, Ch and chloropropene (98%), a chlorohydrocarbon reagent obtained from Shanghai Mc Biochemical Science and Technology Co., Ltd.(Shanghai, China), which were us synthesize the ADTP collector.The methyl isobutyl methanol (MIBC 99%) frother sodium hydroxide (NaOH) modifier were obtained from Shanghai McLean Bioche Science and Technology Co. Ltd., and hydrochloric acid (HCl) was supplied by Sinop Chemical Reagent Co., Ltd.(Shanghai, China) and used for single mineral flotation Deionized water was used for all of the experiments.

Figure 3 .
Figure 3.The flow chart for micro-flotation tests.

Figure 3 .
Figure 3.The flow chart for micro-flotation tests.

Figure 6 .
Figure 6.The flotation performances of chalcopyrite and pyrite with various pHs (a) at ADTP 10.0 mg/L and with various ADTP dosages (b) at pH 8.0.

Figure 6 .
Figure 6.The flotation performances of chalcopyrite and pyrite with various pHs (a) at ADTP 10.0 mg/L and with various ADTP dosages (b) at pH 8.0.

Figure 7 .
Figure 7.The contact angles of original chalcopyrite and pyrite, and the contact angles afte DTP, and ADTP treatment of chalcopyrite and pyrite.

Figure 7 .
Figure 7.The contact angles of original chalcopyrite and pyrite, and the contact angles after Z200, DTP, and ADTP treatment of chalcopyrite and pyrite.

Figure 9 . 14 Figure 9 .
Figure 9. EDS spectra of the chalcopyrite before (a,b) and after (c,d) treatment with ADTP.

Figure 14 .
Figure 14.Putative proposed adsorption model of ADTP on chalcopyrite surfaces.

Figure 14 .
Figure 14.Putative proposed adsorption model of ADTP on chalcopyrite surfaces.

Table 2 .
FTIR and 1 H NMR results of ADTP.

Table 2 .
FTIR and 1 H NMR results of ADTP.

Table 3 .
The results of artificially mixed mineral flotation experiments.