Flotation separation of pyrite and carbonate minerals from a carlin-type gold deposit in Guizhou by a new combined collector and its adsorption mechanism

Abstract

Flotation is the most common method for effective separation of pyrite and carbonate minerals from Carlin-type gold deposits. The effect of conventional xanthate collector on flotation of a Carlin-type gold mine in Guizhou province is poor, and it can not effectively remove carbonate minerals. In this paper, butyl xanthoxanthate and benzohydroxamic acid (BHA) were used as a new combined collector for the flotation separation of a Carlintype gold mine in Guizhou Province. The flotation behavior of pyrite and its adsorption mechanism on pyrite surface were discussed in detail through pure mineral flotation test, actual ore flotation test, contact Angle test, infrared spectrum analysis and XPS analysis. The results showed that the collection capacity of butyl xanthoxime combined with benzohydroxamic acid was obviously stronger than that of BHA or butyl xanthoxime alone. The optimal ratio of pyrite flotation with combined collector is 3, and the recovery rate of pyrite flotation is 37%, which is higher than that of pyrite flotation recovery of 30.5% when benzohydroxamic acid is used alone and 28.5% when butyl xanthate is used alone. The contact Angle test, infrared spectrum and XPS analysis showed that the combined collector of butyl xanthate and benzohydroxamic acid (BHA) produced strong chemical adsorption on the surface of pyrite. Bha can increase the adsorption capacity of butyl xanthate on the surface of pyrite, which is conducive to the flotation recovery of pyrite.

Introduction

Pyrite is a common sulfide ore, usually associated with sphalerite, chalcopyrite, galena, stibnite, gold, coal and other valuable minerals^1,2,3,4,5,6. Research on the floatability of pyrite is conducive to the separation and enrichment of these minerals. In a micro-disseminated gold mine, pyrite is the main carrier mineral of gold^7,8. The extraction of gold from micro-disseminated gold mine requires the separation and enrichment of pyrite. Therefore, flotation separation of pyrite and flotation separation of gold can be regarded as equivalent. Flotation is currently a widely used and effective method for pyrite separation and enrichment^9,10. The most commonly used collector for pyrite flotation is butyl xanthate¹¹. Although butyl xanthate has a strong collecting ability, its selectivity is low¹², so it is particularly important to study efficient pyrite collectors.

In recent years, combined collectors have been widely used in the high-efficiency flotation separation of gold ores. T.n.alksandrova¹³ analyzed dithiopyrromethane (DTM) combined with butyl potassium xanthate (PBX) for the recovery of gold from low sulfide arsenic gold deposits. The results show that the PBX-DTM combination can increase the yield of pure arsenopyrite and gold-containing arsenopyrite simultaneously. With the increase of gold recovery and the decrease of tailings gold recovery, the grade of the concentrate was increased by 3 times. T.N.Matveeva et al.¹⁴ found that morpholine dithiocarbamate (MDTC) and S-cyanoethyl N, n-diethyl dithiocarbamate (CEDETC) can form stable compounds with gold in solution and form an adsorption layer on the surface of gold-bearing sulfide. This suggests that they could be used as new selective collectors to recover gold from refractory ores. Yang Hui et al.¹⁵, aiming at the gold ore with a raw gold grade of 4.48 g/t, used the mixed collector NDM + KAX system to obtain the index of gold recovery of 92.44% under the weak alkaline condition with a pH of 9 and a lower amount of collector, which is better than the sorting effect of a single isopentxanthin system under acidic conditions. Zhu Wenchao¹⁶ showed that for pyrite and arsenic-containing pyrite, the use of long-chain xanthoxanthin such as butyl xanthoxanthin, penxanthoxanthin and Y-89 alone has good selectivity, but poor collection performance, while the use of penxanthoxanthin + Y-89 under the dosage of 120 g/t + 80 g/t can improve the collection performance. The ability of collector to collect gold-bearing components in the high-carbon microfine gold ore can be greatly improved. Xing Xifeng et al.¹⁷ conducted an experimental study on collector variables for a gold mine, and the test results showed that the collection capacity of ethyxanthate was the weakest, and the collection capacity gradually increased with the increase of carbon chain, and butadiamine black as an auxiliary collector helped to improve the recovery rate. The combination of butylxanthoxanthate and butylamine black powder at 7:3 ratio has the best collecting ability, and the lowest grade of tailings selected by the latter is 0.8 g/t and the highest recovery rate is 99.28%. In order to improve the recovery rate and the quality of gold concentrate, Li Jianbai et al.¹⁸ introduced a new collector MC to a gold mine in Longnan and conducted beneficiation experiments. The test results show that the gold concentrate grade is increased from 23.24 g/t to 25.22 g/t and the recovery rate of gold concentrate is increased from 80.57 to 85.21% under the condition of pH 10 when MC and butyl ammonium black powder are used as the collector with mass 1:1, and the good test index is obtained, which provides data support for the field technical reform.

When two agents with complementary harvesting properties are used in combination, the effect of 1 + 1 > 2 is often obtained. The structural formula of benzohydroxamic acid (BHA) is phC(O)NHOH, which is obtained by the reaction of methyl benzoate and hydroxylamine hydrochloride. It has two co-existing tautomers, oxyamic acid and hydroxamic acid, and is a chelating collector¹⁹. The non-polar group of the molecule contains a benzene ring, and the polar group contains multiple bonding atoms that can interact with the active site on the surface of minerals. In addition, the bonded atoms in the molecule can chelate and coordinate with one or several mineral surface active sites, thus achieving the purpose of harvesting valuable minerals²⁰. Benzohydroxamic acid (BHA) has good selectivity for fine minerals but low harvesting capacity^21,22, and the combination of butyl xanthate with strong harvesting capacity but poor selectivity has a good flotation effect. Therefore, in this study, a combination of butyl xanthoxanthate and benzohydroxamic acid (BHA) was used as a flotation collector for pyrite in fine disseminated gold deposits. The feasibility of using benzohydroxamic acid (BHA) as the collector for pyrite flotation was verified by flotation tests, and the mechanism of the combination of butyl xanthoxanthate and benzohydroxamic acid (BHA) on pyrite flotation was studied.

Materials and methods

Materials

The pure mineral samples of pyrite were taken from Guangzhou Mingfa Mineral Specimen Manufacturing Co., LTD., and the samples of -0.075 mm particle size and − 0.075 mm + 0.038 mm particle size were prepared by hand selection, crushing, grinding and screening, respectively, for the pure mineral flotation test. -0.038 mm sample size for XPS and infrared spectroscopy tests.

The pure mineral samples of pyrite were analyzed by X-ray diffraction spectroscopy and chemical multielement chemical analysis. The results are shown in Fig. 1; Table 1 respectively.

Fig. 1

X-ray diffraction pattern of pyrite.

Table 1 Multielement chemical analysis of pure pyrite minerals/%.

As can be seen from Fig. 1, the diffraction peak of pure mineral pyrite is consistent with the standard card data of pyrite, and the diffraction peak of other impurity minerals is not observed. It can be seen from Table 1 that the purity of pyrite can be determined to be 98.18% by combining elemental analysis, and the purity of pyrite selected for the test meets the requirements of pure mineral test.

The samples of fine disseminated gold ore were taken from the ball mill feed belt of a concentrator in Guizhou Province. The selected fine disseminated gold ore was dried at room temperature and crushed by jaw crusher. All samples were passed through 2 mm Taylor screen. The samples were mixed by the “pile cone method” and divided by the “quarter method”. Part of the raw ore analysis and test samples were taken out, and the remaining samples were packed into sealed bags and drained for use.

Multi-element analysis of ore chemistry is mainly to carry out accurate quantitative analysis of ore, according to which to determine which elements must be considered in the mineral processing recovery, which elements are harmful impurities need to be separated. Chemical multielement analysis is an important work to understand ores²³. The main chemical composition analysis results of a fine disseminated gold ore are shown in Table 2, and the main mineral composition in the ore is shown in Table 3; Fig. 2.

Table 2 Main chemical composition analysis results of raw ore %.

Table 3 Main mineral composition in ore /%.

Fig. 2

Main mineral composition and content of Carlin-type gold deposit.

The results in Table 3 show that the ore is mainly composed of quartz, dolomite, calcite, illite, pyrite and other minerals, accounting for 28.4%, 34.1%, 8.7%, 16.168% and 6.8% respectively. The independent mineral of sulfur is mainly pyrite, accounting for 6.8%.

The chemical information used in the test is shown in Table 4.

Table 4 Main chemical information.

Flotation test

Flotation test includes single mineral test and actual ore flotation test. The number of repetitions of all tests was three times, and the test results were the average of the three tests. XFGC aerated hanging cell flotation machine was used for single mineral test, and the spindle speed was 1992 rpm. Add 2 g of pure mineral and 40 mL of deionized water for each test. Adjust the pH of the suspension using NaOH and H₂SO₄ solution (0.1 mol/L) and record the pH value. According to the test process, the required reagents were added, stirred for 2 min, and aerated for 3 min to obtain the tank bottom and flotation foam products. The flotation recovery rate of the product was calculated by filtration, drying and weighing. The actual ore flotation test uses XFDIV1.0 single cell flotation machine with a spindle speed of 1992 rpm. After the flotation is completed, the floating products and the bottom products of the flotation cell are dried, weighed, calculated the yield and carried out chemical analysis to obtain the grade and recovery rate of pyrite. In the flotation process, sodium hydroxide and dilute hydrochloric acid are used to adjust the pH value of the pulp.

Contact Angle measurement

The sample of pyrite block with high purity is selected, and the sample with smooth surface is obtained after cutting, inlaying, coarse sandpaper grinding and fine grinding. For each experiment, the sample was first polished with 800 mesh sandpaper, exposed to a fresh surface, and soaked in a combined butylxanthate and BHA collector solution and butylxanthate solution with a known pH value. After 20 min, the sample was taken out and the surface liquid was dried with filter paper and placed on the JCY-1 contact Angle instrument for measurement.

FT-IR measurement

Fourier infrared spectroscopy (VERTEX 70, Bruker, GER) was used to determine the mineral surface before and after the agent action in a scanning range of 400–4000 cm⁻¹. The samples were ground to 5 μm in an agate mortar, 2.0 g samples were weighed for ultrasonic treatment, 40 mL of deionized water was added, the pH of pulp was adjusted with NaOH and HCl (0.01 mol/L), the corresponding agent was added, the pulp was stirred for 10 min, filtered, rinsed with deionized water and dried in a vacuum oven at 40 ℃ for 12 h. Appropriate amount of mineral sample was mixed with KBr, the ratio was about 1:100, after full mixing, tablet was pressed, and the spectrum of 4000 –400 cm-1 was recorded at room temperature.

XPS measurement

The XPS test was performed using Thermo Scientific K-Alpha (Thermo Fisher Scientific, USA). The mineral sample was ground in an agate mortar to 20 μm, weighed 2 g of sample, added 40 mL of deionized water, ultrasonic treatment for 5 min to adjust the pH, the corresponding agents were added in the flotation sequence, stirred by a magnetic agitator for 5 min, filtered, rinsed with deionized water and dried in a vacuum drying oven for 24 h. In the measurement, the sputtering source is Al Kα, the working voltage is 15Kw, the filament current is 10 mA, and the analysis chamber pressure is lower than 5 × 10⁻¹⁰ Pa. Full spectrum scanning has a pass energy of 100 eV with a step size of 1 eV, and fine spectrum scanning has a pass energy of 50 eV with a step size of 0.05 eV. The resulting spectra were calculated using Thermo Scientific Advantage for atomic concentration and peak fitting. The binding energy of the remaining elements was corrected using the binding energy of C1s at 284.8 eV.

Results and discussion

Flotation test

Single mineral flotation test

Butyl xanthate dosage test

Butyl xanthate dosage test Fixed pulp pH value is 5, 2 # oil dosage is 10 mg/L, the test results are shown in Fig. 3.

Fig. 3

Influence of butyl xanthate dosage on recovery rate of pyrite.

As can be seen from Fig. 3, with the increase of butyl xanthoxanthate dosage, the recovery rate of pyrite presents a trend of significant increase at first and then slightly decrease. The optimal dosage of butyl xanthoxanthate is about 15 mg/L, and the recovery rate is 59%.

Benzohydroxamic acid dosage test

Benzohydroxamic acid dosage test The pH value of the fixed pulp was 5,2 #, and the amount of oil was 10 mg/L. Benzohydroxamic acid was directly used as a collector to flotation pyrite. The test results were shown in Fig. 4.

Fig. 4

Effect of dosage of benzohydroxamic acid on recovery rate of pyrite.

As can be seen from Fig. 4, with the increase of the dosage of benzohydroxamic acid, the recovery rate of pyrite showed a trend of first increasing and then decreasing. The optimal dosage of benzohydroxamic acid was about 10 mg/L, and the recovery rate was 48.5%.

Ratio test of benzohydroxamic acid and butyl xanthate

The pH value of the fixed pulp was 5, the dosage of butyl xanthate was 5 mg/L, and the dosage of 2# oil was 10 mg/L. The combination of benzohydroxamic acid and butyl xanthate was directly used as collector to flotation pyrite, and the test results were shown in Fig. 5.

Fig. 5

Effect of the ratio of benzohydroxamic acid to butyl xanthate on the recovery rate of pyrite.

As can be seen from Fig. 5, with the increase of the ratio of benzohydroxamic acid and butyl xanthate, the recovery of pyrite initially increased and then slightly decreased. The optimal ratio of benzohydroxamic acid and butyl xanthate was about 3, and the recovery rate was 37%. The comprehensive optimal ratio is 3, and the pyrite flotation recovery is 37, which is higher than the pyrite flotation recovery of 30.5% when BHA is used alone and 28.5% when butyl xanthate is used alone.

Actual ore flotation test

The flotation test of Carlin-type gold ore was carried out at room temperature with tap water. Sulfuric acid and 2# oil were removed, and the remaining test reagents were 1% solution by mass fraction. Each test weighed 500 g ore sample, and used XMQ-240 × 90 conical ball mill to grind to test fineness. The actual ore was roughed one time and swept one time for comparison test. The test process is shown in Fig. 6, and the test results are shown in Table 5.

Fig. 6

Actual ore flotation test flow.

Table 5 Comparison test index (%) of different collectors in actual ores.

It can be seen from the results in Table 5 that when butyl xanthate is used as collector, the grade of pyrite concentrate 1 is 33.08, the grade of concentrate 2 is 10.76, and the sum of recovery rates of concentrate is 85.76%. When butyl xanthate + benzohydroxamic acid is used as collector, the grade of pyrite concentrate 1 is 32.78, the grade of concentrate 2 is 7.54, and the sum of recovery rate of concentrate is 88.24%. Compared with the two, the grade of concentrate 1 is not much different, and the recovery rate of concentrate increases significantly when butyl xanthate + benzohydroxamic acid is used as collector. Therefore, the flotation results of butyl xanthoxanthate + benzohydroxamic acid combined collector are superior to those of butyl xanthoxanthate alone. This is consistent with the flotation results of single minerals.

Contact Angle measurement

Under the same test conditions, the effects of the combined collector of butyl xanthoxanthate, butyl xanthoxanthate and benzohydroxamic acid (BHA) on the surface contact Angle of pyrite were investigated, and the results were shown in Fig. 7. The average contact Angle of pyrite in deionized water is about 13.694°, and the hydrophobicity is poor. After single butyl xanthate treatment, the average contact Angle is about 25.162°, which is higher than that of pure water. The surface contact Angle of pyrite treated with butylxanthate and benzohydroxamate increased significantly, and the contact Angle increased from 25.162° to 34.759° compared with that treated with butylxanthate. The results show that benzohydroxamic acid can significantly improve the surface hydrophobicity of pyrite under the action of butyl xanthate.

Fig. 7

Contact angles of pyrite under different conditions

c. Surface contact Angle of pyrite treated with butyl xanthate and BHA.

Figure 7 Contact angles of pyrite under different conditions.

FT-IR measurement

There are four absorption bands of 340, 407, 1065 and 1400 cm⁻¹ in the standard infrared spectrum of pyrite. Since the wave number range of the infrared spectrum in this experiment is 400 ~ 4000 cm⁻¹, there is no absorption band of 340 cm⁻¹ in the standard spectrum in the obtained infrared spectrum (Fig. 8)²⁴.

Fig. 8

Infrared spectrum of pyrite before and after chemical action.

The standard infrared spectrum band of pyrite 407 cm⁻¹ is the stretching vibration band of Fe²⁺ -[S₂]^{[2− 24}. The wave number of pyrite in this zone ranges from 413.24 to 419.71 cm⁻¹, and it can be seen from the data that the absorption peak moves to the high wave number region. The standard infrared spectrum band 1065 cm⁻¹ is the stretching vibration band of disulfide bond, and there is only weak absorption peak on the spectrum.

Figure 8 shows the infrared spectra of pyrite and butyl xanthoxanthate before and after BHA effect in a pulp system with pH = 5. The infrared spectrum of pyrite is shown in the lower curve of Fig. 8, and the infrared spectrum of pyrite adsorbed by butyl xanthate is shown in the middle curve of Fig. 8. The infrared spectrum of pyrite adsorption by BHA + butyl xanthoxanthate is shown in the curve above Fig. 8.

Compared with the infrared spectrum before and after the action of the agent, the spectrum line of pyrite is almost no big difference from the infrared spectrum line of pyrite because of its strong absorption peak, and the absorption peak shifts to the low wave number region, indicating that its molecular structure has changed. It can be seen that BHA produces chemical adsorption of pyrite.

XPS measurement

Figure 9 shows the full spectrum of XPS before and after surface treatment of butyl xanthate pyrite in a system with or without BHA. The characteristic absorption peaks detected by XPS of pyrite mainly include S 2p, S 2s, Fe 2p, C1s and O 1s. Compared with butyl xanthate before, during and after the role that do not produce a new characteristic absorption peak in BHA in the system, there is no new characteristic absorption peak, through the comparison of three spectral line can be found on the surface of pyrite element content changes, therefore, pyrite for butyl xanthate and BHA produce chemical adsorption. The atomic concentration changes of surface elements before and after pyrite treatment are shown in Table 6.

Fig. 9

Full XPS spectrum of pyrite.

Table 6 Atomic concentrations of surface elements of pyrite before and after treatment with chemicals.

Compared with the untreated pyrite, the relative atomic concentration of C element decreased and the relative atomic concentration of Fe, O and S elements increased after the addition of butyl xanthoxanthate, indicating that butyl xanthoxanthate had a certain adsorption of pyrite. Compared with the atomic concentration of pyrite treated with butyl xanthate, after adding BHA, the relative atomic concentration of C element continues to decrease, while the relative atomic concentrations of Fe, O and S elements all increase significantly, indicating that BHA has a certain adsorption of pyrite and can promote the adsorption of butyl xanthate by pyrite.

Fig. 10

Fine spectrum of C 1s on pyrite surface.

Fig. 11

Fine spectrum of Fe 2p on pyrite surface.

Fig. 12

Fine spectrum of O 1 s on pyrite surface.

Fig. 13

Fine spectrum of S 2p on pyrite surface.

Figure 10 shows the changes of C1s peaks on the surface of pyrite under different conditions. In Fig. 10 (A) C1s peak fitting, the binding energies were 288.24 eV and 284.22 eV respectively, which were attributed to the carbon pollution on the mineral surface and the C-O bond in the pharmaceutical. The maximum peak was 284.22 eV, which was the free peak of carbonate. Figure 10 (B) shows that after the interaction of pyrite with butyl xanthate, the binding energy of C1s is 288.168 eV and 284.18 eV, respectively, and the peak position of the free carbonate peak is shifted by 0.04 eV. When pyrite adsorbed BHA and butyl xanthate, only the free peak of carbonate existed, the binding energy of C1s was 284.10 eV, and the peak location was shifted by 0.08 eV. When pyrite adsorbed BHA and butyl xanthate, only the free peak of carbonate existed, the binding energy of C1s was 284.10 eV, and the peak location was shifted by 0.08 eV.

Figure 11 shows the changes of Fe 2p peaks on the pyrite surface under different conditions. In Fig. 11 (A) Fe 2p peak fitting, the binding energies are 719.21 eV and 706.47 eV respectively, corresponding to the -Fe²⁺ peak and -Fe³⁺ peak, respectively. Figure 11 (B) shows that after the interaction of pyrite with butyl xanthate, the binding energy of Fe 2p is 719.24 eV and 706.47 eV, respectively, and the -Fe²⁺ peak is shifted by 0.03 eV. In the case of pyrite adsorption of BHA and butyl xanthoxanthate, the binding energy shown in Fig. 11 (C) is 719.38 eV and 706.50Ev, respectively, and the -Fe²⁺ peak shifts by 0.14 eV. These results indicate that the binding energy of Fe on the surface of pyrite can be changed by the presence of BHA when pyrite adsorbed BHA and then reacts with butyl xanthate or directly reacts with butyl xanthate.

Figure 12 shows the changes of O 1s peaks on the pyrite surface under different conditions. The O 1s peak value is caused by air pollution or oxidation of pyrite surface layer, and is not an inherent component of pyrite. In Fig. 12 (A) O 1s peak fitting, the binding energy of 531.53 eV corresponds to the surface of pyrite -CO₃. Figure 12 (B) shows that after the interaction of pyrite with butyl xanthoxanthate, the O 1s binding energy is 531.36 eV, in which the -CO₃ peak is shifted by 0.17 eV. In pyrite after adsorption with BHA and butyl xanthate role, the binding energy as shown in Fig. 12 (C) 531.25 eV, 0.11 Ev happened - CO₃ peak position offset, shows when pyrite adsorption with BHA and butyl xanthate and pyrite directly compared with butyl xanthate function, the existence of the BHA can change pyrite surface O element binding energy of the size.

Figure 13 shows the changes of S 1s peaks on the surface of pyrite under different conditions. In Fig. 13 (A) S 1s peak fitting, the binding energies were 168.09 eV, 163.01 eV and 161.76 eV, respectively. Figure 13 (B) shows that after the interaction of pyrite with butyl xanthate, the binding energy of S 1s is 168.16 eV, 163.04 eV and 161.84 eV, respectively, and the corresponding peaks are shifted by 0.07 eV, 0.03 eV and 0.08 eV, respectively. After pyrite adsorption of BHA and butyl xanthoxanthate, the binding energies are 168.23 eV, 163.11 eV and 161.89 eV, respectively, as shown in Fig. 13 (C), and the corresponding peaks are shifted. It shows that the binding energy of S element on pyrite surface is changed by the presence of BHA when pyrite adsorbs BHA and then reacts with butyl xanthoxanthate or directly reacts with butyl xanthoxanthate.

After pyrite adsorbed butyl xanthate, the surface element composition and content of pyrite changed. When pyrite interacts with BHA and butyl xanthate, the chemical environment of Fe, S, C and O elements on the surface of pyrite changes accordingly. It shows that both butyl xanthate and BHA are chemically adsorbed on the surface of pyrite.

Mineral after butyl xanthate + BHA treatment, compared with the separate the butyl xanthate work, Fe 2 p binding energy moved more than 0.14 eV, O 1 S binding energy moved more than 0.11 eV, binding energy changes significantly, while C 1 S and 1 S S electron binding energy migration, The difference is only 0.08 eV, 0.07 eV, 0.07 eV, 0.05 eV, which indicates that the surface active particles of the minerals acting with BHA are mainly Fe particles. As can be seen from Fig. 12, regardless of whether pyrite is treated by butyl xanthoxanthate alone or by butyl xanthoxanthate + BHA, the electron binding energy of O 1s is shifted, and the degree of deviation is larger than that of C1s and S1s, which indicates that BHA chelates with iron ion particles on the surface of the mineral “O, O” to form a stable pentacyclic chelate. Adsorbed on the surface of pyrite, and then improve the floatability of pyrite.

Conclusions

(1) The collecting ability of the combination of butyl xanthate and benzohydroxamic acid for pyrite is obviously stronger than that of single use of benzohydroxamic acid or butyl xanthate. The optimum ratio of pyrite flotation with combined collector is 3, and the recovery rate of pyrite flotation is 37%, which is higher than that of pyrite flotation recovery of 30.5% when benzohydroxamic acid is used alone and pyrite flotation recovery of 28.5% when butyl xanthate is used alone.

(2) It can be seen from the contact Angle measurement that the contact Angle of pyrite increases and the hydrophobicity increases after the interaction with butyl xanthate, which is conducive to flotation. After the surface of pyrite is treated with the combined collector of butyl xanthoxanthate and benzohydroxamic acid, the contact Angle is further increased, and the hydrophobicity is further enhanced, which is more conducive to flotation.

(3) Through infrared spectrum and XPS analysis, it can be seen that the combined collector of butyl xanthate and benzohydroxamic acid produces strong chemical adsorption on the surface of pyrite, and benzohydroxamic acid and iron ion particles on the surface of the mineral produce “O, O” chelate to form a stable five-membered cyclochelate, which is adsorbed on the surface of pyrite, and then improves the floating property of pyr