Quartz is the main gangue minerals in phosphate ores, flotation of phosphate minerals during reverse Crago process using cationic amine is a common collector reverse flotation collectors quartz. However, the utilization rate of flotation reagents in Crago process is relatively low. Therefore, research and development of high-efficiency flotation collectors to improve the flotation efficiency of reverse flotation, to make up for the shortcomings in the flotation process, reduce the cost of chemicals, and reduce environmental pollution has become The focus of current research. For the current demand, Georgia-Pacific Chemical Company developed a new cationic amine collector 605G83, which is a derivative of oxidized tal oil fatty acid and diethylene triamine synthesized at 160 ° C, with an acid value of 30.7 and a density of 1.03.
There are many theories and models for the action mechanism of cationic amine collectors and quartz and silicate minerals. Most of these theories and models are studied by infrared spectroscopy, isothermal adsorption curves, ζ-potentials, contact angles, etc. owned. However, all of these methods do not allow a complete real-time measurement of the entire process of adsorption of the agent on the mineral surface. As a high-precision application technology of piezoelectric effect in mass measurement, QCM-D can measure the adsorption process of the agent on the mineral surface in real time, and the measurement accuracy reaches nanometer level.
The core component of Quartz crystal microbalance with dissipation is an AT-cut quartz crystal resonator with a 14mm diameter double-sided deposited gold electrode based on piezoelectric resonance. During the measurement, QCM-D converts the change of the surface quality of the electrode on the quartz crystal resonator into the frequency change (Δf) of the output signal of the quartz crystal oscillator circuit, and then obtains the data of the surface quality change and physical properties of the electrode by calculation and simulation. QCM-D can not only measure the change of Δf, but also measure the change of system energy dissipation (△D). △D is a parameter used to quantitatively express the damping of the oscillating system. It is directly related to the viscoelasticity of the sample to be tested. By measuring the change in energy dissipation, QCM-D can not only measure the mass change of the adsorbed film on the wafer surface, but also Physical properties such as viscoelasticity of the adsorption film were measured to estimate the structure of the adsorption film and the firmness of adsorption. QCM-D has high stability and accuracy. The resonance frequency fluctuation in air is less than 0.5Hz. The resonance frequency fluctuation in water is less than 1Hz, which is very small fluctuation with respect to the fundamental resonance frequency of 5MHz, thus realizing the surface of the counter electrode. High-precision real-time measurement of quality changes.
In this paper, the new cationic collector 605G83 was applied to the reverse flotation of the CF Industries phosphate mine in Florida, and compared with the acetic acid amide PA70 used in the field under the same conditions, the two amines were captured under different dosages and pH conditions. The flotation effect of the collector. At the same time, the adsorption process of 605G83 and PA70 on the surface of quartz plated resonator was measured by QCM-D. The adsorption amount, adsorption rule and mechanism of 605G83 and PA70 on quartz surface were studied by combining flotation effect and ζ-potential.
1. Samples and research methods
(1) Flotation test
The ore used in the reverse flotation test was a product of the FCS of Florida CF Industries, which was subjected to laboratory flotation, pickling and water washing. CF Industries' phosphate was firstly added at a pH of 10.5 by adding 0.45 kg/t mixed fatty acid and 0.3 kg/t diesel mixture, stirring time was 5 min, flotation machine speed was 1500 r/min, and flotation was carried out. The concentrate is pickled with 60% concentrated sulfuric acid to wash away the positive flotation agent attached to the mineral surface. Then rinse with water several times to wash away the acid and fine-grained clay remaining in the ore sample. Due to partial loss of concentrate due to pickling and washing process, the average grade of reverse flotation to ore is 12.3%, and the main gangue is quartz. The ore sample is hereinafter referred to as ore.
The reverse flotation test used a Denver D-12 laboratory flotation machine. In the flotation process, the raw ore is first taken for pH adjustment, and the pH is adjusted using a 15% Na 2 CO 3 solution. Add a certain proportion and amount of 605G83 or PA70 to the pH-adjusted slurry (solid content: 75%), mix it for a certain period of time after mixing, and then transfer the slurry to 1L flotation tank, dilute with water to the solid content. 25% and flotation on the flotation machine.
After the concentrate and tailings separated in the flotation test were filtered and dried, the content of phosphorus was determined by inductively coupled plasma mass spectrometry (ICP), and the P 2 O 5 grade was calculated. In addition, the content of acid insolubles (AI) in concentrates and tailings was also determined. The acid insoluble content AI refers to a component in which the ore sample cannot be dissolved in the mixed strong acid, and is mainly a silicate gangue mineral such as quartz. Since Florida phosphate is mostly used as a phosphate fertilizer or as an animal feed additive, in the further processing, the acid-insoluble components such as quartz in the concentrate are mainly removed. Therefore, the higher the AI ​​content in the flotation product, the greater the cost of subsequent processing. Therefore, in evaluating flotation efficiency, AI is often a more important parameter than the P 2 O 5 grade.
The flotation effect was evaluated by the recovery of phosphorus in the concentrate and the flotation efficiency FE. The calculation formula is as shown in formula (1):
F E =R+R AI -100 (1)
Where R is the removal rate of acid insolubles in the concentrate. The calculation method of R AI is as shown in equation (2):
Where G and T are the masses of concentrate and tailings respectively; c' and t' are the acid insoluble content in concentrate and tailings, respectively.
(2) QCM-D
The test uses the Q-Sense E4 system, which consists of a quartz crystal resonator, flow cell, sample platform, electronic unit, control software (QSoft 401) and analysis software (QTools). In addition, four sample digital display must be configured. Peristaltic pump. The quartz crystal resonator is the core part of the whole system. During the test, only the surface of the coating is in contact with the sample, and the electrode on the reverse side is kept dry. Therefore, it can be ensured that the change in the quality of the quartz crystal resonator during the test can only be produced by the reaction of the solution to be tested with the surface of the coating. The specific calculation method can be found in the literature.
(three) ζ-potential
The quartz sample used for the ζ-potential was supplied by Ward's Natural Science. The sample was crushed and ground into a powder of 10% - 2.7 μm, 50% - 19.55 μm, and 90% - 80.67 μm using an agate mortar. The quartz sample obtained after grinding was subjected to 0.1 g of 20 mL of 1 mmol KCl solution to prepare a 0.5% suspension, followed by pH adjustment, and the conditioning reagent used was 1% HCl and NaOH solution. The solution after adjusting the pH value was added with the corresponding amount of the agent, and after magnetic stirring for 1 hour, it was filtered with a 25 μm pore size filter paper, and the filtrate was used for measuring the ζ-potential, and the pH value of each sample was measured before the measurement as the final pH value of the sample. . The potential was measured using a Zeta Plus potentiometer.
Second, the results and discussion
(1) Study on the effects of different drugs and dosages
The test was conducted on the comparison of the dosage of the two amine collectors of 605G83 and PA70 at pH 7. The pulping time is 5 min and the rotation speed is 1500 r/min.
Figure 1 shows the flotation efficiency and AI content of 605G83 and PA70 at different dosages. It can be seen that the 605G83 at 0.5kg/t can achieve the flotation effect of PA70 at 1.0kg/t, and the dosage can be saved by half.
Fig.1 Flotation efficiency of 605G83 and PA70, relationship between concentrate AI and dosage (pH 7)
Figure 2 is a comparison of the P 2 O 5 grade and recovery curves of 605G83 and PA70 under the same flotation conditions. At pH 7, 605G83 has better trapping and selectivity than PA70 under different dosages.
Fig. 2 Comparison of recovery rate and grade curve of flotation P 2 O 5 between PA70 and 605G83 at different dosages (pH 7)
(2) pH impact test
The effect of different pH values ​​(pH 5～9) on the flotation effect of the reverse flotation collector was investigated. The dosage of the test was 1.0 kg/t, the pulping time was 5 min, and the rotation speed was 1500 r/min. Figure 3 is the effect of pH on flotation efficiency and AI content. The flotation efficiency of 605G83 at pH 7 is similar to that of PA70 at pH 8 and the AI ​​is lower than PA70, indicating that 605G83 can achieve better flotation effect at neutral pH, while PA70 is affected by pH and needs to be increased in pH. In order to get a better flotation effect.
Fig. 3 Flotation efficiency of 605G83 and PA70, relationship between concentrate AI and pH
Figure 4 is a graph comparing the concentrate grade and recovery of 605G83 and PA70 at different pH values. Compared with PA70, the recovery rate of 605G83 is significantly higher than that of PA70 at the same grade, and the highest grade of 605G83 can reach 28%, while PA70 can only reach 24%, which confirms that 605G83 has higher choice under the same flotation conditions. Sex. In addition, the test results also show that the amine collectors have poor flotation effect under acidic conditions, the pH value of the pulp has a great influence on the flotation effect of PA70, and 605G83 can achieve better flotation at pH 7. The effect, so there is no need to adjust the pH of the slurry.
Fig. 4 Comparison of recovery rate and grade relationship between flotation P 2 O 5 of PA70 and 605G83 at different pH values
(III) Reverse flotation kinetics test
The experiment investigated the variation of the recovery rate and grade of 605G83 and PA70 with flotation time. During the flotation process, the concentrated concentrates were collected separately at intervals of 10 s, and the flotation was carried out under the conditions of pH 8. The dosage of the chemicals was 1.0 kg/t, the pulping time was 5 min, and the rotation speed was 1500 r/min.
Figure 5 is a comparison of the flotation recovery and grade of the 605G83 and PA70 as a function of flotation time. It can be seen from Fig. 5 that the flotation recovery rate of 605G83 drops rapidly in the first 10s, from 95.8% to 92.9%, and the downward trend is slower and slower with time. The recovery rate of PA70 is always high, but the concentrate grade is 4% to 5% lower than 605G83 on average. At 40s, the flotation recovery rate of 605G83 reached 92.1%, and the highest grade reached 31.5%.
5 605G83 PA70 and flotation recovery of P 2 O 5, taste and flotation time diagram
(4) ζ-potential research
In order to investigate the adsorption state of cation collector 605G83 on the surface of quartz, the change of ζ-potential before and after the action of quartz and 605G83 was studied. It can be seen from Fig. 6 that the zero point of pure quartz is about pH 2. After mixing with 3.75 mg/L of cationic collector 605G83, the ζ-potential at the same pH value increases, and the zero point shifts to the right. 5, indicating that the amine cations have electrostatic adsorption on the negatively charged quartz surface, changing the charge properties of the quartz surface, so that the ζ-potential rise under the same pH condition, and the floatability of the mineral particles is improved.
Fig. 6 ζ-potential before and after adsorption of 605G83 on quartz surface
(5) QCM-D adsorption research
In order to investigate the adsorption mechanism of oxidized fatty acid derivative 605G83 and acetic acid amide PA70 on the surface of quartz, the adsorption of 605G83 and PA70 on the surface of quartz coating resonator was carried out by QCM-D at two concentrations of 100mg/L and 500mg/L respectively. Real time measurement.
Figure 7 is a comparison of the QCM-D test results of 605G83 and PA70 adsorbed on the quartz surface. The time before the arrow a in the A and B diagrams is to inject deionized water into the QCM-D system, so both Δf and ΔD are zero. The arrow a indicates the time at which the injection of the collector into the measurement system is started, that is, the time at which the adsorption starts. It can be seen that the frequency change amount Δf of 605G83 and PA70 at the arrow a immediately shows a rapid decline, but the energy dissipation change amount ΔD has only a slight rise, and the change of Δf indicates that the 605G83 and PA70 have started on the surface of the quartz wafer. Adsorption occurs and is fast. Further, it can be seen from ΔD < 1 × 10 -6 that the formed adsorption layer has little energy dissipation, and thus the adsorption is tight. According to the calculation of the Sauerbrey model, when Δf and ΔD are stable, the adsorption densities of 605G83 and PA70 are 1.3×10 -9 mol/cm 2 and 6.3×10 -10 mol/cm 2 , respectively . According to Novich's research, the long-chain amine-based collector has a single-molecular adsorption film on the surface of quartz, and the adsorption density is about 1.24×10 -10 mol/cm 2 under the condition of tight alignment. At the time of micelles, the adsorption density is about 3.96×10 -9 mol/cm 2 , and the adsorption molecules are arranged irregularly. From the results of QCM-D, it is known that the adsorption density of 605G83 and PA70 on the quartz surface is between the monolayer and the surface micelle formation, and ΔD<1×10 -6 indicates that the adsorption molecules formed at this time are closely arranged and Rules, and therefore do not generate large system energy dissipation. Since the hydrophobicity of the mineral surface is directly related to the nature of the surfactant forming the adsorption film, when the adsorption layer is dense and the hydrophobic group has a high hydrophobicity when the surface is regularly arranged, if it is not able to form a strong adsorption film and is hydrophobic When the group is irregularly arranged, the hydrophobicity is poor. Therefore, both 605G83 and PA70 can form a tight monomolecular adsorption layer at 100 mg/L, but the adsorption density of 605G83 is higher than that of PA70, indicating that 605G83 is more likely to interact with the quartz surface, and More hydrophobic.
Fig.7 Comparison of QCM-D test results of 605G83 and PA70 adsorbed on quartz surface
Figure 8 is a comparison of QCM-D test results of 605G83 and PA70 adsorbed on the surface of quartz when the frequency is 15MHz and the concentration of the drug is 500mg/L. The change trend of △D and △f of 605G83 is basically the same as that of 100mg/L, and with The concentration of the drug increased, and the adsorption density did not change greatly. According to Sauerbrey's calculation, the adsorption concentration at the time of signal stabilization was still 1.4×10 -9 mol/cm 2 , which was basically the same as that at 100 mg/L, and △ in the B diagram. D < 1 × 10 -6 , indicating that a dense adsorption layer was formed. Comparing the adsorption law of 605G83 at 100mg/L, it can be found that increasing the concentration of 605G83 does not form multi-layer adsorption or precipitation of molecules on the surface, and the adsorption molecules are still closely arranged. Compared with 605G83, the ΔD and Δf of PA70 gradually decreased at the beginning of adsorption, and the adsorption stability was achieved after 1 h. At this time, the amounts of change of ΔD and Δf are very large. Since ΔD≈15×10 -6 >1×10 -6 , the adsorption density at this time is 5.2×10 -9 mol/cm 2 calculated according to the Voigt model, which is much larger than the theoretical adsorption density of the double layer of 3.96×10 -9 . Mol/cm 2 and thus a very high system energy dissipation. From this, it can be seen that the multi-layer adsorption which is generated at this time should be irregular structure or the molecular deposition of the surface occurs. At this time, PA70 cannot form a highly hydrophobic adsorption film on the quartz surface.
Fig. 8 Comparison of QCM-D test results of 605G83 and PA70 adsorbed on quartz surface
According to the Gaudin-Fuerstenau adsorption model (G-F model), at a low concentration, the amine cation is electrostatically adsorbed on the negative charge of the quartz surface, and the adsorption direction is positively charged toward the surface, and the non-polar carbon chain is oriented. The solution causes the quartz surface potential to rise. Under high concentration conditions, a second layer of adsorption is formed on the basis of the formed single molecule adsorption layer according to the G-F model, at which time the positively charged end faces the solution. According to the high concentration adsorption process of QCM-D, the adsorption density and adsorption behavior of 605G83 on quartz surface at 500mg/L is very close to that of 100mg/L, but it has not reached the theoretical value of double layer, and it is △D<× 10-6 It is known that the structure of the adsorption layer should be tight and regular, so unlike the G-F model, the adsorption density does not necessarily increase with increasing concentration. Moreover, the adsorption structure does not necessarily form a double layer covering the entire surface, and may form a part of the surface single layer adsorption, and another part of the double layer adsorption structure, so the adsorption density is smaller than the theoretical double layer adsorption density, which is related to the results of Chernyshova et al. Close.
Third, the conclusion
(1) In the flotation process, when the amount of collector is large enough, both 605G83 and PA70 can achieve higher flotation efficiency, but when the dosage is 0.5kg/t, the 605G83 can reach 1.0kg/t. The flotation effect of PA70 can save half of the dosage, indicating that 605G83 has higher collection and selectivity than PA70.
(2) The experiment shows that the flotation efficiency achieved by 605G83 at pH 7 is similar to that of PA70 at pH 8, indicating that 605G83 can achieve better flotation effect under neutral pH conditions, thus eliminating the need for pH adjustment; PA70 is affected by pH, and it is necessary to increase the pH to get a better flotation effect. Both collectors are not trapped under acidic conditions.
(3) According to the measurement results of ζ-potential, the ζ-potential of quartz is obviously increased under the action of cation collector 605G83, indicating that electrostatic adsorption of amine cations occurs on the surface of negatively charged quartz, which improves the mineral surface. Hydrophobic and floatable.
(IV) Adsorption experiments on quartz surface by 605G83 and PA70 by QCM-D show that the adsorption film formed on quartz surface 605G83 under the same conditions is stronger than PA70, and the arrangement is regular and the adsorption density is higher. It shows that the hydrophobicity of quartz after 605G83 is better, and better flotation efficiency can be obtained.
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