Method for selectively leaching iron from gold ore by micro-bubble reinforced ozone

Abstract

The application discloses a method for selectively leaching iron in a flotation gold ore by micro-bubble reinforced ozone, which comprises the following steps: firstly, grinding and sieving the flotation gold ore to obtain fine gold ore with a particle size less than 200 mesh; secondly, weighing the fine gold ore and pouring it into a reaction container, setting the reaction temperature and keeping the temperature constant for 10 minutes, then introducing micro-bubble ozone into the reaction container, and adding sulfuric acid solution; thirdly, after reaching the reaction time, turning off the ozone generator and constant-temperature water bath kettle to obtain ore slurry; and finally, vacuum-filtering the ore slurry to obtain leaching solution and leaching residue. The method utilizes the strong oxidizing active species generated by micro-bubble ozone under acidic conditions to selectively oxidize and dissolve the iron-containing minerals wrapped around gold particles in the flotation gold ore, realizes efficient leaching of iron, and exposes and dissociates the wrapped gold particles. The method has the advantages of mild reaction conditions, high selectivity, no secondary pollution, high leaching efficiency and the like, and the leaching rate of iron can reach 76.89% under the optimal process conditions, thereby providing a new green and environmentally-friendly approach for the pretreatment of the flotation gold ore.

Description

Technical Field

[0001] This invention belongs to the field of mineral processing and hydrometallurgical technology, specifically relating to a method for selective leaching and flotation of iron in gold ore using microbubbles enhanced ozone. Background Technology

[0002] Gold is an important precious metal widely used in electronics, aerospace, jewelry, and financial reserves. With the increasing depletion of high-grade, easily processed gold ore resources, the development and utilization of low-grade, complex, and difficult-to-process gold ores (such as gold ores containing arsenic, sulfur, or iron minerals) has become a current research hotspot. Flotation is one of the important methods for gold ore pretreatment, but flotation gold ores often contain large amounts of iron-bearing minerals (such as pyrite FeS2 and pyrrhotite Fe). 1-X These minerals (such as S) often encapsulate gold grains in the form of fine particles, forming "encapsulated gold," resulting in extremely low gold leaching rates during subsequent cyanide leaching processes.

[0003] Currently, the pretreatment methods for iron-bearing gold ore containing inclusions mainly include roasting oxidation, pressure oxidation, and biological oxidation. Roasting oxidation has disadvantages such as high energy consumption, generation of toxic gases such as SO2 and As2O3, and easy environmental pollution; pressure oxidation requires high-temperature and high-pressure equipment, resulting in high investment and operating costs, and also poses safety hazards; although biological oxidation is environmentally friendly, the oxidation cycle is long (usually several days to several weeks) and has stringent requirements for the cultivation conditions of microorganisms, making it difficult to achieve large-scale industrial application.

[0004] Ozone (O3), as a strong oxidant, can decompose in acidic aqueous solutions to produce hydroxyl radicals (·OH), with a standard redox potential as high as 2.80 V, effectively oxidizing and decomposing various inorganic pollutants. In recent years, ozone oxidation technology has been widely used in water treatment, but its application in mineral processing is still in its early stages. Traditional ozone aeration methods suffer from problems such as large bubble diameters (typically on the order of millimeters), small gas-liquid contact areas, and low ozone utilization rates (usually below 30%), limiting its effectiveness in mineral leaching.

[0005] Microbubble technology refers to the generation of tiny bubbles with diameters ranging from 10 to 100 μm. These bubbles possess unique physicochemical properties, including large specific surface area, slow rise velocity, high internal pressure, high gas-liquid mass transfer efficiency, and the ability to spontaneously generate free radicals. Combining microbubble technology with ozone oxidation can significantly improve the solubility and utilization rate of ozone in water, enhance the generation of reactive species such as ·OH, and thus substantially increase the oxidation reaction rate.

[0006] Therefore, developing a green and efficient method for selective leaching of iron from gold ore using microbubbles enhanced with ozone is of great significance for improving the comprehensive utilization rate of gold resources and reducing environmental pollution. Currently, there are no reports on the application of microbubble ozone technology for the selective leaching of iron from gold ore flotation. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for selective leaching and flotation of iron in gold ore using microbubbles enhanced ozone, so as to solve the problems of high energy consumption, high pollution and low efficiency in the pretreatment of gold ore in the prior art.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: A method for selective leaching and flotation of iron in gold ore using microbubbles enhanced with ozone includes the following steps: ① After grinding the flotation gold ore, pass it through a 200-mesh sieve to obtain gold concentrate with a particle size of less than 200 mesh; ② Weigh the gold concentrate and pour it into the reaction vessel. Turn on the constant temperature water bath, set the reaction temperature and keep it constant for 10 minutes. Then turn on the ozone generator to introduce microbubble ozone into the reaction vessel. Add sulfuric acid solution. After the reaction time is reached, turn off the ozone generator and the constant temperature water bath to obtain the slurry. ③ The slurry is vacuum filtered to obtain leachate and leaching residue.

[0009] Furthermore, the flotation gold ore mentioned in step ① is a flotation gold ore from Myanmar.

[0010] Furthermore, the grinding time in step ① is 15 minutes.

[0011] Furthermore, in step ②, the liquid-to-solid ratio of the sulfuric acid solution and the gold concentrate is (1.5-3.5):1 mL / g.

[0012] Furthermore, the concentration of the sulfuric acid solution mentioned in step ② is 3-11 mol / L.

[0013] Furthermore, the reaction time described in step ② is 1-5 h.

[0014] Furthermore, the reaction temperature in step ② is 20℃-100℃.

[0015] Furthermore, the operating parameters of the microbubble ozone in step ② are: bubble diameter of 10-100 μm and flow rate of 100-500 mL / min.

[0016] Explanation of the principle of this invention: Under acidic conditions, ozone molecules react with water to generate highly reactive oxidizing species such as ·OH. The reaction formula is as follows:

[0017] Microbubble ozone possesses an extremely large specific surface area and very high gas-liquid mass transfer efficiency, enabling it to continuously generate high concentrations of ·OH at the gas-liquid interface and in the liquid phase. These ·OH molecules can selectively oxidize iron-bearing minerals (such as pyrite FeS2) in gold ore flotation, and the reaction can be expressed as:

[0018] The generated Fe 3+ It can further act as an auxiliary oxidant to oxidize the remaining iron sulfide minerals, while ozone can continuously oxidize the Fe produced in the reaction. 2+ Re-oxidized to Fe 3+ This maintains the system's oxidation capacity, forming an oxidation cycle and continuously enhancing the iron leaching effect. By controlling reaction conditions (acidity, temperature, ozone flow rate, reaction time, etc.), selective oxidation and dissolution of iron-containing minerals can be achieved, while the gold particles themselves remain stable and undissolved in the acidic ozone system. This effectively separates iron from gold, exposing the encapsulated gold particles and creating favorable conditions for subsequent gold extraction processes.

[0019] Beneficial effects of this invention: (1) The present invention uses microbubble ozone technology, which has small bubble diameter, large specific surface area and high gas-liquid mass transfer efficiency, significantly improving the utilization rate of ozone and the oxidation reaction rate. (2) The present invention performs selective iron leaching under acidic conditions, with mild reaction conditions, no need for high temperature and high pressure equipment, low energy consumption and good safety; (3) The reagents used in this invention (sulfuric acid and ozone) are all conventional chemicals. Ozone decomposes into oxygen on its own after the reaction, without producing toxic or harmful byproducts, and is environmentally friendly. (4) The present invention can effectively leach iron from flotation gold ore, break the encapsulation of gold particles by iron-containing minerals, and significantly improve the subsequent gold leaching rate; (5) The process of this invention is simple, easy to operate, and easy to scale up industrially. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0021] 1. Raw materials, reagents and instruments The experimental raw material used in this embodiment was Burmese flotation gold ore. The initial ore sample was mostly grayish-brown in shape and small spherical form, with a hard texture and difficult to grind. Scanning electron microscopy (SEM) characterization showed that the minerals in this gold ore were mainly irregular granular masses. X-ray diffraction (XRD) analysis showed that most of the high-intensity sharp diffraction peaks in the spectrum matched the standard XRD card of pyrite (FeS2), indicating that pyrite was the main mineral carrier in the refined gold ore, with good crystallinity and complete crystal structure. The gold existed in the form of free elemental gold, with a low content and few diffraction peaks with low intensity, indicating well-crystallized elemental gold particles.

[0022] The reagents and equipment used in the experiment are shown in Tables 1 and 2, respectively. Unless otherwise specified, all reagents used were of analytical grade, and the water used was ultrapure water.

[0023] Table 1 Experimental Reagents

[0024] Table 2 Experimental Instruments and Equipment

[0025] 2. Methods and Apparatus 2.1 Mineral Pretreatment Burmese gold ore was placed in a grinder and the grinding time was set to 15 minutes. After removal, the ground minerals were screened using a 200-mesh standard sieve. The sieve material with a particle size smaller than 200 mesh was collected as refined gold ore, while the coarse particles with a particle size larger than 200 mesh were kept for later use.

[0026] 2.2 Solution Preparation (1) Sulfuric acid solution: Calculate the required volume of concentrated sulfuric acid for each concentration according to the dilution formula C1V1=C2V2. In a fume hood, slowly pour the concentrated sulfuric acid along the wall of the beaker into an appropriate amount of ultrapure water, stir at a constant speed with a glass rod, and transfer to a 500 mL volumetric flask after cooling to room temperature. Make up to volume with ultrapure water and shake well for later use. The preparation parameters for each concentration are shown in Table 3.

[0027] Table 3. Parameters for preparing sulfuric acid solution

[0028] (2) 1% dilute nitric acid solution: Take 5.5 mL of concentrated nitric acid and slowly add it to water along the inner wall of the beaker. Stir with a glass rod and transfer to a 500 mL volumetric flask. Make up to volume with 1% nitric acid solution. Prepare and use immediately. It is used for the preparation of iron standard solution and the dilution of leaching solution.

[0029] (3) Aqua regia: In a fume hood, transfer 30.0 mL of concentrated hydrochloric acid to a beaker, then add 10.0 mL of concentrated nitric acid drop by drop in a very slow stream, stir gently, cover the watch glass loosely, and let it stand to mature to room temperature.

[0030] (4) Iron standard solution: Using 1000 mg / L iron standard solution as the stock solution, dilute with 1% nitric acid solution to prepare a series of standard solutions of 20, 40, 60, 80 and 100 mg / L for plotting standard curves.

[0031] 2.3 Leaching apparatus and installation The leaching apparatus consists of an ozone generator, a glass rotor flowmeter, a microbubble generator, a constant-temperature water bath, and a reaction vessel. The ozone generator is placed on a horizontal platform, and its outlet is connected to the flowmeter and the microbubble generator in sequence via rubber tubing. The water bath is placed to one side. The microbubble generator can produce microbubbles with a diameter of approximately 40 μm. The filtration apparatus consists of a Buchner funnel, a filtration flask, and a circulating vacuum water pump connected via rubber tubing.

[0032] 3 Single-Factor Conditional Leaching Examples Using 20 g of concentrated gold ore in a 100 mL Erlenmeyer flask as the basic reaction system, and keeping other conditions constant, the effects of five single factors—sulfuric acid concentration, liquid-to-solid ratio, reaction time, ozone aeration rate, and reaction temperature—on the iron leaching rate were investigated. The gradients of each factor were as follows: sulfuric acid concentration 3, 5, 7, 9, 11 mol / L; liquid-to-solid ratio 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1; time 1, 2, 3, 4, 5 h; aeration rate 100, 200, 300, 400, 500 mL / min; and temperature 20, 40, 60, 80, 100℃.

[0033] The typical operating procedure is as follows: Weigh 20 g of gold concentrate and pour it into a 100 mL conical flask. Turn on the water bath and heat it to the set temperature and keep it at that temperature for 10 min. Turn on the ozone generator and introduce microbubble ozone into the conical flask through the microbubble generator. Then, add a measured amount of sulfuric acid solution by pipetting. After reacting for the set time, turn off the ozone generator and the water bath in sequence to obtain the slurry. The slurry is separated by vacuum filtration to obtain the leaching solution and leaching residue.

[0034] The leachate was transferred to a 500 mL volumetric flask and diluted to volume with 1% dilute nitric acid. Then, 1 mL of the solution was diluted to 50 mL with 1% dilute nitric acid, and the dilution factor was recorded. The iron content was determined using an atomic absorption spectrophotometer (AAS): a standard curve was first plotted using a series of iron standard solutions (the linear correlation coefficient reached 0.9997), and then the sample was measured. The iron leaching rate was calculated according to formula (1):

[0035] In the formula: R is the iron leaching rate (%); C1 is the iron concentration in the leachate (mg / L); V1 is the volume of the leachate; A is the dilution factor (500); Mm is the total iron content in the raw ore (8894 mg). The data for the following examples were all obtained using the above method.

[0036] Example 1 (Sulfuric acid concentration, ozone microbubbles) With a fixed liquid-to-solid ratio of 2.5:1, an aeration rate of 100 mL / min, a temperature of 20℃, and a leaching time of 1 h, leaching was performed by varying the sulfuric acid concentration to 3, 5, 7, 9, and 11 mol / L. The results are shown in Table 4: As the concentration increased, the iron leaching rate peaked at 7 mol / L (18.68%). When the concentration was too low, the acidity was insufficient to promote the decomposition of iron-containing minerals; when the concentration was too high, side reactions were triggered, the ozone oxidation performance was altered, and the leaching rate decreased.

[0037] Example 2 (Liquid-to-solid ratio, ozone microbubbles) With a fixed sulfuric acid concentration of 7 mol / L, an aeration rate of 100 mL / min, a temperature of 20℃, and a leaching time of 1 h, the liquid-to-solid ratios were varied to 1.5:1, 2:1, 2.5:1, 3:1, and 3.5:1. The results are shown in Table 5: the liquid-to-solid ratio of 2.5:1 resulted in the best mineral dispersion and the most sufficient contact with ozone, achieving a leaching rate of 14.28%. Ratios that were too high or too low led to particle agglomeration or contact saturation, resulting in a decrease in the leaching rate.

[0038] Example 3 (Reaction time, ozone microbubbles) With a fixed sulfuric acid concentration of 7 mol / L, a liquid-to-solid ratio of 2.5:1, an aeration rate of 100 mL / min, and a temperature of 20℃, the leaching time was varied for 1, 2, 3, 4, and 5 h. The results are shown in Table 6: the leaching rate increased rapidly with prolonged leaching time, reaching 22.02% at 3 h; thereafter, due to the leaching of most of the easily reactive minerals, reduced activity, or the formation of a product barrier layer, the increase slowed down or even declined.

[0039] Example 4 (Ozone ventilation rate, ozone microbubbles) With a fixed sulfuric acid concentration of 7 mol / L, a liquid-to-solid ratio of 2.5:1, a temperature of 20℃, and a time of 1 h, the aeration rate was varied to 100, 200, 300, 400, and 500 mL / min. The results are shown in Table 7: the leaching rate reached 15.32% when the aeration rate was 400 mL / min; excess ozone decomposed before it could fully react, resulting in a decrease in utilization and a slight drop in the leaching rate.

[0040] Example 5 (Temperature, Ozone Microbubbles) With a fixed sulfuric acid concentration of 7 mol / L, a liquid-to-solid ratio of 2.5:1, an aeration rate of 100 mL / min, and a leaching time of 1 h, the temperatures were varied at 20, 40, 60, 80, and 100 °C. The results are shown in Table 8: Increasing the temperature significantly promoted ozone diffusion and reactivity, with a leaching rate of 38.40% at 80 °C; however, excessively high temperatures decreased ozone solubility, exacerbated side reactions, and reduced the leaching rate.

[0041] Table 4. Effect of sulfuric acid concentration on iron leaching rate (ozone microbubbles)

[0042] Table 5. Effect of liquid-to-solid ratio on iron leaching rate (ozone microbubbles)

[0043] Table 6 Effect of reaction time on iron leaching rate (ozone microbubbles)

[0044] Table 7. Effect of ozone ventilation rate on iron leaching rate (ozone microbubbles)

[0045] Table 8 Effect of temperature on iron leaching rate (ozone microbubbles)

[0046] 4 comparative examples (ordinary microbubble control) To highlight the synergistic enhancement effect of ozone and microbubbles, other conditions of the ozone microbubble experiment were fixed, the ozone generator was turned off, and ordinary air microbubbles were introduced into the system. The experiment was repeated according to the single-factor gradients mentioned above, and the results are shown in Tables 9 to 13.

[0047] Table 9 Comparative examples of sulfuric acid concentration (ordinary microbubbles, %)

[0048] Table 10 Liquid-to-solid ratio comparison (ordinary microbubbles, %)

[0049] Table 11 Time Comparison (Ordinary Microbubbles, %)

[0050] Table 12 Comparative examples of ventilation rates (ordinary microbubbles, %)

[0051] Table 13 Temperature Comparison (Ordinary Microbubbles, %)

[0052] The comparison shows that, under all single-factor conditions, the leaching rate of iron using ozone microbubbles is significantly higher than that using ordinary (air) microbubbles. This fully demonstrates that it is the synergistic effect between the strong oxidizing active species generated by ozone under acidic conditions and the large specific surface area and long residence time of microbubbles that achieves the efficient and selective oxidative dissolution of iron-containing minerals; ordinary air microbubbles alone or simple acid leaching cannot achieve the same effect.

[0053] 5 Best Condition Implementation Examples Based on the results of the single-factor experiments above, the optimal leaching conditions were determined to be: sulfuric acid concentration 7 mol / L, liquid-to-solid ratio 2.5:1, ozone aeration rate 400 mL / min, reaction time 3 h (3 h is the preferred time among the single-factor experiments; in the kinetic study, the reaction tended to plateau after 3 h), and reaction temperature 80℃. Five parallel experiments were conducted under these conditions, and the results are shown in Table 14. The average iron leaching rate reached 76.89%.

[0054] Table 14 Leaching data from parallel experiments under optimal conditions

[0055] The leaching rates of the five parallel experiments showed very small relative standard deviations, indicating that the method has good repeatability and the process is stable and reliable. It can achieve batch selective removal of iron from gold ore under relatively mild conditions, fully exposing the gold grains encapsulated by iron-bearing minerals and creating favorable conditions for subsequent gold extraction.

[0056] 6. Leaching kinetics study To further elucidate the reaction mechanism of the leaching process, six temperature gradients (40, 50, 60, 70, 80, and 90 °C) were set based on optimal process conditions. Samples were taken at eight time points (30, 60, 90, 120, 150, 180, 210, and 240 min), and the iron content was determined and the leaching rate was calculated using the aforementioned method. The results showed that the leaching rate at each temperature initially increased rapidly with time, then tended to level off after about 180 min, and the higher the temperature, the higher the leaching rate at which the level off was reached.

[0057] An unreacted core contraction model of the liquid-solid reaction was used for analysis, and linear fitting was performed on three control steps: chemical reaction control, internal diffusion control, and mixing control. The results showed that the linear correlation coefficients of all three models were high. Further analysis using the Arrhenius equation ln k = −Ea / (RT) + ln A to fit the activation energy of each model's rate constant revealed that the internal diffusion control model showed the best fit, with an activation energy of approximately 18 kJ / mol, indicating that this leaching process closely conforms to the internal diffusion reaction control model. This further confirms that microbubbles play a crucial role in enhancing the leaching process by strengthening gas-liquid mass transfer and shortening the diffusion path.

[0058] The above embodiments are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made by those skilled in the art without departing from the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for selective leaching and flotation of iron in gold ore using microbubbles enhanced with ozone, characterized in that, Includes the following steps: ① Grind the flotation gold ore and pass it through a 200-mesh sieve to obtain gold concentrate with a particle size of less than 200 mesh; ② Weigh the gold concentrate and pour it into a reaction vessel. Turn on the constant temperature water bath, set the reaction temperature, and maintain the temperature for 10 minutes. Then, turn on the ozone generator to introduce microbubble ozone into the reaction vessel. Add sulfuric acid solution, and turn off the ozone generator and the constant temperature water bath after the reaction time is reached to obtain a slurry; ③ Vacuum filter the slurry to obtain leaching solution and leaching residue.

2. The method for selective leaching and flotation of iron in gold ore using microbubble-enhanced ozone as described in claim 1, characterized in that: The flotation gold ore mentioned in step ① is Myanmar flotation gold ore.

3. The method for selective leaching and flotation of iron in gold ore using microbubble-enhanced ozone as described in claim 1, characterized in that: The grinding time in step ① is 15 minutes.

4. The method for selective leaching and flotation of iron in gold ore using microbubbles enhanced ozone according to claim 1, characterized in that: The liquid-solid ratio of the sulfuric acid solution and the gold concentrate in step ② is (1.5-3.5):1 mL / g.

5. The method for selective leaching and flotation of iron in gold ore using microbubble-enhanced ozone according to claim 1, characterized in that: The concentration of the sulfuric acid solution mentioned in step ② is 3-11 mol / L.

6. The method for selective leaching and flotation of iron in gold ore using microbubble-enhanced ozone according to claim 1, characterized in that: The reaction time described in step ② is 1-5 h.

7. The method for selective leaching and flotation of iron in gold ore using microbubble-enhanced ozone as described in claim 1, characterized in that: The reaction temperature described in step ② is 20℃-100℃.

8. A method for selective leaching and flotation of iron in gold ore using microbubbles enhanced ozone, as described in claim 1, characterized in that: The operating parameters for the microbubble ozone in step ② are: bubble diameter of 10-100 μm and flow rate of 100-500 mL / min.

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