Process for improving leaching rate of micro-fine particle coated gold based on combined pretreatment of microwaves and oxidizing agent

Abstract

The invention discloses a technology for improving the leaching rate of micro-fine particle wrapped gold based on microwave and oxidizing agent combined pretreatment, and belongs to the technical field of gold extraction metallurgy. The process comprises the steps of ore pulp pretreatment, concentration and pulp mixing, composite oxidizing agent adding, microwave pretreatment, cyanidation leaching and the like. According to the method, the microwaves and the composite oxidizing agent are utilized, a microfine particle gold wrapping carrier is efficiently destroyed, the leaching rate of gold is increased to 85-92% from 45-55% of a traditional method, meanwhile, energy consumption is reduced by 40% or above, sulfur dioxide emission is avoided, and the method has the advantages of being efficient, low in consumption, environmentally friendly and the like and is particularly suitable for extraction of arsenic-containing, sulfur-containing, carbon-containing and other microfine particle wrapping type refractory gold ores.

Description

Technical Field

[0001] This invention belongs to the field of gold extraction metallurgical technology. It relates to a pretreatment process for refractory gold ores with fine-grained inclusions, which improves the gold leaching rate through pretreatment. This invention is particularly suitable for fine-grained gold ores containing arsenic, sulfur, or carbon. Background Technology

[0002] In the global mineral resource system, gold, as an important strategic reserve resource and precious metal, is of great significance to national economic and industrial development due to its efficient extraction. According to data released by the World Gold Council, fine-grained encapsulated gold deposits account for more than 40% of the world's proven gold resources, and this proportion is increasing year by year. In these ores, gold elements are tightly encapsulated in the interstitial spaces of sulfide minerals such as pyrite and arsenopyrite, or quartz gangue minerals, forming a natural "protective barrier." This makes it difficult for traditional cyanide leaching processes to effectively contact the gold particles, and the gold leaching rate is usually less than 50%. As a result, a large amount of gold resources cannot be fully utilized, leading to resource waste.

[0003] Currently, the pretreatment technologies for finely encapsulated gold in the industry mainly include the following categories, but all of them have obvious shortcomings:

[0004] Roasting oxidation method: This method requires high-temperature conditions of 800-900℃, with energy consumption as high as 800-1000 kWh per ton of ore, resulting in huge energy consumption. At the same time, a large amount of sulfur dioxide gas is generated during the roasting process. The harmful gas emissions from processing 10,000 tons of ore require an investment of over 2 million yuan in desulfurization equipment, which not only increases environmental protection costs but also poses the risk of incomplete waste gas treatment leading to environmental pollution.

[0005] High-pressure oxidation method: The reaction needs to be carried out under high pressure of 2.0-3.0 MPa, which places extremely high demands on the materials of the equipment. Corrosion-resistant and high-strength materials such as titanium alloys are required. The investment for a single set of equipment exceeds 50 million yuan, resulting in high equipment costs. In addition, scaling of the slurry is prone to occur during the reaction process, leading to an equipment downtime rate as high as 15%-20%, which seriously affects production efficiency.

[0006] Biological oxidation method: This method relies on the metabolic activity of specific bacteria such as *Thiobacillus ferrooxidans* to oxidize minerals. The reaction cycle is as long as 7-10 days, resulting in low processing efficiency. Moreover, this method has strict requirements for environmental parameters, requiring temperature control at 28-32℃ and pH control at 1.8-2.2. In low-temperature regions in the north or in environments with large fluctuations in acidity and alkalinity, the activity of the bacteria decreases, making it difficult to achieve stable operation.

[0007] Single microwave treatment method: Although it can utilize the selective heating characteristics of microwaves on sulfide minerals (the absorption rate of sulfide minerals is 3-5 times that of gangue minerals) to break up inclusions, the decomposition rate of sulfide minerals is less than 30%, the exposure of gold is limited, and the leaching rate can only be increased by 15%-20%, which cannot meet the industrial production demand for high leaching rates.

[0008] The shortcomings of the aforementioned existing technologies highlight the urgent need for efficient, low-consumption, and environmentally friendly new technologies in the field of micro-particle encapsulated gold pretreatment. Summary of the Invention

[0009] The technical problem to be solved by the present invention is to overcome the problems of gold being difficult to effectively dissociate, low leaching rate, high energy consumption, serious environmental pollution, high equipment cost and low production efficiency in the existing micro-particle encapsulated gold pretreatment technology, and to provide a process based on microwave and oxidant combined pretreatment to improve the leaching rate of micro-particle encapsulated gold, so as to achieve efficient, environmentally friendly and low-cost extraction of gold ore.

[0010] The technical solution of the present invention is as follows:

[0011] A process for improving the leaching rate of finely encapsulated gold particles based on combined microwave and oxidant pretreatment includes the following steps:

[0012] (1) Pretreatment of ore pulp: The gold ore is ground to control the grinding fineness to be -0.074mm, accounting for 88%-90%, to obtain the raw ore pulp;

[0013] (2) Thickening and slurry preparation: The raw ore slurry obtained in step (1) is thickened using a thickener to adjust the slurry mass concentration to 60%-65%;

[0014] (3) Microwave pretreatment: The slurry with added composite oxidant is placed in a microwave treatment device and treated for 10-15 minutes at a microwave frequency of 2450MHz and a power of 50kW.

[0015] (4) Cyanide leaching: The microwave-pretreated slurry is transported to the cyanide leaching system, the sodium cyanide dosage is controlled at 0.5-1.0 kg / t, and the leaching time is 24-48 hours to complete the leaching and recovery of gold;

[0016] After the concentration and slurry preparation in step (2) and before the cyanide leaching in step (4), a composite oxidant is added. The composite oxidant is composed of sodium persulfate and hydrogen peroxide in a mass ratio of 2:1. The amount of composite oxidant added is 0.5-1.5 kg / t dry ore.

[0017] Preferably, the composite oxidant is added to the raw ore slurry after the concentration operation. Alternatively, the composite oxidant is added in stages, with 60% of the composite oxidant added to the raw ore slurry after the concentration operation, and the remaining 40% added to the slurry after microwave treatment in step (3) and before cyanide leaching in step (4).

[0018] Preferably, the gold-bearing ore is a fine-grained encapsulated refractory gold ore; the gold particle size in the ore is less than 10 μm; and the ore type includes arsenic-containing refractory gold ore, high-sulfur refractory gold ore, and carbon-containing refractory gold ore.

[0019] Preferably, during the microwave pretreatment process in step (3), the heating rate of the slurry is controlled at 5℃ / min; and the temperature of the slurry is stabilized at 60-70℃ at the end of the microwave treatment.

[0020] The beneficial effects of this invention are as follows:

[0021] (1) Significant synergistic effect: The thermal effect of microwave promotes the rapid decomposition of composite oxidant, generating strong oxidizing free radicals such as SO4・⁻ and ・OH with an oxidation potential of +2.6V (aqueous solution system), which accelerates the oxidation and decomposition of sulfide minerals. The oxidation and decomposition rate of sulfide minerals increases from about 30% of single microwave treatment to more than 85%, and the gold particle exposure rate reaches more than 90% (the traditional process is only 35%-45%).

[0022] (2) The selective heating advantage is prominent: the dielectric loss factor of microwave on sulfide minerals (pyrite tanδ=0.15, arsenopyrite tanδ=0.12) is 100-150 times that of gangue minerals (quartz tanδ=0.001, feldspar tanδ=0.002), so that sulfide minerals are preferentially heated and broken, and the gold-encapsulating carrier is precisely destroyed, reducing energy waste.

[0023] (3) Significantly reduced energy consumption: Compared with the traditional roasting process, the energy consumption of this invention is reduced by more than 40%. A production line that processes 1,000 tons of ore per day can save 1.26 million kWh of electricity per year, which is equivalent to reducing the consumption of standard coal by 420 tons (calculated based on the coal consumption of thermal power plants of 330g / kWh).

[0024] (4) Excellent environmental performance: The roasting process is eliminated, thus eliminating sulfur dioxide emissions at the source (the sulfur dioxide emissions of the traditional roasting process are 12.5 kg / t, while that of this invention is only 0.3 kg / t, and it is a trace amount released by the ore itself). The COD value of the wastewater is reduced from 180 mg / L to 65 mg / L, and the amount of solid waste generated is reduced by 3.5%, which meets the national "Emission Standard of Pollutants for Gold Industry" (GB25465-2010).

[0025] (5) Significantly improved leaching rate: Industrial tests show that for gold ores with different types of fine-grained inclusions such as arsenic, high sulfur, and carbon, the gold leaching rate has increased from 45-55% in the traditional method to 85-92%, and the resource utilization rate has been greatly improved. Detailed Implementation

[0026] This invention utilizes the synergistic effect of microwave radiation and composite oxidants to construct a closed-loop treatment system of "heating, oxidation, and dissociation," achieving efficient destruction of gold carriers encapsulated in fine particles and full exposure of gold. The specific steps and technical principles are as follows:

[0027] Slurry pretreatment: The grinding fineness is controlled to be -0.074mm, accounting for 88%-90%. Laser particle size analyzer detection shows that at this fineness, the monomer liberation degree of sulfide mineral inclusions can reach more than 60%, while avoiding excessive mud formation of gangue minerals (if the fineness is higher than 90%, the gangue mud formation rate increases, which will adsorb gold cyanide complexes and lead to a decrease in leaching rate), laying a good foundation for subsequent treatment.

[0028] Thickening and Slurry Preparation: A high-efficiency deep cone thickener is used to adjust the slurry concentration to 60%-65%. At this concentration, microwave energy can effectively act on the mineral particles (the dielectric constant of water is 78.5, which is much higher than that of minerals at 5-15. If the concentration is too low, microwave energy will be largely absorbed by water, increasing energy consumption by more than 30%; if the concentration is too high, the slurry will have poor fluidity, uneven microwave heating, and a local overheating rate of up to 25%), while ensuring good fluidity of the slurry in subsequent processing.

[0029] Addition of composite oxidant: The composite oxidant contains sodium persulfate and hydrogen peroxide in a mass ratio of 2:1. Orthogonal experiments verified that the oxidation potential of the oxidant at this ratio can reach +580mV, which is 1.3-1.5 times that of sodium persulfate alone (+420mV) or hydrogen peroxide alone (+380mV), enabling efficient oxidation of sulfide minerals. The addition amount should be controlled at 0.5-1.5 kg / t of dry ore. Below 0.5 kg / t, the oxidation decomposition rate is less than 40%, and above 1.5 kg / t, it will excessively consume cyanide in subsequent cyanide leaching, increasing reagent costs.

[0030] Microwave pretreatment: Process for 10-15 minutes at 2450MHz (the standard frequency for industrial microwaves to avoid electromagnetic interference to other equipment) and 50kW power. Under these conditions, the slurry heating rate reaches 5℃ / min, and the temperature stabilizes at 60-70℃. This temperature range maximizes the decomposition of the oxidant to generate •OH (hydroxyl radical, redox potential +2.8V, which is 1.8 times that of ordinary oxygen), achieving a synergistic effect between microwaves and oxidants.

[0031] Cyanide leaching: Based on the high gold exposure rate in the pretreated slurry, the sodium cyanide dosage is controlled at 0.5-1.0 kg / t and the leaching time is 24-48 hours. Compared with the traditional process (sodium cyanide dosage 1.2-1.5 kg / t, leaching time 72 hours), the reagent cost is reduced by 30%-40%, the time is shortened by 33%-66%, and the production efficiency is greatly improved.

[0032] The present invention will be further illustrated below with reference to embodiments and experimental data.

[0033] Example 1: Processing of Arsenic-Containing Refractory Gold Ore

[0034] A certain arsenic-containing, difficult-to-process gold mine has a gold grade of 3.5 g / t, of which 75% is encapsulated in fine particles, and the gold particles are all less than 10 μm in size.

[0035] (1) Pretreatment of ore pulp: The gold ore was ground and the grinding fineness was controlled to be -0.074mm, accounting for 89%, by monitoring with a laser particle size analyzer to obtain the raw ore pulp;

[0036] (2) Thickening and slurry preparation: The raw ore slurry is thickened using a high-efficiency deep cone thickener with a diameter of 6m and a cone angle of 60° to adjust the slurry mass concentration to 62%;

[0037] (3) Addition of composite oxidant: Add composite oxidant (sodium persulfate: hydrogen peroxide = 2:1) to the concentrated slurry at a rate of 1.0 kg / t dry ore;

[0038] (4) Microwave pretreatment: The slurry was fed into a microwave treatment device and treated for 12 minutes at a microwave frequency of 2450MHz and a power of 50kW. At the end of the treatment, the oxidation-reduction potential of the slurry was measured to be +425mV. During the microwave pretreatment, the heating rate of the slurry was controlled at 5℃ / min, and the temperature was stabilized at 65℃ at the end of the treatment.

[0039] (5) Cyanide leaching: The microwave-pretreated slurry is transported to the cyanide leaching system, and the sodium cyanide dosage is controlled at 0.7 kg / t, and the leaching time is 36 hours.

[0040] Tests showed that the gold leaching rate in this embodiment reached 88.5%.

[0041] Example 2: Segmented addition of composite oxidant treatment

[0042] A certain arsenic-containing, difficult-to-process gold mine has a gold grade of 3.5 g / t, of which 75% is encapsulated in fine particles, and the gold particles are all less than 10 μm in size.

[0043] (1) Pretreatment of ore pulp: The gold ore was ground and the grinding fineness was controlled to be -0.074mm, accounting for 89%, by monitoring with a laser particle size analyzer to obtain the raw ore pulp;

[0044] (2) Thickening and slurry preparation: The raw ore slurry is thickened using a high-efficiency deep cone thickener with a diameter of 6m and a cone angle of 60° to adjust the slurry mass concentration to 62%;

[0045] (3) Addition of composite oxidant: Add composite oxidant (sodium persulfate: hydrogen peroxide = 2:1) to the concentrated slurry at a rate of 0.6 kg / t (accounting for 60% of the total addition).

[0046] (4) Microwave pretreatment: The slurry is fed into a microwave treatment device and treated for 12 minutes at a microwave frequency of 2450MHz and a power of 50kW. During microwave pretreatment, the slurry heating rate is controlled at 5℃ / min, and the temperature is stabilized at 65℃ at the end of the treatment.

[0047] (5) After microwave treatment, add 0.4 kg / t (40% of the total amount of compound oxidant) to the slurry. After treatment, the redox potential of the slurry was measured to be +425 mV.

[0048] (6) Cyanide leaching: The microwave-pretreated slurry is transported to the cyanide leaching system, and the sodium cyanide dosage is controlled at 0.7 kg / t, and the leaching time is 36 hours.

[0049] Tests showed that the gold leaching rate in this embodiment was increased to 90.2%.

[0050] Comparative Example 1: Traditional Processing

[0051] Using the same arsenic-containing refractory gold ore as in Example 1, without microwave-oxidant combined pretreatment, cyanide leaching was carried out directly, with sodium cyanide dosage controlled at 1.4 kg / t and leaching time at 72 hours.

[0052] Tests showed that the gold leaching rate was only 46.3%.

[0053] Comparative Example 2: Single Microwave Processing

[0054] The same arsenic-containing refractory gold ore as in Example 1 was used, but only microwave pretreatment was performed (with parameters consistent with Example 1). No composite oxidant was added, and the subsequent cyanide leaching parameters were consistent with those in Example 1.

[0055] The leaching rate of gold was found to be 62.1%.

[0056] Comparative Example 3: Treatment with a single oxidizing agent

[0057] The same arsenic-containing refractory gold ore as in Example 1 was used, but only a composite oxidant was added (the amount added was the same as in Example 1). Microwave pretreatment was not performed, and the subsequent cyanide leaching parameters were the same as in Example 1.

[0058] The leaching rate of gold was found to be 58.7%.

Claims

1. A process for improving the leaching rate of fine particles of gold coated by a combination of microwave and oxidizing agent pretreatment, characterized by, The method comprises the following steps: (1) ore pulp pretreatment: grinding the gold-containing ore, controlling the grinding fineness to be 88%-90% of -0.074 mm, and obtaining the raw ore pulp; (2) thickening and slurry preparation: using a thickener to concentrate the raw ore pulp obtained in step (1), and adjusting the mass concentration of the ore pulp to 60%-65%; (3) microwave pretreatment: placing the ore pulp added with a composite oxidizing agent in a microwave treatment device, and treating it under the conditions of a microwave frequency of 2450 MHz and a power of 50 kW for 10-15 minutes; (4) cyanide leaching: delivering the microwave pretreated ore pulp to a cyanide leaching system, controlling the amount of sodium cyanide to be 0.5-1.0 kg / t, and leaching for 24-48 hours to complete the leaching and recovery of gold. The composite oxidizing agent is composed of sodium persulfate and hydrogen peroxide in a mass ratio of 2:1, and the addition amount of the composite oxidizing agent is 0.5-1.5 kg / t of dry ore.

2. The process for improving the leaching rate of micro-fine particle wrapped gold based on combined pretreatment of microwave and oxidizing agent according to claim 1, characterized in that: The composite oxidizing agent is added to the raw ore pulp after the thickening operation.

3. The process for improving the leaching rate of micro-fine particle wrapped gold based on combined pretreatment of microwave and oxidizing agent according to claim 1, characterized in that: The composite oxidizing agent is added in a segmented manner, of which 60% is added to the raw ore pulp after the thickening operation, and the remaining 40% is added to the ore pulp after the microwave treatment in step (3) and before the cyanide leaching in step (4).

4. The process for improving the leaching rate of micro-fine particle wrapped gold based on combined pretreatment of microwave and oxidizing agent according to claim 1 or 2 or 3, characterized in that: The gold-containing ore is a micro-fine particle inclusion type refractory gold ore, the gold in the ore is less than 10 μm in size, and the ore types include arsenic-containing refractory gold ore, high-sulfur refractory gold ore, and carbon-containing refractory gold ore.

5. The process for improving the leaching rate of micro-fine gold particles coated by pre-treatment with a combination of microwave and oxidizing agent according to claim 1 or 2 or 3, characterized in that: During the microwave pretreatment in step (3), the heating rate of the ore pulp is controlled at 5℃ / min, and the temperature of the ore pulp is stabilized at 60-70℃ when the microwave treatment is completed.