Composite binder for iron oxide ore pellets and method for preparing pellets and removing arsenic by using composite binder

Abstract

The invention belongs to the technical field of mineral processing engineering, and particularly relates to a composite binder for iron oxide ore pellets and a pellet preparation and arsenic removal method thereof. Calcium carbonate-ammonium bicarbonate serves as a composite binder, efficient arsenic removal is achieved through the unique action mechanism of ammonium bicarbonate, iron oxide ore powder and a composite binder solution are mixed and pelletized to obtain green pellets, the green pellets are cured for 5-8 h at the temperature of 20-30 DEG C and the humidity of 60-80%, dried for 3-4 h at the temperature of 100 + / -5 DEG C and roasted for 2-4 h at the temperature of 600-800 DEG C; ammonium bicarbonate is decomposed during roasting to generate NHH, the NHH reacts with arsenide in the pellets to generate volatile arsenic ammonia compounds, arsenic removal is completed along with gas escape, and meanwhile calcium carbonate provides framework support for the pellets to guarantee strength. The arsenic removal rate reaches 85% or above, the arsenic content of the pellets is reduced to 0.02% or below, the compressive strength of dry pellets is larger than or equal to 2000 N / pellet, the roasting temperature is reduced by 30% or above compared with a traditional technology, low-energy-consumption and high-purity clean utilization of iron oxide ore resources is achieved, the technological process is short, and the method is suitable for industrial application.

Description

Technical Field

[0001] This invention belongs to the field of mineral processing engineering technology, and relates to a composite binder for iron oxide ore pellets and a method for preparing pellets and removing arsenic, specifically a method for preparing iron oxide ore pellets and removing arsenic based on a calcium carbonate-ammonium bicarbonate composite binder. Background Technology

[0002] In the field of iron oxide ore pellet preparation, the selection and application of binders directly affect the performance, production cost, and environmental friendliness of the pellets. Traditional bentonite binders require high-temperature sintering above 1200℃, which consumes a great deal of energy. Moreover, high temperatures can easily cause harmful elements such as arsenic in the pellets to volatilize and pollute the environment. At the same time, the silicon, aluminum, and other components in bentonite can reduce the iron grade.

[0003] To reduce energy consumption, some studies have attempted to use single-salt binders (such as sodium chloride and sodium sulfate). However, these binders only act as binders and cannot react with arsenic compounds, thus lacking any arsenic removal function. Furthermore, they are prone to decomposition and failure at high temperatures, leading to a sharp drop in pellet strength. In addition, while existing organic binders (such as starch and cellulose derivatives) can reduce the introduction of impurities, they have poor thermal stability and are prone to carbonization during calcination. This not only fails to remove arsenic but also generates harmful gases that pollute the environment.

[0004] Currently, there are no reports on the application of calcium carbonate and ammonium bicarbonate composites as binders for iron oxide ore pellets. In particular, there is a lack of research on the arsenic removal mechanism of ammonium bicarbonate, which involves "decomposition to produce NH3, reaction with arsenic compounds, and generation of volatile products." Furthermore, no optimized schemes have been developed for the relevant process parameters, making it difficult to meet the needs of efficient and clean utilization of arsenic-containing iron oxide ore resources. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing and removing arsenic from iron oxide ore pellets based on a calcium carbonate-ammonium bicarbonate composite binder. This method achieves low-energy preparation and efficient arsenic removal of iron oxide ore pellets by clarifying the arsenic removal mechanism of ammonium bicarbonate. The process is short, clean, and environmentally friendly, making it suitable for industrial applications.

[0006] To achieve the above objectives, the present invention provides the following technical solution: The composite binder for iron oxide ore pellets of the present invention comprises, by weight of iron ore dry basis, 1.0%-3.0% calcium carbonate and 0.5%-2.0% ammonium bicarbonate, with a mass ratio of calcium carbonate to ammonium bicarbonate of (1.5:1)-(3:1). This ratio ensures that ammonium bicarbonate fully exerts its arsenic removal effect while calcium carbonate provides stable skeletal support for the pellets, guaranteeing their strength. Ammonium bicarbonate is the core component for arsenic removal, while calcium carbonate is used to ensure pellet strength; the two form a synergistic "strength-arsenic removal" system.

[0007] This invention also provides a method for preparing iron oxide pellets and removing arsenic from iron oxide pellets using a composite binder, the specific steps of which are as follows: (1) Pelletizing: Iron oxide ore powder is mixed with calcium carbonate-ammonium bicarbonate composite binder solution and pelletized in a disc pelletizer to obtain green pellets; (2) Curing: The green pellets described in step (1) are aged for 5-8 hours at a temperature of 20-30℃ and a humidity of 60-80%. During this process, ammonium bicarbonate decomposes slowly, laying a porous structure foundation for subsequent calcination and arsenic removal. (3) Drying: Dry the cured pellets at 100±5℃ for 3-4 hours; (4) Calcination: The dried pellets are calcined at 600-800℃ for 2-4 hours to obtain arsenic-free iron oxide pellets. This temperature range can promote the complete decomposition of ammonium bicarbonate to produce NH3, and efficiently complete the conversion and volatilization of arsenic compounds.

[0008] Preferably, the liquid-to-solid ratio of the composite binder solution is 8-10%, and it is added to the iron oxide ore powder in an atomized form. The atomized addition allows ammonium bicarbonate to uniformly cover the surface of the ore powder, ensuring that NH3 is generated around each ore powder particle, thereby improving the uniformity of arsenic removal.

[0009] Preferably, the iron oxide ore powder has more than 85% particles with a particle size of <0.074mm; fine-grained ore powder has a large specific surface area, which can increase the contact sites with ammonium bicarbonate solution, so that the reaction between NH3 and arsenic compounds is more complete.

[0010] Preferably, the disc pelletizer has an inclination angle of 40°-45°, a rotation speed of 10-15 rpm, a pelletizing time of 10-15 min, and a green pellet diameter of Φ10-15 mm. Under these parameters, the green pellets have a moderate density and uniform structure, providing good conditions for the formation of porous channels by the decomposition gas of ammonium bicarbonate during roasting. The CO2 and NH3 produced by the decomposition of ammonium bicarbonate during roasting can smoothly form porous channels, providing a path for the volatilization of arsenic compounds, while avoiding insufficient strength due to overly porous green pellets.

[0011] The core innovation of this invention lies in achieving synergistic arsenic removal and pellet preparation through the unique mechanism of ammonium bicarbonate. In the composite binder of this invention, calcium carbonate provides skeletal support for the pellets, combining with iron ore powder through interfacial reactions to enhance pellet strength. The NH3 and CO2 produced by the decomposition of ammonium bicarbonate form porous channels within the pellets, enhancing permeability and reacting with arsenides to generate volatile arsenic-ammonia compounds, achieving highly efficient arsenic removal. The calcination temperature is controlled at 600-800℃, reducing energy consumption by more than 30% compared to traditional processes, while simultaneously avoiding the disorderly volatilization of arsenides caused by high temperatures.

[0012] The pellets prepared by the method of this invention have a green pellet drop strength of ≥5 times / 1m and a dry pellet compressive strength of ≥2000N / pellet, which meets the requirements of subsequent smelting; the arsenic removal rate can reach more than 85%, and the arsenic content of the pellets is reduced to less than 0.02%, realizing the low-energy consumption and high-purity utilization of iron oxide ore resources.

[0013] The steps of the method of the present invention will be described in detail below: In the pelletizing step, the composite binder is mixed with water at a liquid-to-solid ratio of 8-10% to form a uniform solution, which is then sprayed into the iron oxide ore powder using an atomization method. This ensures that the binder solution is evenly distributed on the surface of the ore powder, avoiding uneven pelletizing caused by excessively high local concentrations. Controlling the tilt angle, rotation speed, and pelletizing time of the disc pelletizer ensures that the green pellets have good roundness and initial strength.

[0014] The core of the curing step is to promote the interfacial reaction between the binder and the mineral powder: calcium carbonate gradually dissolves and reacts with the hydroxyl groups on the surface of the mineral powder to form preliminary chemical bonds; ammonium bicarbonate slowly decomposes, releasing a small amount of carbon dioxide and ammonia, laying the foundation for subsequent structural porosity. Suitable temperature and humidity conditions can prevent the green pellets from losing moisture too quickly or absorbing too much water, ensuring a stable reaction.

[0015] The purpose of the drying step is to remove free moisture from the pellets, allowing the initial structure formed by the binder to solidify, thereby increasing the initial strength of the pellets and providing a stable matrix for subsequent calcination processes. Controlling the drying temperature and time can prevent premature and drastic decomposition of ammonium bicarbonate due to high temperatures, while also preventing residual moisture from affecting the calcination effect.

[0016] The roasting step is key to achieving synergistic strength enhancement and arsenic removal: calcium carbonate partially decomposes into calcium oxide and carbon dioxide within this temperature range. Calcium oxide reacts with iron oxides on the surface of the mineral powder to form more stable calcium-iron compounds, further enhancing the strength of the pellets. Ammonium bicarbonate completely decomposes at high temperatures, producing a large amount of ammonia and carbon dioxide. These gases form porous channels inside the pellets, which not only enhances the permeability of the pellets but also provides a pathway for the volatilization of arsenic compounds. NH3 reacts with arsenic compounds in a directed manner: NH3, as a reducing gas, reacts with arsenic compounds (mainly As2O3) in the pellets in a directed manner, first generating the intermediate product As(OH)3 (reaction formula: As2O3 + 3H2O = 2As(OH)3). Subsequently, As(OH)3 and NH3 further combine to generate the low-boiling-point arsenic ammonia compound As(NH2)3 (reaction formula: As(OH)3 + 3NH3 = As(NH2)3 + 3H2O). Ammonia, as a reducing gas, reacts chemically with the arsenic compounds in the pellets to generate volatile arsenic ammonia compounds, which escape with the gas, thus achieving the purpose of arsenic removal.

[0017] Instruction manual attached Figure 2This is a schematic diagram illustrating the arsenic removal mechanism of the present invention, detailing the reaction pathway between NH3 and As2O3: At the calcination temperature, NH3 molecules produced by the decomposition of ammonium bicarbonate react chemically with As2O3 in the pellets, first forming the intermediate product As(OH)3, which then combines with NH3 to form As(NH2)3. Because As(NH2)3 has a low boiling point, it rapidly volatilizes at the calcination temperature, is discharged with the exhaust gas, and is collected and treated, thereby achieving arsenic removal.

[0018] Compared with the prior art, the beneficial effects of the present invention are: (1) The first-ever ammonium bicarbonate dearsenic removal mechanism and bonding synergy system: breaking through the limitation of existing binders that can only "bond into balls", clarifying the action path of ammonium bicarbonate "decomposition to produce NH3-directional reaction-volatilization to remove arsenic", realizing the simultaneous "ball binding" and "arsenic removal", and solving the problem of impurity removal from arsenic-containing iron ore.

[0019] (2) High arsenic removal efficiency and strength meets the standard: the arsenic removal rate can reach more than 85%, the arsenic content of the pellets is reduced to less than 0.02%, and the dry pellet compressive strength is ≥2000N / ball, which meets the requirements of subsequent smelting and avoids the technical bottleneck of "removing arsenic will inevitably reduce strength".

[0020] (3) Low energy consumption and environmental protection: The roasting temperature is only 600-800℃, which reduces energy consumption by more than 30% compared with the traditional process; no additional arsenic removal agent is required, and As(NH2)3 can be collected and treated in a centralized manner with the exhaust gas, avoiding disorderly volatilization pollution of arsenic compounds, which meets the requirements of clean metallurgy.

[0021] (4) The process is simple and easy to industrialize: the process only includes four steps: pelletizing, curing, drying and roasting. The equipment used is a conventional disc pelletizing machine, oven and muffle furnace. No special customized equipment is required. It can be directly adapted to the existing iron ore pellet production line and the promotion cost is low. Attached Figure Description

[0022] Figure 1 The process flow diagram of the iron oxide ore pellet preparation and arsenic removal method provided by the present invention is shown.

[0023] Figure 2 This is a schematic diagram of the arsenic removal mechanism of the present invention (reaction path of NH3 and As2O3); it clearly shows the whole process of NH3 generated by the decomposition of ammonium bicarbonate reacting with As2O3 to form As(OH)3, and then being converted into As(NH2)3 and volatilized.

[0024] Figure 3 This is a schematic diagram of the cross-sectional structure of the pellets of the present invention. Figure 3 a represents a solution not using the present invention (single calcium carbonate bonding), with a dense, non-porous cross-section, preventing arsenic compounds from volatilizing; Figure 3b represents the solution of this invention, where the cross-section forms a porous structure due to the decomposition of ammonium bicarbonate, providing a channel for the volatilization of arsenic compounds, while the framework formed by calcium carbonate ensures strength.

[0025] Figure 4 for Figure 3 a and Figure 3 Comparison chart of (b) (binder, arsenic removal rate, strength). Detailed Implementation

[0026] To further illustrate the present invention, the technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0027] Example 1 This embodiment provides a method for preparing iron oxide pellets and removing arsenic from iron oxide pellets using a composite binder, such as... Figure 1 As shown, the specific process flow is as follows: 1000g of hematite powder with 42% TFe (arsenic content 0.15%, particle size <0.074mm accounted for 88%) was selected. Weigh 20g of CaCO3 (2.0%) and 10g of NH4HCO3 (1.0%) based on the dry weight of iron ore, add 90mL of water, and stir to prepare a uniform binder solution (liquid-solid ratio of 9%). (1) Pelletizing: Add iron ore powder to a disc pelletizer, atomize and spray in binder solution, control the disc tilt angle of 42° and the rotation speed of 12 rpm, pelletize for 12 min to obtain green pellets with Φ10-15mm; atomize and add to ensure that NH4HCO3 evenly covers the ore powder; (2) Curing: Place the green bulbs in an environment of 25℃ and 70% relative humidity for 6 hours for curing; during this stage, NH4HCO3 decomposes slowly and initially forms micropores; (3) Drying: Place the cured pellets into an oven and dry them at 100℃ for 3.5h; remove free moisture to avoid the sudden boiling of water during roasting and damage to the pellet structure; (4) Calcination: The dried pellets were placed in a muffle furnace and calcined at 700°C for 3 hours. After natural cooling, arsenic-free iron oxide pellets were obtained. The cross-section of the pellets prepared in Example 1 is shown in Figure 1. Figure 3 As shown in b.

[0028] The obtained pellets were tested, and the results are as follows: the drop strength of the green pellets was 6 times / 1m, the compressive strength of the dry pellets was 2200N / pellet, the arsenic content of the pellets was 0.015%, and the arsenic removal rate reached 90%. The test results show that ammonium bicarbonate is completely decomposed at 700℃, NH3 reacts fully with As2O3, and the calcium-iron compound formed by calcium carbonate ensures the strength of the pellets.

[0029] Example 2 This embodiment provides a method for preparing iron oxide pellets and removing arsenic from iron oxide pellets using a composite binder, such as... Figure 1 As shown, the specific process flow is as follows: 1000g of limonite powder with 40% TFe (arsenic content 0.12%, particle size <0.074mm accounts for 85%) was selected. Weigh 10g of CaCO3 (1.0%) and 5g of NH4HCO3 (0.5%) based on the dry weight of iron ore, add 80mL of water, and stir to prepare a uniform binder solution (liquid-solid ratio of 8%). (1) Pelletizing: Add iron ore powder to a disc pelletizer, atomize and spray in binder solution, control disc tilt angle 40° and rotation speed 10 rpm, pelletize for 10 min to obtain green pellets with Φ10-15mm; (2) Curing: Place the raw bulbs in an environment of 20℃ and 60% relative humidity for 5 hours for curing; (3) Drying: Place the cured pellets into an oven and dry them at 95℃ for 3 hours; (4) Calcination: The dried pellets are placed in a muffle furnace and calcined at 600°C for 2 hours. After natural cooling, iron oxide pellets are obtained.

[0030] The obtained pellets were tested, and the results are as follows: the drop strength of the green pellets was 5 times / 1m, the compressive strength of the dry pellets was 2000N / pellet, the arsenic content of the pellets was 0.018%, and the arsenic removal rate reached 85%. Even at a lower calcination temperature (600℃) and a smaller amount of ammonium bicarbonate (0.5%), an arsenic removal rate of 85% could still be achieved, proving that the arsenic removal mechanism of ammonium bicarbonate is stable and reliable.

[0031] Example 3 This embodiment provides a method for preparing iron oxide pellets and removing arsenic from iron oxide pellets using a composite binder, such as... Figure 1 As shown, the specific process flow is as follows: 1000g of hematite powder with 45% TFe (arsenic content 0.18%, particle size <0.074mm accounted for 90%) was selected. Weigh 30g of CaCO3 (3.0%) and 20g of NH4HCO3 (2.0%) based on the dry weight of iron ore, add 100mL of water, and stir to prepare a uniform binder solution (liquid-solid ratio of 10%). (1) Pelletizing: Add iron ore powder to a disc pelletizer, atomize and spray in binder solution, control disc tilt angle 45° and rotation speed 15 rpm, pelletize for 15 min, and obtain green pellets with Φ10-15mm; (2) Curing: Place the raw bulbs in an environment of 30℃ and 80% relative humidity for 8 hours for curing; (3) Drying: Place the cured pellets into an oven and dry them at 105℃ for 4 hours; (4) Calcination: The dried pellets are placed in a muffle furnace and calcined at 800°C for 4 hours. After natural cooling, iron oxide pellets are obtained.

[0032] The obtained pellets were tested, and the results are as follows: the drop strength of the green pellets was 7 times / 1m, the compressive strength of the dry pellets was 2500N / pellet, the arsenic content of the pellets was 0.012%, and the arsenic removal rate reached 93.3%; with a high dosage of ammonium bicarbonate (2.0%) and a longer calcination time (4h), the arsenic removal rate increased to 93.3%, and the increased dosage of calcium carbonate further improved the strength of the pellets, verifying the rule that "the dosage of ammonium bicarbonate is positively correlated with the arsenic removal rate".

[0033] Comparative Example 1 This comparative example uses a single calcium carbonate binder to prepare iron oxide pellets, specifically including the following steps: 1000g of the same hematite powder as in Example 1 was selected; The binder used was 30g of CaCO3 (3.0%), added to 90mL of water (liquid-solid ratio consistent with Example 1); The process parameters for pelletizing, curing, drying, and calcining are exactly the same as in Example 1.

[0034] The obtained pellets were tested, and the results are as follows: the dry pellet compressive strength is 1200 N / pellet, and the arsenic removal rate is 30% (the arsenic content of the pellets is 0.105%). Without ammonium bicarbonate, the 30% arsenic removal rate is achieved only by the volatilization of a small amount of arsenic compounds at high temperature. Moreover, the pellet strength is reduced due to the lack of pore support formed by NH3, which fully proves that ammonium bicarbonate is not only the core component for arsenic removal, but also helps to improve strength by forming a porous structure.

[0035] A comparison of Example 1 and Comparative Example 1 shows that the present invention uses a calcium carbonate-ammonium bicarbonate composite binder. By clarifying the arsenic removal mechanism of ammonium bicarbonate and optimizing process parameters, it can significantly improve pellet strength and arsenic removal rate, thus achieving efficient and clean utilization of iron oxide ore resources.

[0036] Figure 3 This is a schematic diagram of the cross-sectional structure of the pellets of the present invention. Figure 3 a is the cross-section of the pellet in Comparative Example 1 that did not adopt the solution of the present invention. It has a dense structure and low porosity, which makes it difficult for arsenic to volatilize, and its strength is limited by a single bonding effect. Figure 3 b shows the cross-section of the pellets prepared in Example 1 of this invention, exhibiting a distinct porous structure. These pores are formed by the gas produced by the decomposition of ammonium bicarbonate, which not only improves the gas permeability of the pellets but also provides channels for the volatilization of arsenic compounds. Simultaneously, the skeletal structure formed by calcium carbonate ensures the strength of the pellets. The comparison clearly demonstrates the optimizing effect of the process of this invention on the microstructure of the pellets. Figure 3 a and Figure 3 b is an example attached Figure 4 As shown.

[0037] As can be seen from the above embodiments, the composite binder for iron oxide ore pellets provided by the present invention, along with its pellet preparation and arsenic removal method, achieves synergistic optimization of pellet strength improvement and the arsenic removal process by clarifying the "decomposition-reaction-removal" arsenic removal mechanism of ammonium bicarbonate and combining it with the strength-supporting effect of calcium carbonate. The pellets prepared by this method meet smelting requirements in terms of strength, have a high arsenic removal rate, and require a low roasting temperature, significantly reducing energy consumption and environmental pollution.

[0038] The method of this invention has a simple process flow and is highly operable. It can realize the low-energy consumption and high-purity utilization of iron oxide ore resources, improve resource utilization efficiency, and has significant economic and environmental benefits. It is suitable for industrial application.

[0039] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. Other embodiments can be obtained based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A composite binder for iron oxide ore pellets, characterized in that, Based on the dry weight of iron ore, it contains 1.0%-3.0% calcium carbonate and 0.5%-2.0% ammonium bicarbonate; the ammonium bicarbonate is used to decompose and generate NH3 during the roasting stage, which reacts with arsenic compounds in the pellets to generate volatile arsenic ammonia compounds, thereby achieving arsenic removal.

2. The composite binder for iron oxide ore pellets according to claim 1, characterized in that: The mass ratio of calcium carbonate to ammonium bicarbonate is (1.5:1) - (3:1).

3. The method for preparing iron oxide pellets and removing arsenic from iron oxide pellets using the composite binder according to claims 1-2, characterized in that, The specific steps are as follows: (1) Pelletizing: Iron oxide ore powder is mixed with calcium carbonate-ammonium bicarbonate composite binder solution and pelletized in a disc pelletizer to obtain green pellets; (2) Curing: The green bulbs described in step (1) are aged for 5-8 hours at a temperature of 20-30℃ and a humidity of 60-80%; (3) Drying: Dry the cured pellets at 100±5℃ for 3-4 hours; (4) Calcination: The dried pellets are calcined at 600-800℃ for 2-4 hours to obtain arsenic-free iron oxide pellets.

4. The method for preparing iron oxide pellets and removing arsenic from iron oxide pellets using a composite binder according to claim 3, characterized in that: In step (1) ball making, the composite binder solution is added in the form of atomization, with a liquid-to-solid ratio of 8-10%.

5. The method for preparing iron oxide pellets and removing arsenic from iron oxide pellets using a composite binder according to claim 3, characterized in that: In step (1), the iron oxide ore powder used has a particle size of <0.074mm, accounting for more than 85% of the particles.

6. The method for preparing iron oxide pellets and removing arsenic from iron oxide pellets using a composite binder according to claim 3, characterized in that: During the pelletizing process, the disc pelletizer has an inclination angle of 40°-45°, a rotation speed of 10-15 rpm, a pelletizing time of 10-15 min, and a raw pellet diameter of Φ10-15 mm.

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