Method for recycling waste dolomite fines

Abstract

The application relates to the field of secondary resource utilization, in particular to a method for recycling waste dolomite fine material, which comprises the following steps: crushing the dolomite fine material, controlling the particle size at-1.6 mm, then carrying out desliming treatment, and then passing through a 1mm sieve to obtain 1-1.6mm and-1mm dolomite fine material; according to the mass ratio (60-80):(30-50), the 1-1.6mm and-1mm dolomite fine material is proportioned, 15%-25% of inorganic binder of the total mass of the dolomite fine material is added, and then water is added and uniformly mixed; the uniformly mixed material is subjected to pressureless briquetting, and then curing is carried out to obtain dolomite blocks for blast furnace flux; the dolomite blocks are continuously calcined to obtain light-burned dolomite for sintering flux. The application realizes recycling of the waste dolomite fine material, and the obtained dolomite blocks do not need to be pressure-briquetted, have good formability, high compressive strength, protect the environment and save resources.

Description

Technical Field

[0001] This invention relates to the field of secondary resource utilization technology, and in particular to a method for recycling and reusing waste dolomite fines. Background Technology

[0002] Dolomite is a natural carbonate rock mineral, characterized by its abundant resources and wide distribution. Its chemical composition is Ca·Mg(CO3)2, and it possesses properties such as surface adsorption, high refractoriness, large specific surface area, and good thermal insulation. In industrial production, dolomite is used as a sintering flux due to its low cost and good bonding properties. However, in current production processes, a certain amount of fine dolomite (typically below 35mm in size) that cannot be used for calcination is generated. After calcination, this fine dolomite has a higher specific surface area and better bonding ability with minerals compared to lightly calcined dolomite (i.e., lightly calcined dolomite obtained directly from calcined dolomite blocks in existing technologies). Furthermore, research shows that dolomite powder is much more effective than dolomite in adjusting the alkalinity of sintered ore. However, the fine particles have a negative impact on adjusting the permeability of the sintering bed, and due to particle size requirements, they cannot be directly used as a flux on-site; therefore, they are generally discarded as tailings. Dolomite fines cannot be effectively utilized in other industries, and controlling costs while utilizing waste dolomite fines is a major challenge for production enterprises. If these fines can be recycled, it will not only reduce environmental pollution and improve resource utilization, but also indirectly lower the production cost of calcination, generating significant economic benefits.

[0003] Patent application CN201110034852.9 discloses a method for utilizing lightly calcined dolomite powder, comprising: 1. Finely grinding the lightly calcined dolomite, then mixing it evenly with a 15%-25% MgCl2 solution and cement. The mass ratio of the three components is: 1 part lightly calcined dolomite powder; 0.02-0.05 parts cement; 0.03-0.05 parts MgCl2; 2. Spraying a 3%-5% polyvinyl alcohol organic-inorganic binder onto the mixture and mixing it evenly; 3. Conveying the mixture with the organic-inorganic binder to a briquetting machine and pressing it into briquettes; 4. Curing. Although this method obtains dolomite briquettes that meet the requirements of converters or electric furnaces by adding inorganic binders and briquetting and curing, it requires the addition of organic-inorganic binders and pressing into briquettes, resulting in a low briquetting rate and material loss.

[0004] Therefore, it is necessary to provide an improved method for recycling and reusing waste dolomite fines to solve the above problems. Summary of the Invention

[0005] The purpose of this invention is to provide a method for recycling and reusing waste dolomite fines. By using a pressureless agglomeration method, waste dolomite fine powder that does not meet the particle size requirements of blast furnace flux can be reused. This not only solves the problem that dolomite fine powder cannot be used directly as flux in the blast furnace smelting process, but can also be used as sintering flux, thus avoiding resource waste. At the same time, it turns waste into treasure, making full use of dolomite of various particle sizes and bringing great economic benefits.

[0006] To achieve the above objectives, the present invention provides a method for recycling and reusing waste dolomite fines, comprising the following steps:

[0007] Step 1: Crush the dolomite fines using a jaw crusher and a double roll crusher in sequence. The jaw crusher uses open-circuit crushing, while the double roll crusher uses closed-circuit crushing to control the particle size to -1.6mm. Then, the dolomite fines are deslimed and passed through a 1mm sieve to obtain dolomite fines of 1-1.6mm and -1mm. The particle size of the crushed raw material is controlled below 1.6mm.

[0008] Step 2: Mix 1-1.6mm and -1mm dolomite fines at a mass ratio of (60-80):(30-50), add 15%-25% inorganic binder of the total mass of the dolomite fines, and then add water and mix evenly; preferably, the mass ratio of 1-1.6mm dolomite fines, -1mm dolomite fines, inorganic binder and water is 72±5:40±5:24±5:11±5;

[0009] Step 3: Place the mixed material into a mold for pressureless agglomeration, and then cure it to obtain dolomite blocks. The cured dolomite blocks can be used as blast furnace flux. This invention's pressureless agglomeration method involves placing the material into the mold and curing it directly without applying pressure.

[0010] The dimensions of the block forming test mold are: a frustum shape with an upper radius R = 35 ± 1 mm, a lower radius r = 30 ± 1 mm, and a height h = 25 ± 1 mm.

[0011] This invention removes fine mud (mainly fine mud with a particle size below 0.074 mm in dolomite fines) through crushing and desliming processes to reduce the adverse effects of fine mud on cement consolidation. Then, the dolomite fines of two particle sizes are screened and blended, with their proportions optimized. Only an inorganic binder needs to be added to achieve pressureless agglomeration and curing, resulting in dolomite blocks with compressive strength meeting the requirements of blast furnace flux. This significantly simplifies the raw material types and preparation process, facilitating industrial application. In particular, the dolomite fines obtained using the crushing method of this invention are more effective at removing fine mud that negatively impacts cement consolidation.

[0012] Furthermore, in the -1mm fine dolomite material, the -0.074mm portion accounts for less than 3%.

[0013] Furthermore, methods for recycling and reusing waste dolomite fines also include: calcining cured dolomite blocks to obtain lightly calcined dolomite for use as a sintering flux. After calcination, the activity level meets the requirements of the sintering flux. After calcination, the dolomite blocks are usually converted into fine powder or granular lightly calcined dolomite.

[0014] Furthermore, the inorganic binder includes cement, such as silicate cement. The inorganic binder has no significant effect on the strength and activity of dolomite after calcination.

[0015] Furthermore, the mass ratio of water to inorganic binder is (0.4-0.5):1.

[0016] Furthermore, the desliming process includes: rinsing the fine dolomite material with water, pouring off the water containing fine mud, repeating this process several times until the water is clear, and then drying it.

[0017] Furthermore, in step 3, the curing conditions are 1-28 days at 20-32℃ and humidity above 95%. Preferably, curing is performed for 3-7 days at room temperature and 95% humidity. After 3 days of curing, the compressive strength of the dolomite blocks is ≥2000N / block, and the molding rate of the dolomite blocks is ≥95%, preferably ≥98%.

[0018] The ingredients of this invention can achieve pressureless briquetting, which is simpler than the briquetting machine process and can reduce energy consumption. At the same time, the strength can meet the requirements, reducing the loss and waste of raw materials, improving the recycling rate, and the pressureless operation is simpler and easier to scale up.

[0019] Furthermore, the calcination temperature is 920-980℃, and the time is 0.5-1.5h, preferably 1-1.2h. Specifically, the cured dolomite green block is placed in a muffle furnace for calcination, and then cooled in a dry place.

[0020] Furthermore, the dolomite block has the following dimensions: a frustum shape with an upper radius R = 35 ± 1 mm, a lower radius r = 30 ± 1 mm, and a height h = 25 ± 1 mm.

[0021] Furthermore, the batching process in step 2 is as follows: first, add dolomite with a particle size range of 1 to 1.6 mm (dolomite under 1.6 mm sieve and dolomite over 1 mm sieve), then add dolomite with a particle size range of -1 mm (i.e., dolomite obtained after passing through 1 mm sieve), then add inorganic binder and mix for 3-5 minutes, and finally add water with a mass ratio of 0.4 to 0.5:1 with the binder and mix for 5-8 minutes.

[0022] Furthermore, the calcined lightly calcined dolomite contains 29.4-36.1% MgO, 48.2-58.4% CaO, 0.12-0.17% SiO2, 0.13-0.35% Fe2O3, and has a loss on ignition of 45.5-46.5% (mass loss after calcination) and an activity >203.0 ml.

[0023] Compared with the prior art, the beneficial effects of the present invention are:

[0024] (1) Compared to dolomite, the dolomite product obtained by briquetting and curing fine dolomite in this invention can fully meet the performance requirements of blast furnace flux. After further calcination, it meets the requirements of sintering flux. Moreover, the fine powder has a better bonding effect with iron ore after calcination, a larger specific surface area, and stronger adsorption. When used as a sintering flux, it has greater advantages in adjusting the basicity and permeability of sintered ore. It also requires less energy during the decomposition process.

[0025] (2) The present invention removes fine mud through desliming treatment to reduce the adverse effect of fine mud on cement consolidation. Then, the two types of dolomite fine materials are compounded by sieving and their ratio is optimized. In this way, only inorganic binder needs to be added to achieve pressureless block curing and dolomite blocks with compressive strength that meets the requirements of flux can be obtained. This significantly simplifies the types of raw materials and the preparation process, and facilitates industrial application.

[0026] (3) This invention realizes the reuse of waste dolomite fines, and the components after calcination are all useful components for sintering and steelmaking, thus protecting the environment and saving resources.

[0027] (4) The pressureless block making method is simple and easy to implement, which is conducive to industrial production. The shape is regular and easy to stack and store. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the production process of the present invention.

[0029] Figure 2 It is the effect of bone meal ratio on compressive strength.

[0030] Figure 3 It is the effect of cement dosage on compressive strength.

[0031] Figure 4 This is the XRD pattern of the dolomite block obtained through maintenance.

[0032] Figure 5 This is the XRD pattern of lightly calcined dolomite obtained after calcining dolomite blocks. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention are described clearly and completely below. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. 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.

[0034] Please see Figure 1 The diagram shown is a schematic representation of the process flow of the present invention. The following embodiments are implemented based on the technical solution of the present invention, providing detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments. Unless otherwise specified, the methods used in the following embodiments are conventional methods.

[0035] In this invention, +1mm refers to the portion above a 1mm sieve, -1mm refers to the portion below a 1mm sieve, and -1.6mm refers to the portion below a 1.6mm sieve.

[0036] Table 1. Particle size distribution of dolomite raw materials in the following examples and comparative examples.

[0037] +14 mesh 5.20 -14 mesh~+65 mesh 53.30 -65 mesh~+160 mesh 29.40 -160 mesh~+200 mesh 3.20 -200 mesh~+325 mesh 6.52 -325 mesh 2.38

[0038] Example 1

[0039] The fine dolomite material (derived from a large amount of dolomite powder smaller than 35mm that could not meet the requirements for kiln feeding, produced by calcining dolomite in a vertical kiln in Guizhou) was crushed (the crushing was carried out sequentially using a jaw crusher and a double roll crusher, with the jaw crusher using open-circuit crushing and the double roll crusher using closed-circuit crushing) to control the particle size to -1.6mm. Then, it underwent desliming treatment: the fine dolomite material was placed in a container and rinsed with water, and the water containing fine mud was poured off. This process was repeated several times until the water was clear. Then it was dried to obtain the deslimed fine dolomite material, which was then passed through a 1mm sieve.

[0040] Weigh out 360g of dolomite fines with a particle size of +1mm (1~1.6mm) after desliming treatment, 200g of dolomite fines with a particle size of -1mm (-0.074mm <3%), 120g of inorganic binder P.O42.5 silicate cement, and 54ml of water. Add these ingredients to a mixer in the following order and mix thoroughly. After adding the inorganic binder, mix for 4 minutes, then add water while mixing for 7 minutes. Place the fully mixed material into a mold (a frustum-shaped mold with dimensions R=35mm, r=30mm, h=25mm) and form blocks under pressureless conditions. Qualified raw blocks (frustum-shaped with dimensions R=35mm, r=30mm, h=25mm) were selected by sieving and placed in a curing chamber for constant temperature and humidity curing for 3 days (temperature 25℃, humidity 95%). The cured raw blocks were then calcined in a muffle furnace (calcination temperature 950℃, calcination time 1 hour). The compressive strength of the cured dolomite blocks, the activity of the calcined light-burned dolomite, the calcium oxide content, and the magnesium oxide content were measured, as shown in Table 2. Examples 1-6 are 6 parallel tests of this example.

[0041] Following the method described above, change the bone meal ratio (i.e., the mass ratio of +1mm and -1mm dolomite fines), such as... Figure 2 As shown, with the increase of the bone meal ratio, the compressive strength of the dolomite blocks obtained after 3 days of curing first increases and then decreases. When the bone meal ratio is 1.8, the compressive strength reaches 2000 N / block. Therefore, this invention significantly improves the compressive strength by controlling the blending of two types of dolomite fines within a certain range, thus achieving high-value utilization of dolomite fines.

[0042] Following the method described above, change the amount of cement used, such as... Figure 3 As shown, the activity decreases with increasing cement content, while the compressive strength increases. This invention, by rationally controlling the cement content, yields dolomite blocks with both high compressive strength and high activity.

[0043] from Figure 4 and Figure 5 It can be seen that the composition of dolomite after block formation is the same as that of the raw materials. After calcination, calcium oxide and magnesium oxide are produced.

[0044] Comparative Example 1

[0045] The fine dolomite material (source same as in Example 1) was crushed (crushing method same as in Example 1) and passed through a 1.6mm sieve. The undersized portion was then passed through a 1mm sieve.

[0046] Weigh out 360g of untreated +1mm (1-1.6mm) dolomite fines, 200g of -1mm (-0.074mm < 3%) dolomite fines, 120g of inorganic binder silicate cement, and 54ml of water. Add these ingredients to a mixer in the following order and mix thoroughly. After adding the inorganic binder, mix for 4 minutes, then add water while mixing for 7 minutes. Form the fully mixed material into briquettes under pressureless conditions and select qualified raw briquettes by sieving. (A frustum-shaped block with dimensions R=35mm, r=30mm, h=25mm) The qualified raw blocks were sent to a curing chamber for constant temperature and humidity curing for 3 days (temperature 25℃, humidity 95%). The cured raw blocks were then calcined in a muffle furnace (calcination temperature 950℃, calcination time 1 hour). The compressive strength of the cured dolomite blocks, the activity of the calcined light-burned dolomite, and the calcium oxide and magnesium oxide contents were measured as shown in Table 2.

[0047] Comparative Example 2

[0048] The fine dolomite material (source same as in Example 1) was crushed (crushing method same as in Example 1) and passed through a 1.6mm sieve. The undersized portion was then passed through a 1mm sieve.

[0049] Weigh out 360g of +1mm dolomite fines (untreated), 200g of -1mm (-0.074mm < 3%) dolomite fines, 120g of silicate cement (inorganic binder), and 54ml of water. Add these ingredients to a mixer in the following order and mix thoroughly. After adding the inorganic binder, mix for 4 minutes, then add water while mixing for 7 minutes. Press the fully mixed material into briquettes using a roller press at 20MPa. Manually select the qualified briquettes. (A frustum-shaped block with dimensions R=35mm, r=30mm, h=25mm) The qualified raw blocks were sent to a curing chamber for constant temperature and humidity curing for 3 days (temperature 25℃, humidity 95%). The cured raw blocks were then calcined in a muffle furnace (calcination temperature 950℃, calcination time 1 hour). The compressive strength of the cured dolomite blocks, the activity of the calcined light-burned dolomite, and the calcium oxide and magnesium oxide contents were measured as shown in Table 2.

[0050] The testing standard for compressive strength is: a pellet compressive strength tester.

[0051] The forming rate refers to the ratio of the clumps that have perfectly met the particle size requirements to all clumps.

[0052] Table 2. Performance and component test results of the examples and comparative examples.

[0053]

[0054] As shown in Table 2, the compressive strength and magnesium oxide content of the cured dolomite blocks decreased significantly without desliming treatment. This indicates that the unremoved fine mud has an adverse effect on the consolidation of the mixture, and consequently affects the elemental content after calcination. When pressure briquetting is used, the compressive strength and magnesium oxide content also decrease to varying degrees, indicating that without the addition of organic binders, pressure briquetting is not conducive to improving strength and also increases the complexity of the process.

[0055] Economic benefit estimation:

[0056] Currently, the price of dolomite used as a flux in steelmaking in my country is 360 yuan / ton; the price is 330 yuan / ton when used as a sintering flux. The main cost of this process lies in the calcination step, which costs approximately 50 yuan / ton. The market price of cement is 335 yuan / ton, so the cement cost is 335 * 16.3% = 54.605 yuan / ton. Adding the remaining costs, the total cost of this process does not exceed 130 yuan / ton. The economic benefit is 230 yuan / ton. Therefore, this invention is cost-effective, economically efficient, and easy to promote and apply.

[0057] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for recycling and reusing waste dolomite fines, characterized in that, Includes the following steps: Step 1: Crush the dolomite fines to control the particle size to -1.6mm, then deslim it, and then pass it through a 1mm sieve to obtain dolomite fines of 1-1.6mm and -1mm. The dolomite fines are derived from a large amount of dolomite powder smaller than 35mm that cannot meet the requirements for entering the kiln, produced by calcining dolomite in a vertical kiln in a certain place in Guizhou. The desliming process includes: rinsing the dolomite fines with water, pouring off the water with fine mud on the top, repeating this several times until the water is clear, and then drying it. Step 2: Mix the 1-1.6mm and -1mm dolomite fines at a mass ratio of (60-80):(30-50), add 15%-25% inorganic binder of the total mass of the dolomite fines, and then add water and mix evenly. The inorganic binder is cement; the mass ratio of water to inorganic binder is (0.4-0.5):1; Step 3: Place the mixed material into a mold for pressureless briquetting, and then cure it to obtain dolomite blocks for blast furnace flux; calcine the cured dolomite blocks to obtain lightly calcined dolomite for sintering flux. In step 3, the curing conditions are 1-7 days at 20-32℃ and humidity above 95%; the calcination temperature is 920-980℃ and the time is 0.5-1.5h. The calcined lightly calcined dolomite has the following mass fractions: MgO 29.4-36.1%; CaO 48.2-58.4%; SiO2 0.12-0.17%; Fe2O3 0.13-0.35%; burn loss 45.5-46.5%; and activity >203.0ml. Here, -1mm refers to the portion passing through a 1mm sieve; -1.6mm refers to the portion passing through a 1.6mm sieve.

2. The method for recycling and reusing waste dolomite fines according to claim 1, characterized in that, The crushing process employs a jaw crusher and a double roll crusher in sequence. The jaw crusher uses an open-circuit crushing method, while the double roll crusher uses a closed-circuit crushing method.

3. The method for recycling and reusing waste dolomite fines according to claim 1, characterized in that, The dolomite block is a frustum-shaped structure with an upper radius R = 35 ± 1 mm, a lower radius r = 30 ± 1 mm, and a height h = 25 ± 1 mm.

4. The method for recycling and reusing waste dolomite fines according to claim 1, characterized in that, After 3 days of curing, the compressive strength of the dolomite block is ≥2000N / block, and the molding rate of the dolomite block is ≥95%.

Images