A pretreatment method for mixed potassium salt raw ore

Abstract

A pretreatment method for mixed mined potassium salt raw ore, comprising the following steps: after crushing and screening the raw ore, feeding it into a heavy medium separation device for gravity separation. The upper light product obtained by gravity separation is a slurry mainly composed of carnallite, which can enter the carnallite decomposition and crystallization operation; the bottom heavy product obtained by gravity separation is the mixed salt of sylvite / halite. The separation medium of the heavy medium separation device is an autogenous medium, which is a suspension slurry composed of mother liquor and fine particle raw ore. A low-cost gravity separation method based on density difference is used to separate carnallite from the mixed salt, so that carnallite and sylvite are preliminarily separated and then separately processed, solving the problems of low decomposition and crystallization efficiency and low overall potassium recovery rate when using the "cold decomposition crystallization - positive flotation process" to prepare potassium chloride with mixed mined potassium salt raw ore as the raw material and a high content of sylvite. This process has obvious technical advantages and application and promotion value in potassium salt mines where carnallite and sylvite are mixed mined.

Description

Technical Field

[0001] The present invention relates to a raw material pretreatment method for the preparation of potassium fertilizers, and in particular to a method for pretreating a mixed potassium salt raw ore when using the mixed potassium salt raw ore to prepare potassium chloride. Background Art

[0002] Potassium fertilizers are important inputs in agricultural production and are also strategic scarce resources in China. China's potassium fertilizer consumption ranks first in the world, with an annual consumption of up to 14 million tons, but the self-sufficiency rate is only about 50%.

[0003] The main potassium fertilizers produced in China are potassium chloride produced around the Qarhan Salt Lake in Qinghai and potassium sulfate produced in Lop Nur, Xinjiang.

[0004] In recent years, due to factors such as the imbalance between supply and demand, price fluctuations, and trade frictions in the global potassium fertilizer market, the potassium fertilizer supply in China faces greater uncertainties and risks. To ensure the potassium fertilizer supply in China, Chinese enterprises are actively promoting the construction of overseas potassium fertilizer bases, especially in Southeast Asia with rich potassium resources. In recent years, continuous investment has been made, and cooperation with local governments has been carried out for development, continuously improving the production capacity scale and market competitiveness. While making contributions to local development, it also makes important contributions to China's potassium fertilizer supply.

[0005] The current mainstream potassium chloride production process is the "cold decomposition crystallization - positive flotation" process, which is widely used in potassium salt resource development and utilization projects and has advanced technology and mature processes. "Cold decomposition crystallization" is the core of this process. As a pre-treatment process for separation, the quality of its effect has an important impact on the efficiency of subsequent separation operations, the potassium recovery rate of the overall process, the energy consumption of subsequent dehydration and drying processes, and the overall technical effect of the process. When the existing "cold decomposition crystallization" process uses carnallite as the main raw material, it is the most applicable. However, when the content of sylvite in the raw material is relatively high (the relative content of sylvite to carnallite is greater than 10%), this part of sylvite will not be able to effectively complete the conversion or dissolution dissociation in the decomposer (crystallizer) due to its large particle size or / and insufficient residence time, resulting in this part of the material directly entering the subsequent flotation operation. This part of sylvite cannot be carried by the foam in the flotation machine and remains in the tailings, resulting in a relatively low potassium recovery rate of the overall process.

[0006] In China, potash mines mainly use salt lake brine as raw materials to prepare carnallite by solar evaporation in salt pans. During the solar evaporation process, the composition of the brine in the salt pan process can be monitored and adjusted to control the content of sylvite in the raw ore entering the potash processing plant. However, potash mines in some regions (such as Laos, Thailand in Southeast Asia) are primary solid minerals. The associated minerals with carnallite include sylvite, kainite, polyhalite, brucite, etc. in addition to halite. Among these associated minerals, sylvite has a relatively high potassium content. Therefore, during underground mining, it will inevitably be mined together with carnallite and become the raw material for the processing plant.

[0007] To solve this technical problem, one technical idea is to grind all the mixed mined raw ore to a particle size of less than -2 mm by grinding and then feed it all into the decomposition crystallizer. Although this method can effectively improve the recovery of sylvite by the "cold decomposition crystallization - positive flotation process" and thus increase the potassium recovery rate, grinding and decomposing and crystallizing all the raw materials will greatly increase the investment in equipment and workshops. Another idea is to improve the decomposition crystallization device. For example: 1) An improved mechanical decomposition crystallization device for potash industry disclosed in CN105597363B sets a bowl-shaped baffle at the lower part of the inner cylinder to change the particle and fluid movement laws of the pulp in the crystallizer, increase the residence time of the raw materials in the decomposition device, and reduce the entrainment of raw materials in the products; 2) A decomposition crystallization device for potash industry disclosed in CN110229024B sets a liquid distribution device and a flow guiding cone in the middle and lower parts of the crystallizer to introduce a local upflow inside the crystallizer to reduce the entrainment of raw materials in the products; 3) A circulating fluidized bed decomposition crystallization device and decomposition crystallization method disclosed in CN111643924B change the liquid feeding method of the crystallizer to form a fluidized bed layer stratified by density at the bottom of the crystallizer, and change the discharging method to make the entrainment rate of raw materials in the final crystal pulp product lower and the average particle size of the product particles larger. The above methods have solved the problem of entrainment of sylvite in the decomposition crystallization products to a certain extent, but the overall effect is still not ideal and needs to be improved. Summary of the Invention

[0008] The technical problem to be solved by the present invention is to provide a pretreatment method for mixed mined potash raw ore to overcome the lack of process adaptability of the existing "cold decomposition crystallization - positive flotation" process when carnallite and its associated minerals are co-mined in solid mining potash mines, reduce the loss of potassium recovery rate of the overall process caused by insufficient dissociation and conversion of sylvite in the decomposition crystallization process when the raw material of the potash processing plant is mixed mined potash, and improve the potassium recovery rate.

[0009] The associated minerals of the carnallite (mainly composed of KCl·MgCl2·6H2O, density 1.60 g / cm 3 ) mainly include sylvite (mainly composed of KCl, density 1.97 - 1.99 g / cm3 ), halite (mainly composed of NaCl, density 2.10 - 2.20 g / cm 3 ), and other associated minerals also include kainite (mainly composed of KMg(SO4)Cl·3H2O, density 2.15 g / cm 3 ), polyhalite (mainly composed of K2Ca2Mg(SO4)4·2H2O, density 2.72 - 2.78 g / cm3), and brucite (mainly composed of Mg(OH)2, density 2.3 - 2.6 g / cm 3 ), etc.

[0010] The technical solution adopted by the present invention to solve its technical problems is a pretreatment method for a mixed - mined potash ore raw material, including the following steps:

[0011] S1. Raw ore crushing and screening: Feed the mixed - mined potash ore raw material into a vibrating screen for screening. The over - size materials are fed into a crusher for crushing, and the crushed materials are returned to the vibrating screen for screening to obtain the undersize material, the raw ore powder.

[0012] S2. Self - generated medium gravity separation: Feed the undersize material, the raw ore powder obtained in step S1, or also including the qualified medium from step S5, into a gravity separation device. In the raw ore powder, carnallite is mainly concentrated in the floating matter due to its lower density, while sylvite, halite, and other associated minerals in the raw ore powder are concentrated in the sinking matter due to their higher density. After the floating - matter slurry of the gravity separation device is discharged, it is the light product obtained after pretreatment, and the light product is mainly composed of carnallite mixed with a large amount of medium slurry. After the sinking - matter slurry of the gravity separation device is discharged, it is the heavy product obtained after pretreatment, and the heavy product is mainly composed of halite / sylvite mixed with a small amount of medium slurry.

[0013] S3. Heavy - product treatment: Feed the heavy product obtained in step S2 directly into a grinding operation to prepare a finely - ground halite / sylvite fine - particle slurry; or feed it into a vibrating screen for medium removal. The large - particle halite / sylvite materials on the over - size are stockpiled; the fine - particle slurry under the screen enters step S5.

[0014] S4. Light - product treatment: Feed the light product obtained in step S2 directly into a decomposition and crystallization operation, or feed it into a vibrating screen for medium removal. The coarse - particle materials on the over - size are mainly carnallite and directly enter the decomposition and crystallization operation. The fine - particle slurry under the screen enters step S5.

[0015] S5. Qualified medium preparation and circulation: Feed the halite / sylvite fine - particle slurry obtained in step S3 and the fine - particle slurry obtained in step S4 into a stirring tank for buffering. Add fine - particle sylvite or halite to it to adjust the slurry density, and then transport it to step S2 through a slurry pump and pipeline.

[0016] Further, in step S1, the vibrating screen is one of a banana screen, a circular vibrating screen, a linear vibrating screen, and a relaxation screen; preferably a relaxation screen.

[0017] Further, in step S1, the effective particle size of the vibrating screen mesh during screening is 5 mm - 25 mm. The effective screening particle size refers to the classification particle size during screening and is related to the size and form of the screen holes. The particle size is adjusted and controlled by replacing the screen plate with different screen hole sizes. Further, in step S1, the crusher is one of a differential pair-roll crusher, a reversible ring hammer crusher, and a ring hammer crusher, preferably a reversible ring hammer crusher.

[0018] Further, in step S1, the material after crushing is directly mixed with the undersize material and enters step S2.

[0019] Further, in step S2, the gravity separation equipment is one of a heavy medium cyclone, a jig, a shallow tank heavy medium separator, an inclined wheel heavy medium separator, and a vertical wheel heavy medium separator; preferably a shallow tank heavy medium separator.

[0020] Further, in step S2, the self-generated heavy medium is a slurry mixture composed of the externally fed supplementary mother liquor and the fine particles in the raw material, and the addition amount of the mother liquor is adjusted by feedback control of the separation effect of the product to control the gravity separation effect.

[0021] Further, the halite / potassium salt material on the screen after medium removal by feeding into the vibrating screen in step S3 can also directly enter the grinding operation.

[0022] Further, in step S5, it is possible to analyze the separation effect in step S2 by measuring the pulp density and the percentage content of fine particles (-0.5 mm) in the mixed potassium salt raw ore in step S1 to determine whether it is necessary to add a part of the high-concentration halite / potassium salt pulp to achieve the density stability of the self-generated medium system and the control of the overall separation effect.

[0023] Further, the halite or potassium salt added in step S5 can be either powder or slurry, preferably the potassium salt slurry prepared after the heavy product from step S3 enters the grinding operation.

[0024] The pretreatment method of the mixed potassium salt ore of the present invention uses a gravity sorting method based on density difference to sort the mixed salt of the mixed potassium salt ore (mainly carnallite / rock salt, with potassium salt) obtained by mining, so that potassium salt and rock salt with higher density are sorted out from the mixed potassium salt in the autogenous heavy medium sorting system due to their higher density and become heavy products; carnallite floats up to become light products due to its lower density, and the treated mixed potassium salt ore is divided into low-density materials (light products) mainly composed of carnallite and high-density materials (heavy products) mixed with rock salt / potash salt. The low-density materials mainly composed of carnallite are subsequently subjected to decomposition and crystallization conversion treatment and then separated by flotation to prepare potassium chloride; the high-density materials mainly composed of rock salt / potash salt enter the grinding operation to dissociate potassium chloride and sodium chloride, and then float separately or mix with the low-density materials after decomposition and crystallization and enter flotation together.

[0025] The pretreatment method of the mixed potassium salt ore of the present invention pretreats the mixed potassium salt ore, cleverly utilizes the natural density difference between carnallites and associated minerals potassium salt and halite, prepares autogenous heavy medium with fine particles in mother liquor and ore as sorting medium, selects gravity separation equipment to pre-sort the mixed potassium salt ore, realizes the preliminary separation of carnallites and associated minerals halite and potassium salt, and sorts out some coarse-grained potassium salt for separate grinding treatment. The application of the present invention can improve the problem of low overall potassium yield of the process when potassium chloride is prepared using the "cold decomposition crystallization-positive flotation" process when potassium chloride is prepared using the mixed potassium salt as the ore because potassium salt cannot be effectively decomposed and crystallized.

[0026] The pretreatment process of the present invention has a simple flow. The use of this pretreatment method to separate carnallite and sylvite for separate treatment can reduce the investment in equipment and plant for decomposition crystallization and grinding, and effectively improve the unit volume efficiency of the decomposition crystallization equipment, reduce the raw material entrainment rate in the product, and has obvious technical advantages and application promotion value. DETAILED DESCRIPTION

[0027] The specific implementation modes of the present invention are described in detail below in conjunction with the embodiments. Example 1

[0028] The mixed potassium salt ore (the mass ratio of carnallite: potassium salt: rock salt is 5:2:11) used in this embodiment is fed from the ore yard to the screw feeder by a loader and then to the belt conveyor. After being iron-removed by the iron remover installed on the belt conveyor, it is transported to the ore bin for buffering.

[0029] This embodiment includes the following steps:

[0030] S1. Crushing and screening of raw ore: Feed the mixed mined potassium salt raw ore (mass ratio of carnallite: sylvite: halite is 5:2:11) into the raw ore vibrating screen (equivalent diameter of the screen mesh d = 20 mm) for screening and classification to obtain the undersize material; the material on the raw ore vibrating screen enters the reversible impact crusher (discharge particle size ≤ 10 mm) for crushing, and the crushed material is mixed with the undersize material to obtain the raw ore powder of the undersize material;

[0031] S2. Gravity separation with self-generated medium: Feed the raw ore powder of the undersize material obtained in step S1 (-0.5 mm mass percentage content is 12.4%) into the feeding end of the inclined wheel heavy medium separator. In the raw ore powder, carnallite is mainly enriched in the floating matter due to its lower density, while sylvite, halite and other associated minerals in the raw ore are enriched in the sinking matter due to their higher density; the slurry of the floating matter is discharged by the low-density product wheel in the inclined wheel heavy medium separator and then is the light product obtained after pretreatment. The sinking matter of the inclined wheel heavy medium separator is lifted from the bottom by the inclined lifting wheel and then discharged to become the heavy product obtained after pretreatment; the light product is mainly composed of carnallite mixed with a large amount of medium slurry; the heavy product is mainly composed of halite / sylvite mixed with a small amount of medium slurry;

[0032] S3. Treatment of heavy product: Directly feed the heavy product obtained in step S2 into the grinding operation to prepare the finely ground halite / sylvite fine particle slurry; or feed it into the vibrating screen for medium removal, and the large particle halite / sylvite material on the screen is stockpiled, and the fine particle slurry under the screen enters step S5;

[0033] S4. Treatment of light product: Directly feed the light product obtained in step S2 into the decomposition and crystallization operation, or feed it into the vibrating screen for medium removal. The coarse particle material on the screen is mainly carnallite and directly enters the decomposition and crystallization operation, and the fine particle slurry under the screen enters step S5;

[0034] S5. Preparation and circulation of qualified medium: Feed the halite / sylvite fine particle slurry obtained in step S3 and the fine particle slurry obtained in step S4 into the mixing tank for buffering, add fine particle sylvite or halite to it, and adjust the density in the medium adjustment tank by adjusting the split flow of the floating matter slurry (the density is controlled at 1.70 g / cm 3 ~1.80 g / cm 3 ). After stirring and pulp adjustment, it is transported to the inclined wheel heavy medium separator through the slurry pump and pipeline to adjust its pulp density, and then transported to the inclined wheel heavy medium separator in step S2 through the slurry pump and pipeline.

[0035] In this embodiment, the vibrating screen used is a linear vibrating screen, the gravity separation equipment is an inclined wheel heavy medium separator, and the classification equipment is a linear vibrating screen.

[0036] In this embodiment, when the pre-treatment method of the mixed potassium salt raw ore of the present invention is used to pre-treat the mixed raw ore of solid-harvested carnallite and sylvite in a certain place, the separation density in the inclined chute heavy medium separator is adjusted and controlled to be between 1.75 g / cm 3 ~1.85 g / cm 3 . The light product is fed into the decomposition crystallizer, and the sylvite content entering the decomposition crystallizer can be controlled below 2.0%, effectively improving the volume efficiency of the decomposition crystallizer; the heavy product is separately ground and dissociated and then sent to the separation operation together with the ore pulp after decomposition crystallization for separation. The potassium recovery rate of the overall process reaches 78.6%. Comparative example

[0037] The pre-treatment method of Embodiment 1 of the present invention is not used to pre-treat the mixed potassium salt raw ore (mass ratio of carnallite: sylvite: halite is 5:2:11), but the "cold decomposition crystallization - positive flotation" process is directly used for decomposition crystallization and separation operations. The potassium recovery rate of the overall process is 75.1%.

[0038] It can be seen that compared with the potassium recovery rate of 75.1% by directly using the "cold decomposition crystallization - positive flotation" process, after pre-treatment with the present invention and then using the "cold decomposition crystallization - positive flotation" process for decomposition crystallization and separation operations, the potassium recovery rate reaches 78.6%, and the potassium recovery rate of the overall process is increased by 3.5%.

Claims

1. A pretreatment method for mixed potassium salt ore, characterized in that: The following steps are involved: S1. Crushing and screening of raw ore: feeding the mixed potassium salt raw ore into a vibrating screen for screening, feeding the material on the screen into a crusher for crushing, and returning the crushed material to the vibrating screen for screening to obtain raw ore powder of the material under the screen; the effective particle size of the screen of the vibrating screen during screening is 5mm-25mm; S2, autogenous medium re-selection: the raw ore powder obtained in step S1, or the qualified medium from step S5, is fed into the re-selection equipment. The carnallite in the raw ore powder is mainly enriched in the floating material due to its low density, while the potassium salt, halite and other associated minerals in the raw ore powder are enriched in the sinking material due to their high density; the floating material slurry of the re-selection equipment is discharged as the light product obtained after pre-treatment, and the light product is mainly composed of a large amount of carnallite mixed with medium slurry; the sinking material slurry of the re-selection equipment is discharged as the heavy product obtained after pre-treatment, and the heavy product is mainly composed of a small amount of halite / potassium salt mixed with medium slurry; the re-selection equipment is one of a heavy medium cyclone, a jig, a shallow tank heavy medium separator, an inclined wheel heavy medium separator, and a vertical wheel heavy medium separator; S3, heavy product processing: the heavy product obtained in step S2 is directly fed into the grinding operation to prepare fine-grained halite / potash slurry; or fed into the vibrating screen for medium removal, and the large-grained halite / potash slurry on the screen is stored; the fine-grained slurry under the screen enters step S5; S4, light product processing: the light product obtained in step S2 is directly fed into the decomposition and crystallization process, or fed into the vibrating screen for medium removal. The coarse particles on the screen are mainly carnallite, which directly enters the decomposition and crystallization process, and the fine particles under the screen enter step S5; S5. Preparation and circulation of qualified medium: the fine-grained slurry of rock salt / potash obtained in step S3 and the fine-grained slurry obtained in step S4 are fed into a stirring tank for buffering, fine-grained slurry of potash or rock salt is added thereto, the slurry density is adjusted, and then the slurry is transported to step S2 through a slurry pump and a pipeline.

2. The pretreatment method of a mixed potassium salt ore according to claim 1, characterized in that: In step S1, the vibrating screen is one of a banana screen, a circular vibrating screen, a linear vibrating screen, and a relaxation screen.

3. A pretreatment method for mixed potassium salt ore according to claim 1 or 2, characterized in that: In step S1, the crusher is one of a differential roll crusher, a reversible hammer crusher and a hammer crusher.

4. The pretreatment method of a mixed potassium salt ore according to claim 3, characterized in that: In step S1, the crushed material is directly mixed with the undersize material and enters step S2.

5. The pretreatment method of a mixed potassium salt ore according to claim 3, characterized in that: In step S2, the amount of mother liquor added is adjusted by feedback regulation of the separation effect of the product to control the gravity separation effect.

6. The pretreatment method of a mixed potassium salt ore according to claim 3, characterized in that: In step S3, the halite / potash material on the vibrating screen is directly fed into the grinding operation after the medium is removed.

7. The pretreatment method of a mixed potassium salt ore according to claim 3, characterized in that: In step S5, by measuring the pulp density and the percentage content of -0.5 mm fine particles in the mixed potassium salt ore in step S1, the sorting effect in step S2 is analyzed to determine whether it is necessary to add some high-concentration halite / potash salt slurry to achieve density stability of the autogenous medium system and control of the overall sorting effect.

8. The pretreatment method of a mixed potassium salt ore according to claim 3, characterized in that: In step S5, the added halite or potassium halite is in the form of powder or slurry.

9. The pretreatment method of a mixed potassium salt ore according to claim 3, characterized in that: In step S5, the added rock salt or potassium salt is potassium salt slurry prepared after the heavy product from step S3 enters the grinding operation.