All-solid waste potassic salt ore closed cycle filling process and system based on old brine magnesium extraction and calcium chloride synergy

Abstract

The invention provides an all-solid waste potassic salt ore closed cycle filling process and system based on old brine magnesium extraction and calcium chloride synergy and belongs to the field of potassic salt ore filling. Potassic salt ore old brine reacts with calcium oxide, and mixed slurry is obtained; flocculating and settling the mixed slurry through a thickener to obtain underflow slurry and overflow water, and performing solid-liquid separation on the underflow slurry to obtain a filter cake and filtrate; drying the filter cake, and calcining to obtain magnesium oxide powder; evaporating and concentrating the overflow water and the filtrate to obtain a calcium chloride solution; magnesium oxide powder, a calcium chloride solution, potassic salt ore tail salt, potassic salt ore old brine, calcium oxide and an additive are mixed to prepare filling slurry, and the filling slurry is conveyed to an underground goaf for filling operation. According to the method, the technologies of extracting magnesium from old brine, concentrating and crystallizing calcium chloride and preparing the filling slurry are integrated, a closed-loop circulation system is formed, and tail salt-old brine all-solid waste co-processing and high-value utilization are achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of potassium salt mine filling, and particularly relates to a closed-loop circulation filling process and system for all-solid waste potassium salt mines based on the synergism of magnesium extraction from old brine and calcium chloride. Background Art

[0002] Potassium salt mines are important raw material sources for potassium fertilizers, mainly including sylvinite mines and carnallite mines. The mass fraction of potassium chloride in sylvinite mines is usually 25 - 35%, while that in carnallite mines is 15 - 22%. During the beneficiation process of potassium salt mines, a large amount of tail salt and old brine are produced. The tail salt is mainly composed of granular sodium chloride crystals, which are easily soluble in water, difficult to stack stably, and easily dissolved by rainwater scouring, thereby polluting surface water bodies. Old brine is a liquid rich in magnesium chloride, with a concentration as high as about 30%. If the tail salt and old brine are not effectively treated, it will not only cause environmental pollution, but also lead to problems such as soil salinization and groundwater pollution, causing serious harm to the ecosystem and the surrounding environment.

[0003] Globally, the exploitation and processing of potassium salt mines have always been important topics in resource utilization and environmental protection. Especially in Laos, the development of potassium salt mines faces many technical bottlenecks. Currently, potassium salt enterprises in Laos generally adopt dry filling and wet "water - sand" filling processes. However, these traditional processes have significant defects and deficiencies: Firstly, the stacking of tail salt is strictly restricted by weather conditions. Especially in the rainy season, the tail salt is easily dissolved and washed away by rainwater, not only causing resource waste, but also polluting the surrounding environment. Secondly, the utilization rate of old brine is extremely low. Due to the lack of economic and effective treatment technologies for high - concentration magnesium chloride solutions, they are often directly discharged, which not only increases the environmental burden, but also causes great waste of resources. In addition, there are other technical problems in the existing filling processes. For example, the magnesium - based cement used in traditional cemented filling processes has a high cost, which limits its addition amount in practical applications. This results in unstable long - term strength of the filling body, a relatively high shrinkage rate, and a strength attenuation rate of more than 30% at 28 days, making it difficult to meet the long - term stable requirements of mines. At the same time, the magnesium ions in old brine are not effectively recovered, with low resource utilization rate, further exacerbating resource waste.

[0004] In view of this, it is necessary to design an improved closed - loop circulation filling process and system for all - solid waste potassium salt mines based on the synergism of magnesium extraction from old brine and calcium chloride to solve the above problems. Summary of the Invention

[0005] In view of the technical problems existing in the background art, the present application provides a closed - loop circulation filling process and system for all - solid waste potassium salt mines based on the synergism of magnesium extraction from old brine and calcium chloride, aiming to solve the technical problems of slow strength formation in the potassium salt mine filling process and incomplete treatment of old brine.

[0006] In a first aspect, the present application provides a closed-circuit circulation filling process for all-solid waste potassium salt ore based on the synergistic extraction of magnesium from bittern and calcium chloride, comprising the following steps: S1. React bittern of potassium salt ore with calcium oxide to obtain a mixed slurry; S2. Flocculate and settle the mixed slurry in a thickener to obtain underflow slurry and overflow water. The underflow slurry is subjected to solid-liquid separation to obtain a filter cake and filtrate; S3. After drying, the filter cake is calcined to obtain magnesium oxide powder; S4. Evaporate and concentrate the overflow water and the filtrate to obtain a calcium chloride solution; S5. Mix the magnesium oxide powder, calcium chloride solution, potassium salt ore tail salt, bittern of potassium salt ore, calcium oxide and additives to prepare a filling slurry; S6. Transport the filling slurry to the underground goaf for filling operation.

[0007] As a further improvement of the present application, in step S1, the molar ratio of calcium oxide to MgCl2 in the bittern is (1 to 1.2):1; the reaction temperature is 50 to 80 °C, the time is 2 to 3 min, and the stirring speed is 200 to 300 rpm.

[0008] As a further improvement of the present application, in step S2, the concentration of the underflow slurry is 30 to 40%, and the moisture content of the filter cake < 20%.

[0009] As a further improvement of the present application, in step S3, the drying temperature is 150 to 200 °C, the time is 3 to 6 h, and the moisture content of the dried material < 5%.

[0010] As a further improvement of the present application, in step S3, the calcination temperature is 400 to 500 °C, and the calcination time is 1 to 2 h.

[0011] As a further improvement of the present application, in step S4, the concentration of the calcium chloride solution is 40 to 50%.

[0012] As a further improvement of the present application, in step S5, the mass ratio of the magnesium oxide powder to the potassium salt ore tail salt is 1:(30 to 50); the mass ratio of the magnesium oxide powder to calcium oxide is 1:(6 to 10); the filling concentration is 70 to 80%.

[0013] As a further improvement of the present application, the additives include a retarder and a water reducer. The retarder is a polycarboxylate retarder, and the addition amount is 0.05 to 0.1% of the total mass of the filling slurry; the water reducer is a polycarboxylate water reducer, and the addition amount is 0.05 to 0.1% of the total mass of the filling slurry.

[0014] As a further improvement of the present application, in step S2, it further includes adding 0.1-0.15% of a polymer flocculant solution to the mixed slurry, and the polymer flocculant solution is a polyacrylamide solution with a concentration of 0.05%.

[0015] In a second aspect, the present application provides a closed-loop circulation filling system for all-solid waste potassium salt ore based on the synergism of magnesium extraction from bittern and calcium chloride, which is processed by using the closed-loop circulation filling process for all-solid waste potassium salt ore based on the synergism of magnesium extraction from bittern and calcium chloride described in the first aspect, and includes: A bittern pretreatment device, an overflow water treatment device, a drying and calcination device, a filling slurry preparation device, and an underground filling pipeline network; The bittern pretreatment device includes a reaction kettle, a thickener, and a filter press connected in sequence; The overflow water treatment device includes an MVR evaporator, a multi-effect evaporator, and a centrifugal crystallizer.

[0016] The beneficial effects of the present application are as follows: The present application provides a closed-loop circulation filling process and system for all-solid waste potassium salt ore based on the synergism of magnesium extraction from bittern and calcium chloride. By reacting potassium salt ore bittern with calcium oxide, a mixed slurry is obtained; the mixed slurry is subjected to flocculation sedimentation by a thickener to obtain an underflow slurry and overflow water, the underflow slurry is subjected to solid-liquid separation to obtain a filter cake and filtrate; the filter cake is dried and then calcined to obtain magnesium oxide powder; the overflow water and filtrate are evaporated and concentrated to obtain a calcium chloride solution; the magnesium oxide powder, calcium chloride solution, potassium salt ore tail salt, potassium salt ore bittern, calcium oxide, and additives are mixed to prepare a filling slurry, which is transported to the underground goaf for filling operations. The present application integrates the processes of magnesium extraction from bittern, calcium chloride concentration and crystallization, and filling slurry preparation to form a closed-loop circulation system, realizing the coordinated disposal and high-value utilization of tail salt-bittern all-solid waste, and through the directional conversion of Mg in bittern by calcium oxide 2+ to achieve a 100% comprehensive utilization rate of tail salt, a 100% consumption rate of bittern, and complete the full resource utilization of solid waste, effectively solving the environmental pollution problems of tail salt storage and bittern discharge during the potassium salt ore mining process.

[0017] By utilizing the synergistic effect of self-produced high-reactivity magnesium oxide (activity ≥ 90%) and by-product calcium chloride (processed into industrial-grade products), the comprehensive filling cost is reduced by 80% compared with the traditional process, and the cost-benefit is significantly improved.

[0018] The process of the present application has no wastewater discharged externally throughout the process, and the discharge or leaching concentrations of key ions such as chloride ions, magnesium ions, and calcium ions all meet the environmental protection standards. The chloride ion recycling rate reaches 100%, significantly reducing the ecological risk and significantly enhancing the environmental friendliness.

[0019] The above description is only an overview of the technical solution of the present application. In order to better understand the technical means of the present application, it can be implemented according to the content of the specification. And in order to make the above and other purposes, features and advantages of the present application more obvious and understandable, the specific embodiments of the present application are given below. Brief Description of the Drawings

[0020] In order to more clearly illustrate the technical solution of the present application, the drawings used in the present application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0021] Figure 1 It is a process flow chart of a closed-circuit circulation filling process for potassium salt ore with all solid wastes based on the synergistic extraction of magnesium from old brine and calcium chloride provided by the present application. Detailed Embodiments

[0022] The embodiments of the technical solution of the present application will be described in detail below with reference to the drawings. The following embodiments are only used to illustrate the technical solution of the present application more clearly, so they are only examples and cannot be used to limit the protection scope of the present application.

[0023] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" and any variations thereof in the specification and claims of this application and the above description of the drawings are intended to cover non-exclusive inclusion.

[0024] In the description of the embodiments of the present application, technical terms such as "first" and "second" are only used to distinguish different objects and cannot be understood as indicating or implying relative importance or implicitly indicating the quantity, specific order or primary-secondary relationship of the indicated technical features. In the description of the embodiments of the present application, "a plurality of" means more than two unless otherwise specifically defined.

[0025] Referring to "embodiments" herein means that specific features, structures or characteristics described in connection with the embodiments can be included in at least one embodiment of the present application. The phrase appears in various places in the specification and does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments. Those skilled in the art will explicitly and implicitly understand that the embodiments described herein can be combined with other embodiments.

[0026] At present, there are problems in the filling process of potash mines in Laos, such as slow strength formation and incomplete treatment of old brine, which increase the operation complexity and cost. A small number of mines adopt the traditional cemented filling process, using magnesium-based cement as a binder to combine tail salt and old brine to form a filling body. However, this process has high costs and low efficiency, restricting its large-scale application. Currently, some processes consider adding calcium oxide to old brine to extract Mg 2+ , but do not fully consider the subsequent disposal problem of the generated calcium chloride, resulting in the inability to truly achieve the green disposal of all solid wastes of potash mine tail salt and old brine.

[0027] In order to solve the technical problems existing in the filling process of potash mines, such as unstable strength, incomplete treatment of old brine, high cost and low efficiency of traditional cemented filling, and the inability to achieve green disposal of all solid wastes due to the unsolved calcium chloride disposal problem, this application provides a closed-loop circulation filling process and system for all-solid-waste potash mines based on the synergy of magnesium extraction from old brine and calcium chloride. Among them, through the environmentally friendly and low-cost extraction of Mg from old brine 2+ , and the hierarchical concentration and utilization of calcium chloride solution, an environmentally friendly green filling for the full disposal of tail salt and old brine is realized.

[0028] Please refer to Figure 1 , in the first aspect, the embodiment of this application provides a closed-loop circulation filling process for all-solid-waste potash mines based on the synergy of magnesium extraction from old brine and calcium chloride, including the following steps: S1. React the potash mine old brine with calcium oxide to obtain a mixed slurry; S2. Flocculate and settle the mixed slurry through a thickener to obtain underflow slurry and overflow water. The underflow slurry is separated by solid-liquid separation to obtain a filter cake and filtrate; S3. After drying, the filter cake is calcined to obtain magnesium oxide powder; S4. Evaporate and concentrate the overflow water and filtrate to obtain a calcium chloride solution; S5. Mix the magnesium oxide powder, calcium chloride solution, potash mine tail salt, potash mine old brine, calcium oxide and additives to prepare a filling slurry; S6. Transport the filling slurry to the underground goaf for filling operations.

[0029] In the technical solution of the embodiment of the present application, two major wastes, old brine and tail salt, generated during the potassium salt mining process are converted into building materials required for filling mined - out areas through a series of chemical and physical processes, realizing the closed - loop circulation of substances within the system and avoiding the discharge of waste. By using the reaction of MgCl2 in the old brine with added CaO to generate Mg(OH)2 and CaCl2, valuable magnesium elements are preliminarily separated. This not only recovers magnesium resources but also provides a basis for the subsequent utilization of magnesium - based materials. This process uses the generated CaCl2 solution as a key component and directly applies it to the subsequent preparation of filling slurry, avoiding the problems of its separate treatment and disposal. Through steps such as thickener and filtration, the mixed slurry after the reaction is efficiently separated. The separated solid filter cake is dried and calcined to dehydrate Mg(OH)2 into a more stable MgO powder, improving the purity and activity of magnesium and facilitating subsequent utilization. The overflow water and filtrate (mainly containing CaCl2) are evaporated and concentrated to obtain a high - concentration CaCl2 solution, which is convenient for storage and precise proportioning for filling. The recovered MgO powder, concentrated CaCl2 solution, potassium salt mine tail salt, potassium salt mine old brine, supplemented CaO, and additives are mixed in proportion to form a composite cementitious system with MgO and CaO as cementitious components and CaCl2 as an activator (promoting the hydration and hardening of MgO and CaO). The main aggregate in the filling slurry is the inexpensive potassium salt mine tail salt, significantly reducing the material cost.

[0030] Further, in some embodiments, in step S1, the molar ratio of calcium oxide to MgCl2 in the old brine is (1~1.2):1; the reaction temperature is 50~80 °C, the time is 2~3 min, and the stirring speed is 200~300 rpm.

[0031] In the technical solution of the embodiment of the present application, the old brine solution is fed into a corrosion - resistant stirring reaction kettle through a transfer pump. The reaction temperature is set at 50~80 °C, and slightly excessive CaO is added to the reaction kettle to ensure that all magnesium chloride reacts, improving the recovery rate of magnesium. The stirring speed is set at 200~300 rpm, and continuous stirring is carried out for 2~3 min to ensure full reaction. Excessive temperature may lead to increased equipment corrosion, excessive energy consumption, or an increase in side reactions.

[0032] Further, in some embodiments, in step S2, the concentration of the underflow slurry is 30~40%, and the moisture content of the filter cake < 20%.

[0033] In the technical solution of the embodiment of the present application, the concentration of the underflow slurry can not only ensure good sedimentation efficiency of the thickener, obtaining relatively clear overflow water, but also enable the underflow to maintain sufficient solid content, facilitating subsequent efficient pressure filtration to obtain a filter cake with a lower water content. If the underflow concentration is too high, it may lead to a poor final separation effect and unclear overflow water; if the underflow concentration is too low, it is not conducive to subsequent solid-liquid separation operations such as direct pressure filtration, which will reduce the treatment efficiency and increase the equipment load and energy consumption.

[0034] Further, in some embodiments, in step S3, the drying temperature is 150 - 200 °C, the time is 3 - 6 h, and the moisture content of the dried material is < 5%.

[0035] In the technical solution of the embodiment of the present application, the main component of the filter cake is magnesium hydroxide. An appropriate drying temperature will not damage the chemical structure of magnesium hydroxide, and the drying time ensures thorough drying to reach the target moisture content.

[0036] Further, in some embodiments, in step S3, the calcination temperature is 400 - 500 °C, and the calcination time is 1 - 2 h.

[0037] In the technical solution of the embodiment of the present application, magnesium hydroxide undergoes a decomposition reaction under high-temperature conditions to generate magnesium oxide. Appropriate temperature and time can ensure the decomposition rate while avoiding grain growth and activity reduction caused by overcalcination.

[0038] Further, in some embodiments, in step S4, the concentration of the calcium chloride solution is 40 - 50%.

[0039] In the technical solution of the embodiment of the present application, the overflow water and the filtrate are evaporated and concentrated by an MVR evaporator to increase the solution concentration. A part of the concentrated solution is used as an activator for the tail salt - old brine - magnesium oxide - calcium oxide filling system, and finally a tail salt - old brine - magnesium oxide - calcium oxide system filling slurry that meets the requirements is formed; the remaining calcium chloride solution is concentrated to saturation by a multi-effect evaporator and centrifugally crystallized into a by-product of calcium chloride dihydrate for other industrial applications.

[0040] Further, in some embodiments, in step S5, the mass ratio of magnesium oxide powder to potassium salt mine tail salt is 1:(30 - 50); the mass ratio of magnesium oxide powder to calcium oxide is 1:(6 - 10); the filling concentration is 70 - 80%.

[0041] In the technical solution of the embodiment of the present application, the tail salt is the main aggregate source of the filling body, and magnesium oxide is the main gelling phase. It undergoes a hydration reaction with calcium chloride solution to generate gelling calcium silicate hydrate, calcium aluminate hydrate, and magnesium hydrate salts (such as Mg(OH)2, hydrated chloromagnesite, etc.), thereby endowing the filling body with strength; calcium oxide is used to supplement the calcium source, directly participates in the hydration reaction to generate calcium hydrate salts, and also serves as an activator / auxiliary gelling agent. Ca(OH)2 generated by the hydration of calcium oxide can stimulate the reaction of potential active components (such as aluminosilicate minerals) in the tail salt, promoting the formation of gelling products. The dosage of calcium oxide is significantly more than that of magnesium oxide, which helps to ensure that there are enough calcium ions participating in the gelling reaction, using calcium oxide as a cheap and widely sourced material to enhance the gelling effect, so as to achieve ideal strength development and cost-effectiveness; calcium chloride solution serves as the reaction medium, providing Ca 2+ ions, and undergoes a hydration reaction with the active components in magnesium oxide and tail salt. At the same time, calcium chloride can accelerate the hydration reaction, shorten the setting time, and improve the early strength, which helps to quickly seal the goaf and ensure underground safety. The dosage of calcium chloride solution is mainly adjusted considering that the soluble chloride ion concentration leached from the filling body at 28 days meets the environmental protection requirements and meets the strength requirements of the filling body age. Usually, it does not exceed 1%; the addition amount of the old brine of potassium salt mine is added according to the filling concentration. The old brine of potassium salt mine plays a role similar to that of water in the filling slurry of metal mines; an appropriate filling concentration ensures that the slurry is not prone to segregation and sedimentation during pipeline transportation, has relatively good fluidity, and can smoothly reach the designated underground position. Excessive concentration may cause the slurry to be too viscous and difficult to transport through the pipeline.

[0042] Furthermore, in some embodiments, the additive includes a retarder and a water reducer. The retarder is a polycarboxylate retarder, and the addition amount is 0.05 - 0.1% of the total mass of the filling slurry; the water reducer is a polycarboxylate water reducer, and the addition amount is 0.05 - 0.1% of the total mass of the filling slurry.

[0043] In the technical solution of the embodiment of the present application, in the potassium salt mine filling process, the filling body needs to be transported to the underground goaf within a certain time and preliminarily stabilized to prevent early solidification, pipe blockage or collapse in the pipeline or the incompletely supported area. The hydration reaction of the tail salt - old brine - magnesium oxide - calcium oxide system filling slurry is relatively fast. Especially when the concentration of magnesium oxide is relatively high, the setting and hardening speed may be too fast. Polycarboxylate retarders are a kind of high - molecular organic compounds. They can delay the hydration reaction and extend the setting time by adsorbing on the surface of the slurry particles to hinder the dissolution and diffusion of hydration ions (such as Ca, Mg, Si, Al, etc.) or by forming complexes or physical coating layers with hydration products (such as Ca(OH)2, hydrated calcium silicate, etc.). Polycarboxylate water - reducing agents are anionic surfactants. They adsorb on the surface of solid particles (mainly tail salt particles and cementitious material particles) to form a negatively charged adsorption layer, generating electrostatic repulsion, making the particles repel each other, reducing the flocculation structure, and making the particles more evenly dispersed in water. At the same time, their long - side - chain structure can also provide a steric hindrance effect to further prevent particle agglomeration. The two effects work together to significantly reduce the frictional resistance between particles, so that while maintaining or improving fluidity, the water consumption can be reduced. By precisely controlling the addition amount, the working performance of the filling slurry can be optimized without significantly affecting the strength and other properties of the final filling body, making it easier to construct and indirectly improving the filling quality.

[0044] Further, in some embodiments, in step S2, it further includes adding 0.1 - 0.15% of a high - molecular flocculant solution to the mixed slurry, and the high - molecular flocculant solution is a polyacrylamide solution with a concentration of 0.05%.

[0045] In the technical solution of the embodiment of the present application, by using the adsorption bridging effect of the high - molecular flocculant, small solid particles are aggregated into larger flocs, thus significantly improving the sedimentation efficiency of the thickener and obtaining a high - concentration underflow slurry and clear overflow water.

[0046] In the second aspect, the embodiment of the present application provides a closed - loop circulation filling system for all solid wastes in potassium salt mines based on the synergism of magnesium extraction from old brine and calcium chloride, including: an old brine pretreatment device, an overflow water treatment device, a drying and calcination device, a filling slurry preparation device, and an underground filling pipe network; the old brine pretreatment device includes a reaction kettle, a thickener, and a filter press connected in sequence; the overflow water treatment device includes an MVR evaporator, a multi - effect evaporator, and a centrifugal crystallizer.

[0047] In the technical solution of the embodiment of the present application, through a closed-loop resource recycling system, the old brine and tail salt generated from potash mining are converted into filling materials required for filling mining voids through steps such as chemical treatment, physical separation, and drying. Through the coordinated work of each device, the tasks of material conversion and separation are efficiently completed. The filling slurry made from these waste materials is used to backfill the mined-out area, which not only solves the problem of waste treatment, reduces environmental pollution, but also reduces the filling cost and improves the filling effect, having significant economic and environmental benefits.

[0048] The following are some specific embodiments. It should be noted that the embodiments described below are exemplary and are only used to explain the present application, and should not be construed as a limitation to the present application. For those without specific technologies or conditions indicated in the embodiments, they shall be carried out according to the technologies or conditions described in the literature in the field or according to the product specifications. For the reagents or instruments without indicating the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0049] Example 1 This embodiment provides a closed-loop circulation filling process for all-solid waste potash mines based on the synergism of magnesium extraction from old brine and calcium chloride, as Figure 1 shown, including the following steps: S1. Feed the old brine of potash ore into a corrosion-resistant stirring reactor through a delivery pump. Set the reaction temperature at 70 °C, and add calcium oxide to the reactor according to the molar ratio of calcium oxide to MgCl2 in the old brine of 1.05:1 to react with MgCl2 in the old brine to generate Mg(OH)2 and other hydroxide flocculent precipitates. The reaction time is 3 min, and the stirring speed is 200 rpm to obtain a mixed slurry; S2. Let the mixed slurry flow by gravity to the flocculation central cylinder, and simultaneously add a 0.1% polymer flocculant solution. The polymer flocculant solution is a polyacrylamide solution with a concentration of 0.05% to promote the rapid sedimentation of the hydroxide flocculent precipitate to the bottom of the thickener to form a bottom flow slurry. By adjusting the flow rate of the old brine entering the reactor, control the bottom flow concentration of the thickener at 35%. The bottom flow slurry is transported to a plate and frame filter press by a centrifugal pump for pressure filtration to obtain a magnesium hydroxide filter cake with a moisture content < 20% and filtrate; S3. Feed the filter cake into a rotary dryer and dry it at 150 °C until the moisture content < 5%, and collect it in powder form. Then, feed it into a rotary kiln and calcine it at 450 °C for 1.5 h to obtain magnesium oxide powder. After cooling through a cooling device, it is collected for subsequent filling or other industrial applications; S4. The overflow water and filtrate are mainly calcium chloride solution, which is easier to increase the concentration by evaporation compared to magnesium chloride solution. Evaporate and concentrate the overflow water and filtrate through an MVR evaporator to obtain a calcium chloride solution with a concentration of 45%, which is used as one of the additives in the tail salt-old brine-magnesium oxide-calcium oxide filling system. The remaining calcium chloride solution is evaporated and crystallized for other industrial uses; S5. Accurately measure magnesium oxide powder, calcium chloride solution, potassium salt mine tail salt, calcium oxide and additives according to the given mass, add them to the stirring tank, start the stirring device, set the stirring time to 2 min, and ensure that the materials are fully and evenly mixed to form a uniform filling slurry; among them, the mass ratio of magnesium oxide powder to potassium salt mine tail salt is 1:40, the mass ratio of magnesium oxide powder to calcium oxide is 1:8, the addition amount of old brine is added according to the filling concentration, and the dosage of calcium chloride solution is 1% of the total mass of the filling slurry; the additives include a retarder and a water reducer, the retarder is a polycarboxylate retarder, and the addition amount is 0.05% of the total mass of the filling slurry; the water reducer is a polycarboxylate water reducer, and the addition amount is 0.05% of the total mass of the filling slurry; the filling concentration is 75%; S6. Transport the prepared filling slurry to the underground goaf through a pump and pipeline to complete the filling operation.

[0050] This application utilizes the synergistic effect of self-produced high-activity magnesium oxide (activity ≥ 90%) and by-product calcium chloride, and the comprehensive filling cost is reduced by 80% compared with the traditional process; there is no wastewater discharged during the whole process of the process, and the emission or leaching concentration of key ions such as chloride ions, magnesium ions, and calcium ions all meet the environmental protection standards. The recycling rate of chloride ions reaches 100%, greatly reducing the ecological risk.

[0051] Comparative Example 1 Comparative Example 1 provides a closed-loop circulation filling process for all-solid waste potassium salt mines based on the synergism of magnesium extraction from old brine and calcium chloride, which is treated by the traditional cemented filling process, including the following steps: S1. Prepare a filling slurry with a mass concentration of 75% from the old brine and tail salt generated during the production of potassium salt mines, with the tail salt as the solute and the old brine as the solution; S2. Add magnesium-based cement, and the mass ratio of magnesium-based cement to tail salt is 1:30; S3. Mix the raw materials with a high-speed mixer at a rotation speed of 200 r / min for 3 min; S4. Transport the prepared uniform slurry to the underground goaf through a pipeline for filling operation.

[0052] The traditional cemented filling process uses magnesium-based cement as a binder to combine with tail salt and a small amount of old brine to form a filling body. The procurement cost of magnesium-based cement is high, which limits its addition amount, resulting in unstable long-term strength of the filling body, and the shrinkage rate of the filling body is relatively high (>5%), and the strength attenuation rate within 28 days exceeds 30%, making it difficult to meet the long-term stability requirements of the mine; in addition, the amount of old brine consumed by this process is small, and it is impossible to fully utilize the old brine of potassium salt mines. At the same time, Mg in the old brine 2+ is not effectively recovered, the resource utilization rate is low, causing unnecessary waste.

[0053] Comparative Example 2 Comparative Example 2 provides a closed-loop circulation filling process for all-solid waste potassium salt mine based on magnesium extraction from old brine and the synergy of calcium chloride. The hydraulic filling process is adopted and includes the following steps: Mix the old brine of potassium salt mine and tail salt in a mass ratio of 3:7 and stir to prepare a slurry, which is transported to the underground goaf for filling operation.

[0054] Although this process is simple, there are the following problems: The filling material relies on the recrystallization of tail salt to form strength, and this process takes a long time, usually several weeks or even months to reach a certain stability; The old brine precipitated by crystallization needs to be collected and transported to the surface old brine pond, which increases the operation complexity and cost. This process can only solve the problem of tail salt disposal, cannot effectively treat the old brine, and it is difficult to ensure the compressive strength and durability of the filling body, and cannot meet the long-term stable needs of the mine.

[0055] Comparative Example 3 Comparative Example 3 provides a closed-loop circulation filling process for all-solid waste potassium salt mine based on magnesium extraction from old brine and the synergy of calcium chloride. The process of extracting magnesium chloride with calcium oxide is adopted and includes the following steps: S1. Add CaO to the old brine of potassium salt mine according to the molar ratio of CaO:MgCl2 of 1.05:1, react at 70 °C for 2 h, and dehydrate with a plate and frame filter press to a moisture content of <30% to obtain a filter cake and filtrate; S2. Feed the filter cake into a rotary dryer and dry it at 150 °C to a moisture content of <5%, collect it in powder form, and then feed it into a rotary kiln and calcine it at 450 °C for 1.5 h to obtain magnesium oxide powder, which is collected after cooling through a cooling device and used for subsequent filling or other industrial applications; S3. Part of the old brine is used as the solution of the tail salt-old brine-magnesium oxide-calcium oxide filling system, and is used to prepare a filling slurry with magnesium oxide powder, potassium salt mine tail salt, calcium oxide and additives, and is transported to the underground goaf for filling operation through a pipeline; Among them, the mass ratio of magnesium oxide powder to potassium salt mine tail salt is 1:40, the mass ratio of magnesium oxide powder to calcium oxide is 1:8, the addition amount of old brine is added according to the filling concentration, and the additives include a retarder and a water reducer. The retarder is a polycarboxylate retarder, and the addition amount is 0.05% of the total mass of the filling slurry; The water reducer is a polycarboxylate water reducer, and the addition amount is 0.05% of the total mass of the filling slurry, and the filling concentration is 75%; S4. The remaining old brine is evaporated and concentrated by an MVR evaporator for crystallization and used for other industrial purposes.

[0056] Existing methods for recovering valuable elements (such as Mg) from old brine using calcium oxide 2+) process is difficult to achieve low-cost industrialization, and does not fully consider the subsequent disposal of the product calcium chloride, which limits its large-scale application; due to the large amount of remaining old brine, the evaporation and crystallization cost of the old brine is much higher than the evaporation and crystallization cost of calcium chloride, resulting in the difficulty and high cost of treating the remaining old brine, and it is impossible to truly achieve the green disposal of all solid wastes of potash mine tailings and old brine.

[0057] Table 1 Performance test data As can be seen from Table 1, the filling process provided by this application has high compressive strength, high durability and stability. This application integrates the magnesium extraction from brine, calcium chloride concentration and crystallization, and filling slurry preparation process to form a closed-loop circulation system, realizing the coordinated disposal and high-value utilization of tail salt-brine solid waste. The overall filling cost is reduced by 80% compared with the traditional process, solving the problem of magnesium chloride in brine being difficult to evaporate, achieving a 100% brine absorption rate, and a 100% chloride ion recycling rate, significantly reducing ecological risks.

[0058] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the present application, any other embodiments that can be conceived by those skilled in the art and that combine some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A closed-circuit circulation filling process for all-solid waste potassium salt ore based on the synergistic extraction of magnesium from old brine and calcium chloride, characterized in that, It includes the following steps: S1. React the old brine of potassium salt ore with calcium oxide to obtain a mixed slurry; S2. Flocculate and settle the mixed slurry in a thickener to obtain an underflow slurry and overflow water. The underflow slurry is subjected to solid-liquid separation to obtain a filter cake and filtrate; S3. The filter cake is dried and then calcined to obtain magnesium oxide powder; S4. Evaporate and concentrate the overflow water and the filtrate to obtain a calcium chloride solution; S5. Mix the magnesium oxide powder, calcium chloride solution, potassium salt ore tail salt, old brine of potassium salt ore, calcium oxide and additives to prepare a filling slurry; S6. Transport the filling slurry to the underground goaf for filling operation.

2. The closed-circuit circulation filling process of all-solid waste potassium salt ore based on the synergism of extracting magnesium from bittern and calcium chloride according to claim 1, characterized in that, In step S1, the molar ratio of calcium oxide to MgCl2 in the old brine is (1~1.2):1; the reaction temperature is 50~80°C, the time is 2~3 min, and the stirring speed is 200~300 rpm.

3. The closed-circuit circulation filling process of all-solid waste potassium salt ore based on the synergistic extraction of magnesium from bittern and calcium chloride according to claim 1, characterized in that, In step S2, the concentration of the underflow slurry is 30~40%, and the water content of the filter cake <20%.

4. The closed-circuit circulation filling process of all-solid waste potassium salt ore based on the synergism of extracting magnesium from bittern and calcium chloride according to claim 1, characterized in that, In step S3, the drying temperature is 150~200°C, the time is 3~6 h, and the water content of the dried material <5%.

5. The closed-circuit circulation filling process of all-solid waste potassium salt ore based on magnesium extraction from bittern and synergistic action of calcium chloride according to claim 1, characterized in that, In step S3, the calcination temperature is 400~500°C, and the calcination time is 1~2 h.

6. The closed-loop circulating filling process for all-solid waste potassium salt ore based on magnesium extraction from bittern and synergistic effect of calcium chloride according to claim 1, characterized in that, In step S4, the concentration of the calcium chloride solution is 40~50%.

7. The closed-loop circulation filling process of all-solid waste potassium salt ore based on the synergism of magnesium extraction from bittern and calcium chloride according to claim 1, characterized in that, In step S5, the mass ratio of the magnesium oxide powder to the potassium salt ore tail salt is 1:(30~50); the mass ratio of the magnesium oxide powder to calcium oxide is 1:(6~10); the filling concentration is 70~80%.

8. The closed-circuit circulation filling process of all-solid waste potassium salt ore based on the synergism of magnesium extraction from bittern and calcium chloride according to claim 6, characterized in that, The additives include a retarder and a water reducer. The retarder is a polycarboxylate retarder, and the addition amount is 0.05~0.1% of the total mass of the filling slurry; the water reducer is a polycarboxylate water reducer, and the addition amount is 0.05~0.1% of the total mass of the filling slurry.

9. The closed-circuit circulation filling process of all-solid waste potassium salt ore based on the synergism of extracting magnesium from bittern and calcium chloride according to claim 1, characterized in that, In step S2, it also includes adding 0.1~0.15% of a polymer flocculant solution to the mixed slurry. The polymer flocculant solution is a polyacrylamide solution with a concentration of 0.05%.

10. A closed-circuit circulation filling system for all-solid waste potassium salt ore based on the synergism of extracting magnesium from old brine and calcium chloride, which is processed by using the closed-circuit circulation filling process for all-solid waste potassium salt ore based on the synergism of extracting magnesium from old brine and calcium chloride described in any one of claims 1-9, is characterized in that, It includes: An old brine pretreatment device, an overflow water treatment device, a drying and calcination device, a filling slurry preparation device and an underground filling pipeline network; The old brine pretreatment device includes a reaction kettle, a thickener and a filter press connected in sequence; The overflow water treatment device includes an MVR evaporator, a multi-effect evaporator and a centrifugal crystallizer.

Images