Full-solid waste potash mine closed-circuit filling process and system based on magnesium extraction from old brine and calcium chloride cooperation

Abstract

The application provides a full-solid-waste potassium salt mine closed-circuit filling process and system based on magnesium extraction from old brine and calcium chloride cooperation, and belongs to the field of potassium salt mine filling. The old brine of the potassium salt mine is reacted with calcium oxide to obtain mixed slurry. The mixed slurry is flocculated and settled by a thickener to obtain underflow slurry and overflow water. The underflow slurry is subjected to solid-liquid separation to obtain filter cake and filtrate. The filter cake is dried and then calcined to obtain magnesium oxide powder. The overflow water and the filtrate are evaporated and concentrated to obtain a calcium chloride solution. The magnesium oxide powder, the calcium chloride solution, tail salt of the potassium salt mine, the old brine of the potassium salt mine, calcium oxide and an additive are mixed to prepare a filling slurry, which is conveyed to an underground empty area for filling operation. The application integrates magnesium extraction from old brine, calcium chloride concentration and crystallization and filling slurry preparation process to form a closed-circuit system, and realizes collaborative treatment and high-value utilization of tail salt-old brine full-solid-waste.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of potash mine filling, in particular to a full-solid-waste potash mine closed-circuit filling process and system based on magnesium extraction from old brine and calcium chloride cooperation. BACKGROUND

[0002] Potash mines are an important source of raw materials for potash fertilizers, mainly including sylvite mines and halite mines. The mass fraction of potassium chloride in sylvite mines is usually 25-35%, while the mass fraction of potassium chloride in halite mines is 15-22%. In the beneficiation process of potash mines, a large amount of tail salt and old brine will be produced. Tail salt is mainly composed of granular sodium chloride crystals, which is easily soluble in water and difficult to be stably stored, and is easily dissolved by rainwater, thereby polluting surface water bodies. Old brine is a liquid rich in magnesium chloride, with a concentration of about 30%. If tail salt and old brine are not effectively treated, not only will it cause environmental pollution, but also will cause problems such as soil salinization and groundwater pollution, causing serious harm to the ecological system and the surrounding environment.

[0003] Globally, the exploitation and processing of potash mines have been an important issue of resource utilization and environmental protection, especially in Laos, the development of potash mines faces many technical bottlenecks. At present, potash enterprises in Laos generally use dry filling and wet "sand-water" filling processes, however, these traditional processes have significant defects and deficiencies: first, the storage of tail salt is strictly limited by weather conditions, especially in the rainy season, tail salt is easily dissolved and lost with rainwater, not only causing resource waste, but also causing pollution to the surrounding environment; second, the utilization rate of old brine is very low, the high-concentration magnesium chloride solution is often forced to be directly discharged due to the lack of economic and effective treatment technology, which not only aggravates the environmental burden, but also causes great waste of resources. In addition, the existing filling process also has other technical problems, for example, the magnesium-based cement used in the traditional cementation filling process has high cost, which limits its addition amount in actual application, which leads to unstable long-term strength of the filling body, high shrinkage rate, and 28-day strength decay rate exceeding 30%, which is difficult to meet the needs of long-term stability of the mine. At the same time, the magnesium ions in the old brine cannot be effectively recovered, the resource utilization rate is low, and the resource waste is further aggravated.

[0004] Therefore, it is necessary to design an improved full-solid-waste potash mine closed-circuit filling process and system based on magnesium extraction from old brine and calcium chloride cooperation to solve the above problems. SUMMARY

[0005] In view of the technical problems in the background art, the present application provides a full-solid-waste potash mine closed-circuit filling process and system based on magnesium extraction from old brine and calcium chloride cooperation, which aims to solve the technical problems of slow strength formation of potash mine filling process and incomplete old brine treatment.

[0006] In a first aspect, the application provides a full-solid waste potash mine closed-circuit filling process based on magnesium extraction from old brine and calcium chloride cooperation, comprising the following steps:

[0007] S1. Reacting the old brine of the potash mine with calcium oxide to obtain a mixed slurry;

[0008] S2. Flocculating and settling the mixed slurry by a thickener to obtain an underflow slurry and an overflow water, and performing solid-liquid separation on the underflow slurry to obtain a filter cake and a filtrate;

[0009] S3. Drying and calcining the filter cake to obtain magnesium oxide powder;

[0010] S4. Evaporating and concentrating the overflow water and the filtrate to obtain a calcium chloride solution;

[0011] S5. Mixing the magnesium oxide powder, the calcium chloride solution, the tail salt of the potash mine, the old brine of the potash mine, calcium oxide, and an additive to prepare a filling slurry;

[0012] S6. Delivering the filling slurry to an empty area underground for filling operation.

[0013] As a further improvement of the application, in step S1, the molar ratio of the calcium oxide to MgCl2 in the old brine is (1-1.2):1; the reaction temperature is 50-80°C, the reaction time is 2-3 min, and the stirring speed is 200-300 rpm.

[0014] As a further improvement of the application, in step S2, the concentration of the underflow slurry is 30-40%, and the moisture content of the filter cake is <20%.

[0015] As a further improvement of the application, in step S3, the drying temperature is 150-200°C, the drying time is 3-6 h, and the moisture content of the material after drying is <5%.

[0016] As a further improvement of the application, in step S3, the calcination temperature is 400-500°C, and the calcination time is 1-2 h.

[0017] As a further improvement of the application, in step S4, the concentration of the calcium chloride solution is 40-50%.

[0018] As a further improvement of the application, in step S5, the mass ratio of the magnesium oxide powder to the tail salt of the potash mine is 1:(30-50); the mass ratio of the magnesium oxide powder to calcium oxide is 1:(6-10); and the filling concentration is 70-80%.

[0019] As a further improvement of the present application, the additive comprises a retarder and a water reducing agent, the retarder is a polycarboxylate type retarder, and the addition amount is 0.05-0.1% of the total mass of the filling material slurry; the water reducing agent is a polycarboxylate type water reducing agent, and the addition amount is 0.05-0.1% of the total mass of the filling material slurry.

[0020] As a further improvement of the present application, in step S2, 0.1-0.15% of a high molecular flocculant solution is further added to the mixed slurry, and the high molecular flocculant solution is a polyacrylamide solution with a concentration of 0.05%.

[0021] In a second aspect, the present application provides a full solid waste potash mine closed-circuit filling system based on magnesium extraction from old brine and calcium chloride cooperation, which is processed by the full solid waste potash mine closed-circuit filling process based on magnesium extraction from old brine and calcium chloride cooperation of the first aspect, and comprises:

[0022] An old brine pretreatment device, an overflow water treatment device, a drying and calcination device, a filling material slurry preparation device, and an underground filling pipe network;

[0023] The old brine pretreatment device comprises a reaction kettle, a thickener, and a filter press connected in sequence.

[0024] The overflow water treatment device comprises an MVR evaporator, a multi-effect evaporator, and a centrifugal crystallizer.

[0025] The present application has the following beneficial effects:

[0026] The present application provides a full solid waste potash mine closed-circuit filling process and system based on magnesium extraction from old brine and calcium chloride cooperation. The old brine of the potash mine is reacted with calcium oxide to obtain a mixed slurry. The mixed slurry is flocculated and settled by a thickener to obtain underflow slurry and overflow water. The underflow slurry is subjected to solid-liquid separation to obtain a filter cake and a filtrate. The filter cake is dried and then subjected to calcination treatment to obtain magnesium oxide powder. The overflow water and the filtrate are evaporated and concentrated to obtain a calcium chloride solution. The magnesium oxide powder, the calcium chloride solution, tail salt of the potash mine, old brine of the potash mine, calcium oxide, and an additive are mixed to prepare a filling material slurry, which is transported to an underground empty area for filling operation. The present application integrates the processes of magnesium extraction from old brine, calcium chloride concentration and crystallization, and filling material slurry preparation, forms a closed-circuit system, realizes the collaborative disposal and high-value utilization of tail salt and old brine, and realizes the directional conversion of Mg 2+ by calcium oxide, realizes the comprehensive utilization rate of tail salt of 100% and the absorption rate of old brine of 100%, and completes the full-amount resource utilization of solid waste, effectively solving the environmental pollution problems of tail salt storage and old brine discharge in the process of potash mine exploitation.

[0027] The application utilizes the synergistic effect of self-produced high-activity magnesium oxide (activity >= 90%) and by-product calcium chloride (processed into industrial-grade products), and the comprehensive filling cost is reduced by 80% compared with traditional process, and the cost benefit is significantly improved.

[0028] The process of the application has no wastewater discharge throughout the process, and the emission or leaching concentration of key ions such as chloride ions, magnesium ions and calcium ions meets the environmental protection standard, the recycling rate of chloride ions reaches 100%, the ecological risk is greatly reduced, and the environmental friendliness is significantly enhanced.

[0029] The above description is only a summary of the technical solutions of the application, in order to more clearly understand the technical means of the application, and can be implemented according to the content of the specification, and in order to make the above and other purposes, characteristics and advantages of the application more obvious and easy to understand, the following specific embodiments of the application are described. BRIEF DESCRIPTION OF DRAWINGS

[0030] In order to more clearly illustrate the technical solutions of the application, the following will briefly introduce the drawings used in the application. Obviously, the drawings described below are only some embodiments of the application, and other drawings can be obtained by those skilled in the art without creating laborious work.

[0031] Figure 1 The application provides a full-solid waste potassium salt mine closed-circuit filling process flow diagram based on magnesium extraction from old brine and calcium chloride synergy. DETAILED DESCRIPTION

[0032] The embodiments of the technical solutions of the application will be described in detail below with reference to the drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the application, therefore only as an example, and cannot limit the protection scope of the application.

[0033] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the application; the terms "include" and "have" in the specification and claims of the application and the above drawing description, and any modification thereof, are intended to cover non-exclusive inclusion.

[0034] In the description of the embodiments of the application, the technical terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the application, the meaning of "a plurality of" is two or more, unless otherwise specifically limited.

[0035] Reference to“an embodiment” herein means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the application. The appearances of the phrase“in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment, nor are they necessarily all directed to the same embodiment, nor are they necessarily all mutually exclusive or alternative embodiments. It is expressly understood that any of the embodiments described herein can be incorporated in a variety of embodiments.

[0036] At present, the filling process of the potash mine in Laos has the problems of slow strength formation and incomplete treatment of old brine, which increases the operation complexity and cost; a small part of mines use traditional cementation filling process, using magnesium-based cement as a cementing agent, combining tail salt and old brine to form a filling body, however, the process has high cost and low efficiency, which limits its large-scale application; at present, some processes consider adding calcium oxide to the old brine to extract Mg 2+ , but the subsequent disposal problem of the product calcium chloride is not fully considered, which leads to the inability to truly realize the full solid waste green disposal of the tail salt and old brine of the potash mine.

[0037] In order to solve the technical problems that the filling process of the potash mine has unstable strength, incomplete treatment of old brine, high cost and low efficiency of traditional cementation filling, and the disposal problem of calcium chloride is not solved, leading to the inability to realize the full solid waste green disposal, the application provides a full solid waste potash mine closed-circuit filling process and system based on magnesium extraction from old brine and calcium chloride cooperation, wherein Mg 2+ is extracted from the old brine by an environmentally friendly and low-cost method, and the calcium chloride solution is concentrated by grading, realizing the full disposal of tail salt and old brine and the environmentally friendly and green filling.

[0038] Please refer to Figure 1 , in a first aspect, the embodiments of the application provide a full solid waste potash mine closed-circuit filling process based on magnesium extraction from old brine and calcium chloride cooperation, comprising the following steps:

[0039] S1. Reacting the old brine of the potash mine with calcium oxide to obtain a mixed slurry;

[0040] S2. Flocculating and settling the mixed slurry by a thickener to obtain underflow slurry and overflow water, and the underflow slurry is separated by solid-liquid separation to obtain a filter cake and a filtrate;

[0041] S3. The filter cake is dried and calcined to obtain magnesium oxide powder;

[0042] S4. Evaporating and concentrating the overflow water and the filtrate to obtain a calcium chloride solution;

[0043] S5. Mixing the magnesium oxide powder, the calcium chloride solution, the tail salt of the potash mine, the old brine of the potash mine, the calcium oxide and the additive to prepare a filling slurry;

[0044] S6. The filling slurry is transported to the underground empty area for filling operation.

[0045] In the technical scheme of the embodiment of the application, two main waste old brine and tail salt generated in the potassium salt mining process are converted into building materials required for filling the mined-out area through a series of chemical and physical processes, realizing closed-loop circulation of matter in the system and avoiding waste discharge; MgCl2 in the old brine is reacted with added CaO to generate Mg(OH)2 and CaCl2, and the valuable magnesium element is preliminarily separated out, which not only recovers magnesium resources but also provides a basis for subsequent use of magnesium-based materials; the CaCl2 solution generated in the process is directly used for subsequent preparation of filling slurry as a key component, avoiding the difficulty of separate treatment and disposal; the mixed slurry after reaction is efficiently separated through a thickener and a filter, the separated solid filter cake is dried and calcined, Mg(OH)2 is dehydrated and converted into more stable MgO powder, the purity and activity of magnesium are improved, and subsequent use is facilitated; the overflow water and the filtrate (mainly containing CaCl2) are evaporated and concentrated to obtain a high-concentration CaCl2 solution, which is convenient for storage and accurate proportioning for filling; the recovered MgO powder, the concentrated CaCl2 solution, the tail salt of the potassium salt mine, the old brine of the potassium salt mine, supplemented CaO and additives are mixed in proportion to form a composite cementing system taking MgO and CaO as cementing components and CaCl2 as an activator (promoting the hydration and hardening of MgO and CaO), and the main aggregate in the filling slurry is the inexpensive tail salt of the potassium salt mine, which significantly reduces the material cost.

[0046] 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℃, the reaction time is 2-3min, and the stirring speed is 200-300rpm.

[0047] In the technical scheme of the embodiment of the application, the old brine solution is pumped into a corrosion-resistant stirring reaction kettle by a delivery pump, the reaction temperature is set to 50-80℃, slightly excessive CaO is added to the reaction kettle to ensure that all magnesium chloride is reacted and the magnesium recovery rate is improved, the stirring speed is set to 200-300rpm, and the stirring is continued for 2-3min to ensure that the reaction is fully carried out. Too high temperature can cause accelerated equipment corrosion, excessive energy consumption or increased side reactions.

[0048] Further, in some embodiments, in step S2, the concentration of the underflow slurry is 30-40%, and the moisture content of the filter cake is <20%.

[0049] In the technical scheme of the embodiment of the present application, the concentration of the underflow slurry can ensure good settling efficiency of the thickener, obtain relatively clear overflow water, and enable the underflow to maintain sufficient solid content, facilitating subsequent efficient pressure filtration and obtaining filter cake with low water content. If the underflow concentration is too high, the final separation effect may be poor and the overflow water may not be clear; if the underflow concentration is too low, it is not conducive to subsequent direct pressure filtration and other solid-liquid separation operations, which may reduce the processing efficiency and increase the equipment load and energy consumption.

[0050] Further, in some embodiments, in step S3, the drying temperature is 150-200 DEG C, the time is 3-6 h, and the moisture content of the material after drying is less than 5%.

[0051] In the technical scheme of the embodiment of the present application, the main component of the filter cake is magnesium hydroxide, and the suitable drying temperature does not damage the chemical structure of magnesium hydroxide, and the drying time ensures complete drying and achieves the target moisture content.

[0052] Further, in some embodiments, in step S3, the calcination temperature is 400-500 DEG C, and the calcination time is 1-2 h.

[0053] In the technical scheme of the embodiment of the present application, magnesium hydroxide decomposes under high temperature to generate magnesium oxide, and suitable temperature and time can ensure the decomposition rate while avoiding excessive calcination to cause grain growth and activity reduction.

[0054] Further, in some embodiments, in step S4, the concentration of the calcium chloride solution is 40-50%.

[0055] In the technical scheme of the embodiment of the present application, the overflow water and the filtrate are evaporated and concentrated by the MVR evaporator to increase the solution concentration, and part of the concentrated solution is used as an activator of the tail salt-old brine-magnesium oxide-calcium oxide filling system to finally form a tail salt-old brine-magnesium oxide-calcium oxide system filling slurry meeting the requirements; the remaining calcium chloride solution is concentrated to saturation by the multiple-effect evaporator and is centrifuged to form calcium chloride dihydrate as a byproduct for other industrial applications.

[0056] Further, in some embodiments, in step S5, the mass ratio of the magnesium oxide powder to the tail salt of the potassium salt mine is 1: (30-50); the mass ratio of the magnesium oxide powder to the calcium oxide is 1: (6-10); and the filling concentration is 70-80%.

[0057] In the technical scheme of the embodiments of the present application, the tailings are the main aggregate source of the filling body, the magnesium oxide is the main cementing phase, and the hydration reaction with the calcium chloride solution generates hydrated calcium silicate, hydrated calcium aluminate and hydrated magnesium salt (such as Mg(OH)2, hydrated bischofite, etc.) with cementitious properties, thereby imparting strength to the filling body; the calcium oxide is used to supplement the calcium source and directly participates in the hydration reaction to generate hydrated calcium salt, and at the same time, the calcium oxide also acts as an activator / auxiliary cementing agent. The Ca(OH)2 generated by the hydration of the calcium oxide can stimulate the reaction of the potential active components (such as siliceous and aluminous minerals) in the tailings, promote the generation of cementitious products, and the amount of the calcium oxide is significantly more than that of the magnesium oxide, which helps to ensure that there is enough calcium ion to participate in the cementing reaction. The calcium oxide is used as a cheap and widely available material to enhance the cementing effect, so as to achieve ideal strength development and cost-effectiveness; the calcium chloride solution acts as a reaction medium and provides Ca 2+ ions for the hydration reaction with the magnesium oxide and the active components in the tailings. At the same time, the 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 safety underground. The amount of the calcium chloride solution is mainly adjusted according to the requirements of the environmental protection and the age strength of the filling body, and the leachable soluble chloride ion concentration of the filling body at 28 days is usually not more than 1%; the amount of the potassium salt mine old brine is added according to the filling concentration, and the potassium salt mine old brine plays a role similar to that of water in the filling slurry of the metal mine. The appropriate filling concentration ensures that the slurry is not easy to separate and settle during pipeline transportation, has relatively good fluidity, can smoothly reach the designated position underground, and the high concentration may cause the slurry to be too viscous and difficult to be transported through the pipeline.

[0058] Further, in some embodiments, the additives include a retarder and a water reducing agent. The retarder is a polycarboxylate type retarder, and the amount of addition is 0.05-0.1% of the total mass of the filling slurry. The water reducing agent is a polycarboxylate type water reducing agent, and the amount of addition is 0.05-0.1% of the total mass of the filling slurry.

[0059] In the technical scheme of the embodiment of the present application, in the filling process of the potash mine, the filling body needs to be transported to the underground empty area within a certain time and preliminarily stabilized to prevent early solidification, pipe blockage or collapse in the pipeline or in the area not fully supported. The hydration reaction of the tail salt-old brine-magnesium oxide-calcium oxide system filling slurry is relatively fast, especially when the magnesium oxide concentration is high, the hardening speed may be too fast. The polycarboxylate retarder is a high-molecular organic compound, which can hinder the dissolution and diffusion of hydrated ions (such as Ca, Mg, Si, Al, etc.) by adsorbing on the surface of the slurry particles, or form a complex or a physical wrapping layer with the hydration products (such as Ca(OH)2, hydrated calcium silicate, etc.), thereby delaying the hydration reaction and prolonging the setting time. The polycarboxylate superplasticizer is an anionic surfactant, which adsorbs on the surface of solid particles (mainly tail salt particles and cementitious material particles) to form a negatively charged adsorption layer, generates electrostatic repulsion, makes the particles repel each other, reduces the flocculation structure, and makes the particles more uniformly dispersed in water; at the same time, the long side chain structure can also provide a steric hindrance effect, further hindering the agglomeration of particles, and the two effects work together to significantly reduce the frictional resistance between particles, thereby maintaining or improving the fluidity while reducing the amount of water used. By precisely controlling the amount of addition, 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 operate, and indirectly improving the filling quality.

[0060] Further, in some embodiments, in step S2, 0.1-0.15% of a high-molecular flocculating agent solution is also added to the mixed slurry, and the high-molecular flocculating agent solution is a 0.05% polyacrylamide solution.

[0061] In the technical scheme of the embodiment of the present application, the adsorption and bridging effect of the high-molecular flocculating agent is used to aggregate fine solid particles into larger flocs, thereby significantly improving the settling efficiency of the thickener and obtaining high-concentration underflow slurry and clear overflow water.

[0062] In a second aspect, the embodiment of the present application provides a full-solid-waste potash mine closed-circuit filling system based on old brine magnesium extraction and calcium chloride cooperation, which comprises: an old brine pretreatment device, an overflow water treatment device, a drying and calcining device, a filling slurry preparation device and an underground filling pipe network; the old brine pretreatment device comprises a reaction kettle, a thickener and a filter press connected in sequence; the overflow water treatment device comprises an MVR evaporator, a multi-effect evaporator and a centrifugal crystallizer.

[0063] In the technical scheme of the embodiment of the present application, through the closed-loop resource recycling system, the old brine and tail salt generated in the potassium salt mining are converted into the filling material required for filling the mined-out area through chemical treatment, physical separation, drying and other steps, and through the collaborative work of various equipment, the material conversion and separation task is efficiently completed, the filling material made of these waste backfills the mined-out area, which not only solves the waste treatment problem, reduces environmental pollution, but also reduces the filling cost, improves the filling effect, and has significant economic and environmental benefits.

[0064] Some specific examples are listed below. It should be noted that the examples described below are exemplary and are used to explain the present application, and cannot be understood as limiting the present application. If the specific technology or condition is not specified in the examples, the technology or condition described in the literature in the art or according to the product manual is used. If the reagent or instrument is not specified by the manufacturer, it is a conventional product that can be obtained by purchase.

[0065] Example 1

[0066] The present embodiment provides a full-solid waste potassium salt mine closed-circuit filling process based on magnesium extraction from old brine and calcium chloride cooperation, as shown in Figure 1 The present embodiment provides a full-solid waste potassium salt mine closed-circuit filling process based on magnesium extraction from old brine and calcium chloride cooperation, as shown in

[0067] S1. The old brine of the potassium salt mine is pumped into the corrosion-resistant stirring reaction kettle by the delivery pump, the reaction temperature is set to 70°C, the calcium oxide is added into the reaction kettle according to the molar ratio of calcium oxide to MgCl2 in the old brine is 1.05:1, the MgCl2 in the old brine is reacted 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;

[0068] S2. The mixed slurry is self-flowed to the flocculation center cylinder, and 0.1% of a high molecular flocculant solution is added synchronously, the high molecular flocculant solution is a polyacrylamide solution with a concentration of 0.05%, the hydroxide flocculent precipitate is promoted to quickly settle at the bottom of the thickener to form a underflow slurry, the flow rate of the old brine into the reaction kettle is adjusted to control the underflow concentration of the thickener to be 35%, and the underflow slurry is delivered to the plate-and-frame filter press by the centrifugal pump for pressure filtration to obtain a magnesium hydroxide filter cake with a water content of <20% and a filtrate;

[0069] S3. The filter cake is sent into the rotary dryer to be dried at 150°C until the water content is <5%, and is collected in the form of powder, and then is sent into the rotary kiln to be calcined at 450°C for 1.5 h to obtain magnesium oxide powder, which is collected after cooling by the cooling device and is used for subsequent filling or other industrial applications;

[0070] S4. The overflow water and filtrate are mainly calcium chloride solution, which is easier to increase the concentration by evaporation than magnesium chloride solution. The overflow water and filtrate are evaporated and concentrated by the MVR evaporator to obtain a calcium chloride solution with a concentration of 45%, which is used as one of the additives of the tail salt- old brine-magnesium oxide-calcium oxide filling system. The remaining calcium chloride solution is evaporated and crystallized for other industrial uses;

[0071] S5. The magnesium oxide powder, calcium chloride solution, potassium salt mine tail salt, calcium oxide and additives are accurately measured according to the given mass and then added to the stirring barrel. The stirring device is started, and the stirring time is set to 2 min to ensure that the materials are fully mixed and uniform to form a uniform filling slurry. 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 amount of old brine is added according to the filling concentration, and the amount of calcium chloride solution is 1% of the total mass of the filling slurry. The additives include a retarder and a water reducing agent. The retarder is a polycarboxylate-based retarder, and the amount of addition is 0.05% of the total mass of the filling slurry. The water reducing agent is a polycarboxylate-based water reducing agent, and the amount of addition is 0.05% of the total mass of the filling slurry. The filling concentration is 75%;

[0072] S6. The prepared filling slurry is transported to the underground empty area through a pump and a pipeline to complete the filling operation.

[0073] The present application utilizes the synergistic effect of self-produced high-activity magnesium oxide (activity ≥ 90%) and byproduct calcium chloride to reduce the comprehensive filling cost by 80% compared to traditional processes. The whole process does not discharge wastewater, and the emission or leaching concentration of key ions such as chloride ions, magnesium ions and calcium ions meets the environmental protection standards. The recycling rate of chloride ions reaches 100%, which greatly reduces the ecological risk.

[0074] Comparative Example 1

[0075] Comparative Example 1 provides a full-solid waste potassium salt mine closed-circuit filling process based on old brine magnesium extraction and calcium chloride synergism, which is treated by using a traditional cementation filling process, including the following steps:

[0076] S1. The old brine produced in the potassium salt mine production process is prepared into a filling slurry with a mass concentration of 75% together with the tail salt. The tail salt is the solute, and the old brine is the solution.

[0077] S2. Magnesium-based cement is added, and the mass ratio of magnesium-based cement to tail salt is 1:30.

[0078] S3. The high-speed mixer is used to mix the raw materials, and the speed is 200 r / min, and the time is 3 min.

[0079] S4. The prepared uniform slurry is transported to the underground empty area through a pipeline for filling operation.

[0080] The traditional cementation filling process uses magnesium-based cement as a cementing agent to form a filling body in combination with tail salt and a small amount of old brine. The magnesium-based cement has a high procurement cost, which limits the amount of magnesium-based cement added, resulting in unstable long-term strength of the filling body and a high shrinkage rate (>5%) of the filling body, and a 28-day strength decay rate of more than 30%, which is difficult to meet the needs of long-term stability of the mine. In addition, the process can only consume a small amount of old brine, and cannot achieve full utilization of the old brine in the potash mine. At the same time, Mg 2+ The old brine is not effectively recovered, and the resource utilization rate is low, resulting in unnecessary waste.

[0081] Comparative Example 2

[0082] Comparative Example 2 provides a full-solid waste potash mine closed-circuit filling process based on magnesium extraction from old brine and calcium chloride cooperation, which adopts a water sand filling process, including the following steps:

[0083] The old brine and tail salt of the potash mine are mixed according to a mass ratio of 3:7 to prepare a slurry, which is transported to the underground empty area for filling operation.

[0084] Although this process is simple, it has the following problems: the filling material relies on tail salt recrystallization to form strength, which takes a long time, usually several weeks or even months to achieve a certain stability; the old brine crystallized out needs to be collected and transported to the surface old brine pool, increasing the operation complexity and cost. This process can only solve the disposal problem of tail salt, but cannot effectively treat old brine, and the compressive strength and durability of the filling body are difficult to guarantee, which cannot meet the needs of long-term stability of the mine.

[0085] Comparative Example 3

[0086] Comparative Example 3 provides a full-solid waste potash mine closed-circuit filling process based on magnesium extraction from old brine and calcium chloride cooperation, which adopts a calcium oxide extraction magnesium chloride process, including the following steps:

[0087] S1. CaO is added to the old brine of the potash mine at a CaO:MgCl2 molar ratio of 1.05:1, and reacted at 70°C for 2h, and then dehydrated to a water content of <30% by using a plate and frame filter press, to obtain a filter cake and a filtrate;

[0088] S2. The filter cake is sent to a rotary dryer at 150°C to dry to a water content of <5%, and is collected in the form of powder, and then is sent to a rotary kiln at 450°C for calcination for 1.5h to obtain magnesium oxide powder, which is collected after cooling by a cooling device for subsequent filling or other industrial applications;

[0089] S3. The part of the old brine is used as a solution of the tail salt-old brine-magnesium oxide-calcium oxide filling system to prepare a filling slurry with magnesium oxide powder, tail salt of the potash mine, calcium oxide and additives, and the filling slurry is transported to the empty area in the well through a pipeline for filling operation; wherein the mass ratio of the magnesium oxide powder to the tail salt of the potash mine is 1:40, the mass ratio of the magnesium oxide powder to the calcium oxide is 1:8, the old brine is added according to the filling concentration, the additives include a retarder and a water reducing agent, the retarder is a polycarboxylate retarder, and the addition amount is 0.05% of the total mass of the filling slurry; the water reducing agent is a polycarboxylate water reducing agent, and the addition amount is 0.05% of the total mass of the filling slurry, and the filling concentration is 75%.

[0090] S4. The remaining old brine is evaporated and concentrated by a MVR evaporator for crystallization, and is used for other industrial purposes.

[0091] The existing process of recovering valuable elements (such as Mg 2+ ) in old brine with calcium oxide cannot be industrialized at low cost, and the subsequent disposal of the generated calcium chloride is not fully considered, 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 that of calcium chloride, resulting in high cost and difficulty in processing the remaining old brine, and the full solid waste green disposal of the tail salt of the potash mine and the old brine cannot be truly realized.

[0092] Table 1: Performance test data

[0093]

[0094] As can be seen from Table 1, the filling process provided by the present application has high compressive strength of the filling body, and has high durability and stability. The present application integrates the magnesium extraction from old brine, calcium chloride concentration and crystallization, and filling slurry preparation process to form a closed-loop system, realizes the full solid waste cooperative disposal and high value utilization of tail salt-old brine, and reduces the filling comprehensive cost by 80% compared with the traditional process, solves the problem of difficult evaporation of magnesium chloride in old brine, realizes the old brine consumption rate of 100%, and the chloride ion recycling utilization rate reaches 100%, and significantly reduces the ecological risk.

[0095] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and embodiments having the same technical idea and playing the same role within the scope of the technical solution of the present application are all included in the technical scope of the present application. In addition, within the scope of the main idea of the present application, various modifications of the embodiments, combination of part of the components in the embodiments to construct other ways can also be included in the scope of the present application.

Claims

1. A full solid waste potash mine closed-circuit filling process based on magnesium extraction from old brine and calcium chloride cooperation, characterized in that, The method comprises the following steps: S1. Reacting potassium salt mine old brine with calcium oxide to obtain a mixed slurry; the molar ratio of the calcium oxide to MgCl2 in the old brine is (1-1.2):1; the reaction temperature is 50-80°C, the reaction time is 2-3 min, and the stirring speed is 200-300 rpm; S2. Flocculating and settling the mixed slurry through a thickener to obtain underflow slurry and overflow water, and separating the underflow slurry to obtain filter cake and filtrate; S3. Drying the filter cake and then performing calcination treatment to obtain magnesium oxide powder; S4. Evaporating and concentrating the overflow water and the filtrate to obtain a calcium chloride solution; the concentration of the calcium chloride solution is 40-50%; S5. Mixing the magnesium oxide powder, the calcium chloride solution, potassium salt mine tail salt, the old brine, calcium oxide and an additive to prepare a filling material slurry; the mass ratio of the magnesium oxide powder to the potassium salt mine tail salt is 1:(30-50); the mass ratio of the magnesium oxide powder to calcium oxide is 1:(6-10); and the filling concentration is 70-80%; S6. Delivering the filling material slurry to an underground empty area to perform filling operation.

2. The closed-circuit filling process of potash salt mine based on the cooperation of magnesium extraction from old brine and calcium chloride according to claim 1, characterized in that, In step S2, the concentration of the underflow slurry is 30-40%, and the moisture content of the filter cake is <20%.

3. The closed-circuit filling process of potash salt mine based on the cooperation of magnesium extraction from old brine and calcium chloride according to claim 1, characterized in that, In step S3, the drying temperature is 150-200°C, the drying time is 3-6 h, and the moisture content of the material after drying is <5%.

4. The closed-circuit filling process of potash salt mine based on the cooperation of magnesium extraction from old brine and calcium chloride according to claim 1, characterized in that, In step S3, the calcination treatment temperature is 400-500°C, and the calcination time is 1-2 h.

5. The closed-circuit filling process of potash salt mine based on the cooperation of magnesium extraction from old brine and calcium chloride according to claim 1, characterized in that, The additive comprises a retarder and a water reducing agent; the retarder is a polycarboxylate retarder, and the addition amount is 0.05-0.1% of the total mass of the filling material slurry; the water reducing agent is a polycarboxylate water reducing agent, and the addition amount is 0.05-0.1% of the total mass of the filling material slurry.

6. The closed-circuit filling process of potash salt mine based on the synergistic effect of magnesium extraction from old brine and calcium chloride according to claim 1, characterized in that, In step S2, 0.1-0.15% of a high molecular flocculant solution is further added to the mixed slurry; the high molecular flocculant solution is a 0.05% polyacrylamide solution.

7. A full solid waste potash mine closed-circuit filling system based on magnesium extraction from old brine in cooperation with calcium chloride, which is processed using the full solid waste potash mine closed-circuit filling process based on magnesium extraction from old brine in cooperation with calcium chloride according to any one of claims 1-6, characterized in that, The method comprises the following steps: The old brine pretreatment device comprises a reaction kettle, a thickener and a filter press connected in sequence; The overflow water treatment device comprises an MVR evaporator, a multi-effect evaporator and a centrifugal crystallizer. ​

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