Process for the preparation of anhydrous calcium chloride in the form of spheres

Abstract

This invention discloses a method for preparing anhydrous spherical calcium chloride, relating to the field of anhydrous spherical calcium chloride technology. The preparation method includes 1) raw material pretreatment; 2) premix preparation; 3) stepwise mixing and granulation; and 4) curing and drying. This invention solves the key problem of moisture absorption and crusting of anhydrous calcium chloride by utilizing industrial waste such as fly ash to construct a "skeleton-gel-pore" composite structure. The product has a several-fold longer anti-crusting time, more uniform and lasting moisture absorption, high particle strength, and very little dust. The raw material cost is low, and the reaction is controllable and easy to industrialize, achieving a balance between high performance, low cost, and green environmental protection.

Description

Technical Field

[0001] This invention relates to the field of anhydrous spherical calcium chloride technology, and more particularly to a method for preparing anhydrous spherical calcium chloride. Background Technology

[0002] Anhydrous calcium chloride is widely used as an industrial desiccant due to its excellent hygroscopic capacity. To improve its ease of use, it is often processed into spherical particles. However, anhydrous spherical calcium chloride prepared by traditional methods (such as melt spraying) suffers from a crusting effect. During moisture absorption, the surface layer of calcium chloride dissolves first, forming a high-concentration saturated liquid film. Subsequently, ions migrate outward and rapidly recrystallize on the surface, forming a dense, hard shell. This severely hinders further moisture absorption by the internal active materials, resulting in low moisture absorption capacity utilization and a sharp drop in performance.

[0003] To alleviate this problem, existing technologies mainly employ physical mixing of porous materials such as molecular sieves or surface coating with porous / polymer coatings. However, physical mixing suffers from weak inter-component bonding, easy deliquescence and disintegration, and poor long-term stability; surface coating faces issues such as easy coating peeling, potential excessive obstruction of mass transfer, complex processes, and high costs. These methods fail to fundamentally alter the ion migration and crystallization behavior during the moisture absorption process and have significant shortcomings in terms of strength, cost, or durability.

[0004] Therefore, developing a novel method for preparing anhydrous spherical calcium chloride that can fundamentally suppress crust formation, while possessing high strength, long lifespan, and controllable cost has become a pressing technical challenge in this field. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing technologies by proposing a method for preparing anhydrous spherical calcium chloride.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: This invention first proposes a method for preparing anhydrous spherical calcium chloride, comprising the following steps: S1. Raw material pretreatment: In the production of barium chloride using the dibarite hydrochloric acid method, lime milk is added to the crude barium chloride solution to adjust the pH, neutralize excess hydrochloric acid, and precipitate Fe(OH)3 and Mg(OH)2 impurities. Barium chloride is separated through a concentration and separation process to obtain a mother liquor rich in calcium chloride. CaSO4 is then added to the mother liquor, filtered, evaporated, and the filtrate is crystallized to obtain anhydrous calcium chloride powder. The mother liquor remaining after separating barium chloride crystals still contains a small amount of barium chloride. When calcium sulfate gypsum is added, the residual barium ions will displace the sulfate ions (SO42-). 2- ), forming barium sulfate (BaSO4) precipitate: .

[0007] The trace amounts or small amounts of barium chloride remaining in the mother liquor that cannot be completely separated by evaporation and crystallization are recovered in the form of barium sulfate, which greatly improves the total barium yield. At the same time, the calcium chloride product obtained by subsequent evaporation and crystallization is free of barium impurities and has higher purity.

[0008] Sift the anhydrous calcium chloride powder and dry the fly ash cenospheres. S2. Preparation of premix: Ammonium bicarbonate and light magnesium oxide are mixed at a mass ratio of 20-40:1 to prepare a slow-release pore-forming agent; water glass is diluted with water to a mass concentration of 25-35% to obtain diluted water glass; S3, Stepwise Mixing and Granulation: Mix 320-330 parts of anhydrous calcium chloride powder and 120-130 parts of fly ash cenospheres by dry mixing for 2-4 minutes; Add 20-25 parts water and mix semi-wetly for 3-5 minutes, controlling the material temperature ≤30℃; water acts as a wetting agent, forming a thin water film on the surface of calcium chloride powder, causing partial hydrolysis of CaCl2 to obtain free Ca. 2+ The hydroxyl groups on the surface of fly ash cenospheres are activated by water, forming a hydrophilic interface; the temperature ≤30℃ inhibits the rapid evaporation of moisture caused by the hygroscopic and exothermic reaction of calcium chloride, ensuring a semi-moist state and avoiding clumping due to excessive dryness or moisture. Add 20-22 parts of slow-release pore-forming agent and 65-68 parts of diluted water glass to carry out calcium silicate gel reaction; mix for 1-3 minutes, and control the material temperature at 30-35℃. Hydration of light magnesium oxide: ; Water glass (Na₂O・nSiO₂) hydrolyzes in a weakly alkaline environment (pH≈9-10) provided by Mg(OH)₂ to form silicic acid (H₂SiO₃), which then reacts with calcium chloride (CaO) 2+ reaction: The amorphous network structure of calcium silicate gel is formed, which firmly encapsulates calcium chloride and fly ash cenospheres, forming a primary particle skeleton. Meanwhile, ammonium bicarbonate (NH4HCO3) decomposes slowly: Gas escapes, forming tiny closed pores.

[0009] Add 320-330 parts of anhydrous calcium chloride powder, 120-130 parts of fly ash cenospheres and 20-22 parts of slow-release pore-forming agent and mix for 2-4 minutes; The supplementary mixing process adds solid components that combine with the primary skeleton, allowing the existing gel skeleton to bond more calcium chloride and cenosphere skeleton materials, increasing particle thickness. At the same time, the hollow structure of fly ash cenospheres further optimizes particle porosity and mechanical strength.

[0010] Add 65-68 parts of diluted water glass and 60-62 parts of hydroxypropyl methylcellulose aqueous solution, carry out the pore-forming reaction and granulate for 3-8 minutes, control the material temperature ≤40℃, and obtain wet granules; The water glass is replenished and the remaining Ca continues to be added. 2+ The reaction produces calcium silicate gel. The hydroxyl groups (-OH) and methoxy groups (-OCH3) on the hydroxypropyl methylcellulose molecular chain form hydrogen bonds with the hydroxyl groups on the surface of the gel, calcium chloride, and cenospheres, which increases the viscosity and plasticity of the material. When the temperature rises to 40℃, the decomposition rate of ammonium bicarbonate accelerates, and the generated NH3 forms continuous channels in the plastic material. Under the mechanical tumbling action of the granulation equipment, the viscous material forms regular spheres.

[0011] S4. Curing and Drying: The wet granules are cured at room temperature and then dried by gradient temperature increase to obtain anhydrous spherical calcium chloride product.

[0012] Preferably, in step S1, the anhydrous calcium chloride powder passes through a 150-mesh sieve; the drying temperature is 120-150℃, and the moisture content of the fly ash cenospheres after drying is ≤1%.

[0013] Preferably, in S2, the D50 of the light magnesium oxide is 1-10 μm, and the activity is 40-80 mg I2 / g. Preferably, in step S3, the modulus of the water glass is 2.5-3.0; and the mass concentration of the hydroxypropyl methylcellulose aqueous solution is 0.5-1.5%.

[0014] Preferably, in step S4, the conditions for room temperature curing are: temperature 20-30℃, relative humidity 40-60%, and curing time 2-4 hours.

[0015] Preferably, in step S4, the gradient temperature drying is performed using a fluidized bed dryer, and the drying process is divided into three temperature zones: the first temperature zone is 60±5℃, drying for 8-12 min, gently removing free water; the second temperature zone is 80±5℃, drying for 12-18 min, promoting gel network reinforcement; and the third temperature zone is 100±5℃, drying for 8-12 min, deeply dehydrating and promoting the complete decomposition of residual bicarbonate.

[0016] The anhydrous spherical calcium chloride prepared by the aforementioned preparation method of the present invention is characterized in that the obtained anhydrous spherical calcium chloride is a regular spherical particle with a particle size of 2-4 mm and a water content of ≤2%.

[0017] Compared with the prior art, the beneficial effects of the present invention are: 1. Existing technology uses physical melting-spray cooling molding to produce CaCl2 solid spheres with uniform composition and dense structure. Upon moisture absorption, water penetrates from the surface of the spheres inwards, causing the surface CaCl2 to dissolve first, forming a high-concentration Ca2+ layer.2+ and Cl - A saturated solution film; because the interior is a dry solid, a huge concentration gradient is formed, driving ions to migrate to the surface. When water evaporates or continues to absorb moisture, the ions recrystallize rapidly on the surface, forming a dense and hard CaCl2·nH2O crystalline shell. This shell completely blocks the contact between the internal dry core and the external water vapor, causing the moisture absorption process to terminate prematurely, and most of the active substances cannot be utilized.

[0018] This invention uses fly ash cenospheres as a dispersion framework to divide calcium chloride into numerous micro-regions. The in-situ generated calcium silicate (CaSiO3·nH2O) gel network encapsulates and binds CaCl2 crystals or ions. After hygroscopic dissolution, Ca... 2+ The long-range migration of ions is significantly inhibited by the steric hindrance and chemisorption of the gel network. Ions are confined to local areas of the gel pores and cannot freely aggregate to the surface. The multi-level interconnected pores formed by the decomposition of ammonium bicarbonate act as channels for rapid inward penetration of water. Water can bypass the surface and be directly transported to the depths of the particles, causing the internal CaCl2 to dissolve preferentially or simultaneously, achieving uniform deliquescence, breaking the concentration monopoly on the surface, and making it difficult for a saturated solution layer to form alone on the surface.

[0019] 2. Existing technology involves physically mixing calcium chloride powder with a porous carrier and granulating it with a binder. The main interactions between the components are physical adsorption and mechanical intercalation.

[0020] This invention relates to a calcium silicate gel generated by the reaction of sodium silicate and CaCl2. This gel is a continuous phase chemically bonded to both the active component (CaCl2) and the cenosphere skeleton, serving not only as a binder but also as the structural backbone. This chemical network is stable in humid environments, imparting excellent wet strength and cyclic structural stability to the product. The decomposition and gelation reactions of the pore-forming agent (NH4HCO3) occur simultaneously and in a controlled manner. Gas escapes from the gel precursor, and the walls of the formed pore channels are themselves part of the gel network, resulting in a robust and non-collapsed pore structure. A weakly alkaline environment alters the decomposition pathway of NH4HCO3, generating CO3... 2- Further with Ca 2+ The reaction generates nano-CaCO3 precipitate, which fills and enhances the gel network in situ, forming a "gel-nanofiller" composite reinforcement.

[0021] 3. Existing technologies often coat the surface of calcium chloride particles with a porous or semi-permeable membrane to control the rate of moisture ingress or block ion permeation and provide some mechanical strength, so that anhydrous calcium chloride does not disintegrate during transportation; however, 1) the coating does not match the core's thermal expansion coefficient and hygroscopic expansion coefficient, and is prone to cracking and peeling in wet-dry cycles. Once damaged, the protective effect immediately fails; 2) the coating itself may hinder the normal passage of water vapor, excessively sacrificing the moisture absorption rate; 3) the process is complex, the uniformity and integrity of the coating are difficult to control, and the cost is high.

[0022] The gel network and pores of this invention permeate the entire particle body, eliminating the obvious "shell-core" interface. Hygroscopic swelling stress is uniformly dispersed by the three-dimensional network, eliminating the risk of interface delamination. Through a stepwise feeding process, a micro-gradient structure is naturally formed, where the internal porosity may be slightly higher than the surface. This ensures rapid moisture ingress while providing a buffer against surface ion efflux. However, this buffering is structurally intrinsic and continuous, rather than relying on a fragile heterogeneous coating. Therefore, the product boasts high reliability, long service life, and no risk of performance abrupt changes due to coating peeling. Furthermore, the process is simpler and more robust, requiring no sophisticated coating equipment.

[0023] In summary, this invention solves the key bottleneck of moisture absorption and crusting in anhydrous calcium chloride by constructing a "skeleton-gel-pore" composite structure. The product exhibits several times longer anti-crusting time, more uniform and lasting moisture absorption, high particle strength, and minimal dust. This process utilizes industrial waste such as fly ash, resulting in low raw material costs. Furthermore, the reaction is controllable and easily industrialized, achieving a balance between high performance, low cost, and environmental friendliness. Attached Figure Description

[0024] Figure 1 This is a process flow diagram for obtaining anhydrous spherical calcium chloride according to the present invention. Detailed Implementation

[0025] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0026] Example 1: A method for preparing anhydrous spherical calcium chloride, such as... Figure 1 As shown, it includes the following steps: S1. Raw material pretreatment: In the production of barium chloride using the dibarite hydrochloric acid method, lime milk is added to the crude barium chloride solution to adjust the pH, neutralize excess hydrochloric acid, and precipitate Fe(OH)3 and Mg(OH)2 impurities. Barium chloride is separated through a concentration and separation process to obtain a mother liquor rich in calcium chloride. CaSO4 is then added to the mother liquor, filtered, evaporated, and the filtrate is crystallized to obtain anhydrous calcium chloride powder. Sift the anhydrous calcium chloride powder and dry the fly ash cenospheres. S2. Preparation of premix: Ammonium bicarbonate and light magnesium oxide are mixed at a mass ratio of 40:1 to prepare a slow-release pore-forming agent; water glass is diluted with water to a mass concentration of 25% to obtain diluted water glass; S3, Stepwise Mixing and Granulation: Mix 330 kg of anhydrous calcium chloride powder and 120 kg of fly ash cenospheres by dry mixing for 3 min; Add 25kg of water and mix semi-wet for 4 minutes, keeping the material temperature ≤30℃; Add 20 kg of slow-release pore-forming agent and 68 kg of diluted water glass to carry out calcium silicate gel reaction; mix for 2 min, and control the material temperature at 30-35℃; Add 320 kg of anhydrous calcium chloride powder, 130 kg of fly ash cenospheres and 20 kg of slow-release pore-forming agent and mix for 3 min; Add 65 kg of diluted water glass and 62 kg of hydroxypropyl methylcellulose aqueous solution to carry out the pore-forming reaction and granulate for 5 min, controlling the material temperature ≤40℃ to obtain wet granules; S4. Curing and Drying: The wet granules are cured at room temperature and then dried by gradient temperature increase to obtain anhydrous spherical calcium chloride product; the obtained anhydrous spherical calcium chloride is a regular spherical particle with a particle size of 2-4 mm and a moisture content of ≤2%.

[0027] In step S1, the anhydrous calcium chloride powder passes through a 150-mesh sieve; the drying temperature is 130℃, and the moisture content of the fly ash cenospheres after drying is ≤1%.

[0028] In S2, the D50 of light magnesium oxide is 1-10 μm, and the activity is 40-80 mgI2 / g. In S3, the modulus of the water glass is 2.5-3.0; the mass concentration of the hydroxypropyl methylcellulose aqueous solution is 0.5-1.5%.

[0029] In S4, the conditions for room temperature curing are: temperature 20-30℃, relative humidity 40-60%, and curing time 3 hours.

[0030] In S4, the gradient temperature drying adopts a fluidized bed dryer, and the drying process is divided into three temperature zones: the first temperature zone is 60±5℃, drying for 10 min; the second temperature zone is 80±5℃, drying for 15 min; and the third temperature zone is 100±5℃, drying for 10 min.

[0031] Example 2: A method for preparing anhydrous spherical calcium chloride includes the following steps: S1. Raw material pretreatment: Sieve anhydrous calcium chloride powder and dry fly ash celery beads; S2. Preparation of premix: Ammonium bicarbonate and light magnesium oxide are mixed at a mass ratio of 30:1 to prepare a slow-release pore-forming agent; water glass is diluted with water to a mass concentration of 30% to obtain diluted water glass; S3, Stepwise Mixing and Granulation: Mix 325 kg of anhydrous calcium chloride powder and 125 kg of fly ash cenospheres by dry mixing for 3 min; Add 22.5 kg of water and mix semi-wet for 4 minutes, controlling the material temperature to ≤30℃; Add 21 kg of slow-release pore-forming agent and 66.5 kg of diluted water glass to carry out the calcium silicate gel reaction; mix for 2 min, and control the material temperature at 30-35℃; Add 325 kg of anhydrous calcium chloride powder, 125 kg of fly ash cenospheres and 21 kg of slow-release pore-forming agent and mix for 3 min; Add 66.5 kg of diluted water glass and 61 kg of hydroxypropyl methylcellulose aqueous solution, carry out the pore-forming reaction and granulate for 5 min, control the material temperature ≤40℃, and obtain wet granules; S4. Curing and Drying: The wet granules are cured at room temperature and then dried by gradient temperature increase to obtain anhydrous spherical calcium chloride product; the obtained anhydrous spherical calcium chloride is a regular spherical particle with a particle size of 2-4 mm and a moisture content of ≤2%.

[0032] In step S1, the anhydrous calcium chloride powder passes through a 150-mesh sieve; the drying temperature is 130℃, and the moisture content of the fly ash cenospheres after drying is ≤1%.

[0033] In S2, the D50 of light magnesium oxide is 1-10 μm, and the activity is 40-80 mgI2 / g. In S3, the modulus of the water glass is 2.5-3.0; the mass concentration of the hydroxypropyl methylcellulose aqueous solution is 0.5-1.5%.

[0034] In S4, the conditions for room temperature curing are: temperature 20-30℃, relative humidity 40-60%, and curing time 3 hours.

[0035] In S4, the gradient temperature drying adopts a fluidized bed dryer, and the drying process is divided into three temperature zones: the first temperature zone is 60±5℃, drying for 10 min; the second temperature zone is 80±5℃, drying for 15 min; and the third temperature zone is 100±5℃, drying for 10 min.

[0036] Example 3: A method for preparing anhydrous spherical calcium chloride includes the following steps: S1. Raw material pretreatment: Sieve anhydrous calcium chloride powder and dry fly ash celery beads; S2. Preparation of premix: Ammonium bicarbonate and light magnesium oxide are mixed at a mass ratio of 20:1 to prepare a slow-release pore-forming agent; water glass is diluted with water to a mass concentration of 35% to obtain diluted water glass; S3, Stepwise Mixing and Granulation: Mix 320 kg of anhydrous calcium chloride powder and 130 kg of fly ash cenospheres by dry mixing for 3 min; Add 20kg of water and mix semi-wet for 4 minutes, keeping the material temperature ≤30℃; Add 22 kg of slow-release pore-forming agent and 65 kg of diluted water glass to carry out calcium silicate gel reaction; mix for 2 min, and control the material temperature at 30-35℃; Add 330 kg of anhydrous calcium chloride powder, 120 kg of fly ash cenospheres and 22 kg of slow-release pore-forming agent and mix for 3 min; Add 65 kg of diluted water glass and 62 kg of hydroxypropyl methylcellulose aqueous solution to carry out the pore-forming reaction and granulate for 5 min, controlling the material temperature ≤40℃ to obtain wet granules; S4. Curing and Drying: The wet granules are cured at room temperature and then dried by gradient temperature increase to obtain anhydrous spherical calcium chloride product; the obtained anhydrous spherical calcium chloride is a regular spherical particle with a particle size of 2-4 mm and a moisture content of ≤2%.

[0037] In step S1, the anhydrous calcium chloride powder passes through a 150-mesh sieve; the drying temperature is 130℃, and the moisture content of the fly ash cenospheres after drying is ≤1%.

[0038] In S2, the D50 of light magnesium oxide is 1-10 μm, and the activity is 40-80 mgI2 / g. In S3, the modulus of the water glass is 2.5-3.0; the mass concentration of the hydroxypropyl methylcellulose aqueous solution is 0.5-1.5%.

[0039] In S4, the conditions for room temperature curing are: temperature 20-30℃, relative humidity 40-60%, and curing time 3 hours.

[0040] In S4, the gradient temperature drying adopts a fluidized bed dryer, and the drying process is divided into three temperature zones: the first temperature zone is 60±5℃, drying for 10 min; the second temperature zone is 80±5℃, drying for 15 min; and the third temperature zone is 100±5℃, drying for 10 min.

[0041] Based on this, the following design was also created: Comparative Example 1: The formulation and experimental methods were the same as in Example 2, but heavy magnesium oxide was used instead of light magnesium oxide; Comparative Example 2: The formulation and experimental methods were the same as in Example 2, but sodium carbonate was used instead of ammonium bicarbonate; Comparative Example 3: Same formulation and experimental method as Example 2, but without the addition of hydroxypropyl methylcellulose; Comparative Example 4: Activated alumina was directly and physically mixed with calcium chloride to form spheres; Comparative Example 5: Calcium chloride microspheres coated with polylactic acid; In a constant temperature and humidity chamber at 25℃ and RH=80%, the weight gain of the samples was continuously weighed and recorded, and a moisture absorption kinetic curve was plotted to determine the moisture absorption rate and moisture absorption capacity. The surface hardening time was observed every 20 minutes to assess the anti-crusting property; porosity was determined according to GB / T21650.2-2008 "Determination of Pore Size Distribution and Porosity of Solid Materials by Mercury Intrusion Porosimetry and Gas Adsorption Method"; and the compressive strength of the particles was determined according to GB / T36384-2018 "Test Method for Crushing Force of Molecular Sieves". The corresponding results are shown in Table 1. Table 1. Test data of various properties of anhydrous spherical calcium chloride Data analysis shows that: The variables in Examples 1-3 were the mass ratio of ammonium bicarbonate to light magnesium oxide (40:1→30:1→20:1) and the concentration of water glass (25%→30%→35%). The data showed a trend of "Example 2 having the best performance," which is essentially due to the difference in the matching degree between process parameters and reaction mechanism. Porosity: A matching index for the sustained-release pore-forming mechanism. The porosity of Example 2 reached 39%, significantly higher than that of Example 1 (36%) and Example 3 (34%). Mechanistically, when the mass ratio of ammonium bicarbonate to light magnesium oxide is 30:1, the hydration rate of light magnesium oxide and the decomposition rate of ammonium bicarbonate are synchronized. This avoids insufficient alkalinity and slow decomposition of the pore-forming agent due to a low magnesium oxide ratio, and also avoids excessive alkalinity and premature and violent decomposition of the pore-forming agent due to a high magnesium oxide ratio. The synchronized pore-forming-gel process forms a highly interconnected and uniformly sized pore network, laying the structural foundation for subsequent moisture absorption and anti-crusting properties.

[0042] Moisture absorption rate and capacity: The effect of pore structure on calcium chloride exposure. In Example 2, the initial moisture absorption rate (0.92 g / g·h), the later moisture absorption rate (0.66 g / g·h), and the moisture absorption capacity (170 g / 100 g) were all the best among the three. High initial rate: The open surface pores allow calcium chloride to come into rapid contact with water vapor, indicating good pore connectivity; Stable growth rate in the later stages: The internal interconnected channels allow moisture to continuously diffuse to the particle core, avoiding the phenomenon of surface saturation and internal lack of moisture absorption; Large capacity: The evenly distributed pores expose more than 90% of the calcium chloride as effective moisture absorption sites.

[0043] Anti-crusting time and compressive strength: Synergistic effect of composite bonding mechanism. Example 2 showed the best anti-crusting time (17.8h) and compressive strength (45N). Long-lasting anti-caking effect: The interconnected channels allow for even moisture diffusion during the absorption process, preventing localized oversaturation and hardening of the surface layer; High compressive strength: When the water glass concentration is 30%, the rigid skeleton of calcium silicate gel and the flexible bonding of hydroxypropyl methylcellulose (HPMC) work together perfectly. It will not cause insufficient bonding force due to too low a concentration, nor will it cause pore blockage and increased skeleton brittleness due to too high a concentration.

[0044] Comparative Example 1 (heavy magnesium oxide replacing light magnesium oxide): The sustained-release pore-forming mechanism failed. The porosity of Comparative Example 1 was only 28%, a decrease of 28.2% compared to Example 2, with a later moisture absorption rate of 0.35 g / g·h, a decrease of 47%, and an anti-crusting time of 5.5 h, a decrease of 69.1%. Mechanistically, heavy magnesium oxide has a D50 > 50 μm and an activity < 30 mg I2 / g, resulting in extremely low hydration reaction activity. It cannot generate enough Mg(OH)2 in time to regulate the decomposition rate of ammonium bicarbonate. The pore-forming agent decomposes violently before gel formation, leading to concentrated overflow of pores and local collapse, ultimately forming a structure with a small number of closed macropores. The high percentage of closed pores prevents moisture from diffusing into the particle interior, resulting in a sharp drop in the rate of moisture absorption later on. Poor pore connectivity causes moisture to concentrate on the surface during absorption, leading to rapid hardening and crust formation (anti-crusting time is only 5.5 hours). The gelation reaction was insufficient due to inadequate alkalinity, and the compressive strength dropped to 40 N, a decrease of 11.1% compared to Example 2.

[0045] Comparative Example 2 (Sodium carbonate instead of ammonium bicarbonate): Lack of pore-forming function and pore blockage. The moisture absorption capacity of Comparative Example 2 was only 145 g / 100 g, a decrease of 14.7%, and the anti-crusting time was 8 hours, a decrease of 55.1%. While the porosity of 31% appeared close to the example, its performance was extremely poor. Mechanistically, sodium carbonate lacks the function of decomposing to produce gas and create pores; its interaction with Ca... 2+ The reaction produces CaCO3 precipitate: The precipitation blocked the original pores formed by the calcium silicate gel, and the actual effective porosity was less than 5%, far lower than the numerical value of 31%. The hygroscopic sites of calcium chloride were blocked, and the capacity dropped sharply. The sealed pores prevent moisture from spreading, causing the surface to quickly saturate and harden, with an anti-crusting time of only 8 hours; The dense structure without pore support is brittle. Although it has a compressive strength of 28N, it is prone to pulverization in actual use, with a drop pulverization rate of >20%.

[0046] Comparative Example 3 (without HPMC): The compressive strength of Comparative Example 3 was only 22 N, a decrease of 51.1% compared to Example 2, and the sphericity was poor. Mechanistically, HPMC is the core of organic plasticization and hydrogen bonding: without HPMC, relying solely on the rigid bonding of calcium silicate gel, the material lacks plasticity during granulation—the particles are prone to cracking and deformation, forming a loose skeleton and a structure with non-connected channels. The loose skeleton resulted in a sharp drop in compressive strength (only 22N), which could not meet the requirements of industrial transportation. The lack of interconnected pores hinders moisture diffusion, reducing the anti-crusting time to 12 hours, a 32.6% decrease compared to Example 2; Although the porosity is 32% and the moisture absorption capacity is 168g / 100g (close to the example), the structural stability is poor, the particles are easily broken during the actual moisture absorption process, and the effective moisture absorption time is shortened by more than 50%.

[0047] Comparative Example 4 (Physical Mixture of Activated Alumina): Without chemical bonding or pore-forming mechanism, Comparative Example 4 exhibits a compressive strength of only 15 N and a moisture absorption capacity of 140 g / 100 g. Mechanistically, the physical mixing process lacks any chemical bonding or slow-release pore-forming process—the activated alumina and calcium chloride are only bonded by mechanical extrusion, resulting in a loose structure. Without a gel skeleton for support, its compressive strength is only 15N, making it unable to withstand stacking pressure; Without a pore-forming process, the porosity is only 25%, and most of the pores are macropores, resulting in few calcium chloride exposure sites and low capacity. The loose structure resulted in poor pore connectivity, and the moisture absorption rate in the later stage was only 0.28 g / g·h, a decrease of 57.6% compared with Example 2.

[0048] Comparative Example 5 (Polylactic Acid Coating): Pore Functional Sealing. The porosity of Comparative Example 5 was only 10%, with a moisture absorption capacity of 125 g / 100 g. Mechanistically, although the polylactic acid coating can improve sphericity, it completely seals the pores inside the particles—moisture can only slowly permeate through the tiny pores of the coating layer. The porosity drops sharply to only 10%, resulting in insufficient calcium chloride exposure sites and low capacity. The slow penetration rate allows the surface to quickly become saturated and hardened, with an anti-crusting time of 6.5 hours; Although the flexibility of the coating improves the compressive strength (35N), the closed structure completely violates the core requirement of calcium chloride, which is "high moisture absorption rate", and it needs to be used after the coating is broken.

[0049] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing anhydrous spherical calcium chloride, characterized in that, Includes the following steps: S1. Raw material pretreatment: In the production of barium chloride using the dibarite hydrochloric acid method, lime milk is added to the crude barium chloride solution to adjust the pH, neutralize excess hydrochloric acid, and precipitate Fe(OH)3 and Mg(OH)2 impurities. Barium chloride is separated through a concentration and separation process to obtain a mother liquor rich in calcium chloride. CaSO4 is then added to the mother liquor, filtered, evaporated, and the filtrate is crystallized to obtain anhydrous calcium chloride powder. Sift the anhydrous calcium chloride powder and dry the fly ash cenospheres. S2. Preparation of premix: Ammonium bicarbonate and light magnesium oxide are mixed at a mass ratio of 20-40:1 to prepare a slow-release pore-forming agent; water glass is diluted with water to a mass concentration of 25-35% to obtain diluted water glass; S3, Stepwise Mixing and Granulation: Mix 320-330 parts of anhydrous calcium chloride powder and 120-130 parts of fly ash cenospheres by dry mixing for 2-4 minutes; Add 20-25 parts water and mix semi-wet for 3-5 minutes, keeping the material temperature ≤30℃; Add 20-22 parts of slow-release pore-forming agent and 65-68 parts of diluted water glass to carry out calcium silicate gel reaction; mix for 1-3 minutes, and control the material temperature at 30-35℃. Add 320-330 parts of anhydrous calcium chloride powder, 120-130 parts of fly ash cenospheres and 20-22 parts of slow-release pore-forming agent and mix for 2-4 minutes; Add 65-68 parts of diluted water glass and 60-62 parts of hydroxypropyl methylcellulose aqueous solution, carry out the pore-forming reaction and granulate for 3-8 minutes, control the material temperature ≤40℃, and obtain wet granules; S4. Curing and Drying: The wet granules are cured at room temperature and then dried by gradient temperature increase to obtain anhydrous spherical calcium chloride product.

2. The method for preparing anhydrous spherical calcium chloride according to claim 1, characterized in that, In step S1, the anhydrous calcium chloride powder passes through a 150-mesh sieve; the drying temperature is 120-150℃, and the moisture content of the fly ash cenospheres after drying is ≤1%.

3. The method for preparing anhydrous spherical calcium chloride according to claim 1, characterized in that, In S2, the D50 of light magnesium oxide is 1-10 μm, and the activity is 40-80 mgI2 / g.

4. The method for preparing anhydrous spherical calcium chloride according to claim 1, characterized in that, In S3, the modulus of the water glass is 2.5-3.0; the mass concentration of the hydroxypropyl methylcellulose aqueous solution is 0.5-1.5%.

5. The method for preparing anhydrous spherical calcium chloride according to claim 1, characterized in that, In S4, the conditions for room temperature curing are: temperature 20-30℃, relative humidity 40-60%, and curing time 2-4 hours.

6. The method for preparing anhydrous spherical calcium chloride according to claim 1, characterized in that, In S4, the gradient temperature drying adopts a fluidized bed dryer, and the drying process is divided into three temperature zones: the first temperature zone is 60±5℃, drying for 8-12 min; the second temperature zone is 80±5℃, drying for 12-18 min; and the third temperature zone is 100±5℃, drying for 8-12 min.

7. The anhydrous spherical calcium chloride prepared by any one of the preparation methods according to claims 1-6, characterized in that, The obtained anhydrous spherical calcium chloride consists of regular spherical particles with a particle size of 2-4 mm and a moisture content of ≤2%.

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