Strontium chloride production method based on oxidation coprecipitation and salting-out crystallization
By introducing carbide slag as a neutralizing agent and combining it with oxidative co-precipitation technology, along with salting-out crystallization and mechanical vapor recompression technology, the problems of high cost and high energy consumption in strontium chloride production have been solved. This has enabled the production of strontium chloride with high purity and high yield, and has also made effective use of industrial waste, meeting the requirements of green manufacturing and circular economy.
Patent Information
- Application Number
- CN202610298249.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-03-12
- Publication Date
- 2026-05-15
AI Technical Summary
Existing strontium chloride production processes are characterized by high costs, difficulty in completely removing trace metal ion impurities, high energy consumption, and difficulty in effectively utilizing industrial waste residue, resulting in poor product quality and resource waste.
Using carbide slag as a neutralizing agent, combined with oxidative co-precipitation technology and salting-out crystallization, and by regulating the high-calcium mother liquor system, highly active strontium sulfate microcrystals are generated to deeply remove impurities. Mechanical vapor recompression technology is used to reduce energy consumption, thereby achieving low-cost production of high-purity strontium chloride.
This technology enables the production of strontium chloride with high purity and high yield, reduces production costs and energy consumption, and effectively utilizes industrial waste, meeting the requirements of green manufacturing and circular economy.
Abstract
Description
Technical Field
[0001] This invention relates to the field of inorganic chemical engineering, specifically to a method for producing strontium chloride based on oxidative coprecipitation and salting-out crystallization. Background Technology
[0002] Strontium chloride, an important strontium salt product, is widely used in magnetic materials, electronic ceramics, liquid crystal glass substrates, pharmaceutical synthesis, and daily chemical products. With the rapid development of downstream high-end manufacturing, the market has placed higher demands on the purity, whiteness, and production cost of strontium chloride products.
[0003] Currently, the main industrial process for producing strontium chloride uses strontium carbonate or celestite as raw materials, involving hydrochloric acid hydrolysis, impurity removal, concentration, and crystallization. Traditional hydrolysis processes typically involve reacting high-purity strontium carbonate powder with industrial hydrochloric acid. To ensure product quality, strict screening of raw materials is often required, or large amounts of impurity-removing agents (such as those for removing iron, barium, and calcium) are added in subsequent processes. However, this production model, reliant on high-quality raw materials, results in persistently high production costs.
[0004] Existing technologies also face numerous challenges in the impurity removal and crystallization stages. On the one hand, trace metal ions (such as iron and manganese) and organic impurities introduced from raw materials are difficult to remove completely through simple physical filtration, often requiring cumbersome chemical precipitation or adsorption steps, and are prone to leaving residues in the product, leading to poor color. On the other hand, strontium chloride has high solubility in water, which changes significantly with temperature. Traditional evaporation crystallization processes are usually energy-intensive, and the yield of a single-pass crystallization is limited by thermodynamic equilibrium. A large amount of strontium ions remain in the mother liquor, requiring multiple cycles of evaporation. This not only increases steam consumption but also easily leads to the accumulation of impurities in the mother liquor system, thereby affecting the quality of subsequent batches of product.
[0005] Furthermore, against the backdrop of the chemical industry's increasing emphasis on "green manufacturing" and "circular economy," finding inexpensive alternative raw materials or addressing calcium- and sulfur-containing waste liquids / residues generated during production have become common challenges urgently needing resolution. Some existing processes attempt to utilize industrial waste residues for neutralization or impurity removal, but these are often difficult to scale up due to the introduction of new impurities or complex processing techniques. Therefore, developing a new strontium chloride production process that is highly adaptable to raw materials, has low energy consumption, provides stable product quality, and offers good economic benefits is currently a research hotspot in the strontium salt chemical industry. Summary of the Invention
[0006] To address the shortcomings of existing technologies, this invention aims to provide a method for producing strontium chloride based on oxidative co-precipitation and salting-out crystallization. This invention introduces calcium carbide slag waste into strontium chloride production, pioneering an "in-situ oxidative co-precipitation" technology to achieve waste-to-impurity treatment. By controlling the high-calcium mother liquor system to generate a strong salting-out effect, the crystallization yield is significantly improved while energy consumption is reduced. The entire process is interconnected, balancing low cost, high yield, and high quality, resulting in significant economic and environmental benefits.
[0007] To achieve the above objectives, the present invention adopts the following technical solution:
[0008] This invention provides a method for producing strontium chloride based on oxidative coprecipitation and salting-out crystallization. This method introduces carbide slag to adjust the pH and construct a high-calcium salting-out system, combined with oxidative coprecipitation technology to deeply remove impurities, thereby producing high-purity strontium chloride products at low cost and high efficiency. Specifically, it includes the following steps:
[0009] (1) Acid hydrolysis and neutralization: Strontium carbonate raw material is reacted with hydrochloric acid to prepare acid hydrolysis solution. In order to ensure the reaction is complete and control the cost, the molar ratio of strontium carbonate raw material to hydrochloric acid is preferably 1:2.0~2.2. After the acid hydrolysis reaction is completed or in the later stage of the reaction, carbide slag is added to the acid hydrolysis solution to adjust the pH value.
[0010] In this invention, the carbide slag not only serves as a cheap neutralizing agent to replace expensive liquid alkali or strontium carbonate powder, but more importantly, it introduces calcium ions to construct the subsequent salting-out background.
[0011] To facilitate operation and ensure uniform reaction, the carbide slag is preferably prepared as a slurry and added, but adding dry or wet slag directly is also within the scope of protection of this invention.
[0012] The amount of calcium carbide slag added should be adjusted to the pH value of the acid hydrolysis solution to a predetermined range, usually to acidic or neutral.
[0013] Preferably, in order to inhibit scale formation and regulate crystal growth, an additive is added to the system in step (1). The additive is hydroxyethylidene diphosphonic acid (HEDP) or its salt, and the amount added is preferably 0.01~0.1% of the dry weight of carbide slag. HEDP, as an excellent scale inhibitor and dispersant, can effectively prevent calcium and magnesium ions from forming scale on the surface of subsequent equipment and help improve the crystal morphology.
[0014] (2) Oxidative coprecipitation
[0015] In step (1), during or after the reaction, an oxidant is added to the system to utilize the oxidation reaction to remove low-valence sulfur ions (S ions) brought in by the carbide slag and raw materials. 2- ) is converted into high-valent sulfur (such as SO4) 2-The generated sulfate ions combine with strontium ions in the system to form slightly soluble strontium sulfate (SrSO4) microcrystals.
[0016] These in-situ generated strontium sulfate microcrystals have a very large specific surface area, which can serve as a carrier to efficiently adsorb and encapsulate colloids and fine impurities such as iron, aluminum, and silicon in the system through co-precipitation.
[0017] After the reaction is complete, solid-liquid separation (such as pressure filtration or centrifugation) is performed to obtain a clear filtrate and a filter residue containing strontium sulfate and adsorbed impurities, thereby achieving deep removal of impurities.
[0018] Preferably, in order to ensure oxidation efficiency and co-precipitation effect, the oxidation reaction temperature is controlled at 80~95℃.
[0019] Preferably, a stepwise pH adjustment strategy is adopted: first, the pH is adjusted to 6.0~6.5, at which point an oxidant is added to carry out an oxidation reaction. This pH environment is conducive to the oxidation and conversion of sulfur ions. After the reaction is completed, the pH is adjusted back to 7.0~7.2. This pH environment is conducive to the coagulation and precipitation of colloidal impurities, further improving the solid-liquid separation effect.
[0020] Regarding the selection of the oxidant, the oxidant is selected from hydrogen peroxide, air, or oxygen-enriched air.
[0021] Hydrogen peroxide is a suitable choice due to its rapid reaction and lack of residue. The preferred amount added is 1.2 to 2.0 times the theoretical amount required for complete oxidation of sulfide ions in the system; excess oxidant ensures a thorough reaction.
[0022] (3) Crystallization in a high-calcium background
[0023] The filtrate obtained in step (2) is sent to an evaporation system for evaporation and concentration. The key to this step is to utilize the "common ion effect" (i.e., salting-out effect). As water evaporates, the concentration of calcium chloride in the solution gradually increases. Since calcium ions and strontium ions are both alkaline earth metals and calcium chloride has extremely high solubility, the high concentration of calcium chloride will significantly reduce the solubility of strontium chloride, forcing strontium chloride to fully precipitate out in crystal form, while calcium chloride and other easily soluble impurities remain in the mother liquor.
[0024] The specific control method is as follows: maintain the concentration of calcium chloride in the mother liquor at the end of evaporation within a predetermined range until a large amount of strontium chloride crystals precipitate out.
[0025] Preferably, the "predetermined range" refers to maintaining the mass fraction of calcium chloride in the mother liquor at the endpoint of evaporation and crystallization between 15% and 25%. Within this concentration range, the crystallization yield of strontium chloride is high, and it is less likely to carry calcium impurities, achieving a balance between high yield and high purity.
[0026] Preferably, to save energy and reduce consumption, the evaporation and concentration process adopts mechanical vapor recompression (MVR) evaporation technology. MVR technology uses a compressor to compress and heat the secondary vapor generated by evaporation and then use it as a heat source for recycling. Compared with traditional multi-effect evaporation, it can significantly reduce energy consumption, and its mild evaporation environment is conducive to the cultivation of high-quality crystals.
[0027] Preferably, to improve crystal quality, an ultrasonic field with a frequency of 20-40 kHz is applied to the system during the evaporation crystallization process. The cavitation effect of ultrasound helps to break up crystal nuclei agglomeration, promotes uniform crystal growth, reduces mother liquor encapsulation, and improves product purity.
[0028] (4) Displacement washing and separation
[0029] The strontium chloride crystals precipitated in step (3) are separated using equipment such as centrifuges. In order to wash away the calcium-rich mother liquor adhering to the crystal surface and avoid crystal dissolution and loss, a saturated strontium chloride solution is used as the washing liquid to replace and wash the crystals, and finally wet strontium chloride product is obtained, which is then dried to become the finished product.
[0030] The washing liquid can be an externally prepared pure saturated strontium chloride solution, or it can be a clean mother liquor generated from subsequent production processes (such as a recrystallization process for producing electronic-grade products), thereby realizing the recycling of water resources.
[0031] The filtrate generated from the replacement washing (containing the washed-off calcium impurities) is returned to the evaporation system in step (3) for recycling, or periodically discharged through an open circuit according to the accumulation of impurities, in order to ensure the balance of impurities in the system.
[0032] Compared with the prior art, the present invention has the following beneficial effects:
[0033] This invention innovatively introduces calcium carbide slag, an industrial waste, as a neutralizing agent, replacing traditional liquid alkali or recycled strontium carbonate powder. Calcium carbide slag is not only extremely inexpensive (usually only transportation costs are involved), but also rich in calcium hydroxide, effectively neutralizing residual acid in the acid hydrolysis solution. This approach not only solves the environmental disposal problem of calcium carbide slag but also significantly reduces the raw material cost in strontium chloride production, realizing the green chemical industry concept of "treating waste with waste and turning waste into treasure."
[0034] This invention does not simply use carbide slag as a neutralizing agent, but creatively develops an "oxidative co-precipitation" impurity removal process by utilizing its high sulfur ion content. By adding an oxidant, the sulfur ions released from the carbide slag are converted in situ into sulfate ions, which combine with strontium ions in the solution to generate highly active strontium sulfate microcrystals. These in-situ generated microcrystals have a large specific surface area and high adsorption activity, enabling them to efficiently adsorb and remove trace impurities such as colloidal iron, aluminum, and silicon that are difficult to remove from the co-precipitation system. Compared to adding external flocculants, this "in-situ self-generated" purification method removes impurities more thoroughly and does not require the introduction of external organic polymer impurities.
[0035] Traditional strontium chloride production typically requires a complex calcium removal process, resulting in significant strontium loss and high energy consumption. This invention takes a different approach, utilizing the abundant calcium ions introduced by carbide slag to create a "high-concentration calcium chloride background" during the evaporation stage. By controlling the calcium chloride concentration in the mother liquor at 15-25%, the solubility of strontium chloride is significantly reduced through the common ion effect (salting-out effect), forcing more complete crystallization. This not only avoids the high costs of deep calcium removal but also significantly improves the single-pass crystallization yield of strontium chloride and reduces the amount of mother liquor recycled.
[0036] To address the challenges of high impurities in carbide slag and the tendency for scaling in high-calcium systems, this invention introduces HEDP and ultrasonic fields, playing a crucial "bridging" role: In the upstream oxidation stage, HEDP acts as a "stabilizer," preferentially chelating trace amounts of transition metal ions such as iron and manganese introduced by the carbide slag, effectively inhibiting the catalytic decomposition of hydrogen peroxide by these ions, ensuring that the oxidant focuses on the conversion of sulfur ions, thus making the low-cost "carbide slag-hydrogen peroxide" impurity removal route controllable in engineering; In the mid-to-downstream crystallization stage, HEDP and ultrasound work synergistically: HEDP utilizes the threshold effect to prevent scaling of high-calcium mother liquor on the MVR pipe wall, while ultrasound utilizes the cavitation effect to break up crystal nuclei agglomeration. The combination of the two eliminates mother liquor encapsulation, enabling the growth of uniformly sized, crystal-clear, high-purity strontium chloride crystals even under high viscosity and high salt conditions.
[0037] This invention employs MVR (Mechanical Vapor Recompression) evaporation technology, significantly reducing steam consumption during the evaporation process. Simultaneously, the filtrate after replacement washing is returned to the evaporation system, and the washing liquid is either externally supplied saturated liquid or refined mother liquor. This achieves material balance and water resource recycling within the system, minimizing the discharge of waste gas, wastewater, and solid waste, and meeting the requirements of modern clean chemical production.
[0038] The various steps in this invention exhibit a close synergistic effect, rather than a simple technological superposition. Calcium carbide slag plays a dual crucial role: it is both an inexpensive neutralizing agent and a "seed source" for the impurity removal process (providing sulfur ions to generate strontium sulfate), as well as a "salting-out agent" for the crystallization process (providing calcium ions). Using pure calcium hydroxide would not achieve the impurity removal effect of "in-situ generation of strontium sulfate"; removing calcium ions would prevent the high yield of "salting-out crystallization." As a "dirty raw material," calcium carbide slag inevitably introduces transition metal ions such as iron and manganese, which are typically strong catalysts for hydrogen peroxide decomposition, leading to a sharp drop in oxidation efficiency. HEDP utilizes its superior chelating ability to "in-situ shield" and passivate these metal ions, eliminating their catalytic activity and ensuring that the oxidant acts directionally and efficiently on sulfur impurities rather than ineffectively decomposing them. This allows the invention to achieve precise oxidation control even under extensive conditions without prior deep impurity removal. This invention cleverly utilizes the two elements "calcium" and "sulfur" in carbide slag, which are usually considered burdensome elements, and with the help of additives, transforms them into beneficial factors that improve product quality and yield, thus realizing a closed-loop logic and resource utilization throughout the entire process. Detailed Implementation
[0039] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. Of course, the specific embodiments described herein are only for explaining the invention and are not intended to limit the invention.
[0040] Unless otherwise specified, all chemical reagents and materials in this invention are purchased from the market or synthesized from raw materials purchased from the market.
[0041] A method for producing strontium chloride based on oxidative co-precipitation and salting-out crystallization includes the following steps:
[0042] (1) Strontium carbonate raw material is reacted with hydrochloric acid at a molar ratio of 1:2.0~2.2 to obtain an acid hydrolysate. Calcium carbide slag is added to the acid hydrolysate to adjust the pH value. The amount of calcium carbide slag added is based on adjusting the pH value of the acid hydrolysate to acidic or neutral. Preferably, in step (1), an auxiliary agent, hydroxyethylidene diphosphonic acid or its salt, is also added to the system, and the amount added is 0.01~0.1% of the dry basis mass of the calcium carbide slag.
[0043] (2) During or after step (1), an oxidant is added to the system. The oxidation reaction temperature is controlled at 80-95℃. It is preferable to operate by adjusting the pH value in steps: first, adjust the pH to 6.0-6.5, add the oxidant to carry out the reaction; after the reaction is completed, adjust the pH back to 7.0-7.2. The oxidant is selected from hydrogen peroxide, air or oxygen-enriched air; when hydrogen peroxide is used, the amount added is 1.2-2.0 times the theoretical amount required to completely oxidize the sulfur ions in the system. After the reaction is completed, solid-liquid separation is performed to obtain a clear filtrate and a filter residue containing strontium sulfate and adsorbed impurities.
[0044] (3) The filtrate is fed into an evaporation system for evaporation and concentration. Mechanical vapor recompression (MVR) evaporation is preferred. During evaporation, the concentration of calcium chloride in the mother liquor at the evaporation endpoint is controlled within a predetermined range; specifically, the concentration of calcium chloride in the mother liquor at the evaporation crystallization endpoint is controlled. The mass fraction of strontium chloride is maintained between 15% and 25%, forcing the strontium chloride crystals to fully precipitate under the effect of the common ion. Preferably, during the evaporation and crystallization process, an ultrasonic field with a frequency of 20 to 40 kHz is applied to the system to improve the crystal growth environment.
[0045] (4) Separate the precipitated strontium chloride crystals and wash them using a saturated strontium chloride solution as the washing liquid. The saturated strontium chloride solution can be an externally prepared pure saturated solution or the mother liquor generated in the subsequent recrystallization process. The filtrate after washing is returned to the evaporation system in step (3) for recycling. The washed wet crystals are dried to obtain a high-purity strontium chloride product.
[0046] The present invention will be further described below through specific embodiments.
[0047] Example 1
[0048] A method for producing strontium chloride based on oxidative co-precipitation and salting-out crystallization includes the following steps:
[0049] (1) Acid hydrolysis and neutralization regulation:
[0050] An acid hydrolysate was prepared by reacting industrial strontium carbonate powder with hydrochloric acid at a molar ratio of 1:2.1. In the later stages of the reaction, calcium carbide slag was added to the acid hydrolysate to adjust the pH value. The amount of calcium carbide slag added was sufficient to adjust the pH value of the acid hydrolysate to 6.8. In this step, hydroxyethylidene diphosphonic acid (hydroxyethylidene diphosphonic acid) was also added to the system at a concentration of 0.05% of the dry weight of the calcium carbide slag.
[0051] (2) Oxidative coprecipitation for impurity removal:
[0052] The system was heated to 90℃. A stepwise pH adjustment method was used: first, the pH was adjusted to 6.2, and hydrogen peroxide was added as the oxidant. The amount added was 1.5 times the theoretical amount required for complete oxidation of sulfur ions in the system (the theoretical amount was determined using iodometric titration). After 30 minutes of reaction, the pH was adjusted back to 7.1. After the reaction was complete, pressure filtration was performed to separate the filtrate and the filter residue containing strontium sulfate and adsorbed impurities.
[0053] (3) Salting out crystallization under high calcium background:
[0054] The filtrate was fed into an MVR evaporation system for concentration. During evaporation, the mass fraction of calcium chloride in the mother liquor was maintained at 20% at the end of the evaporation process, utilizing the salting-out effect of high-concentration calcium ions to force strontium chloride crystals to precipitate. An ultrasonic field with a frequency of 30 kHz was applied to the system during the evaporation and crystallization process.
[0055] (4) Replacement washing and product acquisition:
[0056] The precipitated strontium chloride crystals were separated by centrifugation and washed with a pre-prepared pure strontium chloride saturated solution. The filtrate after washing was returned to the evaporation system in step (3) for recycling. The washed wet crystals were dried to obtain high-purity strontium chloride product.
[0057] Example 2
[0058] A method for producing strontium chloride based on oxidative co-precipitation and salting-out crystallization includes the following steps:
[0059] (1) Acid hydrolysis and neutralization regulation:
[0060] An acid hydrolysate was prepared by reacting industrial strontium carbonate powder with hydrochloric acid at a molar ratio of 1:2.0. Calcium carbide slag was added to adjust the pH to acidic (pH=5.5). Sodium HEDP was then added to the system at a concentration of 0.01% of the dry weight of the calcium carbide slag.
[0061] (2) Oxidative coprecipitation for impurity removal:
[0062] The oxidation reaction temperature was controlled at 80℃. The pH was adjusted to 6.0, and oxygen-enriched air was introduced as an oxidant for bubbling oxidation. After the reaction was completed, the pH was adjusted back to 7.0. Solid-liquid separation was performed after the reaction to obtain the filtrate.
[0063] (3) Salting out crystallization under high calcium background:
[0064] The filtrate was then evaporated and concentrated. The mass fraction of calcium chloride in the mother liquor at the end of evaporation was maintained at 15%. During the evaporation and crystallization process, an ultrasonic field with a frequency of 20 kHz was applied to the system.
[0065] (4) Replacement washing and product acquisition:
[0066] The precipitated strontium chloride crystals were separated and washed with the mother liquor from the subsequent recrystallization process. The washed filtrate was returned to step (3) for recycling. After drying, the strontium chloride product was obtained.
[0067] Example 3
[0068] A method for producing strontium chloride based on oxidative co-precipitation and salting-out crystallization includes the following steps:
[0069] (1) Acid hydrolysis and neutralization regulation:
[0070] An acid hydrolysate was prepared by reacting industrial strontium carbonate powder with hydrochloric acid at a molar ratio of 1:2.2. Calcium carbide slag was added to adjust the pH to neutral (pH=7.0). HEDP was then added to the system at a concentration of 0.1% of the dry weight of the calcium carbide slag.
[0071] (2) Oxidative coprecipitation for impurity removal:
[0072] The oxidation reaction temperature was controlled at 95℃. The pH was adjusted to 6.5, and hydrogen peroxide was added, at a rate of 2.0 times the theoretical amount. After the reaction was completed, the pH was adjusted back to 7.2. Solid-liquid separation was then performed after the reaction was completed.
[0073] (3) Salting out crystallization under high calcium background:
[0074] The filtrate was then evaporated and concentrated. The mass fraction of calcium chloride in the mother liquor at the end of evaporation was maintained at 25% to maximize the salting-out effect. During the evaporation and crystallization process, an ultrasonic field with a frequency of 40 kHz was applied to the system.
[0075] (4) Replacement washing and product acquisition:
[0076] The precipitated strontium chloride crystals were separated, washed with a saturated strontium chloride solution, and dried to obtain the strontium chloride product.
[0077] Example 4
[0078] A method for producing strontium chloride based on oxidative co-precipitation and salting-out crystallization includes the following steps:
[0079] (1) Acid hydrolysis and neutralization regulation:
[0080] Industrial strontium carbonate powder was reacted with hydrochloric acid at a molar ratio of 1:2.05. Calcium carbide slag was added to adjust the pH. HEDP was then added at a concentration of 0.03%.
[0081] (2) Oxidative coprecipitation for impurity removal:
[0082] The oxidation reaction temperature was controlled at 85℃. The pH was adjusted to 6.2, and filtered compressed air was passed through for an extended period to carry out the oxidation; after the reaction was completed, the pH was adjusted back to 7.1. The solid and liquid were separated to obtain the filtrate.
[0083] (3) Salting out crystallization under high calcium background:
[0084] The filtrate was subjected to MVR evaporation. The mass fraction of calcium chloride in the mother liquor at the end of evaporation was maintained at 18%. An ultrasonic field with a frequency of 35 kHz was applied.
[0085] (4) Replacement washing and product acquisition:
[0086] The crystal separation and washing were the same as in Example 1, and strontium chloride product was obtained.
[0087] Comparative Example 1
[0088] A method for producing strontium chloride, differing from Example 1 only in the choice of neutralizing agent, is described below:
[0089] (1) Acid hydrolysis and neutralization regulation:
[0090] Industrial strontium carbonate powder was reacted with hydrochloric acid at a molar ratio of 1:2.1. Analytical grade calcium hydroxide (sulfide-free) was used instead of calcium carbide slag to adjust the pH to 6.8. 0.05% HEDP was added.
[0091] (2) Oxidative coprecipitation for impurity removal:
[0092] The procedure is the same as in Example 1 (although hydrogen peroxide is added, strontium sulfate microcrystals cannot be generated because there are no sulfur ions in the system).
[0093] (3) Salting out crystallization under high calcium background:
[0094] Same as in Example 1, but with the endpoint controlled at 20% calcium chloride in the mother liquor.
[0095] (4) Replacement washing and product acquisition:
[0096] Same as Example 1.
[0097] Comparative Example 2
[0098] A method for producing strontium chloride, which differs from Example 1 in that calcium ions are removed, is described in the following steps:
[0099] (1) Acid hydrolysis and neutralization regulation:
[0100] Same as in Example 1, but using carbide slag for neutralization.
[0101] (2) Oxidative coprecipitation for impurity removal:
[0102] Same as in Example 1, perform oxidation to remove impurities.
[0103] (3) Ordinary crystallization under low calcium background:
[0104] Before evaporation, sufficient strontium carbonate powder is added to the filtrate to precipitate calcium ions in the solution as calcium carbonate. The solution is then filtered before evaporation. Evaporation is continued until strontium chloride precipitates, at which point the calcium chloride content in the mother liquor is extremely low (<1%). Ultrasonic treatment is not applied.
[0105] (4) Replacement washing and product acquisition:
[0106] Same as Example 1.
[0107] Comparative Example 3
[0108] A method for producing strontium chloride, differing from Example 1 in that no oxidation treatment is performed, is described below:
[0109] (1) Acid hydrolysis and neutralization regulation:
[0110] Same as in Example 1, but using carbide slag for neutralization.
[0111] (2) Solid-liquid separation (non-oxidation):
[0112] Without adding an oxidant, the pH is adjusted stepwise, and solid-liquid separation is performed after the neutralization reaction is completed to obtain the filtrate.
[0113] (3) Salting out crystallization under high calcium background:
[0114] Same as in Example 1, but with the endpoint controlled at 20% calcium chloride in the mother liquor.
[0115] (4) Replacement washing and product acquisition:
[0116] Same as Example 1.
[0117] Comparative Example 4
[0118] A method for producing strontium chloride, differing from Example 1 in that it does not include the HEDP additive, is described below:
[0119] (1) Acid hydrolysis and neutralization regulation:
[0120] Same as in Example 1, using carbide slag for neutralization, but without the addition of HEDP additive.
[0121] (2) Oxidative coprecipitation for impurity removal:
[0122] Same as Example 1.
[0123] (3) Salting out crystallization under high calcium background:
[0124] Evaporation was carried out in the same manner as in Example 1, with the final mother liquor containing 20% calcium chloride.
[0125] (4) Replacement washing and product acquisition:
[0126] Same as Example 1.
[0127] The following comparison of Examples 1-4 with Comparative Examples 1-4 in terms of product purity, impurity content, crystallization yield, and appearance indicators verifies the creative contribution and technical advantages of "in-situ oxidation and co-precipitation of carbide slag," "high calcium background salting-out effect," and "synergistic effect of additives and ultrasound" to the strontium chloride production process in this invention.
[0128] I. Experimental Design
[0129] Raw materials were standardized: all examples and comparative examples used the same batch of industrial-grade strontium carbonate (SrCO3 content 97.5%) and the same batch of industrial by-product hydrochloric acid.
[0130] Specifications of calcium carbide slag: The calcium carbide slag used in Examples 2-4 was taken from the same acetylene plant in the same chemical industrial park. Testing showed its solid content was 15%, and the filtrate contained sulfur ions (S...). 2- The content is approximately 200 ppm.
[0131] Consistent equipment: All experiments were conducted in identical 5L jacketed glass reactors and matching small MVR simulated evaporation devices.
[0132] II. Detection Indicators and Methods
[0133] Strontium chloride purity (%): determined by EDTA volumetric method.
[0134] Single-pass crystallization yield (%): The calculation formula is (mass of Sr in precipitated crystals / total mass of Sr in raw materials) × 100%.
[0135] Iron content (Fe, ppm): determined by o-phenanthroline spectrophotometry (to characterize the impurity removal effect).
[0136] Sulfide content: tested using qualitative olfactory identification and lead acetate test paper (to characterize the completeness of oxidation).
[0137] Whiteness: Measured using a whiteness meter (characterizing appearance quality).
[0138] Scaling condition: Visually inspect the wall of the evaporator heating tubes for scale buildup.
[0139] Table 1 Comparative experimental test results of different embodiments
[0140] Group SrCl2 purity (%) Single-pass crystallization yield (%) Iron content (Fe, ppm) White (WG) Sulfides / Odor Scaling Remark Example 1 99.82 92.5 <2 94.5 Not detected / odorless No scaling Best overall effect Example 2 99.65 88.4 <3 92.8 Not detected / odorless No scaling Lowest cost Example 3 99.78 93.1 <2 93.5 Not detected / odorless slight Highest yield Example 4 99.71 90.5 <3 93.0 Not detected / odorless No scaling Air oxidation is feasible Comparative Example 1 99.35 92.0 15.8 86.5 Not detected / odorless No scaling High impurity level Comparative Example 2 99.75 74.2 <3 93.5 Not detected / odorless No scaling The yield plummeted Comparative Example 3 98.40 92.2 12.5 78.0 Detection / Odor No scaling Extremely poor quality Comparative Example 4 99.52 91.8 4.5 90.5 Not detected / odorless Obvious scaling Crystal heterogeneity
[0141] 1. Calcium carbide slag is superior to pure raw materials (Example 1 vs. Comparative Example 1)
[0142] Example 1 (using carbide slag) had a significantly lower iron content (<2 ppm) than Comparative Example 1 (using pure calcium hydroxide, Fe=15.8 ppm) and higher whiteness.
[0143] Although Comparative Example 1 used a purer neutralizing agent, the lack of sulfur ions in the system prevented the in-situ generation of strontium sulfate microcrystals during the oxidation stage, resulting in the loss of the "co-precipitation purification" mechanism and the inability to effectively remove trace amounts of colloidal iron.
[0144] This invention demonstrates that the technical solution of converting sulfur impurities in carbide slag into a decontamination agent has outstanding inventiveness and achieves "using waste to treat impurities".
[0145] 2. The decisive impact of "high calcium background" on yield (Example 1 vs. Comparative Example 2)
[0146] The single-pass crystallization yield of Example 1 was as high as 92.5%, while the yield of Comparative Example 2 (with calcium ions removed) was only 74.2%, a decrease of nearly 18 percentage points.
[0147] In Comparative Example 2, after calcium removal using the traditional process, the lack of common ion effect in the solution resulted in a high solubility of strontium chloride. A large amount of product remained in the mother liquor and could not be precipitated, which not only caused a loss in yield but also increased the energy consumption of mother liquor recycling.
[0148] This demonstrates that retaining a high concentration of calcium chloride for salting-out crystallization is key to improving yield and reducing energy consumption.
[0149] 3. The necessity of the "oxidation step" (Example 1 vs. Comparative Example 3)
[0150] Comparative Example 3 was not oxidized, and the product had extremely low whiteness (78.0, grayish-yellow) and a distinct hydrogen sulfide odor, with a purity of only 98.4%.
[0151] The lack of an oxidation step results in residual sulfur ions in the carbide slag, and impurities are not precipitated.
[0152] The oxidation process is an indispensable bridge in transforming "waste" into "resources".
[0153] 4. Optimizing effect of adjuvants (Example 1 vs. Comparative Example 4)
[0154] Comparative Example 4, without the addition of HEDP, showed two obvious problems: first, there was significant scaling on the evaporator wall; second, the iron content rebounded slightly (4.5 ppm vs <2 ppm) and the crystal whiteness decreased (90.5 vs 94.5).
[0155] The increased iron content in Comparative Example 4 suggests an incomplete oxidation process. This confirms that HEDP acted as an "oxidation stabilizer" in Example 1—it chelated free metal ions in the carbide slag, preventing them from catalytically decomposing hydrogen peroxide, thereby ensuring efficient oxidation and deep removal of colloidal iron.
[0156] In a high-calcium, high-salt system, Example 1 successfully inhibited scale formation by utilizing the threshold effect of HEDP, and combined it with the cavitation effect of ultrasound to break up crystal nuclei agglomeration, reducing mother liquor encapsulation, thereby obtaining whiter and purer crystals.
[0157] This demonstrates that HEDP is not only a scale inhibitor, but also a key additive that breaks down the barriers between "dirty raw materials" and "efficient oxidation," and is crucial for maintaining equipment stability and improving microstructure.
[0158] In summary, the steps of the technical solution of this invention are interconnected, and the experimental data fully demonstrate its synergistic inventiveness in achieving high purity and high yield production with low-cost raw materials.
[0159] 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 producing strontium chloride based on oxidative co-precipitation and salting-out crystallization, characterized in that, Includes the following steps: (1) The strontium carbonate raw material is reacted with hydrochloric acid to prepare an acid hydrolysate, and carbide slag is added to adjust the pH value; (2) Add an oxidant to the system in step (1), and after the oxidation reaction is completed, perform solid-liquid separation to obtain filtrate and filter residue containing strontium sulfate; (3) The filtrate is evaporated and concentrated, and the concentration of calcium chloride in the mother liquor at the end of evaporation is controlled to be maintained within a predetermined range until strontium chloride crystals precipitate. (4) Separate the precipitated strontium chloride crystals and wash them with a saturated strontium chloride solution to obtain the strontium chloride product.
2. The method according to claim 1, characterized in that, In step (1), carbide slag is added to adjust the pH of the acid hydrolysate to acidic or neutral. The amount of carbide slag added is based on adjusting the pH of the acid hydrolysate to a predetermined range.
3. The method according to claim 1, characterized in that, In step (1), the molar ratio of strontium carbonate raw material to hydrochloric acid is 1:2.0~2.
2.
4. The method according to claim 1, characterized in that, In step (1), an additive is also added to the system, which is hydroxyethylidene diphosphonic acid or its salt, and the amount added is 0.01~0.1% of the dry basis mass of carbide slag.
5. The method according to claim 1, characterized in that, In step (2), the oxidation reaction temperature is controlled at 80~95℃, and the pH value is adjusted in two steps: first, the pH is adjusted to 6.0~6.5 and the oxidant is added to carry out the reaction. After the reaction is completed, the pH is adjusted back to 7.0~7.
2.
6. The method according to claim 1, characterized in that, In step (2), the oxidant is selected from hydrogen peroxide, air or oxygen-enriched air; when hydrogen peroxide is used, the amount added is 1.2 to 2.0 times the theoretical amount required to completely oxidize the sulfur ions in the system.
7. The method according to claim 1, characterized in that, In step (3), maintaining the concentration of calcium chloride in the mother liquor at the evaporation endpoint within a predetermined range means maintaining the mass fraction of calcium chloride in the mother liquor at the evaporation and crystallization endpoint between 15% and 25%.
8. The method according to claim 1, characterized in that, In step (3), the evaporation and concentration process adopts mechanical vapor recompression evaporation process.
9. The method according to claim 1, characterized in that, In step (3), during the evaporation and crystallization process, an ultrasonic field with a frequency of 20~40kHz is applied to the system.
10. The method according to claim 1, characterized in that, In step (4), the saturated strontium chloride solution is either an externally prepared saturated strontium chloride solution or the mother liquor generated in the subsequent recrystallization process; the filtrate after washing is returned to the evaporation system in step (3) for recycling.