Magnesium Chloride

Product Overview

Magnesium chloride is commercially available in two main categories: anhydrous magnesium chloride and hexahydrate magnesium chloride. The hexahydrate form, commonly known as "halogen tablets" or "halogen granules," serves as a bulk, fundamental inorganic salt raw material for magnesium-based applications. Hexahydrate magnesium chloride appears as white or faintly yellowish sheets or granular crystals; anhydrous magnesium chloride is presented as white, porous granules or a powder. These products are odorless and have a bitter taste; they possess an extremely strong hygroscopic and deliquescent property, making them the salt variety with the most pronounced deliquescence among common salts – when exposed to air, they rapidly absorb moisture and dissolve into a liquid solution.

Magnesium chloride is highly soluble in water, with the dissolution process being highly exothermic; its aqueous solution is weakly acidic. It is slightly soluble in ethanol but insoluble in most organic solvents. It possesses excellent properties-including coagulation and setting, gelation and hardening, freezing point depression, promoting coagulation and precipitation, and complexation with metal ions-while also exerting a certain corrosive effect on metals. Based on purity, impurity content, and intended application, it is classified into several standardized grades and is widely used in industries such as building material curing, road deicing, agriculture, food additives, water treatment, and metallurgy; it is a highly versatile industrial raw material for magnesium salts.

underlying parameter

production engineering

Depending on the application scenario and the manufacturing process employed, the methods for preparing magnesium chloride are like different keys-each unlocking a unique gateway into the field of magnesium chloride production.

Magnesium oxide–hydrochloric acid reaction method: Add a certain amount of magnesium oxide slowly into a reaction vessel containing hydrochloric acid, stirring continuously during the addition. The reaction equation is MgO + 2HCl → MgCl₂ + H₂O. During this process, the concentration of the hydrochloric acid and the addition rate must be precisely controlled; if the acid concentration is too high, the reaction will be too vigorous, potentially causing the solution to splash; if the addition rate is too fast, the reaction may not proceed fully. Additionally, the reaction temperature should be monitored carefully-excessively high temperatures can not only accelerate the volatilization of the hydrochloric acid but also adversely affect the purity of the product.

Magnesium carbonate–hydrochloric acid reaction method: Gradually add magnesium carbonate to hydrochloric acid; the reaction is: MgCO₃ + 2HCl → MgCl₂ + H₂O + CO₂↑. During the procedure, monitor the release of carbon dioxide gas and ensure the reaction is carried out in a well-ventilated environment. After the reaction is complete, filter the solution to remove any unreacted impurities.

Magnesium–chlorine gas reaction method: Under heating conditions, magnesium is allowed to come into full contact with chlorine gas to undergo the reaction Mg + Cl₂ → MgCl₂. However, this method imposes stringent requirements on the experimental apparatus; the apparatus must be tightly sealed to prevent any leakage of chlorine gas.

Magnesium sulfate–barium chloride reaction method: Mix magnesium sulfate solution and barium chloride solution in a specific ratio; the reaction is MgSO₄ + BaCl₂ → MgCl₂ + BaSO₄↓. During mixing, stir thoroughly to ensure complete reaction. After the reaction is complete, remove the barium sulfate precipitate by filtration to obtain a magnesium chloride solution. Note that barium chloride is a toxic substance; therefore, handle it with care during the procedure to avoid contact or inhalation.

Magnesite reaction with hydrochloric acid method: First, crush the magnesite to increase the reaction contact area. Then, add the crushed magnesite to hydrochloric acid; the reaction is: MgCO₃ + 2HCl → MgCl₂ + H₂O + CO₂↑. During the reaction, stir continuously to ensure thorough reaction completion. Additionally, since a large amount of carbon dioxide gas is produced, the reaction vessel should have sufficient volume to prevent gas buildup and excessive pressure. After the reaction is complete, filter the solution to remove any unreacted impurities.

Seawater extraction method: To extract magnesium chloride from seawater, lime milk is first added to the seawater to convert magnesium ions into magnesium hydroxide precipitate; the reaction equation is Mg²⁺ + 2OH⁻ → Mg(OH)₂↓. The magnesium hydroxide precipitate is then filtered out and dissolved in hydrochloric acid; the reaction is Mg(OH)₂ + 2HCl → MgCl₂ + 2H₂O. This process is relatively complex and involves multiple steps, each requiring strict control of the reaction conditions. For example, the amount of lime milk added must be precisely calibrated: too much will introduce excess impurities, while too little will result in incomplete precipitation of magnesium ions.

Magnesium–hydrogen chloride gas reaction method: Under heating conditions, allow magnesium powder to come into full contact with hydrogen chloride gas to initiate the reaction Mg + 2HCl → MgCl₂ + H₂↑. During the experiment, ensure that the reaction apparatus is tightly sealed to prevent any leakage of hydrogen chloride gas; simultaneously, carefully control the heating temperature to avoid an overly vigorous reaction.

Hydrated magnesium chloride dehydration method: Heating hydrated magnesium chloride (MgCl₂·6H₂O) under dehydration conditions yields magnesium chloride. Place the hydrated magnesium chloride into a heating apparatus and gradually increase the temperature. However, this process is not straightforward-direct heating can trigger hydrolysis, leading to the formation of impurities such as magnesium oxide. Therefore, the material should be heated in an atmosphere of hydrogen chloride gas to suppress the hydrolysis reaction. The chemical equation is: MgCl₂·6H₂O → MgCl₂ + 6H₂O (under hydrogen chloride gas atmosphere, upon heating). During the operation, the heating temperature and the flow rate of hydrogen chloride gas must be precisely controlled. If the temperature is too high, the magnesium chloride may decompose; if the flow rate is insufficient, the hydrolysis reaction will not be effectively suppressed.

Garnierite separation method: Garnierite (KCl·MgCl₂·6H₂O) contains magnesium chloride. The garnierite is first dissolved in hot water, and then the components are separated based on the differences in their solubility at different temperatures. As the temperature decreases, potassium chloride crystallizes out first; the remaining solution primarily consists of magnesium chloride solution. Subsequent steps-such as evaporation and concentration followed by cooling and crystallization-are then performed to obtain magnesium chloride crystals. During this process, it is essential to precisely control both the temperature variations and the crystallization time; otherwise, the separation efficiency may be compromised.

Magnesium alloy waste recycling method: The magnesium alloy waste is subjected to pretreatment to remove surface impurities. It is then dissolved in hydrochloric acid according to the reaction equation: Mg + 2HCl → MgCl₂ + H₂↑. The solution may also contain other metal ions; therefore, a series of purification steps-such as adding specific reagents to precipitate these other metal ions-are required to obtain a relatively pure magnesium chloride solution. In this method, the pretreatment and purification steps of the waste are crucial, as they directly determine the purity of the final product.

Magnesium chloride ore acid leaching method: The magnesium chloride ore is crushed and then soaked in hydrochloric acid to allow the magnesium element in the ore to dissolve into the solution as magnesium chloride. During the acid leaching process, the solution should be stirred to enhance the leaching efficiency. Additionally, impurities present in the ore may affect the purity of the magnesium chloride; therefore, subsequent purification steps are required.

Product Grade

The core difference between magnesium chloride standards primarily lies in two dimensions: chemical composition and physical properties. For food-grade magnesium chloride, the minimum content (expressed as MgCl₂) must be ≥ 98.0%, whereas for industrial-grade standards, the minimum content for premium-grade products is only required to be ≥ 47.0% (hexahydrate). This distinction arises from the differing requirements of the respective application scenarios: food additives demand higher purity to ensure safety, while industrial applications place greater emphasis on cost-effectiveness.

Food-grade magnesium chloride

The stringent hygiene requirements specified in food-grade standards ensure the safe use of this material in food processing applications, such as as a tofu coagulant or a nutritional fortifier. Practical experience has shown that tofu prepared using magnesium chloride solutions (commonly known as brine) that comply with the GB25584-2010 standard exhibits superior protein coagulation performance compared to products made using the gypsum coagulation process; furthermore, the yield of the final product can be increased by 8–12%, and the flavor compounds are better preserved.

Industrial-grade magnesium chloride

The graded design based on industrial-grade standards meets diverse industrial requirements. Premium-grade magnesium chloride (MgCl₂ ≥ 47%) is primarily used in the production of high-end magnesium cement; its stringent impurity control ensures that the flexural strength of building materials exceeds 15 MPa. First-grade magnesium chloride is suitable for the manufacture of de-icing agents; compared to sodium chloride, its ice-point depression efficacy at –35°C reduces its corrosiveness to metals by 60%. Qualified-grade magnesium chloride is commonly employed in applications where high purity is not strictly required, such as wastewater treatment. Notably, the industrial magnesium chloride standard specifically defines the "magnesium-to-calcium ratio" parameter, which plays a decisive role in controlling the slag volume in electrolytic cells within the metallurgical industry.

Upstream and downstream industrial chains

Magnesium chloride serves as a core raw material for magnesium salts, featuring a well-defined and comprehensive industrial chain with clear division of labor. The upstream supply chain utilizes magnesium-rich brine from salt lakes, magnesium oxide, magnesium hydroxide, industrial hydrochloric acid, purified water, and refined additives; the downstream applications span a wide range of sectors, including the building materials industry, road maintenance, food processing, environmental water treatment, metallurgical and chemical industries, and flame-retardant materials.

Upstream raw materials: by-product brine from salt lake extraction, magnesium oxide, magnesium hydroxide, industrial grade hydrochloric acid, purified water, impurity removal and sedimentation reagents, recrystallization aids

Downstream product categories: magnesia-based building material curing agents, snow-melting and anti-freezing raw materials, soybean product coagulation aids, water treatment descaling and sedimentation agents, metallurgical magnesium salt intermediates, refractory materials, textile and paper manufacturing auxiliaries

Safety, Storage and Transportation – Basic Information

Magnesium chloride is an ordinary inorganic salt raw material; it is non-flammable, non-explosive, and not highly toxic, and does not fall under the category of hazardous chemicals; therefore, it should be stored and transported as general cargo. The product exhibits strong deliquescence; both its powder form and aqueous solution can cause mild irritation to the skin, eyes, and respiratory tract mucosa. Under high-temperature conditions, slight deliquescence may occur, releasing irritating hydrogen chloride gas; it also exerts a mild corrosive effect on ordinary steel materials.

Storage Specifications: The product must be stored in a dry, cool, well-ventilated, and clean dedicated warehouse; it shall be packaged in fully sealed containers with strict isolation from air and moisture; open-air storage or exposure to rain or humidity is strictly prohibited; humidity levels in the warehouse shall be strictly controlled to minimize air convection; the product shall be stored in separate designated zones; mixing with strong alkalis, carbonates, or oxidizing agents is strictly prohibited to prevent chemical reactions or degradation; the product shall be stored away from ordinary carbon steel equipment to minimize the risk of corrosion contact.

Transportation Specifications: Comply with standard transportation regulations for general chemical goods; implement comprehensive protective measures throughout the entire transport journey to prevent rain, moisture, damage, and excessive sun exposure; ensure that packaging remains intact and tightly sealed to prevent air leakage or moisture ingress; strictly prohibit the mixed transport of alkaline materials, toxic or odorous substances, or corrosive goods to prevent cross-contamination and chemical reactions.

Safety precautions: The substance remains stable in a sealed environment at ambient temperature; powder dust or high-concentration solutions may irritate mucous membranes; exposure to high temperatures may lead to hydrolysis, generating irritating fumes. During handling, wear a dust mask, safety goggles, and protective gloves; ensure proper ventilation at the work site; in the event of skin or eye contact, rinse immediately with plenty of running water. Proper storage and transportation, along with compliant use, pose no significant safety risks.

FAQ

Q: How should one choose between magnesium chloride hexahydrate and anhydrous magnesium chloride? What is the key difference between them?

A: Both products contain magnesium chloride as their core component; however, their differences lie in the amount of water of crystallization, magnesium content, deliquescence intensity, and application scenarios. Anhydrous magnesium chloride boasts a high magnesium content and exhibits strong deliquescence properties, making it suitable for applications requiring high magnesium concentrations, dehydration systems, or precision industrial environments; hexahydrate magnesium chloride offers high cost-effectiveness, relatively controllable deliquescence, and resistance to excessive liquefaction, making it the preferred choice for building materials, snow melting applications, and conventional additive scenarios – suitable for the vast majority of general industrial applications.

Q: Magnesium chloride is highly deliquescent; how can storage losses be effectively controlled?

A: Magnesium chloride is the salt with the most pronounced deliquescence property; in high-humidity environments, it absorbs moisture rapidly and liquefies. Key control measures: maintain the storage facility in a dry, well-ventilated condition with strict humidity control; ensure all product packaging is fully sealed and undamaged; avoid storing products outdoors or handling them during rainy or snowy weather; minimize frequent opening of storage doors for ventilation; prioritize using granular forms over powdered forms, as this can significantly reduce the rate of deliquescence and minimize product loss.

Q: What are the key differences and precautions between industrial-grade and food-grade magnesium chloride?

A: The two products share identical chemical compositions; their primary distinction lies in the precision of impurity control and their respective compliance certifications. The industrial-grade version focuses on basic impurity control and is suitable for various industrial manufacturing applications but is not intended for use in food production; the food-grade version undergoes deep purification, stringent heavy metal control, and sterile purification processes, holds valid food safety compliance certifications, and is permitted solely for use in food processing scenarios permitted by regulatory authorities. Its use in industrial or agricultural applications is strictly prohibited to mitigate safety risks.