Zinc sulfate: full analysis of characteristics, preparation and multiple applications

Zinc sulfate (Zinc sulfate) is an important sulfate compound of the zinc element with the chemical formula ZnSO₄. As a widely used inorganic chemical raw material, it has both natural existence and artificial synthetic properties. It can be divided into anhydrous zinc sulfate (Zn) according to the crystal water content. SO₄) and crystalline hydrates, of which zinc sulfate heptahydrate (ZnSO₄·7H₂O), commonly known as "a vitriol", is the most common form in industrial production and daily life. The two complement each other in properties and application scenarios, supporting production activities in many fields.
1. Core psychological properties

1. Physical properties

Anhydrous zinc sulfate is a white powdery solid with an orthorhombic crystal structure, a density of 3.54 g/cm³, and a melting point of about 680°C. It will decompose at high temperatures; zinc sulfate heptahydrate is a colorless and transparent prismatic crystal, odorless, slightly astringent, and has a density of 1.957 g/cm³, melting point 100°C. When heated to 30°C, it begins to lose crystal water and gradually converts into zinc sulfate monohydrate. If it continues to be heated to 280°C, it can be completely dehydrated to form anhydrous zinc sulfate. Zinc sulfate is easily soluble in water, and its solubility increases significantly as the temperature increases. It is slightly soluble in ethanol and glycerol, but insoluble in acetone. Its aqueous solution is weakly acidic. This solubility characteristic provides convenience for its preparation and application.

2. Chemical properties

Zinc sulfate has relatively stable chemical properties and is not easily decomposed under normal temperatures and pressures. It has the typical chemical properties of sulfate. First, it can undergo a metathesis reaction with soluble barium salts to generate barium sulfate precipitate that is insoluble in water and acid. This is a classic reaction for testing sulfate ions. The equation is as follows:

$${\displaystyle {\ce {{ZnSO4}+{BaCl2}\rightarrow {BaSO4\downarrow }+{ZnCl2}}}}$$

Secondly, it can react with alkali solution to form zinc hydroxide precipitate. If the alkali is excessive, the precipitate will further dissolve to form zincate; thirdly, it can react with sulfide to form black zinc sulfide precipitate. This reaction is often used for the separation and purification of zinc ions. In addition, zinc sulfate has certain reducing properties and can undergo oxidation reactions under the action of strong oxidants. At the same time, its aqueous solution can undergo a displacement reaction with metallic zinc to adjust the concentration of zinc ions in the solution.

2. Preparation process

The preparation of zinc sulfate is mainly based on artificial synthesis, with natural extraction accounting for only a small proportion. Industrial production is mostly based on zinc-containing raw materials, and products of different purity are obtained through acid leaching, purification, crystallization and other processes. The core process is adapted to various raw material endowments.

1. Natural extraction

Natural zinc sulfate mainly exists in ores, hot spring water and salt lakes. By evaporating, concentrating, and cooling crystallization of zinc-containing mineral springs, crude zinc sulfate heptahydrate can be obtained. After further purification to remove impurities, it can be used in low-purity demand scenarios. However, due to limitations in the distribution of natural resources, this method is difficult to meet large-scale industrial needs and is only applied in a few resource-rich areas.

2. Artificial synthesis method

Roasting and leaching method: This is the mainstream process in the industry. It uses zinc concentrate (the main component is zinc sulfide) as raw material. The zinc concentrate is first roasted in the air to convert zinc sulfide into zinc oxide. At the same time, the sulfur element is removed to generate sulfur dioxide (which can be recycled to prepare sulfuric acid). After the roasted product is crushed, it is leached with dilute sulfuric acid to obtain a crude zinc sulfate solution. Subsequently, impurities such as copper and cadmium are removed through oxidation and zinc powder replacement. The purified refined solution is evaporated, concentrated, cooled and crystallized. After separation and drying, the finished product of zinc sulfate heptahydrate is obtained. If anhydrous zinc sulfate needs to be prepared, the crystallized product can be further dehydrated at high temperature. The core reaction equation is as follows:

$${\displaystyle {\ce {{2ZnS}+{3O2}\;\xrightarrow {\triangle } \;{2ZnO}+{2SO2\uparrow }}}}$$

$${\displaystyle {\ce {{ZnO}+{H2SO4}\rightarrow {ZnSO4}+{H2O}}}}$$

Scrap zinc material recycling method: Use scrap zinc plates, zinc slag, zinc alloy scraps and other renewable resources as raw materials, directly leaching with dilute sulfuric acid, controlling the reaction temperature and pH value, fully dissolving zinc to generate zinc sulfate solution, and removing iron, aluminum and other impurities in the raw materials at the same time. After purification and crystallization, the product is obtained. This method has both environmental protection and economic benefits, and is in line with the "dual carbon" strategy. The proportion of recycled zinc raw materials is increasing year by year.

Other methods: In laboratories and small-scale production, zinc sulfate can be prepared through the direct neutralization reaction of zinc oxide, zinc hydroxide and sulfuric acid. The reaction conditions are mild and the product purity is high. It is suitable for the production of reagent-grade zinc sulfate. The neutralization reaction equation is:

$${\displaystyle {\ce {{Zn(OH)2}+{H2SO4}\rightarrow {ZnSO4}+{2H2O}}}}$$

3. Main application areas

Zinc sulfate plays a key role in agriculture, medicine, chemical industry, electroplating and other fields due to its solubility, stability and physiological activity of zinc element. Products with different purity correspond to differentiated demand scenarios, and their application coverage is wider than zinc carbonate.

1. Agriculture

Zinc sulfate is an important trace element zinc fertilizer in agricultural production. It can effectively supplement the zinc required for crop growth, promote photosynthesis, enhance crop stress resistance (cold resistance, disease resistance), improve crop quality, and increase yield. It is suitable for various crops such as rice, corn, wheat, fruit trees, vegetables, etc. It can be used as base fertilizer, top dressing, or made into foliar fertilizer for spraying. It is especially suitable for promotion and application in zinc-deficient soil. At the same time, zinc sulfate can also be used as a feed additive to supplement the zinc nutrition of livestock, poultry, and aquatic animals, promote growth and development, and improve the body's immunity and feed utilization.

2. Pharmaceutical and daily chemical fields

In the field of medicine, zinc sulfate heptahydrate has astringent, antiseptic, emetic and other effects. It can be used to prepare external drugs to treat skin diseases such as eczema, prickly heat, dermatitis, etc. It can also be used as a component of ophthalmic rinses to relieve eye inflammation. However, it should be noted that zinc sulfate is toxic when taken orally. Excessive intake can cause poisoning symptoms such as vomiting and diarrhea, and the dosage needs to be strictly controlled. In the daily chemical industry, zinc sulfate can be used in products such as talcum powder, conditioner, and skin care products to shrink pores, control oil, and inhibit bacteria. It can also enhance the stability of the product.

3. Chemical industry and new materials field

Zinc sulfate is the core raw material for the preparation of other zinc compounds (such as zinc oxide, zinc carbonate, zinc sulfide, etc.), providing basic support for the zinc chemical industry chain; in the textile industry, it can be used as a mordant to enhance the binding force between dyes and fibers, making dyeing more uniform and lasting; in the field of battery manufacturing, high-purity zinc sulfate can be used to prepare zinc-ion battery electrolytes to help the development of the new energy battery industry; in addition, it can also be used as a catalyst and preservative in organic synthesis, water treatment and other scenarios.

4. Electroplating and metallurgy fields

In the electroplating industry, zinc sulfate is the main electrolyte in the galvanizing process. It is used to prepare electroplating solutions so that zinc ions can be uniformly deposited on the surface of the workpiece to form a dense zinc coating, which plays an anti-corrosion and wear-resistant role. It is widely used in the electroplating processing of hardware, machinery, auto parts and other products. In the metallurgical industry, it can be used for the electrolytic refining of zinc to improve the purity of zinc products. It can also be used as an additive in alloy smelting to improve alloy properties.

4. Industry development status and trends

China is the world's largest zinc sulfate producer, consumer and exporter. In 2024, the country's zinc sulfate production capacity will reach 1.2 million tons, and apparent consumption will exceed 850,000 tons. Among them, the demand in the agricultural field accounts for the highest proportion (about 45%), followed by the chemical industry and electroplating fields. The industry structure shows the characteristics of "regional concentration and distinct echelons". Production capacity is mainly concentrated in Inner Mongolia, Yunnan, Hunan and other places with rich zinc ore resources. Leading companies rely on their raw material advantages and purification technology to occupy a dominant position in the mid-to-high-end market. Small and medium-sized production capacity mostly focuses on low-purity agricultural-grade products.

The current development of the industry is driven by two major factors: First, the advancement of agricultural modernization, and the demand for trace element fertilizers continues to grow, driving the expansion of agricultural-grade zinc sulfate production capacity; second, the increasing demand for high-purity zinc sulfate (purity ≥ 99.9%) in new energy, high-end electroplating and other fields, promoting industry technology upgrades, low-energy consumption, environmentally friendly production processes gradually replace traditional high-pollution processes, and the recycling rate of recycled zinc raw materials has increased to 28%, in line with the concept of green development.

In the future, the zinc sulfate industry will transform towards "high purification, greenness and diversification", focusing on breakthroughs in high-purity product preparation technology, expanding application scenarios in high-end fields such as new energy and biomedicine, while optimizing the industrial chain layout and improving resource recycling efficiency. Enterprises with technical advantages and resource integration capabilities will continue to lead the market.

5. Safe operation and storage

Zinc sulfate has certain irritation. Its powder or aqueous solution can irritate the skin, eyes and respiratory mucosa. It is toxic when taken orally. The NFPA 704 hazard level is 1-0-0. During operation, you need to wear protective clothing, protective glasses and masks, work in a well-ventilated environment, avoid flying dust, and strictly prohibit direct contact with the skin and eyes; if you accidentally come into contact, you need to rinse with plenty of water immediately and seek medical treatment if necessary; those who suffer from oral poisoning need to induce vomiting in time and send them to the hospital for treatment.

When storing, it should be sealed and placed in a dry and ventilated warehouse, away from fire and heat sources, to avoid moisture and clumping. It should also be stored separately from food, medicine, oxidants, and alkaline substances to prevent reactions that affect product quality or cause safety hazards. During transportation, it must be packed and unloaded with care to prevent packaging damage and ensure transportation safety.

In summary, zinc sulfate, as the core intermediate of the zinc chemical industry, has diverse application values ​​in agriculture, industry, medicine, etc. The iteration of its production technology and the expansion of application scenarios will continue to empower the upgrading of related industries, showing broad market prospects in the context of green development and industrial transformation.