Comprehensive Utilization of Waste By-products--Comprehensive Utilization of Ferrous Sulfate

Ferrous sulfate, also known as green vitriol, titanium white powder Production of sulfuric acid is the main by-product, depending on the ore source, per ton of titanium dioxide to byproduct ferrous sulfate heptahydrate 2.5 ~ 4t. The comprehensive utilization can turn waste into treasure; the comprehensive utilization is not good, which not only affects the normal production of production, but also a large amount of ferrous sulfate treatment is still a big problem. Because of the large output, low product value and high transportation cost, foreign countries have high production costs. Except for a small amount of comprehensive utilization, most of them are shipped to the deep sea for discharge, or the mountain can be purchased, the bottom is used for long-term landfill after anti-seepage treatment, or acid-soluble titanium slag is used as raw material to reduce or simply not produce by-product ferrous sulfate. . China's sulfuric acid method titanium dioxide factory uses ilmenite as raw material, and each ton of titanium dioxide has a by-product of about 3t of ferrous sulfate heptahydrate. With the continuous increase of titanium dioxide production, the comprehensive utilization of ferrous sulfate is becoming more and more prominent. .

There are many channels for comprehensive utilization of ferrous sulfate. In the US, the consumption of ferrous sulfate (including the by-product of ferrous sulfate in steel plants) is 80% for iron pigments, 8% for fertilizers and feed additives, and 5%. In the water treatment agent, 3% for the catalyst, according to domestic and foreign experience, such as ferrous sulfate can use the following comprehensive utilization route.

(1) Direct sales to users who do not make secondary deep processing

a. For the synthetic ammonia plant as a raw material for the preparation of iron catalyst, the iron catalyst can promote the hydrogen generation of water vapor and carbon monoxide, and can weaken the chemical bond of nitrogen and hydrogen molecules, reduce the reaction activation energy of synthetic ammonia, and enable the reaction to proceed rapidly. Iron is the main component of iron oxide catalyst and chromium acid anhydride, to use the reduction of iron oxide Fe ₃ O _4, iron catalyst which is the main active ingredient.

The iron catalyst is prepared by neutralizing the ferrous sulfate solution with ammonium carbonate (or sodium carbonate) to form an oxide precipitate, boiling it to further grow the crystal, and then filtering, washing, drying and rolling with chromic anhydride. After calcination, cooling and sieving at 300 °C, it is an iron catalyst for ammonia synthesis. The 1t iron catalyst consumes 3.5 tons of ferrous sulfate. The reaction formula is as follows:

FeSO ₄ +Na ₂ CO ₃ →FeCO ₃ ↓+Na ₂ SO ₄

FeCO ₃ →FeO+CO ₂ ↑

4FeO+O ₂ →2Fe ₂ O ₃

FeO+Fe ₂ O ₃ →Fe ₃ O ₄

b. For chemical fertilizer (iron fertilizer) ferrous sulfate as iron fertilizer can be used as base fertilizer, seed fertilizer or root dressing in agriculture, and can also be directly injected into the trunk. Iron fertilizer is one of the trace element fertilizers, which can make plants fully absorb nitrogen and phosphorus , can regulate the redox process in plants, accelerate the decomposition of soil organic matter, and use it to mix with organic fertilizers to prevent plant chlorosis (such as Yellow leaf disease of apple trees). The mixture of ferrous sulfate and lime can prevent rice fever, cotton anthracnose, angular spot disease, etc., and can also prevent insects such as snails and breeding flies. In 1963, Hebei Agricultural Journal introduced 10% ammonium sulfate and 40% sulfuric acid. The compound fertilizer made of ferrous iron and 50% straw ash can increase the yield of corn and spring valley by 14.9%~37.1%. In addition, impregnation of barley and wheat seeds with ferrous sulfate solution can prevent smut and streak, and some flowers also need Ferrous sulfate is used as a fertilizer.

Since ferrous sulfate is an acidic inorganic salt, it can improve the saline-alkali soil with compost made of green manure. In alkaline soil, ferrous iron will gradually oxidize to ferric iron and be fixed by soil. Many parts of northern China belong to calcareous soil. The iron problem is outstanding and it is the area where iron fertilizer is mainly used. Japanese Patent JK-61-252289 was introduced in 80% of FeSO ₄ · 7H ₂ O was mixed with 20% of coal ash, and 0.5 ~ 1h heated at 65 ~ 85 ℃, after removal of the water can be used as soil improver; U.S. Ferrous sulfate is also described as a soil amendment in the patent USP4077794.

c. Industrial water treatment agent Ferrous sulfate itself is a coagulant, which is hydrolyzed into colloidal iron hydroxide in water and coprecipitated with impurities in water. It can replace industrial wastewater treated by alum, such as ferrous sulfate-lime method. The theoretical dosage ratio of wastewater is Cr ⁶⁺ :FeSO ₄ ·7H ₂ O=1:16, and the reaction formula is as follows:

H ₂ Cr ₂ O ₇ +6FeSO ₄ +6H ₂ SO ₄ →Cr ₂ (SO ₄ ) ₃ +3Fe ₂ (SO ₄ ) ₃ +7H ₂ O

Cr ₂ (SO ₄ ) ₃ +3Ca(OH) ₂ →2Cr(OH) ₃ ↓+3CaSO ₄

In addition, it can also be used as a complexing agent for the treatment of cyanide-containing wastewater: cyanide-containing wastewater (30~5000mg/L) is added with ferrous sulfate at pH 4~10, and after removing impurities such as sulfides, ferrous sulfate is added again at pH 6~10. Deacylation complexes to form ferrocyanide, and further complexation can also produce iron blue.

In the coking and printing and dyeing industry, it is also possible to treat organic wastewater from coking plants and sulfurized waste liquid in printing and dyeing plants with ferrous sulfate. In 1984, Shanghai Environmental Science magazine reported that a certain color weaving factory was treated with 10% ferrous sulfate solution. Dyeing waste liquid, the desulfurization rate can reach 95%, and the alkaline waste liquid is reduced from pH14 to neutral.

d. Concrete additives, the former Soviet Union and Poland have studied the addition of 2% to 4% ferrous sulfate in the cement clinker roasting, which can improve the combustion efficiency of heavy oil fractions in the fuel; or use ferrous sulfate together with sodium hydroxide as concrete The composite additive can enhance the strength of the concrete.

e. Feed additive, ferrous sulfate can be used as a trace element (iron) in the feed industry. Most factories in China use the ferrous sulfate heptahydrate for purification, drying and pulverization as a feed additive, but it is best to make a water. After the ferrous sulfate, the ferrous sulfate of one water is not easy to agglomerate when used, and the addition amount and the transportation amount can be reduced. Iron is a component of hemoglobin, myoglobin, cytochrome and various oxidases. Iron also detoxifies the toxin gossypol contained in cottonseed cakes eaten by pigs and chickens. It also prevents pigs from anemia and vitality. Drops, rough hair, loose skin, respiratory urges and other symptoms.

f. Other direct uses, for the manufacture of ferrous gluconate for iron deficiency anemia; refrigerators, toilet deodorants; manufacture of blue and black inks; photoengraving; wood preservatives; additives in foam fire extinguishing agents, printing sensitizers Wait. [next]

(2) used in the manufacture of polymeric ferric sulfate water purifying agent

Polyferric sulfate, also known as iron hydroxysulfate, referred to as polyferric iron (PFS), is a high-efficiency broad-spectrum polymer inorganic flocculant with the molecular formula: Where n is less than 2, m (degree of polymerization) is greater than 10, m = ƒ (n). Commercial poly-iron has two forms of liquid and solid, which was first developed by Japan Nippon Steel Mining Co., Ltd. in 1974 and applied for a patent. (日特昭49-53195), the Tianjin Chemical Industry Research Institute of the former Ministry of Chemical Industry began research in the early 1980s, and in 1984 built the first domestic industrial production plant in Nanjing Oil Chemical Plant. Due to the good coagulation effect of poly-iron, simple process and low price, there are nearly 100 factories in China producing polyferric sulfate (mostly liquid). Some foreign titanium dioxide factories also use ferrous sulfate to prepare polyferric sulfate. For example, Tioxid allows the company to produce polyferric iron by-product ferrous sulfate in its plant in Spain.

Liquid polyferric iron is a homogeneous reddish brown viscous liquid, and solid polyferric iron is a pale yellow to dark yellow powder or solid granule. The relative density of liquid poly-iron is ≥1.45, the freezing point is ≤-13°C, the viscosity at 20°C is 10×10 ^-3 Pa·s (cP), the pH is 0.5~1.0, the alkalinity is 8~1.6, and the ferric content is ≥160g. /L, ferrous iron content ≤ 1g / L.

Polyferric iron has a multi-nuclear complex ion structure or a multi-nuclear hydroxy iron complex, and is an inorganic polymer coagulant having a high cationic charge density. The polyferric iron is hydrolyzed in an aqueous solution to form a large amount of [Fe ₂ (OH) ₃ ] ³⁺ , [Fe ₂ (OH) ₂ ] ⁴⁺ , [Fe ₈ (OH) ₂₀ ] ⁴⁺ and other complex ions to rapidly neutralize the water. The negatively charged colloidal particles bridge between the neutralized or adsorbed particles, collide with each other, entangle the particles to cause the particles to settle and settle down, and have the functions of reducing COD, BOD, decolorization and deodorization, in industrial wastewater and tap water. Especially in the Yangtze River system, the sedimentation speed is fast, the pH range is wide, and it has excellent coagulation effect. Compared with aluminum sulfate and polyaluminium chloride, it is cheaper and has a faster sedimentation rate, and is not only cheaper but also less corrosive than ferric chloride.

There are two main methods for preparing liquid polyferric iron.

a catalytic oxidation method of ferrous sulfate solution mixed with sulfuric acid and a catalyst, (NaNO ₂ , H ₂ O ₂ , MnO, etc.), directly oxidized with oxygen, due to the presence of a catalyst, ferrous sulfate can be oxidized under acidic conditions, The chemical reaction formula is as follows:

2FeSO ₄ +2NaNO ₂ +H ₂ SO ₄ ===2Fe(OH)SO ₄ +Na ₂ SO ₄ +2NO

FeSO ₄ +NO===Fe(NO)SO ₄

2Fe(NO)SO ₄ +0.5O ₂ +H ₂ O===2Fe(OH)SO ₄ +2NO

2NO+0.5O ₂ ===N ₂ O ₃

2NO+O ₂ ===2NO ₂

2FeSO ₄ +N ₂ O ₃ +H ₂ O===2Fe(OH)SO ₄ +2NO

2FeSO ₄ +NO ₂ +H ₂ O===2Fe(OH)SO ₄ +NO

Most of the factories in China adopt this method. This method is simple in process and low in cost. However, because it is a gas-liquid reaction, a long reaction time, and a large amount of catalyst, the NO and NO ₂ generated in the reaction process pollute the environment and need to be treated.

b. Direct oxidation method, direct oxidation method is to directly oxidize the oxidant KC1O ₃ , H ₂ O ₂ , HNO ₃ , HNSO ₄ (nitrosylsulfate) and the ferrous sulfate solution.

The H ₂ O ₂ method is a method in which sulphur ferrous iron and sulfuric acid are mixed and heated to a temperature of 50 ° C, and H ₂ O ₂ is added for oxidation reaction to obtain polyferric iron. However, the method H ₂ O ₂ is expensive and difficult to store. It is inefficient to use. Another method is to first react a ferrous sulfate solution with H ₂ O ₂ to form an oxidizing agent (A), and then use another aqueous solution of ferrous sulfate to a pH of 8 to 9 to form a dark green mother liquor (B). Then, the A and B solutions are mixed and reacted at a normal temperature for 1.5 hours at a certain ratio to obtain a reddish brown polyferric solution.

Since KC1O ₃ is a strong oxidant under acidic conditions, the ferrous sulfate and sulfuric acid are mixed and heated to 40~50 °C during operation, and KC1O ₃ is added for oxidation to obtain poly-iron, but the method is mixed with Cl ^- root. And residual KClO ₃ , can not be used in some areas, and KC1O ₃ is also more expensive.

HNO ₃ method is to mix ferrous sulfate, sulfuric acid and nitric acid in a certain ratio, and oxidize by air at 50~70 °C and 0.1~0.2 MPa, then complete the hydrolysis polymerization at 102~103 °C, and the reaction time is short ( 2h), the concentration of the obtained product is high, but the pressure production and equipment investment are high, and the pollution problems of NO ₂ and NO are also present. [next]

There are several methods for preparing solid polyferric iron.

The ferrous sulfate is heated to 150-400 ° C in a rotary kiln for dehydration, and at the same time, it is oxidized by passing air (it can also directly pass oxygen). After the oxidation is complete, the sulfuric acid is slowly added for acidification polymerization, and then cooled and pulverized. High consumption, unstable quality and serious environmental pollution;

Directly spray-drying with liquid poly-iron, solid-state (powdered) poly-iron from liquid poly-iron. The method has good quality, high total iron content, light color and fast dissolution rate, but high energy consumption and high cost. . It is also possible to concentrate the liquid poly-iron and then smash it after drying;

U.S. Patent No. 4,507,273 describes the heating of a heated bed in a fluidized bed to FeSO ₄ ·5.5H ₂ O, followed by continued dehydration to form FeSO ₄ ·4H ₂ O, and finally converts 80% to 90% of ferrous sulfate at 250 ° C. Iron sulfate is formed, then 96% sulfuric acid is added at 180-200 ° C to produce a product containing 26% ferric iron, 1.69% ferrous iron and 1.87% free sulfuric acid, and the air is cooled in the fluidized bed to room temperature. Discharge, the method is complicated to operate, high energy consumption, and industrial production is rarely used. _

In recent years, the remarkable development of polyferric sulfate is related to organic flocculants such as cationic organic polymer flocculant polydimethyldiallylammonium chloride (CH ₂ =CHCH ₂ ) ₂ N(CH ₃ ) ₂ C1 ^- equivalence, or iron or aluminum composite to form a composite polyferric iron (CN1101896A, CN1110664A, etc.) or sodium phosphate to form polyphosphorus ferric sulfate to improve the use of polyferric iron and reduce corrosion, and Does not lower the pH of the raw water.

(3) Production of a permanent ferrous sulfate

The use of ferrous sulfate monohydrate (FeSO ₄ ·H ₂ O) is similar to that of ferrous sulfate heptahydrate, but the purity and content of ferrous sulfate monohydrate are higher than that of ferrous sulfate heptahydrate, which is not easy to deliquesce agglomerate and is convenient for long-distance transportation and Storage, the application range is wider than ferrous sulfate heptahydrate.

Ferrous sulfate heptahydrate at 56.8 deg.] C dehydration FeSO ₄ · 4H ₂ O, 64 ~ 90 ℃ converted to ferrous sulfate monohydrate (64 ℃ dehydration of _{FeSO 4 · H 2 O, 73} ℃ into a white, 80 ℃ sintering , melting at 90 ° C). A method for preparing ferrous sulfate monohydrate. There are mainly the following.

a. Vacuum drying and dehydration, generally adopting vacuum 干燥 dryer, this method is to make ferrous sulfate under vacuum, low temperature drying and dehydration, good product quality, light appearance, but high energy consumption, low production efficiency, cost Also higher.

b. Direct drying method, generally can be heated and dried in a rotary kiln. In order to prevent oxidation of ferrous sulfate at high temperature, nitrogen gas protection is sometimes required. The ferrous sulfate monohydrate after dehydration and drying needs to be pulverized. Not stable and energy consumption is high.

c. Boiling drying method, Department of Chemistry, Jinan University and Drying Center of Shandong Academy of Sciences, used to use coal-fired hot blast stove as heat source, using continuous multi-chamber single-layer fluidized drying bed to produce feed grade ferrous sulfate monohydrate, which can only National standards can be achieved by one-step drying.

d. Wet production of ferrous sulfate monohydrate From the solubility of ferrous sulfate in water, it can be known that ferrous sulfate monohydrate can be obtained by saturating ferrous sulfate between 64 and 90 °C. The specific operation method is that in the enamel reaction pot, the ferrous sulfate is dissolved in water under stirring, and the temperature is raised to boiling to evaporate and concentrate. When the temperature reaches 102 ° C, it starts to become an off-white suspension, and then the heating is stopped and the centrifugal filtration is stopped. The filter cake is dried and pulverized and packaged. The filtrate was purified may be returned for dissolving ferrous sulfate, the filtrate if heavy metals lead, arsenic exceeded, can be added to the active iron powder, a method of improving the pH removed. The above wet method can also be carried out in concentrated sulfuric acid, and the effect is even better.

(4) Iron pigment

Iron pigment is an important inorganic pigment. It is generally resistant to alkali, light, non-toxic, and inexpensive. It is widely used in coatings, plastics, rubber, construction and other industries. It is the main way to comprehensive utilization of ferrous sulfate. one.

1 Refinement and purification of ferrous sulfate; iron-white powder by-product ferrous sulfate contains oxides or sulfates of Ti, Mn, V, Al, Ca, Mg, etc., and it has been proved that the content of TiO _{2 in} ferrous sulfate exceeds 0.3%. It has a very obvious influence on the hue of iron pigments. Therefore, it must be refined and purified before use. The methods for refining ferrous sulfate are as follows:

a. The former Soviet National Institute of Coatings Research and Design, the ferrous sulfate is beaten in the titanium dioxide hydrolysis waste acid (15% ~ 20%), at this time the ferrous sulfate is still a solid phase, and the impurities in the ferrous sulfate are beaten into In the liquid phase waste acid, the refined and purified ferrous sulfate is obtained by vacuum or centrifugation.

b. Adjust the pH of the ferrous sulfate solution to 0.4~0.5 with sulfuric acid, heat to about 70 °C, add barium chloride solution and boil for 2~3h, then add flocculant (PAM) to make titanyl sulfate in ferrous sulfate. Hydrolyzed into white feather floc, the purification rate of titanium after filtration and separation can reach more than 96%, and the content of TiO _{2 in} ferrous sulfate can be reduced to less than 0.03%.

c. Adding iron powder or iron sheet to the ferrous sulfate solution to reduce the ferric iron into divalent iron. As the pH increases, the hydrolyzed metatitanic acid is gradually precipitated, and then refined by sedimentation. Ferrous sulfate solution.

d. The purified ferrous sulfate solution can also be obtained by adjusting the pH of the ferrous sulfate solution to 4 with an acid or a base to precipitate titanium as a hydroxide, and then removing the titanium hydroxide.

In order to obtain a ferrous sulfate solution having as little impurities as possible, it is preferable to use two of the above purification methods in combination. [next]

2 Preparation of iron oxide red, iron oxide red is the most important one of iron pigments. Preparation of iron oxide red (Fe ₂ O ₃ ) with ferrous sulfate can be divided into dry and wet methods:

Dry method: dry method for producing iron oxide red has spray calcination method, direct calcination method, ferrous sulfate monohydrate plus carbon calcination method, ferrous sulfate monohydrate plus sulfur calcination method, and basic ferric sulfate thermal decomposition method. The easiest way is to first dry and dehydrate the ferrous sulfate to form FeSO ₄ ·H ₂ O, then calcin it at 800 ° C to form crude iron oxide red (Fe ₂ O ₃ ), crush the crude iron oxide red, wash it, Drying and re-grinding are the finished products. The exhaust gas SO ₃ can be recycled for the production of sulfuric acid. The calcination temperature of the method is very important. The temperature is low and the hue has a yellow phase and a high blue phase. The chemical reaction formula is as follows:

The process of reducing the calcination of ferrous sulfate monohydrate with carbon is to first dry and dehydrate FeSO ₄ ·7H ₂ O to form FeSO ₄ ·H ₂ O, and then add carbon (reducing agent such as coke , coal, wood powder, etc.) in one Calcination at 750 ° C in a closed kiln can obtain dry iron oxide red;

The sulfur calcination method is mainly used to thermally decompose partially dehydrated ferrous sulfate by using the heat released by sulfur combustion. The addition of sulfur can increase the concentration of SO ₂ and SO ₃ in the calcined exhaust gas, and is convenient for recovering sulfuric acid;

The basic iron sulphate thermal decomposition method is carried out in a two-layer ebullating bed, first dehydrating ferrous sulphate in the lower layer, and introducing an oxygen-containing gas (oxygen-enriched air) to form basic ferric sulphate (Fe ₂ O ₃ ·nSO ₃ · nH ₂ O), and then blown into the upper boiling bed, using iron oxide as a catalyst to roast and calcine to form iron oxide red, the SO ₃ in the furnace gas is higher, and can be directly absorbed by sulfuric acid to form concentrated sulfuric acid;

Niobium Chemical Co., Ltd. dehydrated ferrous sulfate heptahydrate at 300 ° C to form ferrous sulfate monohydrate, and then oxidized with air at 500 ° C to form Fe ₂ O ₃ ·Fe(SO ₄ ) ₃ , and then at 700-800 ° C The high temperature decomposes into Fe ₂ O ₃ , and after surface treatment, it is made into iron oxide red pigment. The monthly output is nearly 400t, and SO ₃ and SO ₂ in the exhaust gas can be used to produce sulfuric acid. [next]

Wet method: In the industrial production, the wet process is more ammonia neutralization method. The manufacturing process is to first neutralize the ferrous sulfate solution with ammonia, precipitate the ferrous hydroxide, and then pass the air oxidation to make the seed crystal. The seed crystal is added to the ferrous sulfate solution, heated to 80-90 ° C by steam, and simultaneously blown into the air to oxidize, the ferrous hydroxide is oxidized to ferric oxide, precipitated on the seed crystal, and then filtered, It is washed, dried and pulverized to form an iron oxide red pigment, and at the same time, by-produced ammonium sulfate, ammonia can also be recovered by evaporation. However, the oxidation time of this method is too long. The recent new process is to add sodium nitrite during oxidation, and the NO formed by using it as a catalyst can significantly accelerate the oxidation reaction speed. In addition to neutralization with ammonia, it can also be neutralized with a base (NaOH, Na ₂ CO _{3 ,} etc.), but the quality of the ammonia neutralization oxidation method is better, and the chemical reaction formula is as follows:

_{2FeSO 4 + 4NH 4 OH + H} 2 O + 0.5O 2 → Fe 2 O 3 +2 (NH 4) 2 SO 4 + 3H 2 O

2FeSO ₄ +4NaOH+H ₂ O+0.5O ₂ →Fe ₂ O ₃ +2Na ₂ SO ₄ +3H ₂ O

2FeSO ₄ +2Na ₂ CO ₃ +H ₂ O+0.5O ₂ →Fe ₂ O ₃ +2Na ₂ SO ₄ +H ₂ O+CO ₂

In the process of producing iron oxide red by wet method, there is also a yellow a-hydrated iron oxide, which is then calcined at 700-800 ° C to obtain acicular iron oxide red pigment (direct calcination is obtained by spherical iron oxide) Red), the process flow is shown in Figure 2.

In addition, sulfuric acid and sodium chlorate are added to the ferrous sulfate solution for oxidation, and the ferrous sulfate is converted into iron sulfate, and then heated, separated, washed, and dried by adding sodium hydroxide, and 27.5 can be obtained per 100 parts of ferrous sulfate. A- mica iron oxide and 50 parts sodium sulfate (USP 3987156). The iron oxide red produced by different wet methods differs slightly in color depth due to the difference in particle size.

3 Preparation of iron oxide yellow, iron oxide yellow is also one of the iron pigments, the correct name should be a-hydrated iron oxide, the molecular formula Fe ₂ O ₃ ·H ₂ O, is a goethite type, the temperature exceeds 177 ° C The gradual dehydration begins, and finally red iron oxide (iron oxide red) is formed from the yellow a-hydrated iron oxide.

The preparation process of iron oxide yellow is similar to the process of preparing iron oxide red by wet method. First, the ferrous sulfate solution is neutralized with dilute ammonia to form a dark green colloidal ferrous hydroxide, and then oxidized by air to form a seed crystal. The formula is as follows:

FeSO ₄ +2NH ₄ OH→Fe(OH) ₂ +(NH ₄ )aSO ₄

4Fe(OH) ₂ +O ₂ →4FeOOH+2H ₂ O

The second step is to add the seed crystals to the ferrous sulfate solution, add iron filings, heat to 70-75 ° C by steam, and inject air into the oxidation to form a-hydrated iron oxide and sulfuric acid:

4(FeSO ₄ ·7H ₂ O)+O ₂ →2(Fe ₂ O ₃ ·H ₂ O)↓+4H ₂ SO ₄ +22H ₂ O

4H ₂ SO ₄ +4Fe+28H ₂ O→4(FeSO ₄ ·7H ₂ O)+4H ₂ ↑

The sulfuric acid formed in the reaction reacts with the iron filings to form ferrous sulfate, and the ferrous sulfate continues to be oxidized to hydrated iron oxide. The formed hydrated iron oxide precipitates on the seed crystal and gradually grows, from light to deep, until it reaches The standard color, then filtered, washed, dried, and pulverized is the finished product. The key of the process is the neutralization speed of ammonia and the concentration of ferrous sulfate during oxidation. These two points have a significant impact on the quality of the product. , the process flow is shown in Figure 3.

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In addition, the ferrous sulfate solution can be reacted with sodium carbonate to precipitate ferrous carbonate, and then the precipitate is oxidized by air at 20 to 25 ° C, or oxidized with potassium chlorate at 50 to 60 ° C to be oxidized. Iron yellow (Mass Yellow-Fe ₂ O ₃ · nH ₂ O).

4 Preparation of iron blue, iron blue, also known as Hualan [FeNH ₄ Fe (CN) ₆ ], is an inorganic pigment widely used in coatings and inks, can use ferrous sulfate and xanthate (potassium or sodium) The reaction is made.

In the production, the ferrous sulfate is purified by sulfuric acid and iron scraps in advance, the ferric iron in the ferrous iron is reduced to divalent iron, and the purified ferrous sulfate solution is added to the xanthate solution, and the temperature is raised to 90-100. °C, add ammonium sulfate, add sulfuric acid for 2h, then cool to 70 ~ 75 ° C, slowly add potassium chlorate solution for oxidation, heat for 2 ~ 3h to oxidize the ferrous iron into high-priced iron into blue, then filter, wash, add when zinc naphthenate or zinc naphthenate grinding aid to increase its wettability and dispersibility and to prevent fading, followed by drying, pulverizing iron blue after finished. Since iron blue is easy to burn at a high temperature, it is preferably pulverized by a jet mill.

5 Preparation of iron oxide black, iron oxide black can be combined with excess soda ash with water vapor (95 ° C), and then filtered, washed, dried, pulverized, the chemical reaction formula is as follows:

6FeSO ₄ +6Na ₂ CO ₃ +O ₂ →2Fe ₃ O ₄ +6Na ₂ SO ₄ +6CO ₂ ↑

It can also be obtained by dehydration reaction of iron hydroxide and ferrous hydroxide, and the chemical reaction formula is as follows:

2Fe(OH) ₃ +Fe(OH) ₂ →2Fe(OH) ₃ ·Fe(OH) ₂

2Fe(OH) ₃ ·Fe(OH) ₂ →Fe ₃ O ₄ +4H ₂ O

It is also possible to react ferrous sulfate with sodium hydroxide to form ferrous hydroxide, and then dehydrate it at a high temperature to obtain ferrous oxide, and the new ferrous oxide is reacted with ferric oxide (iron oxide red) to form black ferroferric oxide. The raw material ratio at the time of manufacture is: ferrous sulfate: ferric oxide: liquid alkali (30%) = 2.2:1:2.2, first heat the ferrous sulfate solution to about 60 ° C, add ferric oxide, and heat up to Boiling, slowly adding liquid alkali to neutralize to pH 7~8, and then check whether the color light is qualified. The color light can be mastered by adjusting the amount of ferrous sulfate. After the color light reaches the requirement, continue to add the material for the second time according to the above ratio for neutralization reaction. When the reaction is near the end point, ammonium nitrate is added to convert the remaining divalent iron into ferric iron. When the color light reaches the standard, the stirring and discharging are stopped, precipitation, water washing, pressure filtration, and the filter cake is not higher than 100 ° C. Dry, cool, pulverize, and package. The reaction formula is as follows:

FeSO ₄ +2NaOH→Fe(OH) ₂ ↓+Na ₂ SO ₄

Fe(OH) ₂ →FeO+H ₂ O

FeO+Fe ₂ O ₃ →Fe ₃ O ₄

6 transparent iron oxide, transparent iron oxide is red, yellow, brown, black, etc. Among them, transparent iron oxide red and transparent iron oxide yellow pigment are widely used. The method described in <Coating Industry>1997·NO2 is: first use concentrated Sulfuric acid and sodium chlorate oxidize ferrous sulfate, and the chemical reaction formula is as follows:

6FeSO ₄ +NaClO ₃ +3H ₂ SO ₄ →3Fe ₂ (SO ₄ ) ₃ +NaCl

Then, sodium hydroxide is added to the oxidation reaction material to form Fe ₂ (SO ₄ ) ₃ to form colloidal iron hydroxide. The chemical reaction formula is as follows:

Fe ₂ (SO ₄ ) ₃ +6NaOH→2Fe(OH) ₃ +3Na ₂ SO ₄

The iron hydroxide colloid formed by the reaction is an amorphous compound, and crystal form stable a-hydrated iron oxide is formed in the presence of iron filings, and the reaction formula is as follows:

2Fe(OH) ₃ →Fe ₂ O ₃ ·H ₂ O+2H ₂ O

Fe(SO ₄ ) ₃ +4Fe+4H ₂ O→Fe ₂ O ₃ ·H ₂ O+3FeSO ₄ +6[H]

Finally, the surface treatment is carried out with sodium dodecylbenzenesulfonate. After surface treatment, it is flocculated with diphenyl hydrazine, and then washed, filtered, dried and pulverized to obtain a transparent iron oxide yellow pigment.

7 Other iron pigments, further deep processing of the above iron pigments, and other ferric pigments such as iron oxide red, iron oxide black and a small amount of iron oxide yellow, which are mixed and dispersed in a certain ratio, can be used to obtain iron oxide. Brown pigment. Iron oxide brown pigment can also be reacted with ferrous sulfate and aluminum sulfate and sodium carbonate, and the precipitate is calcined at 400 to obtain iron oxide brown;

After mixing and dispersing Hualan (iron blue) and iron oxide yellow in a certain ratio, an iron oxide green pigment can be obtained;

In the preparation of iron oxide red, by controlling the crystal state and particle size of Fe ₂ O ₃ , iron oxide orange and iron oxide purple can be obtained. When the particles are in the form of flakes, the particle size is 0.25 μm to obtain orange Fe ₂ O. ₃ ; When the particles are nucleated, the particle size is 0.75 μm, and purple Fe ₂ O ₃ can be obtained. [next]

(5) Ferrous sulfate is used to produce sulfuric acid

Germany's Kronos and Italy's Montessen Company dehydrated ferrous sulfate at high temperatures to form ferrous sulfate monohydrate, which was then calcined with pyrite to produce sulfuric acid and was put into industrial production. The process is characterized by making full use of the heat of pyrite oxidation, decomposing ferrous sulfate to lower the calcination temperature, increasing the concentration of SO ₂ , and also removing some impurities such as arsenic, containing 28% to 30% of sulfur. Iron ore can be blended with 30% FeSO ₄ ·7H ₂ O. This method has been practiced in some units in China. Similar to the above principle, ferrous sulfate can also be blended into sulfur to produce sulfuric acid.

Britain and the former Soviet Union and after high temperature firing coal with ferrous sulfate dehydration, furnace gas containing _{SO 2 9.2%, SO 3 0.5} %, for the production of sulfuric acid. Japan Ishihara Industry Co., Ltd. produces pyrosulfite by calcining pyrite with ferrous sulfate and petroleum refining residue.

Bayer and Sabinbin's method is to dehydrate ferrous sulfate heptahydrate in 30%~65% concentrated waste acid to form ferrous sulfate monohydrate, and then roast with pyrite to produce sulfuric acid, 30%~ 65% of the concentrated acid is obtained by the preparation of 70% concentrated waste acid from the waste acid concentration workshop and 20% of the waste acid. The advantage of this method is that it can save energy consumption during the dehydration of ferrous sulfate. Concentrated waste acid, and wet decrystallized water is less polluted. The method of preparing sulfuric acid using waste acid and ferrous sulfate as described in U.S. Patent No. 4,163,047 is also of this type.

(6) Manufacturing magnetic iron oxide

Magnetic iron oxide refers to a magnetic Fe ₃ O ₄ black powder, which can be used as photoelectric copying powder, laser inkjet printing ink, audio tape, etc.; the other is γ-Fe ₂ O ₃ red with strong magnetic permeability. Brown powder, mainly used for magnetic recording materials, generally contains cobalt Co-γ-Fe ₂ O ₃ , which is more effective; there is also a high-purity iron oxide for ferrite, which belongs to a-Fe ₂ O ₃ , The main raw material of soft ferrite (70% of its composition). The above three kinds of magnetic iron oxide can be produced by using ferrous sulfate as raw material, and high-purity iron oxide for ferrite is produced in many factories in China. .

The raw material source of ferrite for iron oxide used to be the ferrous sulfate extracted from the waste liquid when the steel plant pickled steel. The famous Ruthner iron oxide is the pickling waste liquid (HCl or H when rolling). ₂ SO ₄ ), first concentrated and then high temperature spray calcination, the ferrous chloride or ferrous sulfate is decomposed at high temperature to form iron oxide (Fe ₂ O ₃ ), and the produced HCl gas and SO ₃ gas can be recycled to produce hydrochloric acid and sulfuric acid. This method has low production cost. Several large steel conglomerates such as Baosteel and Anshan Iron and Steel Co., Ltd. have introduced devices to produce a-Fe ₂ O ₃ by this method.

Japan Ishihara Industry Co., Ltd. first developed the production of iron oxide for ferrite by the production of by-product ferrous sulfate in the production of titanium dioxide. China Metallurgical Minister Sha Mining and Metallurgy Research Institute, Nanjing Oil Chemical Plant and the Third Design Institute of the Ministry of Chemical Industry in 1989 In the year, we established the first pilot plant in China to produce iron oxide iron oxide by the by-product of ferrous sulfate in the titanium dioxide factory. At present, several titanium dioxide factories in China have built this production device, and the product quality is in full compliance. National standards, although the production cost is higher than the Lu's method, this method is a higher value-added product in the comprehensive utilization of ferrous sulfate in the titanium dioxide factory. The production process is as follows.

Since the by-product ferrous sulfate in the production of titanium dioxide contains impurities such as titanium sulfate, the ferrous sulfate solution is first purified and purified, and the refined ferrous sulfate solution is used to prepare the seed crystal. Colloidal iron hydroxide, and then adding the seed crystal to the purified ferrous sulfate solution, introducing air, ammonia, steam into several series of oxidation reactors, and continuously adding ferrous sulfate solution for continuous The oxidation reaction is followed by filtration, washing with water, and calcination, which is iron oxide for ferrite. Since the product has strict requirements on impurities such as SiO ₂ and A1 ₂ O ₃ , the water quality of the washing water is high, and in addition, hydrogencarbonate can be used instead of ammonia for the reaction, and the process flow is shown in FIG. 4 .

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(7) Production of manganese sulfate and manganese carbonate

Manganese sulfate can be produced by reacting ferrous sulfate and hydrolyzed spent acid with pyrolusite. In order to improve the utilization of manganese, the mother liquor can be reacted with ammonium carbonate or ammonium hydrogencarbonate to form manganese carbonate, and the chemical reaction formula is as follows:

MnO ₂ +2FeSO ₄ +2H ₂ SO ₄ →MnSO ₄ +Fe ₂ (SO ₄ ) ₃ +2H ₂ O

MnSO ₄ +(NH ₄ ) ₂ CO ₃ →MnCO ₃ +(NH ₄ )2SO ₄

MnSO ₄ +NH ₄ HCO ₃ +NH ₃ →MnCO ₃ +(NH ₄ ) ₂ SO ₄

During production, pyrolusite powder, spent acid and ferrous sulfate are heated together, and iron scraps are added to reduce Fe ₂ (SO ₄ ) ₃ to FeSO ₄ . Because of the high content of ferric iron in the solution, it cannot be used conventionally. The method of forming iron hydroxide precipitates to remove iron, otherwise the iron hydroxide colloid in the solution makes the filtration of the solution difficult. Generally, the ammonium sulfate is used to remove iron, and the yellow ammonium ferrite precipitate is formed [(NH ₄ ) ₂ Fe ₆ ( SO ₄ ) ₄ (OH) ₁₂ ] was removed, and the filtered solution was adjusted to pH 5.4 with MnCO ₃ , and MnS was added to precipitate a heavy metal ion in the solution to form a poorly soluble primary sulfide.

The solution of the sulfide precipitate is removed by filtration, and in order to prevent hydrolysis thereof, the pH is adjusted to 4.5 by using sulfuric acid, and then concentrated and crystallized to precipitate pink manganese sulfate, and the mother liquor is further reacted with ammonium carbonate or ammonium hydrogencarbonate to prepare manganese carbonate. See Figure 5 for the process flow.

(8) Other comprehensive utilization products

The ferrous sulfate and sodium carbonate are calcined together to produce Glauber's salt (Na ₂ SO ₄ ). The production process is that FeSO ₄ ·7H ₂ O is mixed with Na ₂ CO _{3 and} pulverized at 600 ° C for 1 h, then water immersion. Take and adjust the pH to neutral with sulfuric acid; filtered, concentrated, crystallized to obtain thenardite, Fe ₂ O ₃ in the filtrate can be used to produce iron oxide red, the chemical reaction formula is as follows:

4FeSO ₄ ·7H ₂ O+4Na ₂ CO ₃ +O ₂ →2Fe ₂ O ₃ +4Na ₂ SO ₄ +4CO ₂ +28H ₂ O

After boiling with ferrous sulfate and filtered suspension of magnesium oxide, magnesium sulphate can be obtained.