Iron oxide, CAS number: 1332-37-2, molecular formula: Fe2O3, molecular weight: 159.69, EINECS number: 215-570-8
physical properties
Iron oxide is available in both natural and artificial forms. The natural one is called west red, which is basically pure iron oxide and is a red powder. Due to different production methods and operating conditions, their crystal structures and physical properties are very different, and their colors vary from orange to blue to violet. The covering power and tinting power are great. Density 5-5.25. It has excellent light resistance and high temperature resistance, and is resistant to atmospheric influences, pollutant gases and all alkali. It will only gradually dissolve if heated in concentrated acid.
Basic performance
Appearance: Orange-red to purple-red trigonal crystal powder. There are two types of iron oxide: natural and synthetic. The natural one is called western red, with a relative density of 55.25. Fineness 0.4~20um. Melting point 1565 (decomposition). Oxygen is released during burning and can be reduced to iron by hydrogen and carbon oxide. Insoluble in water, soluble in hydrochloric acid and sulfuric acid, slightly soluble in nitric acid and enzymes. Iron oxide has excellent light resistance, high temperature resistance, acid resistance, alkali resistance, and rust resistance. It has good dispersion, strong tinting and hiding power, and no oil or water permeability. Non-toxic. The maximum allowable concentration in the air is 5mg/m³.
Iron oxide is the second largest inorganic pigment after titanium white and the largest colored inorganic pigment. Iron oxide pigments mainly refer to four types of coloring pigments: iron oxide red, iron yellow, iron black and iron brown, which are based on iron oxides. Among them, iron oxide red is the main one (accounting for about 50% of iron oxide pigments) , mica iron oxide used as anti-rust pigments and magnetic iron oxide used as magnetic recording materials also belong to the category of iron oxide pigments.
The main purpose
In the building materials industry, iron oxide is mainly used in colored cement, colored cement floor tiles, colored cement tiles, imitation glazed tiles, concrete floor tiles, colored mortar, colored asphalt, terrazzo, mosaic tiles, artificial marble and wall painting, etc.; used in various coatings Coloring and protective substances, including water-based interior and exterior wall coatings, powder coatings, etc.; can also be used for oil-based paints including epoxy, alkyd, amino and other primers and topcoats; can also be used for toy paints, decorative paints,function and can replace expensive red paint to save non-ferrous metals.
Application
Used for coloring plastic products, such as thermosetting plastics and thermoplastic plastics, and rubber products, such as car inner tubes, aircraft inner tubes, bicycle inner tubes, etc. Used for high-grade fine grinding materials, used for polishing precision hardware instruments, optical glass, etc. High purity is the main base material for powder metallurgy and is used to smelt various magnetic alloys and other high-grade alloy steels. It is obtained by mixing ferrous sulfate or iron oxide yellow or scrap iron and calcining it at high temperature, or it is made directly from the liquid medium.
Manufacturing method
It can be divided into two categories: dry method and wet method.
(1) Wet method
Mixed acid method. The main raw materials are nitric acid, sulfuric acid and iron sheets, the latter being leftovers from industrial processing of iron sheets or scrap iron chips after machine tool processing. The production process is divided into two steps: seed crystal preparation and iron salt oxidation. The seed crystal is produced by the reaction of nitric acid and iron sheet.
The ferric oxide suspension (Fe2O3·nH2O) with an indefinite amount of crystal water is orange-red and is used as a seed crystal for the production of iron red. In the presence of seed crystals, add ferrous nitrate solution and scrap iron sheets, and blow in air for oxidation. At this time, Fe2+ in the ferrous nitrate solution is oxidized by oxygen in the air into iron oxide, which is deposited on the seed crystal. At the same time, the generated nitric acid reacts with the iron sheet to generate ferrous nitrate, in which Fe2+ is oxidized again, and so on. The iron oxide particles continue to grow, and the color changes from light to dark. When the desired color is reached, the oxidation process can be terminated. During the oxidation process, when the material liquid reaches the hair gel stage, ferrous sulfate solution can be added to supplement Fe2+. After the oxidation is completed, the finished product is obtained through sieving, filtering, rinsing, and drying.
a. Preparation of ferrous nitrate: The iron sheet is pretreated to remove oil stains, impurities, etc., then placed in the reaction barrel ① (full), and water is added to a certain level (approximately 1/2 volume of the container). Dilute 96% nitric acid with water at a ratio of 1:2 to about 32%, and slowly add it to the reaction barrel. The reaction temperature should not exceed 60°C. In order to prevent local overheating and cause decomposition of nitric acid, a pump should be used to circulate the material and liquid during the reaction to make the temperature of the material and liquid uniform and reduce the temperature. The reaction endpoint pH=3~4, the ferrous nitrate content is about 15%, and then the clarification bucket is sent to standby.
b. Preparation of ferrous sulfate: Fill the reaction barrel ② with iron sheets, add water, and then slowly add 98% concentrated sulfuric acid. m (water): m (concentrated sulfuric acid) = 4:1. When the reaction stops, steam is heated to 95°C to allow the remaining acid to continue reacting until pH = 4~6. The FeSO4·7H2O content reaches 500 g/L. Move in Set aside the clarification bucket.
c. Preparation of seed crystal: first put water in the seed crystal bucket, add steam to heat it, and at the same time put in the loosened iron sheet (full bucket), add 32% nitric acid, V (dilute nitric acid): V (water) ≈ 1: 6. About 2/3 of the nitric acid is slowly added within 3 hours. The reaction temperature is 90~95°C. The temperature change should not be too large to avoid aging of the seed crystal, deterioration of active performance, low yield and high unit consumption during oxidation. When cooling to 87°C, add the remaining 1/3 of the acid at a faster rate. After the reaction slows down (about 20 minutes later), continue to add the remaining acid. The total acid addition time is about 3.5 hours. When the reaction proceeds to pH = 2-3, the seed crystals obtained are orange-red slurry in color and do not precipitate within 8 hours.
Add the seed crystal and the prepared ferrous nitrate into the oxidation barrel at the same time (the barrel is filled with iron sheets). The amount of seed crystal liquid added is about 1/3 of the effective volume of the oxidation barrel, and the amount of ferrous nitrate solution added is about the effective volume. 1/4 of the barrel, the content of ferrous nitrate in the barrel is about 0.3% to 4%. After feeding, vent steam and air at the same time to keep the oxidation temperature at 80-85°C. When the temperature rises to 80°C, the content of ferrous nitrate measured should be 3% to 4%. If it is insufficient, it needs to be added. After oxidation for 48 hours, the content of ferrous nitrate in the feed liquid is about 0.3%, and the feed liquid has reached the gel stage. Ferrous sulfate should be added immediately to dissolve (FeSO4·7H2O content is 50%), and the ferrous sulfate in the feed liquid should be measured. The iron content is about 4% to 5%. Continue the oxidation for about 30 hours to control the ferrous iron content to 1%. During this period, the evaporated water should be added frequently to maintain a certain liquid level (about 20 cm from the mouth of the barrel). After 90 hours of oxidation, start taking samples to check the color light, once every 4 hours, until the color light is close to the standard, then discharge the material. When the color light is close to the standard and the ferrous iron in the material liquid is about 0.5%, add a small amount of 15% ferrous nitrate solution to prepare for discharging until the ferrous solution is exhausted. The concentration of ferrous iron [including Fe(NO3)2 and FeSO4] must be strictly controlled during the oxidation process, and Fe2+ is not allowed to be depleted during the reaction, otherwise the color will be dark. During the oxidation process, as much air as possible is introduced to ensure that the particles in the reaction barrel do not precipitate and the reaction is sufficient. The slurry discharged from the oxidation barrel should be sieved through a screen to remove unreacted iron filings, etc., and then rinsed and filtered. The filter cake should be dried at 150 to 200°C and crushed into finished products.
2)Sulfuric acid-ferrous sulfate method.
Use sulfuric acid and iron sheets (or iron filings) to prepare ferrous sulfate, or use industrial by-product ferrous sulfate crystals as raw materials to produce iron red by wet methods. The main processes are seed crystal preparation and oxidation process.
a. Seed crystal preparation: Use ferrous sulfate and sodium hydroxide to react to produce ferrous hydroxide precipitate, which is oxidized by air under alkaline conditions to ferric hydroxide, which is a reddish-brown colloidal suspension and is used as a precursor to produce iron oxide red. seed crystal.
If the concentration of the ferrous sulfate solution is too high or the oxidation time is long, the seed crystals will be thin and the crystal grains will be large, and a colloidal solution will not be formed. Generally, a 50-60 g/L FeSO4·7H2O solution is prepared with a pH of 2-3 and placed in a seed bucket. Add about 5% sodium hydroxide solution under stirring. The molar ratio of sodium hydroxide to ferrous sulfate is generally between 2 and 1.1, and keep the amount of residual alkali in the mother liquor at 0.3 to 0.5 g/L, and the pH at 9 ~12 range. Neither too small nor too high pH can form iron red seed crystals. Blow air at normal temperature. Only when the air volume is sufficient can you obtain colloidal reddish-brown seeds that are not easy to settle. Iron black is easily generated when the air volume is insufficient. The air consumption in general factories is around 0.7 m3/min. The reaction temperature for seed crystal oxidation is preferably between 10 and 20°C. If the temperature exceeds 40°C, even with appropriate pH and air volume, the seed crystal will turn black (become Fe3O4) and lose its carrier function. In order to improve the stability of the seed crystal and improve the color of iron red, an accelerator for crystal form conversion can be added to the seed crystal preparation solution to change the crystal lattice and narrow the particle size distribution, thus making the color pure. Commonly used accelerators include calcium carbonate, magnesium sulfate, phosphate, etc. Currently, more factories use phosphate. At normal temperature, the seed crystal is prepared in about 1 to 2 hours, and then moved into the oxidation barrel.
b. Oxidation process: At this stage, ferrous sulfate is oxidized into ferric salt, which is hydrolyzed and then dehydrated into Fe 2O3 to precipitate on the surface of the seed crystal, causing the crystal to grow. As the particles continue to grow, the color will gradually turn brighter and darker. At the same time, the sulfuric acid generated during hydrolysis reacts with the iron to form FeSO4, which is then oxidized into ferric salts and hydrolyzed.
Fill the oxidation barrel with iron sheets (or iron filings). The iron sheets should be loosened and impurities removed, and they are processing waste of low carbon steel. Add ferrous sulfate solution, the ferrous iron content is 50-70 g/L. The crystal seed liquid is neutralized with dilute sulfuric acid to a slightly acidic pH of about 6, and then added to the oxidation barrel. If the amount of seed crystals is too small and the iron red formation speed is too fast, the unit output will be low, the consumption of raw materials will increase, the color and light will progress quickly, and the quality will be difficult to control. If the amount of seed crystals is too much and the iron red formation speed is slow, the unit output will be higher and the raw material consumption will be less. However, the slurry will be too thick in the later stage of oxidation, which will hinder the oxidation process and affect the progress of the color light. Generally, the amount of seed crystal added is about 1/4 of the effective volume of the oxidation barrel. The oxidation temperature should be maintained at 80 to 85°C. If the oxidation temperature is high, the iron red matures quickly, the yield is low, and the color is purple; if the oxidation temperature is low, the oxidation time is long and the color is not bright. If the air volume is large, the reaction will be more complete, the unit output will be higher, and the color will be more pure. Therefore, the air volume should be increased as much as possible during the oxidation process, and the gas must not be stopped. After the color light reaches a level similar to that of the standard sample, the oxidation is stopped, and the finished product is obtained after sieving, rinsing, filtering, and drying at 150 to 200°C.
(2) Dry method
There are mainly the thermal decomposition method of iron yellow powder, the thermal decomposition method of ferrous sulfate and the ferrous sulfate-soda ash method.
1) Thermal decomposition method of iron yellow powder. The dried iron yellow powder is calcined in a calcining furnace (rotary furnace) at 500 to 600°C for about 40 to 60 minutes to obtain brown iron oxide red. After cooling and sieving, the finished product is obtained.
2) Ferrous sulfate thermal decomposition method. The ferrous sulfate is dehydrated, oxidized and calcined in a rotary kiln or muffle furnace at a high temperature of 700 to 800°C to generate iron oxide. The soluble matter is removed by washing with water, and then filtered, dried, crushed and sieved to obtain the finished iron red product. .
3) Ferrous sulfate-soda ash method. Ferrous sulfate reacts with sodium carbonate at high temperature to produce iron red and mirabilite.
Mix sodium carbonate and ferrous sulfate according to n (Na2CO3): n (FeSO4·7H2O) = 1:1.25, grind them into fine pieces and put them into the roasting furnace. The roasting temperature is 700°C (Na2CO3 is easy to decompose if the temperature is too high). The roasted material is leached with water at room temperature to dissolve Na2SO4. Then it is filtered (the filter cake can be washed with 2 mol/L H2SO first to remove residual Na2CO3), then washed with water, and dried at 150~200°C to obtain the iron red product. Or after the filtrate is evaporated and concentrated, NaSO4·10H2O is obtained.
(3) Raw material consumption quota,
Producing 1 ton of product consumes approximately:
product analysis
(1)Determination of Fe2O3 content
1) Potassium dichromate solution determination method: Accurately weigh 0.2 to 0.3 g of the dried sample (accurate to 0.0002 g), place it in a 500 mL Erlenmeyer flask, add 30 mL of 1:1 hydrochloric acid, and heat to completely dissolve it. , and continue to heat to a slight boil; then add 20% stannous chloride solution dropwise until the color of the liquid just turns colorless, then add 1 more drop; add 20 mL of distilled water, and cool to room temperature. Add 10 mL of 2% mercuric chloride solution, shake for 3 seconds, add 20 mL of sulfuric acid, phosphoric acid mixed acid [V (sulfuric acid): V (phosphoric acid): V (distilled water) = 150: 150: 700] and diphenylamine sulfonic acid Add 5 to 7 drops of sodium indicator solution (0.5% aqueous solution), and titrate with potassium dichromate standard solution until the purple color remains unchanged for 30 s, which is the end point.
Measurement tools: 4# ink-adjusting oil (made from linseed oil), tracing paper, scraper (length 178 mm, width 7-18 mm), glass plate, syringe.
Use a balance with an accuracy of one thousandth to accurately weigh 1 g each of the sample and standard sample, and place them on a clean glass plate respectively. Use a syringe to extract 0.8 mL of ink-adjusting oil (or 0.6 g), use a scraper to carefully blend the sample and oil, and then use a scraper to scrape it into a uniform ink slurry until no fine particles exist. Then use the same method to mix the standard sample into ink paste. Use a scraper to pick a small amount of the standard sample and the product ink paste, and apply them on the tracing paper. The distance between the two is about 1 cm. Use a scraper to scrape them off evenly and scatter them toward the north in the room. Compare the differences in color under light. The grading of color and light differences is: approximate, slightly, slightly, and relatively.
Toxicity protection, storage and transportation: non-dangerous goods. Store in a dry place to prevent moisture. Isolate from acid and alkaline items.
