Light calcium carbonate is also called precipitated calcium carbonate, referred to as light calcium, with a molecular formula of CaCO3 and a molecular weight of 100.09. Light calcium is to calcine limestone and other raw materials to generate lime (the main component is calcium oxide) and carbon dioxide, then add water to digest the lime to generate lime milk (the main component is calcium hydroxide), and then add carbon dioxide to carbonize the lime milk to generate calcium carbonate precipitation, and finally It is obtained by dehydration, drying and crushing. Or first use sodium carbonate and calcium chloride to perform a metathesis reaction to generate calcium carbonate precipitate, and then dehydrate, dry and pulverize it to obtain it. Since the sedimentation volume of light calcium carbonate (2.4-2.8mL/g) is larger than that of heavy calcium carbonate (1.1-1.4mL/g), it is called light calcium carbonate.
Production technology and methods of light calcium carbonate Properties of light calcium
White powder, tasteless and odorless, with a specific gravity of about 2.71. It decomposes at 825~896.6ºC and has a melting point of 1339ºC. There are two forms: amorphous and crystalline. The crystalline form can be divided into orthorhombic crystal system and hexagonal crystal system, which are columnar or rhombus. Insoluble in water and alcohol. Dissolved in acid, carbon dioxide is released at the same time, showing an exothermic reaction. Also soluble in ammonium chloride solution. It is stable in the air and has slight moisture absorption ability.
Production technology and methods of light calcium carbonate and uses of light calcium
Can be used as filler in industries such as rubber, plastics, papermaking, coatings and inks. It is widely used in organic synthesis, metallurgy, glass and asbestos production. It can also be used as a seeding agent for industrial wastewater, an antacid for gastric and duodenal ulcers, an antidote for acidosis, an SO2 eliminator in SO2-containing waste gas, a dairy feed additive, and an anti-sticking agent for linoleum felts. . It can also be used as raw material for tooth powder, toothpaste and other cosmetics.
Production technology and method of light calcium carbonateProduction technology
From the perspective of foreign production of light calcium carbonate, compared with China, it is more advanced in automation control and environmental protection measures. Foreign light calcium carbonate is mostly used to produce slurry products and is therefore used in the paper industry. Relatively extensive. The relevant foreign process technical indicators are different from our domestic standards. On the whole, they are more suitable for the needs of light calcium carbonate users than our domestic ones.
The production process of light calcium carbonate is mainly divided into two types: intermittent bubbling carbonization process and continuous spray carbonization process.
Production technology and methods of light calcium carbonate 1. Traditional production method of light calcium carbonate
Traditional light CaCO3 production process The traditional production process of light calcium carbonate in the industry uses limestone as raw material. The limestone is calcined at more than 900°C to generate quicklime and release CO2. The production process is: lime satin burning-slaked lime digestion-lime milk carbonization-solid-liquid separation-drying-packaging potassium trifluoroborate.
The main chemical reactions are as follows:
Calcining limestone releases CO2 CaCO3→CaO+CO2 (1)
Lime (calcium oxide) reacts with water to produce hydrated lime CaO+H2O→Ca(OH)2 (2)
CO2 is injected into slaked lime, and the reaction produces light calcium carbonate Ca(OH)2+CO2→CaCO3+H2O (3)
Production technology and methods of light calcium carbonate 2. Production process of light CaCO3 from steel slag
The process of producing light CaCO3 by the acetic acid method of steel slag is as follows: extracting calcium ions from steel slag with acetic acid medium, removing cobalt hexahydroxypentacarbonate from steel slag, removing silicon, dissolving and carbonating reaction of CO2, precipitating and generating pure calcium carbonate, and Filtration separates 4 processes. The main chemical reactions are as follows:
Extraction of steel slag with acetic acid medium:
Ca2+CaSiO3+2CH3COOH → Ca2++2CH3COO-+SiO2+H2O (4)
Alkalizing with NaOH:
Ca(CH3COO)2+2NaOH → 2CH3COONa+Ca(OH)2 (5)
Carbonation reaction:
Ca(OH)2+CO2 → CaCO3+H2O (6)
Production technology and method of light calcium carbonate 3. Preparation of high-quality light calcium carbonate by leaching phosphogypsum calcium residue with nitric acid
Crude Ca(NO3)2 solution: Use an appropriate amount of nitric acid solution to leach phosphogypsum calcium residue, react until no bubbles are generated, filter, remove nitric acid insoluble matter, and obtain a crude Ca(NO3)2 solution containing impurities. Impurities The main components are soluble nitrates such as Fe(NO3)3, Al(NO3)3, Mn(NO3)2, and anions such as SO2-4 and PO3-4.
Refined Ca(NO3)2 solution: Pour NH3 into the crude Ca(NO3)2 solution, adjust the pH value of the solution, and adjust the alkali to remove impurities. At this time, cations such as Al3+, Fe3+, and Mn2+ are generated in the solution. Hydroxide is insoluble, and anions such as SO2-4 and PO3-4 generate calcium salts which are insoluble. Filter these interfering impurities to remove them and obtain a refined Ca(NO3)2 solution. .The relevant chemical reaction equations are:
M2++2OH-→M(OH)2↓(M=Fe, Mn, etc.); Ca2++ SO2-4 →CaSO4↓
M3++3OH-→M(OH)3↓(M=Fe, Al, etc.); 3Ca2++ 2PO3-4 →Ca3(PO4)2↓
Carbonization: Dilute the refined Ca(NO3)2 solution to a certain volume and transfer it to a four-neck flask, control the reaction temperature, and the flow rate of NH3 and CO2 gases.Chemistry. The chemical reaction equation is as follows:
Ca(NO3)2+2NH3+CO2+H2O→CaCO3↓+2NH4NO3
Washing: Filter the precipitate and wash it multiple times until there is no nitrate ion in the filtrate. Drying: Dry the washed precipitate in an oven at 120°C for 2 hours to obtain a light calcium carbonate product.
Production technology and method of light calcium carbonate 4. Preparation of light calcium carbonate by ammonium chloride method
Quick lime reacts with NH4Cl to generate CaCl2 and NH3. Excess quick lime reacts with water to generate Ca(OH)2, and the solution is strongly alkaline. In addition to alkali metal ions, other metal ions such as Mg2+, Fe3+, Mn2+, etc. generate hydroxides and are insoluble. In addition to halogen ions, other anions such as SO2-4.PO3-4 form calcium salts and are insoluble. They and other insoluble impurities can be removed by filtration. The filtrate is carbonized by CO2 to form CaCO3 precipitate, and other soluble impurities can be removed by filtration and washing. The reaction formula is as follows:
CaO+2NH4Cl → CaCl2+2NH3+H2O
CaO+H2O → Ca(OH)2
M2++OH– → M(OH)2 (M=Mg, Fe, Mn, etc.)
M3++OH– → M(OH)3 (M=Fe, Al, etc.)
Ca2++SO2- → 4CaSO4
Ca2++PO3- → 4Ca3(PO4)2
CaCl2+2NH3+CO2+H2O → CaCO3+2NH4Cl
The filtered CaCO3 mother liquor, i.e. NH4Cl solution, can be recycled.
