Natural limestone is mainly composed of CaCO3, bound into solid blocks of gray color or bearing the color of impurities, specific gravity of 2.7 means that 1 cubic meter of rock weighs up to 2.7 tons. is "heavy as a rock". But from that ore people can make a substance that is also it, ie CaCO3, chemical nature like natural CaCO3 but very light, less than 1/6 when it is in the ore, called light calciumcarbonate or powder light. It is a white powder, sparingly soluble in water, but soluble in most acids. CO2-saturated water also significantly dissolves CaCO3 because CaHCO3 is much more soluble than CaCO3. Light powder has many applications. In the pharmaceutical industry, it is used as an excipient for some tablets with high quality requirements.
In industry, people use light powder as an additive to rubber processing, cream soap, toothpaste, mushroom culture medium, cosmetic production, etc. It's so common that almost every industry has it. demand for light powder. Every year, the whole world consumes millions of tons. But producing light powder is only favorable in countries where limestone and coal are available. From this point of view, our country does have an advantage in producing light powder, limestone mountains are not only abundant but also rich in CaCO3, coal is also available. Light powder production technology is relatively simple, with little initial investment, we can actively meet domestic and export demand. Want to produce light powder, people are based on the following principle: for CO2 gas flow. Boiled in lime milk solution, precipitated and collected CaCO3. The main raw materials for making light powder are quicklime and CO2 gas, but lime is revived.
calcined limestone ore. The reaction process from calcination to light powder is:
CaCO3 -> CaO + CO2(ore)
CaO + H2O -> Ca(OH)2
Ca(OH)2 + CO2 -> CaCO3 ( precipitate) + H2O
Thus, the light powder production process can be done at the same time as the lime calcination process.
* Create lime milk: Choose freshly baked lime, all without impurities. I lime into clean water, stir well to puree, soak for 48 hours for a thorough reaction, then take lime milk about 7-8 degrees Bome. Do not add too thick lime milk, the reaction will be long and difficult to convert to CaCO3. Lime milk is too diluted, the efficiency is low and uneconomical. Before putting the lime milk into the reaction tank, the pump is run through the hydraulic cyclonic system to remove all solid particles mixed in the lime milk.
* CO2 absorption: CO2 source can be obtained from lime kiln gas. The burnt lime kiln gas is no longer emitting black smoke. CO2 is collected by sealing the kiln's mouth with a corrugated iron lid with a conical cap for CO2 to pass through the duct into the air filter system with continuous irrigation water upstream. Clean the gas and cool it down before entering the reactor. To facilitate aeration and reaction, the solution in the reaction tank is continuously stirred by a specialized stirrer.
The higher the CO2 concentration in the reaction tank, the better, usually the lime kiln gas with 20-30% CO2 is a satisfactory reaction, if the CO2 is below 15%, the reaction is very long and the product is not good, then it is necessary to Add more coal, stone to the kiln. Check the reaction solution with 1% alcohol phenolphthalein reagent. It is okay to add that the reagent does not appear pink. Remove the reaction solution to the filter tank covered with white canvas to retain the CaCO3 in the form of a paste. It is not
recommended to aerate CO2 for a long time because then CaCO3 is easily converted into CaHCO3 which is soluble in a considerable amount in water.
* Drying: before drying, put the paste into the extractor (centrifuge) to remove the water. After centrifugation, the water content is only about 50%, put the powder on the drying rack directly or dry it with hot air in a rotary kiln. The drying temperature is 110o C, the obtained product has a moisture content of ≤ 0.50%. The dry powder is ground through a hammer mill. Packed in kraft paper (4-5 layers of cement bags), or PE bags Stored in specialized warehouses, dry clean. The quality of light calcium carbonate must meet the following criteria:
+ CaCO3 content ≥ 98%.
+ Alkalinity (calculated as CaO) ≤ 0.15%
+ Humidity ≤ 0.50.
+ Content of insoluble matter in hydrochloric acid (HCl) ≤ 0.25.
+ Fineness through sieve 0.125 φ mm ≥ 98.