Hardness refers to the crushing resistance of activated carbon. The hardness of activated carbon is closely related to its wear resistance, which refers to the ability to resist wear and friction.
These mechanical properties directly affect the performance of activated carbon, such as the thickness of powdered charcoal affects filtration; The particle size distribution of granular carbon affects fluid resistance and pressure drop; Fragmentation affects the service life and waste carbon regeneration.
The determination of the hardness of activated carbon is very important. At present, the hardness testing method is to load a certain mass of activated carbon into a rotating device, sieve it after ball milling, and obtain the sieved mass. Then, compare it with the mass before ball milling to determine the hardness of the sample. However, this method can not simulate the scouring of water, so it is not suitable for hardness measurement of activated carbon in water treatment. Technicians in this field have proposed a hardness measurement device specifically designed for water treatment granular activated carbon. The device simulates the wear of activated carbon caused by water flow erosion by filling the testing chamber with water. However, it can not adjust the hardness of water flow erosion on activated carbon. Moreover, some water treatment activated carbon is also subject to wear by other water treatment substances. Therefore, simply injecting water cannot simulate the actual working environment of activated carbon, which affects the accuracy of measurement results.
Generally, the hardness of activated carbon is required to be greater than 88%, the normal range of iodine value is greater than 800-1200mg/g, the specific surface area is generally required to be greater than 1000m2/g, the moisture requirement is less than 5%, the pH requirement is neutral (because neutrality has little effect on acidity and alkalinity), and a series of other indicators are required.
In activated carbon products, an important specification that affects the adsorption performance of activated carbon is the iodine value. Generally, customers require an iodine value of 1100mg/g when purchasing activated carbon. Once the iodine value is lower than 1100mg/g, or activated carbon with low hardness is no longer chosen. The iodine value of activated carbon is inversely proportional to its hardness, meaning that the higher the iodine value of activated carbon, the lower its hardness. For example, if the iodine value of activated carbon is greater than or equal to 1000, then the hardness of activated carbon is greater than or equal to 97%; If the iodine value of activated carbon is greater than or equal to 950, the hardness of activated carbon is greater than or equal to 95%, and so on.
Activated carbon is made by carbonization. As the iodine value of activated carbon increases, the carbonization time becomes longer, resulting in a lower specific gravity, lighter weight, and larger volume of activated carbon. Therefore, the yield of finished products decreases. That's why activated carbon with higher iodine values is more expensive.
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