How to detect the quality of lime calcined in a mixed lime shaft kiln
The calcination of lime in mixed firing lime kilns and vertical kilns has a wide range of applications in various industries, such as construction, metallurgy, chemical engineering, etc. The quality of lime directly affects its effectiveness in these industries, therefore, it is crucial to establish a comprehensive lime quality testing system. This article will provide a detailed introduction to various aspects of quality testing for calcined lime in a mixed firing lime kiln, including physical property testing, chemical property testing, and activity testing.
1、 Physical property detection
Granularity analysis
Sampling method
Collect lime samples from different parts (such as the top, middle, and bottom) and at different times (such as the beginning, middle, and end of the batch) of the mixed fired lime kiln shaft kiln to ensure representativeness of the samples. Use specialized sampling tools, such as sampling shovels or sampling tubes, to collect samples according to the specified amount. For example, for large-scale lime production, the sampling amount should not be less than 5 kilograms per time, and then the samples collected from multiple locations and times should be mixed evenly to form a comprehensive sample for particle size analysis.
test method
The commonly used particle size analysis method is sieving. Pass the lime sample through a series of standard sieves with different pore sizes, arranged in sequence from large to small. For example, standard sieves with apertures of 8mm, 4mm, 2mm, 1mm, 0.5mm, 0.25mm, etc. can be used. Place a certain amount (such as 1000 grams) of lime sample on the top large aperture sieve, and use mechanical vibration or manual shaking to pass the lime particles through the sieve. Weigh the lime particles left on each sieve separately and calculate the proportion of lime particles in different particle size ranges. This method can intuitively reflect the particle size distribution of lime, and the particle size requirements vary for different uses of lime. For example, in the steel metallurgy industry, lime used for steelmaking slag making generally requires a large proportion of particles with a particle size between 2-8mm to ensure the reaction rate and melting effect of lime in the furnace.
Appearance and color observation
Appearance inspection
Directly observing the appearance and shape of lime, normally calcined lime should have a block like structure, regular block shapes, and a relatively flat surface. If there are obvious cracks, holes or irregular shapes on the surface of the lime block and it is severely broken, it may indicate that there are problems during the calcination process, such as uneven temperature or uneven mixing of raw materials.
Color judgment
Color is also an important indicator for judging the quality of lime. High quality blended lime kilns and vertical kilns usually produce white or off white calcined lime. If the color of lime is yellowish, reddish, or black, it may be due to impurities (such as iron, manganese, etc.) in the raw materials or incomplete combustion or excessive calcination during the calcination process. For example, when the raw limestone contains a high amount of iron impurities, the calcined lime may appear pale yellow. Abnormal color of lime may affect its application in industries with high color requirements, such as the production of high-end building decoration materials.
Density measurement
measuring principle
According to Archimedes' principle, the density of lime is calculated by measuring the mass of lime in air and water. Specifically, first weigh a certain mass (such as 500 grams) of lime sample, denoted as m1, then suspend the lime sample with a thin wire and completely immerse it in a container filled with water. Measure the mass of the lime sample in water at this time, denoted as m2. According to the formula: density ρ=m1/(m1- m2) × ρ water (ρ water is the density of water, usually taken as 1g/cm ³), calculate the density of lime.
Quality correlation
The density of lime is related to its internal structure and composition. A high density may indicate the presence of incompletely decomposed limestone particles or impurities inside the lime, while a low density may indicate a loose lime structure, which may be caused by excessive calcination or loose raw material structure. In different application scenarios, there are different requirements for lime density. For example, in the production of lime based refractory materials, lime with moderate density and dense structure is required to ensure the performance of the refractory material.
2、 Chemical property testing
Determination of Calcium Oxide (CaO) Content
Chemical analysis method
The commonly used method is acid titration. Dissolve a certain mass (such as 1 gram) of lime sample in an excess of known concentration (such as 0.5 mol/L) hydrochloric acid solution, and a reaction occurs: CaO+2HCl=CaCl2+H2O. Then titrate excess hydrochloric acid with a known concentration (such as 0.25mol/L) of sodium hydroxide standard solution, and calculate the content of calcium oxide in the lime sample based on the initial amount of hydrochloric acid, the consumption of sodium hydroxide, and the reaction equation.
Another method is complexometric titration. Using disodium ethylenediaminetetraacetic acid (EDTA) as a titrant, under suitable pH conditions (such as pH=12-13), EDTA forms a stable complex with calcium ions. By adding a calcium indicator, the endpoint of titration is when the color of the solution changes from burgundy to pure blue during the titration process. Calculate the content of calcium oxide based on the consumption of EDTA.
Quality significance
The content of calcium oxide is a key indicator for measuring the quality of lime. In most applications, such as the construction and metallurgical industries, it is desirable to have the highest possible content of calcium oxide in lime. For example, in the steelmaking process, lime with high calcium oxide content helps to better remove impurities from the steel and improve its quality. Generally speaking, the calcium oxide content of high-quality blended lime kiln and vertical kiln calcined lime should be above 85%.
Determination of Magnesium Oxide (MgO) Content
Measurement method
Adopt flame atomic absorption spectroscopy or chemical analysis method. In flame atomic absorption spectroscopy, after dissolving the lime sample, the solution is sucked into the atomic absorption spectrometer to measure the absorbance of magnesium ions at a specific wavelength, and the content of magnesium oxide is calculated based on the standard curve. In chemical analysis, the precipitation weight method can be used. After dissolving the lime sample, ammonium dihydrogen phosphate solution is added to precipitate magnesium ions in the form of magnesium ammonium phosphate. After filtration, washing, drying, and weighing, the content of magnesium oxide is calculated based on the mass of the precipitate.
The correlation between influencing factors and applications
Although the content of magnesium oxide in lime is relatively low, it can also affect the performance of lime. In some special applications, such as the production of magnesium refractory materials, lime containing a certain amount of magnesium oxide is required. However, in ordinary building lime, excessive magnesium oxide content may affect the setting time and strength development of lime, and it is generally required to control the magnesium oxide content below 5%.
Determination of impurity content such as silicon dioxide (SiO2), aluminum oxide (Al2O3), and iron oxide (Fe2O3)
Analysis method
For the determination of silicon dioxide content, the weight method can be used. Melt the lime sample with a sodium carbonate borax mixed flux, then dissolve the melt in hydrochloric acid to form a silica precipitate. After filtration, washing, drying, and calcination, weigh and calculate the silica content.
The determination of aluminum oxide and iron oxide content can be carried out using inductively coupled plasma emission spectroscopy (ICP-AES). After dissolving the lime sample, the solution is introduced into an ICP-AES instrument, and the emission intensities of aluminum ions and iron ions are measured at specific wavelengths. The content of aluminum oxide and iron oxide is calculated based on the standard curve.
The impact on the quality of lime
The presence of these impurities can affect the quality and performance of lime. For example, excessive silica content can reduce the activity of lime and affect the reaction efficiency between lime and other substances in the metallurgical industry. Excessive iron oxide content can cause the color of lime to deteriorate, and in some applications that require high purity, such as the production of electronic grade materials, it can affect the quality of the product.
3、 Activity testing
Detection principle
The activity of lime refers to its ability to react with water or acid, which reflects the reactivity of lime. The commonly used method for activity detection is the hydration method. Place a certain mass (such as 50 grams) of lime sample into a container containing a certain amount (such as 2000 milliliters) of water, and stir at a specific temperature (such as 40 ° C) for a certain period of time (such as 10 minutes). Then titrate the reaction solution with hydrochloric acid of known concentration (such as 0.5mol/L), and calculate the activity of lime based on the consumption of hydrochloric acid.
The significance and application correlation of activity level
Activity is an important quality indicator for the calcination of lime in a mixed firing lime kiln shaft kiln. In the metallurgical industry, highly active lime can quickly react with impurities during the steelmaking process, improving steelmaking efficiency and reducing energy consumption. In the construction industry, highly reactive lime reacts quickly in materials such as concrete and mortar, helping to improve the early strength of the material. For example, lime with an activity level between 280-330 can better meet the requirements of steelmaking slag making in steel metallurgy and effectively improve the performance of building materials in construction.
The quality inspection of co fired lime kiln and vertical kiln calcined lime is a multi-faceted system, covering physical properties, chemical properties, and activity testing. By accurately detecting indicators such as particle size, appearance, density, calcium oxide content, magnesium oxide content, impurity content, and activity of lime, the quality of lime can be comprehensively evaluated, ensuring its effective application in various industries such as construction, metallurgy, and chemical engineering. At the same time, continuously improving and optimizing detection methods is of great significance for improving lime quality, meeting the needs of different industries, and promoting the development of related industries.