Loss on Ignition
Loss on Ignition (LOI) is a process widely used in inorganic analytical chemistry and soil science to determine the chemical makeup of minerals and soils. The test is performed by strongly heating a sample of the material at a specified temperature, allowing volatile substances to escape until the mass ceases to change. The LOI process is widely used in various pyroprocessing industries such as cement, refractories, and lime manufacturing, where it determines the loss of mass that the raw materials undergo in the kiln. In this article, we will discuss the theory, procedure, and applications of the LOI process.
Theory of LOI
The LOI process involves heating a sample of the material at a specific temperature until its mass ceases to change. The volatile materials lost during the process are usually hydrates, labile hydroxy-compounds, and carbon dioxide from carbonates. The loss on ignition of a mineral is reported as part of an elemental or oxide analysis. It is a quality test that is commonly carried out for minerals such as iron ore. For example, fly ash's LOI consists of contaminant unburnt fuel. The LOI of the product indicates the extent to which pyroprocessing was incomplete.
Procedure for LOI
The LOI process is implemented to determine the components of the entire soil mass, such as living organisms, water, carbonates, carbon-containing material, and decomposing matter. To perform the LOI test, the researcher takes the mass of the soil sample before the process and places it into a heating device. Depending on the component being investigated, the temperature of the device is set accordingly. The soil sample is kept at this temperature for a set period, after which it is removed, allowed to cool, and then weighed again. The difference in the mass of the sample before and after the LOI treatment represents the mass of the component being analyzed. The typical materials needed to perform the LOI include a high-precision mass balance, a drying oven, a temperature-controlled furnace, preheated crucibles, and soil samples from the location of interest.
Steps for LOI
The steps for performing LOI are as follows:
Weigh the empty crucible that the sample is to be placed in and record its weight in a lab book.
Place the sample in the crucible and weigh the crucible again with the sample in it. The new weight minus the empty crucible weight is the sample's wet weight.
Place the sample in the drying oven or blast furnace as required.
Set the oven or furnace to the desired temperature. If the researcher wants to find the dry weight of the soil, the furnace should be set to 100° Celsius.
Leave the sample in the furnace for the desired length of time. If the researcher wanted to know the sample's dry weight and used a furnace set at 100° Celsius, they would usually leave the furnace on overnight.
Open the oven but back away from it simultaneously since the hot air escaping from the furnace can burn bare skin.
Allow the oven and sample to cool down before removing the sample from the oven.
Weigh the crucible with the sample again. Subtract the empty crucible weight from this new weight, and that is the sample's dry weight.
Applications of LOI
The LOI process is primarily used to determine the levels of water content, carbon levels, the amount of organic matter, and volatile compounds in the soil. It is also widely used in pyroprocessing industries such as cement, refractories, and lime manufacturing. Combustion engineers also use LOI, but at temperatures lower than the cement industry's range.
Safety Measures for LOI
The LOI process involves high temperatures, so safety measures are crucial.