Loss on ignition (LOI) is a test used in inorganic

analytical chemistry Analytical chemistry studies and uses instruments and methods to separate, identify, and quantify matter. In practice, separation, identification or quantification may constitute the entire analysis or be combined with another method. Separati ...

and

soil science Soil science is the study of soil as a natural resource on the surface of the Earth including soil formation, classification and mapping; physical, chemical, biological, and fertility properties of soils; and these properties in relation to th ...

, particularly in the analysis of

mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. ( ...

s and the chemical makeup of soil. It consists of strongly heating ( "igniting") a sample of the material at a specified temperature, allowing volatile substances to escape, until its mass ceases to change. This may be done in air, or in some other reactive or inert atmosphere. The simple test typically consists of placing a few grams of the material in a tared, pre-ignited

crucible A crucible is a ceramic or metal container in which metals or other substances may be melted or subjected to very high temperatures. While crucibles were historically usually made from clay, they can be made from any material that withstands te ...

and determining its mass, placing it in a temperature-controlled

furnace A furnace is a structure in which heat is produced with the help of combustion. Furnace may also refer to: Appliances Buildings * Furnace (central heating): a furnace , or a heater or boiler , used to generate heat for buildings * Boiler, used t ...

for a set time, cooling it in a controlled (e.g. water-free, CO₂-free) atmosphere, and redetermining the mass. The process may be repeated to show that mass-change is complete. A variant of the test in which mass-change is continually monitored as the temperature is changed, is

thermogravimetry Thermogravimetric analysis or thermal gravimetric analysis (TGA) is a method of thermal analysis in which the mass of a sample is measured over time as the temperature changes. This measurement provides information about physical phenomena, such ...

Theory

The loss on ignition is reported as part of an elemental or oxide analysis of a mineral. The volatile materials lost usually consist of "combined water" (

hydrate In chemistry, a hydrate is a substance that contains water or its constituent elements. The chemical state of the water varies widely between different classes of hydrates, some of which were so labeled before their chemical structure was understo ...

s and labile hydroxy-compounds) and

carbon dioxide Carbon dioxide (chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is transpar ...

from carbonates. It may be used as a quality test, commonly carried out for minerals such as

iron ore Iron ores are rocks and minerals from which metallic iron can be economically extracted. The ores are usually rich in iron oxides and vary in color from dark grey, bright yellow, or deep purple to rusty red. The iron is usually found in the fo ...

. For example, the loss on ignition of

fly ash Fly ash, flue ash, coal ash, or pulverised fuel ash (in the UK) plurale tantum: coal combustion residuals (CCRs)is a coal combustion product that is composed of the particulates (fine particles of burned fuel) that are driven out of coal-fired ...

consists of contaminant unburnt fuel. In

pyroprocessing Pyroprocessing (from Greek Πυρος = ''fire'') is a process in which materials are subjected to high temperatures (typically over 800 °C) in order to bring about a chemical or physical change. Pyroprocessing includes such terms as ore-ro ...

industries such as

lime Lime commonly refers to: * Lime (fruit), a green citrus fruit * Lime (material), inorganic materials containing calcium, usually calcium oxide or calcium hydroxide * Lime (color), a color between yellow and green Lime may also refer to: Botany ...

, calcined

bauxite Bauxite is a sedimentary rock with a relatively high aluminium content. It is the world's main source of aluminium and gallium. Bauxite consists mostly of the aluminium minerals gibbsite (Al(OH)3), boehmite (γ-AlO(OH)) and diaspore (α-AlO(O ...

refractories In materials science, a refractory material or refractory is a material that is resistant to Thermal decomposition, decomposition by heat, pressure, or chemical attack, and retains strength and form at high temperatures. Refractories are polycr ...

cement A cement is a binder, a chemical substance used for construction that sets, hardens, and adheres to other materials to bind them together. Cement is seldom used on its own, but rather to bind sand and gravel ( aggregate) together. Cement mix ...

manufacture, the loss on ignition of the raw material is roughly equivalent to the loss in mass that it will undergo in a

kiln A kiln is a thermally insulated chamber, a type of oven, that produces temperatures sufficient to complete some process, such as hardening, drying, or chemical changes. Kilns have been used for millennia to turn objects made from clay int ...

. Similarly, for minerals, the loss on ignition represents the actual material lost during smelting or refining in a furnace or smelter. The loss on ignition of the product indicates the extent to which the pyroprocessing was incomplete.

ASTM ASTM International, formerly known as American Society for Testing and Materials, is an international standards organization that develops and publishes voluntary consensus technical standards for a wide range of materials, products, systems, an ...

tests are defined for limestone and lime and cement among others.

Procedure

Soil Soil, also commonly referred to as earth or dirt, is a mixture of organic matter, minerals, gases, liquids, and organisms that together support life. Some scientific definitions distinguish ''dirt'' from ''soil'' by restricting the former te ...

is composed of living organisms, water, carbonates, carbon containing material, decomposing matter and much more. To determine how much one of these soil components make up the entire soil mass, the LOI procedure is implemented. Initially, the researcher will take the mass of the sample prior to LOI and then place the sample into a heating device. Depending on what the researcher is trying to determine in the soil, the temperature of the device can be set to the corresponding temperature. The soil sample is kept at this temperature for an extended period of time after which it is removed and allowed to cool down before re-weighing the sample. The amount of mass lost after the LOI treatment is equal to the mass of the component the researcher is trying to determine. The typical set of materials needed to use LOI include: a high precision mass balance, a drying oven, temperature controlled furnace, preheated crucibles and soil sample from the location of interest. There are many ways to properly utilize loss on ignition for scientific research. A

soil Soil, also commonly referred to as earth or dirt, is a mixture of organic matter, minerals, gases, liquids, and organisms that together support life. Some scientific definitions distinguish ''dirt'' from ''soil'' by restricting the former te ...

sample left overnight in a drying oven at 100° Celsius would have its water content completely evaporated by morning. This could allow the researchers to determine the amount of water initially in the soil sample and its

porosity Porosity or void fraction is a measure of the void (i.e. "empty") spaces in a material, and is a fraction of the volume of voids over the total volume, between 0 and 1, or as a percentage between 0% and 100%. Strictly speaking, some tests measure ...

by comparing the change in weight of the sample before and after the

evaporation Evaporation is a type of vaporization that occurs on the surface of a liquid as it changes into the gas phase. High concentration of the evaporating substance in the surrounding gas significantly slows down evaporation, such as when humidi ...

. This new weight of the sample is called the dry weight and its previous weight is called the wet weight.

Steps

A general procedure of how to perform a loss on ignition is as follows: # Weigh the empty

that the sample is to be placed in and record its weight in a lab book. # Place the sample in the empty 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 then the furnace would need to be 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 is using a furnace set at 100° Celsius, then the researcher would usually leave the furnace on overnight. # Open the oven but also back away from it at the same time 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.

Application

Typically, this method is used to determine water content levels, carbon levels, amount of organic matter levels, amount of volatile compounds. LOI is also used in the cement industry which operates the furnace in the 950° Celsius range (e.g.

cement kiln Cement kilns are used for the pyroprocessing stage of manufacture of portland and other types of hydraulic cement, in which calcium carbonate reacts with silica-bearing minerals to form a mixture of calcium silicates. Over a billion tonnes of ...

s), combustion engineers also use LOI but at temperatures lower than 950° Celsius range.

Safety

In many research labs, the use of asbestos gloves is required when operating the furnace as it can reach very hot temperatures. The use of face masks is also recommended at higher temperatures to ensure safety of researchers and junior lab members. It is also recommended that researchers performing LOI procedure remove all jewelry and watches as they are great conductors of heat. When removing samples at high temperatures, these accessories can easily heat up and result in burns.

Other Uses

The cement industry uses the LOI method by heating up a cement sample to 900-1000° Celsius, and it is heated until the mass of the sample stabilizes. Once the mass has stabilized the mass lost due to LOI is determined. This is usually done to determine the high water content in the cement or carbonation as these reduce the quality of cement.{{Cite web, url=https://www.pavementinteractive.org/reference-desk/testing/cement-tests/portland-cement-loss-on-ignition/, title=Portland Cement Loss on Ignition, website=Pavement Interactive, language=en-US, access-date=2019-03-17 High losses are usually due to poor storage conditions of cement or manipulation of cement quality by suppliers. This ensures that the cement used in a site is of the correct composition to meet safety protocols and requirements of customers. In the mining industry, the use of LOI is vital in determining moisture and volatile material present in the rock. Hence when performing whole-rock analysis to determine total volatiles the LOI method is used. In order to remove all volatiles and to oxidize all iron into iron oxides, the temperature of the LOI is set to 900-1000° Celsius.

References

Analytical chemistry Cement Concrete Tests in geotechnical laboratories