ASTM D7348 Standard Test Methods for Loss on Ignition (LOI) of Solid Combustion Residues

The standard "ASTM D7348 Standard Test Methods for Loss on Ignition (LOI) of Solid Combustion Residues," published by the American Society for Testing and Materials (ASTM), describes test methods for determining the mass loss of solid combustion residues when heated to a specified temperature in an air or oxygen atmosphere. Mass loss can result from moisture, carbon, sulfur, and similar losses resulting from the decomposition or combustion of the residues.

Loss on ignition (LOI) refers to the mass loss that occurs when a combustion residue is heated to high temperatures in an atmosphere of air or oxygen. In the cement industry, the term LOI typically refers to the mass loss in a sample heated to 950°C. For combustion engineers, the term LOI typically refers to the mass loss in samples heated to temperatures below 950°C.

These test methods establish a procedure for determining the LOI values ​​of combustion residues heated to 750 or 950 degrees Celsius. The LOI values ​​obtained from these test methods can be used by industries that use combustion residues in a variety of processes and products. If solid combustion residue is heated to estimate the amount of combustible or unburned carbon in the sample, it has been shown that the LOI and unburned carbon estimate do not agree completely, and the LOI should not be used as an estimate of unburned carbon in all combustion residues. Direct determination of unburned (combustible) carbon can be accomplished using ASTM D6316.

If solid combustion residue is heated to prepare ash for determination of mass fractions of major and minor elements, the heating procedure described in ASTM D3682, ASTM D4326, and ASTM D6349 or the procedures for determining 750-degree LOI (Method A) described herein are used. If solid combustion residue is heated to prepare ash for determination of mass fractions of trace elements, the heating procedure described in ASTM D3683 and ASTM D6357 is used.

In industries where combustion processes are central, such as cement production, coal-fired power generation, and waste incineration, understanding the composition of residual materials is crucial for efficiency, emissions control, and regulatory compliance. Solid combustion residues, such as fly ash, bottom ash, or clinker, often contain volatile components that affect material properties and environmental impact. ASTM D7348 is designed to quantify these components. This standard provides precise protocols for determining the mass loss of these residues when heated under controlled conditions, providing information on moisture, carbon, sulfur, and other volatile substances.

ASTM D7348 describes two basic procedures that provide flexibility depending on the sample type and required resolution. Both involve precision weighing, muffle furnace heating, and post-ignition mass measurement, but the ignition conditions vary to accommodate varying residual volatilities:

• Procedure A: Standard LOI at 950 degrees
  • Setup: 1-5 g of ground residue sample (passed through a No. 50 sieve) is placed in a preheated platinum or ceramic crucible.
  • Heating protocol: Raise the temperature to 950 degrees in air at a rate of 20 degrees/min, hold for 20-60 minutes until constant mass is reached, then cool in a desiccator.
  • Calculation: LOI (percentage) = ((Initial kmass - Final mass) / Initial kmass) x 100.
  • Features: Ideal for cement kiln residues or fly ash, where 950°C simulates clinker formation temperatures and determines the amount of organic carbon or sulphate. It is the most common method in compliance with cement industry standards.
• Procedure B: High temperature LOI in oxygen
  • Setup: Similar sample preparation, but using an oxygen-enriched atmosphere (e.g., 100 percent O at 50 mL/min)₂ flow).
  • Heating protocol: Ignite at 750-1000 degrees for 30 minutes, aiming for complete oxidation of resistant carbons.
  • Calculation: Same as Procedure A except for optional corrections for ash fusion.
  • Features: Suitable for high carbon residues such as boiler ashes and accelerates oxidation for faster results. Useful where air ignition would lead to incomplete combustion.

In cement production, low LOI ensures high-quality clinker with minimal free lime, reducing energy costs by up to 5%. In power plants, it monitors the carbon content of fly ash, affecting its reuse in concrete and compliance with carbon emission limits.

• Cement and lime industries: Measures carbonate segregation. LOI greater than 3 percent may indicate over-combustion or inadequate raw mix.
• Coal and biomass combustion: Evaluates burnout efficiency. High LOI (greater than 10 percent) encourages burner adjustment to reduce fuel use.
• Waste-to-energy plants: Help achieve circular economy goals by tracking organic residues for ash disposal or metal recovery.
• R&D: Supports studies on alternative fuels where LOI is related to calorific value and ash fusion behavior.

By minimizing unburned carbon, facilities can reduce annual carbon dioxide emissions equivalent to thousands of tons.

As a result, ASTM D7348 uncovers hidden variations in combustion residues, transforming raw data into actionable information for greener, more efficient operations. As global demands for sustainable energy intensify, this standard remains indispensable, enabling industries to progress without excessive losses.

Our organization, which has been operating for many years and meticulously follows global developments in science and technology, conducts testing, measurement, and analysis in a wide range of areas for businesses across all sectors with a skilled team and extensive infrastructure. In this context, we also provide testing services in accordance with ASTM D7348 Standard Test Methods for Loss on Ignition (LOI) of Solid Combustion Residues.