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Proximate Analysis: Moisture, Ash, and Volatiles

Thermogravimetric analysis (TGA) in mining geology is often applied to proximate analysis of coal and coke – determining moisture content, volatile matter, and ash yield – as well as to similar measurements in other minerals (e.g. determining loss on ignition in ores or sediments). 

In a TGA-based proximate analysis, a sample is heated in a controlled program and weight changes are recorded to sequentially measure: moisture (mass loss at ~105 °C), volatiles (mass loss on heating to e.g. 900 °C in inert conditions), and ash (residue remaining after combustion in air at ~750–815 °C).

The purpose of proximate analysis is to quickly characterize fuel properties of coal:

  • Moisture affects handling and heating value.
  • Volatile matter influences combustion behavior and rank classification.
  • Ash yield indicates mineral impurity content and is used for pricing (ash is ballast that does not burn) and for design of boilers (high ash yields more residue).

In geology, similar weight-loss methods (often termed Loss on Ignition, LOI) are used to measure organic matter in soils or carbonates in rocks by seeing how much mass is lost on high-temperature ignition. For instance, LOI at 550 °C can estimate organic content in sediments, and LOI at 950 °C can quantify carbonate content by releasing CO₂. 

TGA can automate these determinations.

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Standard Methods for Thermogravimetric Analysis

 

TGA methods follow ASTM D7582 / ISO 11722 which allow automated thermogravimetric determination of these parameters. Thermostep is noted to measure moisture, ash, volatiles in coal, coke, or ore fully automatically. This approach is standard-compliant and yields results equivalent to other traditional methods, but with higher throughput. 

The importance of these measurements is codified in international standards. ISO 17246 defines coal proximate analysis parameters and ISO 11722 / ASTM D7582 provide the method for TGA. By automating LOI-type analyses, even geological materials like laterite or bauxite (to measure combined water) or limestone (to measure CO₂ loss) can be analyzed with precision. 

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Ash Fusibility Testing of Coal

Coal ash fusibility tests determine the temperatures at which coal ash transforms, mining labs and coal quality laboratories routinely measure ash fusibility to predict how a coal’s ash will behave in boilers or gasifiers. The test produces characteristic temperatures: IDT (Initial Deformation Temp), ST (Softening or Shrinking Temp), HT (Hemispherical Temp), and FT (Fluid or Flow Temp) . 

The purpose of the test is to ensure operational safety and efficiency in coal utilization. Different coal produces ashes that melt at different temperatures depending on their mineral composition (high iron or alkali content lowers ash melting point, for example). Power plants often specify that the ash fusibility temperatures must exceed the furnace operating temperature to avoid slagging. 

The ash fusibility test involves preparing a pellet or cone of coal ash (per a standard procedure, coal is ashed at a set temperature, then the ash is molded into a cone). This cone is then heated in a specialized furnace with observation. The Carbolite CAF G5 ash fusibility furnace is an example designed for this test. 

Key aspects:
  • It heats up to 1600 °C and can be realized with an inert atmosphere option. Is it also possible to set up the furnace heating in a reducing atmosphere as well, to simulate boiler conditions.
  • A camera system continuously observes the shape of the ash cone. The furnace’s software records images or video, and the temperatures at which the ash cone first deforms (starts rounding or melting), forms a hemisphere, and completely flows are noted. The automatic image capture allows technicians to review the test later instead of watching the furnace continuously.
  • The furnace conforms to multiple standards: e.g. ISO 540:2008, ASTM D1857/D1857M – 18, DIN 51730, and corresponding ISO/TS for alternative fuels. These standards define the ash fusibility test method and how to report results.
  • The sample is typically heated at a controlled rate (e.g. 8 °C/min) until deformation is observed.

By using a furnace like Carbolite’s, mining labs can deliver precise ash fusion temperature data. The inclusion of automatic image recording in the CAF G5 is a notable advancement – it prevents human error in missing an endpoint and provides a record for quality assurance. Additionally, the furnace can test biomass or waste-derived fuel ashes (with some modifications), indicating its flexibility beyond coal. 

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Loss on Ignition (LOI) and Ash Content Determination

LOI is a simple but informative test: it quantifies the total volatile or combustible portion of a sample. In mining:

  • For soils and sediments, LOI gives a quick estimate of organic matter, important for understanding soil fertility or sediment composition. 
  • For bauxite and iron ores, LOI indicates combined water (goethite to hematite conversion releases water) or CO₂ (in carbonates) which affects processing (e.g., high LOI in iron ore means more mass loss in a blast furnace). Standards for iron ore sometimes include LOI in the technical specification.
  • In cement and limestone mining, LOI can reflect purity (a high LOI in limestone means lots of calcite that will decompose).
  • For coal and coke, ash LOI tests measure how much solid residue remains (which affects handling of coal combustion residuals in power plants)
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Overall, LOI helps in material characterization, quality control, and suitability assessment for various industrial processes. For instance, an iron ore’s LOI (due to goethite dehydration) can influence its sintering behavior; a coal’s ash LOI indicates how much residue a boiler will have to deal with.

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Loss on ignition refers to the measurement of weight loss when a sample is heated to a specified high temperature, causing volatile components to burn off or decompose. In geology and mining, LOI tests are used for:

  • Determining organic matter or moisture in soil, sediments, and waste. For example, heating a sediment sample to 550 °C for several hours will burn off organic matter; the percent weight loss indicates organic content. Similarly, heating at 105 °C might measure moisture (loss on drying).
  • Measuring carbonate content in rocks or cement raw materials. Heating a limestone or cement sample to ~950 °C will decompose carbonates (e.g. CaCO₃ → CaO + CO₂↑), so the weight loss corresponds to CO₂ released, which can be back-calculated to carbonate content.

Standard Methods for LOI

 
There are numerous standards methods for LOI depending on material:
  • ASTM D7348 covers LOI for solid combustion residues (e.g. fly ash, which is analogous to ore in technique).
  • ASTM D2974 (for soils) uses LOI at 550 °C for organic matter in peat and soil.
  • ISO 11536 (iron ores — method for LOI) defines how to measure loss mass in iron ores by ignition at 1000 °C.
  • ASTM C25 (for limestone) and ASTM C114 (for cement) include LOI as part of the chemical analysis.
Carbolite  furnaces can cover all different needing.

 

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AAF

Swelling Number Index Testing of Coal

The Swelling Number Index (SNF) test is a fundamental analysis in coal and coke laboratories, used to evaluate the caking properties of coal. This test measures the ability of coal to soften, swell, and re-solidify when heated under standardized conditions—properties that are critical for determining its suitability for metallurgical coke production.

Understanding coal’s swelling behavior is essential for mining companies, steel producers, and quality control labs, as it directly affects coke oven performance and final coke quality.

Application Relevance

  • Coal Classification: Differentiates between caking and non-caking coals, guiding their economic use.
  • Coke Making Suitability: Identifies whether coal can produce strong, porous coke required for blast furnaces.
  • Process Optimization: Supports coal blend selection to achieve desired coke properties and reduce variability.
  • Quality Control: Ensures compliance with industrial standards and reduces the risk of costly furnace disruptions.
CARBOLITE: SNF
SNF

Carbolite Gero Swelling Number Index Furnaces are designed for precise, reproducible SNF testing. With controlled heating rates, robust chamber design, and compliance with international standards, these furnaces deliver reliable results that mining and metallurgical laboratories can trust. By providing accurate swelling data, they enable better decision-making in coal grading, blend optimization, and steel production efficiency.

Sieve Analysis for Particle Size Distribution of Aggregates and Soils

Sieve analysis is one of the most established and widely used methods to determine the particle size distribution of soils, sands, aggregates, and other granular materials. By passing a sample through a stack of woven wire sieves with decreasing mesh sizes, laboratories can quickly quantify the proportion of coarse and fine fractions. This method remains fundamental in geology, construction, mining, and geotechnical engineering—where understanding grain size directly affects material classification, strength, compaction, and performance. 

AS
Sieve Shakers

Key Information to Know

 

Range of analysis: Typically from a few micrometers up to several millimeters, covering gravel, sand, and finer soil fractions down to about 75 µm. 

Applications: Used in soil classification, aggregate quality control, monitoring milling efficiency, and sediment characterization. 

Methodology: Involves drying the sample, weighing, and sequentially sieving through certified test sieves, followed by calculating weight percentages retained. 

Complementary techniques: For particles finer than 75 µm, sieve analysis is combined with hydrometer testing or modern laser diffraction methods. 

Reference to Standard Methods

 

ASTM C136 – Standard Test Method for Sieve Analysis of Fine and Coarse Aggregates: Specifies sample preparation, sieving procedure, and reporting for construction materials. 

ASTM D6913 / D6913M-17 – Particle-Size Distribution of Soils by Sieve: Widely used in geotechnical engineering to classify soils by grain size. 

ASTM E11 – Specification for Woven Wire Test Sieve Cloth and Test Sieves: Defines the quality and tolerances of sieves used in laboratory testing. 

Retsch sieve shakers and certified test sieves are designed to fully comply with these international standards, ensuring reproducibility, reliability, and traceability in particle size distribution testing. 

 

Applications Explained in Practice

Sieve analysis plays a critical role across disciplines: 

Soil classification (geotechnical engineering): Determines the proportions of gravel, sand, silt, and clay. This data is essential for foundation design, slope stability, and groundwater studies. 

Aggregate quality control (construction): Concrete and road-building aggregates must meet strict gradation envelopes for compaction, durability, and strength. Sieve analysis confirms compliance with these specifications. 

Mining & milling operations: Even with advanced laser particle size analyzers, sieves are still used to check coarser fractions or quickly assess grinding efficiency (e.g., % passing 200 mesh). 

Sedimentology (geology): Field geologists often use sieving to classify sands and sediments on-site, where rapid particle size information supports stratigraphic or environmental studies. 

Sieve analysis remains a trusted, standard-compliant method for characterizing particle size distributions in soils, aggregates, and sediments. With Retsch’s precision-engineered sieve shakers and ASTM-certified sieves, laboratories and field geologists can rely on robust, reproducible results. Whether ensuring construction material quality, monitoring mining operations, or classifying geological samples, sieve analysis continues to bridge tradition and modern standards in particle size evaluation. 

Volatile Matter Analysis in Coal and Coke

Determining the volatile matter content of coal and coke is a critical step in mining and metallurgical quality control. This parameter, part of the standard proximate analysis, provides key insights into fuel value, combustion behavior, and suitability for steelmaking or power generation.

Application Relevance

  • Coal Characterization: Volatile matter content helps classify coal ranks and determine market value.
  • Combustion Behavior: High volatile matter supports faster ignition, while low values indicate slower, more stable combustion.
  • Coke Production: Ensures coal blends produce strong, stable coke for blast furnace operations.
  • Standards Compliance: Tests conform to ISO 562 and ASTM D3175, guaranteeing reliable, comparable results.

Carbolite Gero VMF Furnaces provide precise, reproducible volatile matter determinations under controlled heating conditions, supporting mining labs and industrial users in optimizing resource utilization and maintaining product quality.

VMF

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