Precious Metal Recovery

Proximate Analysis for Fuel and Ore Characterization >
Cupellation for Precious Metals >
Optimizing Mineral Analysis – Challenges and Retsch Solutions >
Precious Metal Recovery from E-Waste >

Proximate Analysis for Fuel and Ore Characterization

Thermogravimetric analysis (TGA) plays a key role in mining and metallurgy by providing rapid, automated proximate analysis of coal, coke, and mineral samples. By sequentially heating a sample under controlled conditions, TGA quantifies moisture, volatile matter, and ash yield—critical parameters for evaluating fuel behavior and ore quality.

Moisture influences handling efficiency and effective heating value.
Volatile matter governs combustion behavior and classification of coals and cokes.
Ash yield reflects mineral impurities, affecting pricing, smelting performance, and residue management.

In precious metal recovery, these insights are equally important: ash content and loss-on-ignition (LOI) analyses help assess impurities in ores, tailings, and concentrates. LOI measurements also indicate organic matter or carbonate content (e.g., CO₂ release at 950 °C), impacting metallurgical processing and recovery efficiency.

ELTRA’s Thermostep TGA analyzers fully automate proximate analysis in line with ASTM D7582, ISO 11722, and ISO 17246, ensuring compliance, reproducibility, and high throughput. These instruments deliver precise weight-loss data for coal, coke, ores, and residues—supporting optimized fuel selection and improved downstream recovery of valuable metals.

Parameters which typically are measured via TGA are:

% Moisture

% Volatile

% Ash

% Lost on ignition

Cupellation for Precious Metals

Cupellation is the classical and most accurate method for determining precious metals, especially gold and silver, in ores, concentrates, and metallurgical products. In mining geology, fire assay is routinely used to measure gold (and platinum group metals) in rock or soil samples to evaluate ore grades. It is also used in the refining and jewelry industries for hallmarking. The method involves melting the sample with fluxes and lead (or other collectors) to separate precious metals, then oxidizing the lead to absorb base metals in a porous cupel, leaving behind a precious metal bead which is weighed or analyzed.

Cupellation is considered the benchmark method for gold analysis because of its accuracy and ability to concentrate trace amounts of noble metals. In exploration, knowing the gold content of drill cores or rock chips guides investment and mining decisions. Even in modern labs with spectrometers, fire assay remains indispensable for:

Determining low concentrations of Au, Ag, PGM in geological samples where other methods might lack sensitivity or be hampered by matrix effects.
Legal and commercial certainty: many mining contracts and resource estimates rely on fire assay data as it’s a total extraction method (virtually all the gold is recovered into the assay bead, so it’s a true measure).
It’s also used for metallurgical accounting: e.g., to check how much gold is in a concentration vs. tailings (to calculate recovery).

Learn more about cupellation

Carbolite Gero manufactures cupellation furnaces (CF series) specifically designed with this key feature:

Achieve the necessary temperatures (>1000 °C) and have rugged chamber designs to withstand corrosive vapors (lead oxide fumes are very corrosive). Carbolite highlights features like corrosion resistance and safe handling of vapors
When is required can include pre-heated airflow or afterburners to carry away and treat the lead oxide fumes (ensuring operator safety and environmental compliance).
Are built to accommodate multiple cupels at once (high throughput – a typical furnace might process 20+ cupels per batch).
Comply with standards such as ISO 11426:2014, which is actually a jewelry standard for gold determination by fire assay (cupellation). ISO 11426 is for gold content in gold alloys, but the fundamental technique is the same for ores, just with different sample size and flux. Another relevant standard is ASTM E1335

Contact us for info Discover our furnace

Optimizing Mineral Analysis – Reliable Sample Preparation

Accurate mineral analysis is essential for process optimization, yet achieving representative and homogeneous samples remains a challenge due to the natural heterogeneity of ores. Contamination, dust formation, and time constraints can compromise results, leading to unreliable data for decision-making.

Retsch addresses these issues with integrated sample preparation solutions, combining robust jaw crushers, high-performance disc mills, and innovative crusher–mill–cyclone systems. These instruments enable coarse pre-crushing, fine homogenization, and dust-free

handling in a single workflow, ensuring maximum sample recovery. Vibratory Disc Mills like the RS 200 deliver exceptional reproducibility, achieving analytical fineness within minutes for reliable XRF and XRD analysis.

By minimizing cross-contamination and securing precise particle size control, Retsch systems support faster, safer, and more consistent workflows. This ensures laboratories and processing plants obtain the accurate mineralogical data required to optimize grinding, flotation, and leaching, ultimately improving recovery rates, reducing costs, and supporting sustainable resource utilization.

Precious Metal Recovery from E-Waste

Electronic waste recycling has become a critical source of precious and strategic metals such as gold, silver, copper, and rare earth elements. Efficient comminution is the first step in liberating these valuable materials from complex electronic components.

Retsch’s Cutting Mill SM 300 is designed for this demanding task, offering robust construction and high rotor speeds that enable effective shredding of printed circuit boards, cables, magnets, and batteries. By reducing e-waste to fine, uniform particles (<1 mm), the SM 300 ensures optimal conditions for subsequent hydrometallurgical processing, where increased surface area accelerates metal dissolution. Research projects across Europe have validated this approach, demonstrating that fine grinding significantly enhances the recovery of precious metals while reducing the need for new mining.

By providing reproducible, scalable, and contamination-controlled comminution, Retsch solutions play a key role in advancing circular economy practices, lowering environmental impact, and enabling efficient recovery of valuable resources from electronic waste

Enabling Progress in GEOLOGY AND MINING

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