ISO 20904:2020

Overview

ISO 20904:2020 - Hard coal - Sampling of slurries defines standardized methods for obtaining representative samples of fine hard coal, rejects or tailings (nominal top size < 4 mm) when mixed with water to form a slurry. Published in 2020 (second edition), the standard focuses on sampling from moving streams - falling streams or flows confined in pipes, launders, chutes, spirals and similar channels. It explicitly excludes sampling of stationary slurries (settled or stirred in tanks/dams) and high-solids pastes. The procedures aim to produce damp solid samples (after fluid drainage and fluid volume measurement) suitable for drying, chemical analysis and physical testing with known precision and minimized bias.

Key topics and technical requirements

ISO 20904:2020 covers practical and statistical aspects of slurry sampling to ensure representativity and traceability. Major technical topics include:

• Principles of sampling: guidance on representativity, sources of sampling error and error minimization.
• Sampling schemes: time-based, stratified random and sub-lot approaches to construct lot and sub‑lot samples.
• Mechanical and manual sampling methods: design and operation of cutters and sampler devices for moving streams, plus manual implement guidance.
• Increment mass and number: requirements for primary increment mass, number of increments per lot/sub-lot and avoidance of bias.
• Precision and variance: definitions and calculation of sampling variance, preparation and overall variance, and procedures for routine checking.
• Sample preparation, division and reduction: mills and division methods to obtain test and analysis sub-samples.
• Packing and marking: requirements for sample handling, labelling and chain-of-custody.
• Annex material: informative examples of correct and incorrect sampling devices and a normative annex on manual sampling implements.
• Reference method: diverting the entire stream into a vessel for a defined interval (corresponding to the stopped-belt method in ISO 13909-2) is identified as the benchmark where flow rates permit.

Practical applications and users

ISO 20904:2020 is intended for organizations and professionals involved in coal handling and quality control, including:

• Mining companies and coal preparation plants conducting routine quality sampling of slurries.
• Laboratory analysts requiring representative samples for chemical and physical testing.
• Quality assurance and compliance teams verifying product specifications.
• Trading partners and auditors using samples as the basis for settlement or contract verification.
• Equipment manufacturers and site engineers designing mechanical sampling systems.

Using ISO 20904 helps reduce sampling bias, quantify sampling precision, and produce legally and commercially defensible samples for analysis and dispute resolution.

Related standards

• ISO 13909-2 (stopped-belt sampling method reference)
• ISO 1213-1 / ISO 1213-2 (vocabulary for solid mineral fuels and sampling/testing terms)

Keywords: ISO 20904:2020, slurry sampling, hard coal sampling, coal slurries, sampling methods, representative sample, sampling variance, mechanical sampling, manual sampling.