Assay Sampling Protocols for Industrial Metal Scrap Valuation
Assay sampling protocols establish true dry weight and payable metal content, directly governing settlement values, working capital allocations, and lender borrowing base limits.
Cryogenic Grinding
Meaning
Low-temperature pulverisation is a sample preparation technique that uses liquid nitrogen to freeze materials before milling. Applying cryogenic grinding prevents thermal degradation of volatile elements and makes soft or ductile materials brittle enough to be easily crushed. This method is used for plastics, organic samples, and certain metal alloys that would otherwise smear or melt.
Mechanical Milling
Standard mills generate intense heat through friction, which can ruin heat-sensitive samples. Submerging the sample or the milling chamber in liquid nitrogen changes the physical properties of the material, making it highly brittle. This brittle state allows the grinding media to shatter the sample instead of tearing it.
The resulting powder is fine and uniform. It also prevents the loss of volatile compounds during the preparation.
Temperature Control
Maintaining the ultra-low temperature requires specialised insulated equipment and a continuous flow of liquefied gas. Technicians monitor the cooling phase to ensure the sample is fully frozen before the mill starts. This process prevents the sample from warming up during the grinding cycle.
If the temperature rises, the milling efficiency drops.
Pulverisation Mechanism
High-speed impactors or balls strike the frozen material to reduce its size quickly. This mechanical action takes place within a sealed chamber to prevent condensation from adding moisture to the dry powder. The frozen material turns into a fine powder within minutes.
This speed prevents any moisture build-up.