2620.21.00.40 - Silver content

This HTS category, 2620.21.00.40, specifically classifies residues from the refining of leaded gasoline, commonly known as leaded gasoline sludges, and similar residues from leaded anti-knock compounds. These materials are characterized by their origin in the processing of lead-containing fuels and additives and are distinct from general slag, ash, and other metal-bearing residues. Their physical form can vary but typically includes powders, sludges, or solidified masses.

Unlike its sibling categories, which differentiate based on the primary metal content (copper, lead, zinc, or gold), this subcategory precisely targets residues generated from specific lead-based anti-knock compounds used in older gasoline formulations or from the refining processes associated with such fuels. While it falls under the broader heading of "Containing mainly lead," its specificity lies in the *source* of the lead contamination, directly linking it to the petrochemical industry's use of lead additives.

As a leaf node, there are no further subcategories under 2620.21.00.40. Classification at this level is determined by the identification of the material as a sludge or residue originating from the specific processes described, with lead being a primary component due to its presence in the original gasoline or anti-knock compounds.