A byproduct of the kraft and sulfite pulping processes, residual lyes carry commercial value primarily through their lignin sulfonate content, which is used as a dispersant, binder, and plasticizer across construction, agriculture, and industrial sectors. The heading explicitly excludes tall oil, which is classified separately. Lignin sulfonates recovered from spent pulping liquors are traded both as concentrated liquids and dried powders, and classification hinges on processing stage and intended end use. Importers should confirm whether the material has been further processed beyond the residual lye stage, as that can shift the applicable tariff heading.

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