crud
in solvent extraction
A deposit or emulsion at the interface between two partially settled phases.
Notes:
  1. The phenomenon of crud formation arises from many causes and this definition does not imply any single one.
  2. Other terms -- some unprintable -- have been used but crud is the generally accepted term.
Source:
PAC, 1993, 65, 2373 (Nomenclature for liquid-liquid distribution (solvent extraction) (IUPAC Recommendations 1993)) on page 2387