Method for contaminant removal using natural convection flow and changes in solubility concentration by temperature

Apparatus and methods are described for removing contaminants from an article using a supercritical or near supercritical solvent fluid held at substantially constant pressure in a pressure vessel. The article to be cleaned is first contacted with a solvent fluid in which the contaminant is soluble at a first supercritical or near-supercritical temperature. The contaminate-containing fluid is then cooled or heated to a second supercritical or near supercritical temperature to lower the solubility of the contaminant in the supercritical fluid and thereby precipitate or phase separate the contaminant. The contaminant is then recovered. Movement of the solvent fluid within the pressure vessel is preferably by convection induced by heating and cooling means in the vessel.