“United Nations Statistics Division - 2001 Industrial Commodity Statistics Yearbook
…
Bentonite - Bentonite is a clay derived from volcanic ash, largely used as an ingredient of moulding sand, as a filtering and de-colourizing agent in oil refining, and for de-greasing of textiles. (SITC, Rev.3: 27827-0).”
(http://unstats.un.org/unsd/industry/yearbook/commdef.xls)


“Tariff Schedule of Canada
…
- Kaolin and other kaolinic clays, whether or not calcined.
- Bentonite
- Decolourizing earths and fuller's earth
- Fire-clay
- Other clays
…”
(http://www.sice.oas.org/trade/cancr/spanish/cancrsch.pdf)


“Process for regenerating exhausted oils
United States Patent 4233140
…
From these necessities, it emerges, for the refineries, the need of disposing of the exhausted decolorizing earths and/or the exhausted acidic muds, and the always severer specifications as to environmental pollution make this task more and more difficult.

In addition, such treatments are economically objectionable on account of the high cost of the decolorizing earths and sulphuric acid and on account of the low yields which can be obtained.”
(http://www.freepatentsonline.com/4233140.html)