Leonardite is a soft waxy, black or brown, shiny, vitreous mineraloid that is easily soluble in alkaline solutions. It is an oxidation product of lignite, associated with near-surface mining.[ The mineral industry of North Dakota, USGS report on non-fuel minerals in North Dakota] in the remediation of Pollution environments and as a Well drilling additive.[ Hoffman, G.L., Nikols, D.J., Stuhec, S., Wilson, R.A. Evaluation of Leonardite (Humalite) Open File Report 1993-18, Resources of Alberta, Alberta Geological Survey ] It was named after A. G. Leonard, first director of the North Dakota Geological Survey, in recognition of his work on these deposits.[ Odzoba, D.M., Blyth, J.C., Engler, R.F., Dinel, H. & Schnitzer, M. 2001. Leonardite and humified organic matter. In Ghabbour, E.A. & Davies, G. (eds.) Humic Substances: Structures, Models and Functions (Special Publication), Royal Society of Chemistry 388pp. ]
Formation
Leonardite is found associated with near surface lignite deposits. They are thought to have been formed by the oxidation of the lignite, an interpretation supported by chemical analysis of leonardite compared to lignite.
[ Youngs, R.W. & Frost, C.M. 1963. Humic acids from leonardite – a soil conditioner and organic fertilizer. Ind. Eng. Chem., 55, 95–99]
Occurrence
Leonardite was first described from North Dakota and is found associated with virtually all the lignite deposits in the state.
Leonardite has also been described worldwide from deposits of lignite or sub-bituminous coals e.g. in
Alberta,
Canada,
in
Achlada and
Zeli,
Greece,
in
Turkey and in
Bacchus Marsh,
Australia.
[Victorian Competition & Efficiency Commission, Inquiry into Regulatory Barries to Regional Economic Development, 15 November 2004. Submission 54]
Uses
Soil conditioner
It is used to condition soils either by applying it directly to the land, or by providing a source of humic acid or
potassium humate for application. The carbon
geosequestration potential of Leonardite, particularly to rapidly accelerate microbial action to lock up and retain carbon in soils, provides the basis for extensive research in Victoria on the organic fertilising aspect of brown coal.
[Latrobe Fertilisers Holdings Ltd official website]
Remediation of polluted soils
Leonardite can be added directly to soils to reduce the uptake of metals by plants in contaminated ground, particularly when combined with
compost.
[ Gore, A.B. 2007. Environmental research at the leading edge, Nova Science Pub Inc., 353pp.]
Drilling additive
Leonardite is used to
deflocculation the
drilling fluid used to make in oil, gas, and geothermal wells. It was first employed extensively during World War II when
quebracho tannin became difficult to obtain.
[ Darley, H.C.H. & Gray, D.R. 1988. Composition and properties of drilling and completion fluids, Gulf Professional Publishing, 644pp.] It has very good temperature stability and prevents solidification of lime muds near 150 °C.
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