LEONARDITE AND HUMIFIED ORGANIC MATTER
D.M. Ozdoba1, J.C. Blyth1, R.F. Engler2, H. Dinel3, M. Schnitzer3
1 Specialty Products Division, Luscar Ltd., 13044 Yellowhead Trail, Edmonton, Alberta,
Canada. T5L 3C1.
2 Luscar Ltd., 1600 Oxford Tower, 10235 101 Street, Edmonton, Alberta, Canada T5K 3J1.
3 Eastern Cereal and Oilseed Research Centre, Agriculture and Agri-Food Canada,
Ottawa, Canada. K1A 0C6.
Leonardite and humified organic matter have been mentioned synonymously for many years yet what do they have in common. Leonardite was named after Dr. A.G. Leonard in recognition of his work and is associated with lignite coal reserves. Leonardite and similar materials from oxidized sub-bituminous coals and carbonaceous shales are good sources of humic substances or organic material. Further work by Schnitzer and Dinel1, have shown these organic materials can exhibit similar chemical properties as soil humified organic matter.
The term soil organic matter is generally used to represent the organic constituents in the soil including identifiable high molecular weight organic materials, simpler substances (sugars, amino acids) and humic substances as characterized by Stevenson2. Hayes and Himes3 have further defined humic substances as being humus that is composed of organic macromolecular substances arising in soils from which they were derived. Humic acids, fulvic acids and humin materials are regarded as humic substances. As a result, the measurement of humic acid and substances is critical to demonstrate the link between known deposits and soil organic matter.
The objective of this work was to characterize the different geological deposits of leonardite type materials in North America, the key factors associated with them and some common applications of such materials.
2. MATERIALS AND METHODS
Six locations were identified in North America to represent the most common reserves of leonardite or similar materials containing humified organic matter as shown in Figure 1. Leonardite is an oxidized form of lignite, which is a soft brown, coal-like substance that is associated with location #2 (South Eastern Saskatchewan) and location #3 (North Dakota). Currently, the North Dakota reserves have several locations in which the leonardite material is mined and processed from.
In addition to leonardite, other sources of rich organic materials exist like Humalite. Humalite is defined by G. Hoffman et al4 as a naturally occurring organic material, that is highly oxidized or weathered, brownish-black in color and found adjacent to sub-bituminous coals fields in Alberta. Reserves of humalite are shown by location #1.
Location #4 (Wyoming) and location #5 (New Mexico) are also associated with weathered sub-bituminous coal fields and carbonaceous shales. New Mexico contains several locations in which material is mined and processed today.
Location #6 (Idaho) is significantly different from the above locations and is more closely associated with carbonaceous shales.
All samples were oven-dried and then heated to at 700 C for 3h to determine their ash content. Total carbon, hydrogen and nitrogen analyses were done by dry-combustion and total sulfur by oxygen-flask combustion. Geological factors and characterization were from previously determined sources.
Humic acid content has been measured by two methods; A&L method which is a qualitative method using light refractory and the CDFA (California) method which is more quantitative using chemical analysis.
3. RESULTS AND DISCUSSION
The formation of organic matter and coal is best illustrated in Figure 2, which shows how oxygen content and compaction effect the degree of characterization of organic matter or coal. When characterizing organic materials, it is important to note that they are all formed from plant material. Buckman and Brady5 describe peat as an unconsolidated soil material, consisting largely of undecomposed, or slightly decomposed, organic matter accumulated under conditions of excessive moisture. Based on the formation process shown in Figure 2, humus is formed from peat. This in turn leads to humic substances which have been defined by MacCarthy et al.6 as heterogeneous mixtures of naturally occurring organic materials. All of the materials or ores described in the six locations come from being weathered or exposed to the elements over millions of years and thus can be considered as a form of organic matter. Also, the data indicates that humalite is quite different from the other ore deposits in terms of purity. One of the reasons is the origin of the material being from poorly drained fresh water swamps and not salt water deposits.
Ash content is extremely important when comparing each of the deposits in terms of purity and humic acid content. Both the A&L (qualitative) and CDFA (quantitative) are two common methods used today to measure humic acid. However, one of the main problems is in the consistency of reporting, since some methods report humic acid and others humic substance. Further to this, neither method discussed above is done on an ash-free basis, which often leads to inaccuracies in reporting or communicating humic acid content. Based on the six locations, humalite from Alberta contained the lowest amount of ash (11.1%) compared to the Idaho deposit (84.7%), which was extremely high in ash and silica (carbonaceous shale origin). Leonardite from the North Dakota and Saskatchewan deposits are somewhat higher at 20 22% ash as they are essentially salts of humic acids admixed with mineral matter such as gypsum, silica and clay (Fowkes and Frost7). Lastly, the New Mexico deposits are the most common and widely talked about reserves but have a very high ash content of 35.7%. This is a result of being associated with carbonaceous claystone, mudstone and shale (G. Hoffman et al8).
Other key parameters like cation ion exchange capacity (CEC) are very important when evaluating the quality or purity of organic materials. It has been reported that CEC is often associated with highly decomposed organic matter. CEC was measured in all deposits with the New Mexico deposits ranging from 55-70 and Alberta greater than 200. Deposits from North Dakota and Wyoming were somewhat lower and in the range of 100-140.
Sulphur content was another factor that was significantly different between the deposits. Humalite from Alberta had the lowest sulphur content of 0.5% or less with the Wyoming and New Mexico reserves much higher at 2-3%. Furthermore, the Wyoming deposit also showed a higher humic acid and heat content than the New Mexico deposits even though these deposits have many similar characteristics.
Wax content is often over looked when comparing different deposits but can effect the overall purity of the raw material especially when extracting the humic acid material from the ore. North Dakota based deposits have showed higher analysis of wax compared to Alberta, which was non-detectable. In addition to wax, sodium is another factor, which varied between deposits. This is somewhat based on whether the deposits originated in bodies of salt or fresh water. The highest amounts were reported in the North Dakota and Saskatchewan based deposits.
Based on the results and work over the last 25 years, the application and usage of humic substances has been evident but reserved. Opportunities exist today to further exploit and demonstrate the value of such products. In the discussion above, there are many similar characteristics among the deposits but some have distinct advantages over the others depending on their application in the agricultural, horticultural, environmental or industrial areas. Overall, humalite has shown to have the highest CEC and lowest ash content thus indicating a higher purity than some of the other deposits. This becomes important when evaluating the deposits and the application they are being used.
There are many issues today, which make the use and understanding of humic substances a problem. One of these is quality. Quality products that are readily available on a commercial scale must be consistent to achieve success. Key parameters need to be identified and methods for analyzing such deposits have to be more quantifiable. Education on the benefits of such substances and the interpretation of data are critical to the future. If industry wants to survive or progress further, we must have products that are beneficial to the end users, contain low levels of metals, improve plant growth and minimize environmental impact. Environmentally friendly and value-added products are the future.
1. M. Schnitzer, H. Dinel, T. Pare, H-R, Schulten, D. Ozdoba. Proc Humic Substances Seminar V, Boston, MA, March 21-23, 2001.
2. F.J. Stevenson, 1982, Humus Chemistry; Genesis, Composition, reactions. John Wiley, New York.
3. M.H.B. Hayes and F.L. Himes. Nature and Properties of Humus-Mineral Complexes in P.M. Huang and M. Schnitzer, Eds., Interactions of Soil Minerals with Natural Organics and Microbes, Special Publication 17, Soil Science Society of America, Madison, 1986, p. 104-158.
4. G.K. Hoffman, J.M.. Barker and G.S. Austin. New Mexico Bureau of Mines and Mineral Resources, Campus Station, Socorio, New Mexico 1995, p 55-68.
5. H.O. Buckman, N.C. Brady, 1996, The Nature and Properties of Soils, The MacMillan Company, Toronto, Canada
6. P. MacCarthy, R.L. Malcom, C.E. Clapp and P.R. Bloom. An Introduction to Soil Humic Substances. In Humic Substances in Soil and Crop Science Society of America, 677, South Segoe Road, Madison, WI.USA
7. W.W. Fowkes, C.M. Frost, 1973, Leonardite. North Dakota Geological Survey, Bulletin 63, p. 72-75.
8. G.L. Hoffman, D.J. Nikols, S. Stuhec, R.A. Wilson, Evaluation of Leonardite (Humalite) Resources of Alberta, Energy, Mines and Resources Canada, 1993, Alberta Research Council, Canada.
Figure 1. North American Deposits of Humic Substances
Figure 2. The Formation of Organic Matter and