Part 1.  What is Leonardite
By Karen Dailey, Ph.D., American Colloid Company

What is Leonardite?
Leonardite is a low rank coal derived from terrestrial plant matter. Leonard Dave of the University of North Dakota discovered it in 1919. Leonardite is found in North Dakota, Utah and New Mexico. It is found as outcropping of lignite deposits, usually very close to the surface.

There are two theories on the origin of Leonardite. The first one is that it is an oxidized lignite. Compared to Lignite it has about 30-35% of oxygen whereas Lignite has about 25-30%. The second theory is that it is predominately Humic acid leached from topsoil by alkaline waters and subsequently precipitated into subsurface soil strata. (Humic acid is a form of organic plant matter).

Leonardite Characterization:
Humic Matter: Humic matter is complex organic molecules formed by the breakdown of organic matter. Humic matter is a class of compounds with variable structure, functionalities and reactivities. Leonardite typically contains greater than 85% Humic acid.

Humic Matter Characterization:
Three types of organics are identified in Leonardite. They are

1. Fulvic Acid
2. Humin
3. Humic Acid

It is important to note that Leonardite has less than 7% of Fulvic acid and greater than 85% Humic Acid.

Leonardite has many industrial uses.

Leonardite, after mining, has a pH of about 3.5. However, foundry sands have a pH of greater than 7.0. So to make the Leonardite compatible to the foundry sand, it is made into "Causticized Leonardite." You raise the pH of the Leonardite with the addition of a base such as NaOH. But this changes the reactivity of the Leonardite! It makes the material soluble.

Humic Acid Interactions with Bentonite:
There is flocculation of the clay. Humic acid blocks electrostatic interactions, and makes the clay unwettable.

The conclusions:

1. Leonardite is likely derived from Lignite (Oxidized Lignite).
2. Leonardite is composed of Humic Substances (<85% is Humic Acid).
3. Leonardite ore is acidic. Hence it is causticized to increase it pH.
4. Humic Acid in Leonardite disrupts bentonite and its electrostatic interactions and modifies its ability to swell.
5. Causticized Leonardite is a reactive material.

Leonardite & Its Effects on Green Sand Molding
Part 2.  Applications in Green Sand Systems
by Mike Van Leirsburg, American Colloid Company

The use of Leonardite in Green Sand Systems is well established. Its effects on the Green Sand are:

1. Reduces clay viscosity
2. Improves Muller efficiency
3. Increases mold permeability
4. Absorbs and retains water
5. Improves shakeout
6. Improves foundry environment

Leonardite reduces clay viscosity.
(See Fann Viscometer graph) Leonardite retards the free swelling of clay. It improves flowability and clay efficiency.

Leonardite improves Muller efficiency.
(See Remull Tests for Existing vs Leonardite graph)  Leonardite works well in foundries where the mulling cycles are short due to demand of mulled sand. By using Leonardite, for the same compactability, there is an increase of green strength. Foundrymen can use less clay in their sand system. This can be a big cost saving in the long run.

Use of Leonardite increases the permeability of the green sand.
This increase in permeability could result in the reduction of Gas defects. Cold iron defects such as misrun, cold shut is also reduced. Use of Leonardite does not replace the good practice of venting of the molds.

Leonardite helps the absorption and retention of water in the sand system.
(See Moisture vs Compactability graph)  Use of Leonardite helps improve the sand system performance especially in the hot sand conditions. Free water defects in the castings are reduced. The use of Leonardite requires more water in the sand system to obtain the same compactability.

Leonardite improves shakeout.
(See Remull Tests for Existing vs Leonardite graph)  The use of Leonardite allows the use of more Western Bentonite in Foundries with less than vigorous shake out systems. It reduces dry strength, resulting in less sand carry out.

Leonardite does not affect clay durability.
Despite lowering dry strength, sodium clays (Western) retain their natural, high durability when blended with Leonardite. The durability of the clay is obviously a function of clay chemistry.

Leonardite improves foundry environment.
The use of Leonardite reduces smoke on the cooling lines and at shakeout.

Leonardite may reduce foundry emissions.
Initial testing at the CERP foundry in California has been completed recently. Preliminary results look very encouraging.

Leonardite affects the methylene blue testing.
Methylene blue tests measure the cation exchange of the clay. Since Leonardite has its own cation exchange capacity of its own, Bentonite/Leonardite systems will have higher methylene blue readings than Bentonite systems without Leonardite.

Exercise caution when reducing clay.
It is important that one should be very familiar with the sand system. Sand testing should be done frequently when reducing the clay. Reducing the clay based on green strength or methylene blue alone may result in too great of a loss in dry strength.

Conclusion.
The use of Leonardite to the green foundry sand systems can be beneficial to the foundryman seeking to improve clay efficiency, increase sand permeability and improve the foundry environment.

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