Leonardite & Its Effects on Green Sand Molding
What is Leonardite?
Part 1. What is Leonardite
By Karen Dailey, Ph.D., American Colloid Company
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).
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.
Three types of organics are identified in Leonardite. They are
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.
|Agriculture||soil amendments and fertilizers|
|Waste Water||organics and metal filtration|
|Oil Drilling||drilling muds|
|Foundry||green sand additives|
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.
Acid Interactions with Bentonite:
There is flocculation of the clay. Humic acid blocks electrostatic interactions, and makes the clay unwettable.
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:
reduces clay viscosity.
(See Fann Viscometer graph) Leonardite retards the free swelling of clay. It improves flowability and clay efficiency.
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.
of Leonardite increases the permeability of the green
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.
helps the absorption and retention of water in the sand
(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.
(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.
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.
improves foundry environment.
The use of Leonardite reduces smoke on the cooling lines and at shakeout.
may reduce foundry emissions.
Initial testing at the CERP foundry in California has been completed recently. Preliminary results look very encouraging.
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.
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.
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.