OVERVIEW OF HUMATE PRODUCTION IN NORTH AMERICA

Hoffman, Gretchen, K., Barker, James M., and Austin, George S., New Mexico Bureau of Geology and Mineral Resources, Campus Station, Socorro, New Mexico, USA, 87801. Humate is formed by weathering of organic material in coal, lignite, or mudstone and it is rich in humic acid (HA) and fulvic acid (FA). Weathered coal and organic mudstone constitute the humate resources of New Mexico, Utah, and Wyoming. Organic-rich lacustrine sandstone in the uranium region of New Mexico is referred to as humate as is similar organic-rich sand and sandstone along the Gulf Coast of Alabama and Florida. Weathered lignite (called leonardite if humate?bearing) occurs in North Dakota, Texas, Louisiana, Saskatchewan, and Alberta.

Humate has been produced in North America for several decades. It is mined by front-end loaders and stockpiled to dry before crushing and screening. For some uses, the material is custom blended to obtain a specific HA content. After the material is crushed, it is shipped in bulk, bagged, or liquified. No rigorous evaluation of humate resources is available. Resources in western North Dakota are 7.4 Mt and production is 28.1 ktpy. Humate resources in the San Juan Basin, New Mexico, are 4.5 to 6.8 Mt and production is about 18.1 ktpy. Humate production in Wyoming is 25.4 ktpy.

Agricultural use of humate is controversial because soils and plants do not always benefit from its application. HA and FA are organic colloids, similar in behavior to clay minerals that increase the water retention and cation exchange capacity of the soil. The pH of alkaline soil is lowered by humate thus increasing plant nutrient availability and stimulating growth of micro-organisms. Organic mudstones have greater clay content than weathered coal so they are more beneficial to sandy soils by enhancing nutrient and moisture retention. A clayey soil benefits more from humate derived from weathered coal. Clay minerals in weathered coal and organic mudstone are dominantly kaolin.

HA in humate acts as a dispersant, thinner, or viscosity modifier in drilling mud. HA is stable at high temperatures and is preferred for hot or deep drilling. HA is not used when salt in the drillhole causes HA to precipitate. Leonardite and weathered coal are or have been mined in North Dakota, Wyoming, and New Mexico for drilling mud additives. Humate is also used as a wood stain, binder for briquets, casting sand additive, and to stabilize ion-exchange resins. Potential or emerging uses for humate are neutralization of herbicides and pesticides, livestock feed supplement, soil stabilization, or feedstock for synfuels.

We determined the HA and FA contents in humate?bearing rocks using a simplified method consisting of basic washings, acid precipitation, and ashing. Reporting of HA and FA content, ash-free basis, enhances accuracy and precision by eliminating differences due to varying leach times, NaOH-HCl concentrations, and non?humate residues. A comparison of values derived from this method with previous humate analyses are lower because weight added during the analytical procedure are not counted as humate.