future market for aggregate industry fines
by ROBERT J. ABLE
Pit & Quarry, June 1995
The U.S. aggregate industry produces more than 2 billion tons of crushed stone, sand and gravel annually. In generating these products approximately 200 million tons, or an average 10 percent, of fine material (minus #200 mesh) are produced simultaneously. Marketing these fines has been an age-old industry challenge. Typically, fines are left to be disposed of as waste, or used for reclamation.
Assuming a potential market would pay $2.50 per ton for this fine material, it would lead ultimately to $500 million in sales of what is now commonly considered a problem product. Soil remineralization-adding aggregate fines to soils to improve and sustain crop land-may provide an answer to a market for this product, and may be an image booster for the aggregates industry.
What is remineralization?
Remineralization is the replacement of lost minerals and trace elements to regenerate and restore soils essentially depleted of these vital elements. Years of intensive cropping, applications of chemical fertilizer products and acidic atmospheric conditions have led to the depletion of important elements.
The Center for Aggregate Research (CAR) was established by a foundation set up by members of the National Aggregates Association and the National Stone Association. Texas University and Texas A&M were selected as the host facility to administer the research program.
In establishing the foundation, the industry was polled to determine its major concerns. This study determined that the primary industry concern was the limited marketability of fines generated during processing to meet specification requirements.
At the Third Annual CAR Symposium held in March, a task force (T-6 Remineralization) was established to investigate the potential aggregate fines have for replenishing lost elements to the soil and will be working in conjunction with the National Aggregates Association Sub-Committee on Remineralization.
What are remineralization's benefits?
Potential advantages of applying fines to soils include:
The benefits from fines are added to soils via a variety of mechanisms which allow the nutrient elements in the rock to become available to the plant root system. These mechanisms include dissolution, ingestion and digestion by macro-organisms (earthworms and moles, etc.), microbial attack on the surface on fine particles, and direct ion exchange.
Particle size considerations
Because of the nature of these transfer mechanisms, the material size is an important factor in determining its applicability for soil remineralization. Typical aggregate products available that are too coarse for this application include concrete sand, abrasive sand, filter sand, mason sand, blow sand and screenings. The fines referred to are pond settlings, rock dust (product from dust collectors), rock flour, and classifier tailings.
For best results, at least 75 percent of the rock dust should pass a #200 mesh (75 micron) sieve. Application rates should be between 2 and 20 tons of fines per acre and would be tailored to soil deficiencies if known.
Mineralogy of the material is as vital as size in determining the success of soil remineralization. It is best to tailor the elemental analysis of the fines to provide elements deficient in the local soil, if known.
Typically, the best suited aggregate types include:
Comparative tests are still needed, however, to evaluate the performance and costs of different types of rock in the vast varieties of soil types and conditions that exist.
The concept of remineralization is much further advanced in the European community and Australia than in the U.S. Their current practices include hydroseeding of fines to forests dying from acidic atmospheric conditions. Similar conditions exist in a few forest areas of the U.S. It is encouraging, however, that interest in remineralization is growing with a variety of studies being conducted.
Dr. Robert Bruck at North Carolina University has an on-going project involving planting Fraser fir and red spruce trees in the Appalachian Mountains. Trees in the upper reaches of the mountains have been dying from acidic atmospheric conditions and the depletion of minerals in the soils necessary to sustain survival. Young trees have been planted and studied with and without the application of fines to the soils. Those in soils with added fines have a noticeable increase in the survival and growth rate.
Recently the U.S. Department of Agriculture at the Beltsville, MD Agricultural Research Station has funded a three-year pilot project to study the affects of various aggregate industry by-products as an agricultural soil amendment. This study includes glacial rock, granite and basaltic fines.
Corn was grown the first summer, then winter wheat, and the USDA now plans to plant soybeans. The demonstration plots were on the tour for the agency's sustainable agricultural field day. USDA is planning more rigorous experiments for next year using mineral fines in some composting studies.
Growing interest in the remineralization concept
There is a growing public concern about agricultural soil and ground water in regards to both quality and quantity. There is a general awareness that food products are tainted by fertilizers, pesticides, herbicides and fumigants utilized by the agricultural industry. This, along with the thrust for sustainable agricultural practices, has driven an interest in the concept of remineralization.
Fertile regions of the Nile River Basin, Matanuska Valley in Alaska, and the Mississippi River Valley area give testimony to the effect of aggregate mineral fines (generated by the grinding action of stones in a moving water system) when flooding deposits new, enriched mineral fines to lowland areas.
By taking an active role in promoting the use of these by-product fines, both publicly and through government agencies, the industry can forge new markets for products that currently have very limited market application. For those seeking further information on the subject, contact:
Rick Meininger, PE.
Ronald Korcak (left) from the Beltsville, MD. Research Facility of the U.S. Department of Agriculture stands with Robert Able at the agency's Agricultural Research Station.
The U.S. Department of Agriculture at the Beltsville, MD Agricultural Research Station has funded a three-year pilot project to study the affects of various aggregate industry by-products as an agricultural soil amendment. This study includes glacial rock, granite and basaltic fines.
The Earth Renewal and Restoration Alliance — www.ancientforests.us — www.carbon-negative.us — www.nutrient-dense.info — 2/14/2009