ARS | Publication request: Amelioration of physical strength in waste foundry green sands for reuse as a soil amendment

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 28, 2008
Publication Date: October 23, 2008
Citation: De Koff, J.P., Lee, B.D., Dungan, R.S. 2008. Amelioration of physical strength in waste foundry green sands for reuse as a soil amendment. Journal of Environmental Quality. 37:2332-2338.

Interpretive Summary: As available landfill space and profit margins steadily decrease, it becomes more important for U.S. foundries to find ways of diverting 8-12 million tons of waste foundry sand (WFS) away from landfills each year. A major drawback to the reuse of some WFSs (which are often clay coated) as a soil amendment is their high soil strength under dry conditions to a point where root growth may be limited. Fifteen WFSs were analyzed for strength properties. Sands which are predominantly coated with sodium-dominated clay exhibited high strength values. When the sodium was exchanged with calcium, the WFSs had substantially lower strength values. These results indicate that high strength WFSs have properties similar to hardsetting soils, which are caused by a high sodium clay content, and can be ameliorated by the addition of calcium.

Technical Abstract: As available landfill space and profit margins steadily decrease, it becomes more important for U.S. foundries to find ways of diverting 8-12 million tons of waste foundry sand (WFS) away from landfills each year. A major drawback to the reuse of some WFSs as a soil amendment is their high soil strength under dry conditions to a point where root growth may be limited. Fifteen WFSs were analyzed for strength to rupture using lab-formed clods (produced by saturation by capillarity followed by drying for 48 hours at 40 degrees Celsius), exchangeable cations (Na, Mg, Ca), metal oxide concentration (Fe, Mn, Al), cation exchange capacity (CEC), and percent clay. Some WFSs exhibited high strength to rupture values (1.5 to 4.6 MPa) which may inhibit root growth and the use of WFS as a soil amendment. The percentage of Na-bentonite exhibited a positive correlation (R2 = 0.80) with strength to rupture values for those with high strength values and similar particle size fractions. When WFSs containing more Na-bentonite were saturated with 1M Ca ions, strength values were found to decrease by about 70%. Waste foundry sands containing less Na-bentonite were saturated with 1M Na ions and exhibited a 3-fold increase in strength. Additions of gypsum to high strength WFSs also caused corresponding decreases in strength. These results indicate that high strength WFSs have properties similar to hardsetting soils, which are caused by high Na clay content and can be ameliorated by the addition of Ca.