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Amelioration of Physical Strength in Waste Foundry Green Sands for Reuse as a Soil Amendment

De Koff, J.P., Lee, B.D., Dungan, R.S.
Journal of environmental quality 2008 v.37 no.6 pp. 2332
metallurgy, waste utilization, industrial wastes, soil amendments, sand, soil strength, sodium, magnesium, calcium, iron oxides, manganese oxides, aluminum oxide, silicon, cation exchange capacity, clay, iron, root growth, bentonite, gypsum, physical properties
To avoid increasing costs of landfill disposal, it has become increasingly important for U.S. foundries to identify beneficial reuses for the 8 to 12 million tons of waste foundry sand (WFS) generated annually. A major drawback to the reuse of some WFSs as a soil amendment is their high soil strength, under dry conditions, where root growth may be limited. Fifteen WFSs were analyzed for strength to rupture using lab-formed clods, exchangeable cations (Na, Mg, Ca), metal oxide concentration (Fe, Mn, Al, Si), cation exchange capacity (CEC), and % clay. Several WFS samples from gray iron foundries demonstrated high strength to rupture values (> 1.5 MPa), and could potentially restrict root growth in amended soils. The percentage of Na-bentonite exhibited a positive correlation (R2 = 0.84) with strength to rupture values. When WFSs containing more Na-bentonite were saturated with 1 mol L-1 Ca ions, strength values decreased by 70%. Waste foundry sands containing less Na-bentonite were saturated with 1 mol L-1 Na ions and exhibited a threefold increase in strength. Additions of gypsum (up to 9.6 g kg-1 sand) to high strength waste foundry sands also caused 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 Ca2+.