BENEFICIAL REUSE OF SPENT FOUNDRY SAND

The foundry industry generates a number of byproducts, of
which the largest volume is a “spent sand” that consists of
silica or olivine sand with residuals of phenolic resin, clay
or no-bake binders. The Clean Washington Center's
Recycling Technology Assistance Partnership is working
with the Washington State Chapter of the American
Foundrymen's Society (AFS) toward the implementation of
beneficial re-use applications for spent foundry sand. This
fact sheet describes common uses of foundry sand,
provides an overview of several beneficial reuse options,
and discusses issues for future development of a viable
market for the recycled sand.
Background
All foundries produce castings by pouring molten metal
into molds. The characteristics of the residuals vary from
foundry to foundry, and depend on the type of metal being
poured (iron, steel, aluminum, brass/bronze), the type of
casting process (sand casting, investment casting), and the
technology employed, particularly the type of furnace
(induction, electric arc, cupola) and the type of finishing
process (grinding, blast cleaning, coating).
Sand Casting
The most common type of casting process is known as
sand casting. There are two basic types of mixtures for
sand casting: "green" sand and "no-bake" sand. Green
sand uses a mixture of clay and water to achieve bond
strength, while no-bake sand uses synthetic resins. Sand
casting involves making a pattern of the component to be
cast, and packing sand around the pattern to produce a
hollow mold. Molds are typically made in two halves to
facilitate removal of the pattern, and then the molds are
assembled to form a "hollow" that matches the pattern's
shape. Cores, made of packed sand with special binders,
may be inserted into a mold, prior to assembly, to form
interior surfaces for complex shapes. Molten metal is
poured into the mold cavity and allowed to solidify and
cool. The casting is shaken out of the sand mold using
vibratory machines, mechanically cleaned of extraneous
metal by cutting or grinding, and blast cleaned to remove
casting sand and other surface contaminants.
Sand casting generates residuals from metal melting and
pouring, and molding processes. Residuals consist of
"spent sand" from molding and core-making, slags, and
wastes from cleaning rooms, dust collectors or scrubbers.
Depending upon the process, some foundry wastes,
including spent sand, slags, and dust collector/scrubber
wastes, may be hazardous.
Spent Foundry Sand
It is standard foundry practice to reuse molding and coremaking
sands. Residual sand is routinely screened and
returned to the system for reuse. As the sands are
repeatedly used, the particles eventually become too fine
for the molding process; and, combined with heat
degradation from repeated pourings, requires periodic
Key Words
Materials: Spent foundry sand.
Technologies: Fine aggregate substitution;
stabilization.
Applications: Asphalt concrete, bricks & pavers,
compost additive, concrete, flowable
fill, mineral wool products, portland
cement.
Market Goals: Establish variety of regional markets
throughout Washington State.
Abstract: Summary of beneficial re-use
options for spent foundry sand.
replacement of "spent" foundry sand with fresh sand.
This "spent sand" is typically non-hazardous, black in
color, and contains a large amount of fines (particles of
100 sieve size or less). Olivine and silica sands are most
common in Washington State foundries.