Spent foundry sand

Foundries purchase new, virgin sand to make casting molds, and the sand is reused numerous times within the foundry. However, heat and mechanical abrasion eventually render the sand unsuitable for use in casting molds, and a portion of the sand is continuously removed and replaced with virgin sand. The removed sand becomes spent foundry sand, which is discarded from the foundry facility. 

Spent foundry sand can be divided, based upon bonding processes, into two categories—spent green sand and spent chemically bonded sand. Spent green sand is black in color due to its carbon content, and has clay contents that result in a fraction of the material passing a No. 200 sieve (0.075 mm). Chemically bonded sands are generally yellowish in color and coarser in texture than clay bonded sands. 

Physical properties involve tests of the physical index parameters of the materials. For spent foundry sand, these parameters include particle gradation, unit weight, specific density, moisture content, adsorption, hydraulic conductivity, clay content, plastic limit, and plastic index. These parameters determine the suitability of spent foundry sand for uses in potential applications. Typical physical properties of spent green foundry sand are listed in Table 4.5. 

The grain size distribution of spent foundry sand is very uniform, with approximately 85 to 95% of the material between 0.6mm and 0.15mm (No. 30 and No. 100) sieve sizes. Five to twelve percent of foundry sand can be expected to be smaller than 0.075 mm (No. 200 sieve). The particle shape is typically subangular to round. Spent foundry sand gradations are too fine to satisfy the fine aggregate standard specified in specification ASTM C33 Standard Specification for Concrete Aggregates. 

Spent foundry sand has low absorption and is nonplastic. Reported values of absorption were found to vary widely (0 to 5%), which can also be attributed to the presence of binders and... 

The chemical compositions of materials are usually expressed in terms of simple oxides calculated from elemental analysis determined by x-ray fluorescence. For spent foundry sand, the chemical parameters include bulk oxides mass composition, loss on ignition, and total oxygen demand. Table 4.6 lists the general chemical properties of spend foundry sand. It is shown that spent foundry sand consists primarily of silica dioxide. 

Depending on the binder and type of metal cast, the pH of spent foundry sand12 can vary from approximately 4 to 8. As such, it has been reported that some spent foundry sands can be corrosive to metals.14 Spent foundry sand must be monitored to assess the need to establish controls for potential phenol discharges.91516... 

Few studies have been conducted to determine organic residues in spent foundry sand and leachates from disposal sites. It is reported that several organic compounds are present in the spent foundry sand but have concentrations below the regulated toxicity characteristic limits. Organic compounds of concern include benzoic acid, naphthalene, methylnaphthalenes, phenol, methylenebisphenol, diethylphenol, and 3-methylbutanoic acids.12 These compounds are thought to be derived from the decomposition of organic binders such as phenolic urethane, furan, and alkyd isocyanate. 

Typical mechanical properties of spent foundry sand are listed in Table 4.7. Spent foundry sand has good durability characteristics as measured by low microdeval abrasion and magnesium sulfate... 

Typical Mechanical Properties of Spent Foundry Sand... 

In-plant reclamation refers to the sand reclamation process in a foundry facility, which directly minimizes the generation of spent foundry sand. Sand reclamation includes physical, chemical, or thermal treatment of foundry sands so they may be safely substituted for new sand in molding and core-making mixes. 

The beneficial reuse of foundry solid waste has long been carried out informally, particularly in the U.S. Foundry solid waste has always been used as fills around the foundry or nearby neighborhood. With the promulgation of strict environmental protection laws, foundry solid waste is now required to be landfilled. Later, spent foundry sand was selected as a daily cover for landfills that are cover short. However, many recyclers believe that foundry solid waste should not necessarily be disposed of in landfills where other hazardous industrial waste belongs, simply because the main fraction of foundry solid waste is nonhazardous and has value in fully or partially substituting for currently in-use materials, for example, construction aggregates, soils, and minerals. Thus, reuse of foundry solid waste is marketable. 

Spent foundry sand is thought of as a beneficial substitute for fine sand for use in portland cement concrete. Prior to acceptance of inclusion, test standards applied on conventional fine sand shall be referred to as the standards for spent foundry sand to compare the physical properties of conventional sand and spent foundry sand. The most important parameters are particle size distribution, fineness modulus, dust content, density, organics content, deleterious materials content, and grain shape. Although no spent foundry sand satisfies all of the specifications, foundry sand can be blended with conventional sand to be incorporated into the concrete matrix. The replacing ratio normally starts at one-third. 

Spent foundry sand can be used as a good source of silica in manufacturing portland cement. Also, the clay fraction of foundry sand is an additional source of iron and aluminum oxides. According to the portland cement industry, spent foundry sand can be beneficially used in the manufacture of Portland cement, as sand possesses the following characteristics ... 

Manufacturers also request that spent foundry sand should be cleaned from other foundry byproducts. Core butts should be ground to a uniform grain size to improve the kiln process. In addition, adequate supplies of spent foundry sand are viable in the manufacturing process. 

Embankment and fill applications are the biggest end-user of spent foundry sand. Natural soils are often composed primarily of sand, clay, and water. Most spent foundry sands have these same constituents, which suggests spent foundry sand as a good fill material. The immediate benefits include saving virgin soil materials and reduce the bottom line of the foundry industry. It is also reported that foundry sand as a fill material may present better performance then conventional materials, including better resistance to freeze-thaw distress. 

The physical properties of concern for construction fill applications are the relationship between moisture and density, plasticity, the liquid limit, and particle size distribution. The same set of construction machinery for conventional fills, such as bulldozers, compactors, and grabbers, is suitable for fill earth works containing spent foundry sand. 

Natural sand is a major component of most flowable fill mixes. Ferrous spent foundry sand can be used as substitute for natural sand (fine aggregate) in flowable fill.48 49 Spent sands from nonferrous foundries and foundry baghouse dust can contain high concentrations of heavy metals that may preclude their use in flowable fill applications. Some of the engineering properties of spent foundry sand that are of particular interest when foundry sand is used in flowable fill applications include particle shape, gradation, strength characteristics, soundness, deleterious substances, and corrosivity. 

Most spent foundry sand discarded is green sand. The primary components of green sand are silica and bentonite. Thus, green sands are essentially a sand-bentonite mixture, which makes them potentially useful as a liner and cover materials, that is, for hydraulic barrier layers. 

Spent foundry green sand is of particular interest to soil blending companies that produce topsoil, because of its dark color, clay content, moisture retention, and consistency. A high sand content is required in topsoil, so spent foundry sand could be a major component. Spent sand reduces the... 

Solid waste regulations are frequently cited as barriers for metal industrial byproduct recycling. Research indicates that most ferrous spent foundry sand meets nonhazardous standards under the... 

Some end-use applications may prefer the characteristics of foundry solid waste. For instance, spent foundry sand is a uniformly graded fine aggregate containing chemically active iron and organics. Spent foundry sand can be superior to other types of granular materials, such as compacted soils or clays, for hydraulic barriers. In this case, spent foundry sand provides better performance at lower cost. 

MOEE, Spent Foundry Sand—Alternative Uses Study, report for Ontario Ministry of the Environment and Energy and the Canadian Foundry Association, Ontario, Canada, July 1993. 

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