Technical Guidance 07: Development of policies for the handling, disposal and/or beneficial reuse of used foundry sands – a literature review

A large amount of research conducted recently and practical experience gathered worldwide over the last 30 years has indicated that with very few exceptions, beneficial reuse of used foundry sand (UFS) is not detrimental to human health or the environment.

Characteristics

• UFS is not uniform and the type of contaminant issues that may be experienced varies both spatially and temporally. Spatial variation is due to the differences in procedures and foundry processes which vary from one company to another and from one application to another. The main differences occur between foundries that use green sands to produce moulds, as opposed to foundries which use resin sands with a higher content of organic contaminants due to the organic resin binders used to prepare moulds. Temporal variations in UFS consistency can occur even at the same location due to changes in foundry production.
• UFS is currently poorly characterised with regard to the type and extent of contaminants, especially organic contaminants including potentially unhealthy contaminants such as polyaromatic hydrocarbons (PAHs) produced during the foundry process at elevated temperatures due to pyrolytic reactions. There is a need to better understand how these reactions occur so they can be controlled and minimised.
• Most organic residues are present in UFS at low concentrations, usually below detection limits. When detected the organic residues are either PAHs (phenanthrene, naphthalene, fluorene, anthracene and pyrene) or phenolic compounds (phenol, 2-methyphenol, 3- and 4-methylphenol and 2,4-dimethyl phenol). 

Beneficial reuses

• While a number of beneficial uses have been proposed, few are economically viable unless the foundry and the site of reuse are close and thus limit the costs associated with transporting UFS for treatment or reuse.
• Beneficial reuses that are well advanced include many construction applications, whereas agricultural application of UFS is limited, not due to any real environmental concern but rather the perception that UFS will be detrimental to human health. Indeed, substantial research conducted worldwide has indicated that metal contaminants in UFS, especially those derived from green sands, are not of environmental concern and are often present at levels comparable to native soils.
• Several studies have indicated that UFS from brass foundries are generally not suitable for beneficial reuse due to high levels of metal contaminants.
• For land application of UFS, greater research needs to be conducted to unequivocally demonstrate that UFS as part of a manufactured soil is completely safe.

Legislative aspects

• A number of legislative frameworks have been adopted worldwide. The more successful of these use some form of classification of UFS based on specified criteria for both metal and organic concentrations, usually TCLP (toxicity characteristic leaching procedure) extraction, and then define specifically what reuse is applicable to that classification.
• While the levels of metal contamination in UFS are normally well below any legislated levels of concern and are often comparable to the original clean sand, organic contaminants are poorly characterised in UFS and are consequently poorly legislated for. In part this results from the plethora of different potential organic binder technologies currently in use.
• Lack of clarification by the state EPAs as to what criteria would be suitable for classification of UFS is one of the major barriers to successfully reusing UFS. This is coupled with disagreement between states on clear legislative guideline levels for different contaminants.
• There is a need to streamline the approvals process to encourage beneficial reuse.
• Research is required to establish not only the types of UFS constituents, but also the magnitude of investigation levels for these constituents that would be required to ensure protection of the environment and human health.
• Legislative guidelines should include information on sampling plans and the frequency of sampling required.

Further research

In the short term the most pressing need for industries and regulators intent on the adoption of beneficial reuse of UFS is to focus on dialogue that fosters beneficial reuse. The development of regulatory guidelines which address the needs of industries in clear and unequivocal terms needs to be a priority. Generic guidelines are not required, rather, a clear statement of what is required on the quality of UFS fit for a specific purpose. There is a need for guidelines to be developed specifically for the reuse of UFS.

These guidelines should initially focus on land application, which would be the most difficult to define and implement due to the greatest potential risk associated with this reuse. However, reuse should not be limited to this avenue alone as many other applications such as road base and construction are relatively low risk alternatives that can quickly be used to demonstrate beneficial reuse.