Beneficial reuse of foundry sands and slag has been going on informally in the U.S longer than you think. From the start, many foundry sands and slags were used to build up low-lying areas around the foundry or nearby neighborhoods. The creation of the U.S. Environmental Protection Agency, as well as state regulatory agencies, changed all that, and as a result foundry sands and slags started going to solid waste landfills. While many things that are generated by industry in general belong in a landfill, many recyclers believe that foundry sands and slags do not, simply because many discarded foundry sands and slags are clean and have value as aggregates.
Beneficial use of foundry byproducts depends on several critical factors. Among the more obvious of these are rules and regulations, disposal costs, and the availability of similar virgin materials. Those committed to finding end-uses for their material should consider all of these factors, as well as reasonable transportation costs.
Disposal vs. recycling — Starting a recycling program may seem simple, but anyone who has attempted it will confirm that it is time-consuming. So, if your foundry’s disposal costs are very low and your foundry does not generate significant quantities of material, consider looking elsewhere for cost savings. If you proceed, you will need to honestly and accurately evaluate your disposal costs, including transportation, box rental charges, and additional costs, such as bags, etc. The bottom line: look specifically at the average cost per ton for disposal.
Many times disposal companies will low-ball the cost to remove a container of sand, and then maximize their profits with the add-on service costs. They may pick up the boxes more often than necessary, limiting the tonnage but increasing the number of pull charges — resulting in an increased cost per ton. Prompt service is great, but make certain it benefits you, and not the disposal company. You should also review whether or not their trucking fleet is suited to handle heavy loads. Make sure you accurately account for costs by developing a model for the disposal activity on a "per ton" basis.
Reviewing regulations — Before you begin recycling, make sure that your materials are being tested according to federal regulations to determine whether they are hazardous or non-hazardous. It is critical that you become familiar with the federal and state regulations relative to your materials. Also, foundry sands and slags are being well received in some states, but others restrict their reuse in certain applications, or prohibit them entirely. Know and understand the rules and regulations that apply to your materials in your state.
Make sure your lab is running to the proper detection limits, and if you are unsure about how to do this engage a reputable environmental consultant familiar with the foundry industry.
Market potential — One particular mistake that foundries make is improperly defining the market potential of their byproducts. For example, if a similar virgin sand is available to the local asphalt plant for $2.00/ton, you may have trouble gaining their attention. If the local consumer of aggregate has a similar material available and he is purchasing it from his cousin, you can forget about earning that account, too, unless they have family feud. Study the landscape before attempting to enter the market.
Successful uses — Several "good to excellent" markets have been developed for recycled foundry sands and slags. All end-uses are dictated to some extent by each state’s regulatory agency, but there are some common successes that may be categorized as 1) old school-low tech, 2) generally accepted applications, and 3) new applications that are being developed. For old school-low tech applications, the local landfill still may be the best example.
Applying foundry sand as a daily cover continues to be a viable option for landfills that are "cover short," and this is a relatively simple end-use for a foundry’s material. Foundries should make an effort to keep the material free from dusts and debris. Landfills that need good cover material may take some foundry sands suitable for this application at lower gate rates than general refuse — a significant savings to both the foundry and the landfill.
There are some successful examples of directing foundry sands into aggregate substitutes. Sub-base and structural fill applications are among the most successful of these applications. When foundry sands are properly processed and managed with care, many of them possess engineering properties that make them highly suitable for sub-base construction applications. Usually, they are very uniform, which also lends confidence to the end-users.
Foundry sands are also being used in embankment projects in some states.
Recycled sands have been used as a silica substitute in Portland cement, asphalt, flowable fill, and concrete. Foundry slags are an excellent fit for asphalt, as well, when they are properly processed. Competitive material availability and transportation costs will dictate the market acceptance in most cases.
New horizons — Foundry sands show promise in several new, experimental applications. Baghouse dusts have been used successfully to make some polymer composites. Polymer composite counterweights have been developed for a furniture manufacturer in Michigan, and while commercialization of this process is incomplete, the materials’ engineering properties are sound.
Another promising application involves using custom-blended foundry process residuals to remediate groundwater. Iron-carbon-silica sands derived from foundry sands are being blended to engineered specifications to treat contaminated groundwater in a special iron wall technology. Several projects have been completed using these materials, and several more are on the horizon. The process is patented and licensed, but if demand increases there may be opportunities for more foundries to participate.
Top soils continue to show promise for foundry sands. Kurtz Bros. Inc. pioneered this application, and incorporates tens of thousands of tons into high-end horticultural soil blends annually. It’s important to note that their efforts have been well researched and developed, as evidenced by their partnerships with The Ohio State University soil scientists to develop suitable mix designs.
Approaching the end user — Dropping off a 5-gal. pail of the foundry sand or slag at a concrete plant and asking the foreman to let you know what he thinks of it is no way to impress a future customer. It’s fairly certain that bucket will be in the same spot when you return in a few weeks.
Try a more strategic approach. The simplest thing you can do when approaching what you believe to be a "reuse" prospect is to ask for the specs on the material they currently purchase. It is also critical that you ask the potential end-user about their existing aggregate source(s).
If their fine-aggregate source is a sister-company, you’ll have a hard time convincing them to try your product. But, many potential customers are cost-conscious, and that is your advantage. Aiming low to establish a market is a great strategy for getting in the door. Foundries need to value market sustainability and cost reduction over the best short-term deal. Build partnerships with your end-users and your long-term progress will be greater.
The bottom line with reuse is understanding the material you have, making sure it is characterized properly, and then marketing it according to the appropriate regulations.