Becoming a More Sustainable Foundry

Over the past four decades, foundries have significantly increased their recycling efforts. However, the disposal of materials like baghouse dust, sand, slag, and refractories has continued to rely heavily on landfilling, often at relatively low cost. In recent years, environmental regulations and a reduction in landfill capacity have led to higher disposal costs and greater liability risks. Compounding the issue, some foundry waste is now classified as hazardous, further increasing financial and regulatory pressures on the industry.

Foundry Waste

The UK government has set ambitious targets to reduce municipal landfill waste to less than ten per cent by 2035 and to near zero by 2045. These targets are expected to compel local councils to close landfill sites or face penalties for non-compliance. As a result, disposing of foundry waste sand via general landfill is becoming increasingly challenging and expensive.

Currently, foundry waste sand benefits from a reduced landfill tax – £4.05 per tonne, compared to the standard rate of £126.15 – provided its Loss on Ignition (LOI) is <10 per cent. However, the government is now consulting and may eliminate this lower tax rate. If implemented, disposal costs could rise by a factor of thirty, significantly increasing financial pressure on the foundry industry.

Waste Acceptance Criteria (WAC) and Classification Challenges

While the landfill tax exemption for foundry sand offers some relief, it does not affect WAC, which determine whether waste is classified as inert, non-hazardous, or hazardous. Increasingly, foundry sand is being designated as hazardous due to high levels of dissolved organic carbon (DOC) exceeding 800mg/kg, or the presence of phenols. Disposal costs for such hazardous waste can range from £45.00 to £600.00 per tonne, depending on the severity of contamination.

Hazardous sand waste cannot be repurposed without additional treatment. Many chemically bonded sand foundries using basic dry attrition reclamation methods produce sand that surpasses these thresholds. Although these regulations have been in place for some time, their enforcement has varied significantly depending on location. That inconsistency is now changing, and foundries are seeing a sharp rise in disposal costs – a trend likely to continue unless proactive measures are taken. Foundries need to look at their processes to reduce the amount of waste being generated.

Green Sand Reclamation

Green sand systems are complex, requiring precise balance across multiple inputs and outputs (see process map). As castings become more complex and core heavy, the volume of new and core sand introduced has risen, leading to increased waste and the need for more bentonite and carbonaceous additives. This shift has driven up both material and disposal costs.

To combat this, reclamation systems have emerged to recover waste sand, bentonite, and carbonaceous materials. In recent years, several technologies have been developed to scrub waste greensand and return it to the core shop, significantly reducing new sand usage and landfill burden.

However, non-thermal reclamation methods can produce significant amounts of dust with a LOI above ten per cent, disqualifying it from landfill disposal under current regulations. Recent innovations to rehydrate the high fraction of bentonite and carbonaceous materials in the dust are allowing them to be reintroduced into the greensand system, reducing waste and raw material costs. Alternatively, the material needs to be mixed with waste greensand in a dilution process, keeping the overall LOI below ten per cent, which will reduce overall reclamation levels. The type of reclamation system – whether cold or with a thermal component – should be carefully evaluated based on the nature of the waste it generates.

Collaborative Solutions and Cost-Efficient Waste Reduction Strategies

Given the high capital costs associated with reclamation technologies, small- and medium-sized greensand foundries may benefit from forming partnerships or clusters with similar operations. By sharing expenses and investing jointly, these groups can explore more economically viable methods for repurposing waste materials – such as incorporating greensand into asphalt and other construction products. In fact, some landfill sites already use waste greensand as capping material. For any beneficial reuse strategy to be successful, maintaining consistency and preventing cross-contamination in the waste stream is essential. The era of indiscriminate waste disposal is rapidly ending.

In addition, there are several low-cost, practical actions that can reduce overall waste generation:

Refine core designs by reducing bulky, oversized cores, e.g. hollowing out of heavy cores.
Monitor and control LOI and methylene-blue clay levels to avoid unnecessary overdosing.
Recycle waste core sand and core butts from screening using basic dry attrition reclamation methods.
Improve planning to reduce the number of tool changes to minimise mixed core-sand waste and reduce core scrap.
Test dust collector fines regularly for methylene-blue content and LOI, ensuring sand cooling and extraction systems are performing optimally.
Regularly inspect cyclones and drop-out boxes to ensure excessive fines are not being pulled into baghouses.

Core Package Casting and the Shift Away from Greensand

In recent years, some foundries – particularly those producing castings like truck engine blocks and cylinder heads – have transitioned away from greensand processes entirely. This evolution has led to facilities that produce minimal, if any, sand waste. Most of these foundries use large core shooters to blow phenolic urethane cores, creating integrated core packages that are then placed into a support system for pouring.

By incorporating thermal reclamation technologies, these foundries are achieving high levels of sand reuse while dramatically cutting down waste. Furthermore, this level of efficiency opens the door to replacing traditional silica sand with ceramic sands such as Cerabeads, eliminating serious health and safety risks associated with respirable crystalline silica.

This shift also enables greater control of casting tolerance, more flexibility in casting design, especially with recent advances in rapid 3D sand printing, and cellular manufacturing. Altogether, the core package approach represents a significant leap toward a more sustainable and adaptable foundry model.

Challenges for No-Bake Foundries

Most jobbing foundries in the UK rely on mechanical attrition paired with organic binders, predominantly alkaline phenolic furan or phenolic urethane systems. Reclamation rates for these systems typically range from sixty to ninety per cent with the waste sand, much of which is classified as hazardous due to the presence of leachable organic compounds such as phenols.

The associated dust from the classification process is also hazardous, complicating disposal efforts and raising environmental compliance challenges. Additionally, this high concentration of organic compounds in the waste makes it difficult to repurpose or recycle through beneficial reuse pathways, posing a growing problem for foundries that depend on these organic binder systems. Levels of reclamation can be increased to over ninety per cent by introducing secondary attrition, incorporating thermal reclamation as part of the process, or substituting mechanical attrition altogether.

Thermal Reclamation and Binder Process Considerations

Thermal reclamation paired with the phenolic urethane process offers the most effective method for eliminating hazardous sand waste, as it fully removes organic compounds from the sand. This results in a clean, reusable material and virtually eliminates hazardous waste classification.

However, each binder system presents its own unique challenges:

Furan binders: While effective, the thermal reclamation process for furan systems generates some sulphur emissions, which may raise environmental concerns and require mitigation strategies.
Alkaline phenolic binders: Achieving reclamation rates above ninety per cent can lead to the accumulation of potassium and sodium oxides within the sand. This buildup may compromise mould strength and reduce the sand’s sintering temperature, potentially affecting casting quality. To maintain optimal performance, an addition of up to ten per cent new sand is typically required.

Despite these limitations, sand processed through thermal reclamation – regardless of binder type – is no longer classified as hazardous, greatly easing disposal and enhancing opportunities for beneficial reuse.

No-Bake Foundries and Inorganic Binder Innovation

Traditionally, many UK jobbing foundries have relied on organic binder systems combined with single mechanical attrition for sand reclamation, producing hazardous waste sand, making disposal increasingly complex and costly, and limiting the potential for beneficial reuse.

As a result, such inorganic binder systems are gaining traction as a more sustainable alternative. Though they often yield lower reclamation rates when using standard dry attrition, the resulting sand is non-hazardous and significantly easier to reuse or repurpose.

This gives the foundry the opportunity to omit these liabilities without incurring significant capital investment. Furthermore, with a double mechanical attrition process coupled with drying, reclamation levels of eighty to ninety per cent can be achieved using the John Winter & Co Ltd range of inorganic binders.

Other Foundry Wastes and Recovery Potential

Beyond sand waste, foundries generate by-products from melting, shot-blasting, and fettling operations. These streams can hold untapped value and call for smarter management:

Dust collector fines from electric melting can often be repurposed. For example, fumes from galvanised steel scrap contain zinc oxide, which can be extracted and sold for industrial use.
Silica-rich dusts may have beneficial reuse potential in the glass & ceramics industries.
To preserve reuse potential, it’s essential to segregate dust containing heavy metals, preventing contamination of other waste.
Small foundries may benefit from clustering together to create viable pathways for reusing baghouse dust from melting shops.
Aluminium dross can be sent for metal recovery, though economies of scale again favour collaborative efforts.
Using the John Winter range of fluxes helps reduce aluminium carryover into dross, minimising melting losses.
Some slag by-products are suitable for construction applications, but segregation is crucial – furnace waste with heavy metals must be kept separate.
Collaborate with customers to phase out heavy-metal alloys (e.g. leaded gun metals). In the US, bismuth is now preferred in copper-based alloys, virtually eliminating lead use.

Material Choices to Enable Reuse

To promote waste reuse and reduce environmental hazards, foundries should explore:

Non-crystalline silica refractories, which simplify safe disposal and repurposing.
Ceramic sands, which reduce crystalline silica content in shot-blast and fettling dusts.
Good housekeeping practices to minimise chemical waste and waste oils, ideally working with suppliers for recycling or take-back schemes.
Transitioning to non-hazardous materials throughout the process wherever possible.
Regular audits of all waste streams to uncover potential reuse or safe treatment options.
Airborne emissions and sustainable alternatives.

Foundries in Europe face increasing pressure to control volatile organic compound (VOC) emissions and airborne pollutants like formaldehyde. Some sites have installed afterburner systems, but these carry high carbon footprints.

More Sustainable Alternatives Are Emerging

Inorganic binders are now widely adopted in the aluminium sector and are being trialled in ferrous casting applications to reduce emissions.
Products like JW’s Winterbond and Geopol inorganic no-bake systems contain zero VOCs and yield non-hazardous waste sands, ideal for beneficial reuse.
JW’s Zero-VOC greensand release agents include:

PF880 (hydrocarbon-based)
PF990 (vegetable-based), which significantly lowers the carbon footprint.

By implementing these materials, foundries can virtually eliminate airborne emissions and odours.

Conclusion – Managing Foundry Sand Waste

Increase beneficial reuse opportunities.
Invest in advanced reclamation technologies.
Adopt non-hazardous processes to enable safe reuse.
Continuously audit and optimise sand waste handling.

Conclusion – Handling Metallurgical and Process Waste

Segregate waste with heavy metals to avoid cross-contamination.
Collaborate with customers to remove hazardous alloy elements.
Use low silica refractories to reduce airborne hazards.
Recover and reuse aluminium dross and slag.
Cut melting losses with proper fluxing.
Minimise chemical waste – work with suppliers on take-back schemes.

Strategic Takeaway

Above all, foundries should prioritise non-hazardous production, waste stream optimisation, and collaborative approaches like clustering to make sustainable practices economically viable.