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molten slag

Globally, smelters separate ore into matte and slag. Slag is the waste by-product and non-ferrous slag for the extraction of copper, nickel, phosphorus, etc. is predominantly perceived as waste and a liability.

Molten slag can instead be cast into large self-annealing stone blocks for architecture projects. Slag can profitably be a substitute for other products, reduce the impact of hazardous leaching and help reclaim natural habitats from both mining and other industries by substituting new material extraction with unused slag.

Currently, 66 million tons of slag from global non-ferrous smelting sites are wasted each year and the mining industry pays to manage this liability. 

Slag is typically poured from crucibles onto huge slag heaps and mining companies spend millions on insurance, lining dumps with HDPE impermeable membranes and covering slag in a custom mulch of wood fibres and glues. Slag leaches heavy metals into surface and ground waters and the metal-containing soils or sediments are transported by wind to further extend the areas of contamination. Therefore it is difficult to find a use for the granulated crush as small particles will leach more than consolidated masses. 

Concerns about leaching now limit mines from selling slag and it is instead stockpiled pending future extraction of minimal residual ore. At the same time, natural habitats are perpetually disturbed to produce 120 million tons of finished stone, immeasurable brick volume and 2 billion tons of concrete each year.

Even though researchers have confirmed that leaching risks could be mitigated if slag is just removed from contact with water, we continue our discriminatory consumption of “valuable” materials and neglect these “waste” materials that actually retain considerable value. We need to regain the historically understood method for thriving on a whole systems approach to consumption.

slag benefits

A key insight for our strategy came from seeing 18th century slag buildings around the world. For example this building still stands in Falun, Sweden next to a very old copper mine that is now designated as a UNESCO world heritage site.

In order to align with our current leaching knowledge, molten slag from crucibles can be diverted to large formwork to produce lower surface area to volumne slag products. We can capitalize on the liquid state by casting large cubes near smelters. Due to this reduced ratio of surface area to volume for leachine, the cubes also benefit thermally as they self anneal into stone without the addition of any thermal energy. 

These large consolidated masses of material resemble granite or basalt and can be quarried down to transportable dimensions. They can subsequently be taken to a fabrication site near the smelter for finer work.

Beyond the historical examples, slag can be squared, honed, polished, sealed, mounted with brackets or structural joints and used for compression structures or as surfaces for steel, wood or concrete buildings. These slag blocks have value due to their high compressive strength, sound isolation, thermal absorption, fireproof nature, castability, hardness, low cost, and positive environmental impact. Construction with prefabricated pieces also limits waste on project sites. 

key milestones

We have already productively made use of slag in our Formid seat design as a dense counterweight material for the carbon sequestering structural paper above. This product is meant to initiate a change in the perception of industrial molten slag from a waste product into a viable design medium.

We have been designing with slag since our architectural graduate thesis at the University of British Columbia, School of Architecture + Landscape Architecture. Since then we have been working with VALE in Sudbury to develop a molten casting strategy. 

We have iterated the casting process for blocks a few times already and with our latest revision we have yielded our first consolidated massive block.

Ongoing success and impact will be measured according to the conversion of a single key performance indicator, the slag volume consumed. This metric will indicate the economic impact on mining operations, reductions in leaching impact, the reduction in carbon dioxide emissions, and recovery of natural habitat through the substitution of three primary product streams (stone, brick and concrete) and it can be easily measured.

slag architecture

Our architectural prototype is currently being iterated in order to identify uses and techniques for slag that are materially appropriate leading to a unique method of building with slag unlike conventional construction strategies.

Stay tuned for more...

get involved

Mining companies are required to draw minerals from the ground for everyone’s use but are then expected to deal with the repercussions of mine waste alone. We would like to help relieve pressure from mining operations by transferring the responsibility for this waste over a larger network. We anticipate many positive outcomes from this collective approach and we need your help to identify building projects in your community that are a good fit for slag!

We are currently investigating the material properties of the cast cube and are planning for a simple use of a few cubes as a simple starting point to demonstrate the basic premise. The next phase will entail more precise structural testing to generate a single story structural pavillion. This will significantly broaden the potential applications for slag. The end goal will be to organize a multi-story use of slag. Ultimately, the mission of this work will be to eliminate any further slag waste and propogate the architectural solution to other mining sites around the world.

Global material consumption of extracted metals should be equivalent to the consumption of its waste products such as slag in order to maintain homeostasis. Therefore ideally a proportionately equal amount of metal and slag designs would need to be built. We can calibrate the production of one design to the other in order to conclude with balanced overall consumption (lowest environmental impact) as long as we have a design capable of consuming both sides of the equation. For instance, animals create CO2 and destroy O2 while vegetation creates O2 and destroys CO2 and neither gas is waste but we need both organisms to stabilize the gases. In a closed system like our planet it is more important to proportion the two sides to maintain balance but our contemporary problem is that we don't have a slag material design capable of balancing the equation of our metal extraction.  


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