Integration of a novel mechanical sand reclamation technology in a steel foundry to maximise SFS valorisation in foundry and construction applications

Spent Foundry Sand (SFS) generation is intrinsic to metal casting processes. Most of the foundries use sand moulds and cores for casting, which are discarded after pouring. The nearly 3000 active foundries in Europe generate over 9 Mt of waste sand annually, being ferrous industries the major generators. Only 25-30% of that waste sand is recovered in a few applications, namely in cement industry, agricultural soils and landfill covering. But these sectors are unable to absorb the total amount of sand generated, so the remaining percentage is still landfilled.

Landfill of foundry sand remains a severe environmental problem in Europe due to its significant quantity. Besides, it means that a huge amount of available material with interesting properties for potential recycling (silica mineral) is missed. Silica sand, although abundant in nature, is a non-renewable resource, whose extraction (quarrying and dredging), processing and
transportation translates into significant environmental impacts in terms of Global Warming Potential (92-120 g CO2 equiv. per 1 kg of dry silica sand obtained), air pollutants, noise, loss of soil (estimated at 0.4 ha per tonne of sand extracted) and altered natural landscape, with associated loss of wildlife habitat. The re-use of foundry sand would minimise these impacts.
Use of SFS as secondary fine aggregates in a material intensive sector such as construction offers promising valorisation options. The sand must meet relevant technical specifications for each application and, additionally, fulfil several environmental conditions for unbound uses, where the sand is directly in contact with the soil. The EU-funded LIFE ECO-SANDFILL project is investigating the use of SFS as fine aggregate in construction applications, specifically for geotechnical applications (embankments) and for flowable mortars and Controlled Low Strength Material (CLSM). The potential for high-quality reuse in foundry is being evaluated also.

To this end, a prototype of a novel mechanical SFS reclamation system, based on attrition of the sand grains by means of centrifugal force, has been constructed and integrated in the moulding sand circuit of a steel foundry located in the Basque Country (ES). The SFS generated in the foundry, after metal casting and de-moulding, is being treated in the prototype to remove impurities from binders and the casting process and to make the reclaimed sand reach the required quality for the different applications envisaged in the project. The environmental, technical and economic performance of the solution will be validated in three full-scale case studies to be executed in the construction works for the Madrid-Irun High-Speed Railway
Network, in the vicinity of the foundry and through a pilot casting trial of steel parts in the foundry itself, using reclaimed sand in the manufacture of the moulds.

This paper describes the preparatory activities carried out before executing the casting and construction demos, focused on dosage studies and characterisation tests of a series of sand samples and specimens manufactured using SFS (untreated and reclaimed) in their formulations. From the chemical analysis results, it has been concluded that the reclaimed sand obtained in the integrated prototype coupled to the chemical sand circuit of the foundry fulfils environmental conditions for construction applications and could be safely used in mortar, CLSM and embankment demos, provided that applicable technical requirements are met. In the case of foundry applications, it has been found that reclaimed sand does not meet the stringent specifications for coremaking. The performance of several moulding mixtures for a PEP SET system, with varying quantities of thermally reclaimed sand, primarily mechanically recovered sand and sand reclaimed in the LIFE ECO-SANDFILL prototype is compared.