Abstract
The management of waste sand generated by foundries has recently become a crucial concern and has attracted the attention of the South African legislature. Most foundries in South Africa use sand for moulding purposes. Waste foundry sand represents up to 80% of solid waste generated by metal casting facilities. Hence, the characterisation of those wastes is an important area of investigation to determine the composition, nature and classification of this foundry by-product. This work aimed to conduct both physico-chemical and leachate characterisation of the waste foundry sand using X-ray fluorescence (XRF), X-ray diffraction (XRD), scanning electron microscopes equipped with an energy disperse spectrum (SEM-EDS), a Fourier transform infrared (FTIR) sulphur (%S) and carbonaceous content analyser (indicated as loss on ignition or LOI), atomic absorption flame spectrometer (AAFS) and gas chromatography mass spectrometer (GC-MS). In addition the environmental attributes of the foundry sand was assessed by means of the South African waste management regulation. Lastly the eventual reuse options of the foundry sand in other applications were explored.
The results revealed that the waste sand is a completely different material compared to the new sand. The physico-chemical characterisation demonstrated that the waste sand was contaminated by the casting process. Metallic traces from the cast alloy, residual binder, new mineralised phases, coated or fusing sand grains, carbonaceous material, sulphur content and different vibration bonds of silicium-oxygen (Si-O) was noticed within the waste sand. These observations were respectively noticed during XRF, XRD, SEM-EDS, LOI, %S and FTIR analysis. The waste sand leachate characteristic showed a leachable content of metals and organic compounds individually detectable by AAFS and GC-MS. Conversely, the environmental sand classification revealed that apart from the aluminium casting waste sand, brass, cast iron, high chrome and steel casting sand exhibit a marginally higher content of their stipulated hazardous metallic concentrations disqualifying them from being regarded as inert waste. Lastly, the reuse options have proven that the sand could be beneficially diverted to applications such as concrete fine aggregate and hot asphalt mixes.
M.Tech. (Extraction Metallurgy)