PROJECT DESCRIPTION
BACKGROUND
Thermal spraying refers to a group of versatile coating technologies used to deposit thick (50 μm - >1 mm) layers of ceramic, metallic or composite materials for a variety of applications. This technology is used, for example, in industry to protect mechanical parts (e.g. shafts, joints and plungers), in aeronautics and energy production to provide thermal insulation, and in the biomedical industry (e.g. coatings on metallic prosthetic implants for dentistry and orthopaedics). During conventional spraying processes, as much as 80 % of the powder is unused and this ‘overspray’ has to be recovered for treatment as waste. These waste treatments have negative environmental impacts. The metallic powders used in thermal spray coatings are often based on nickel (Ni), which is considered to be a human carcinogen. In addition, ceramic powders such as yttria-stabilised zirconia (YSZ) are also considered potentially hazardous. Both Ni-alloys and YSZ are valuable materials, and their waste disposal equates to a loss of primary resources.
OBJECTIVES
The main objective of the LIFE ReTSW-SINT project was to demonstrate the feasibility of valorising and recycling different types of thermal spray waste into high-value products for industrial and household use. The project aimed to select particles with the same base chemical composition in two streams: a) spherical or with size below 60 μm and b) splat-like or with larger dimensions. The plan was to reuse spherical particles to manufacture simple-shaped parts by spark plasma sintering (SPS). Remaining particles were immobilised in a glass matrix to avoid the leaching of heavy metals, and these were used in both reactive and non-reactive silica-based systems to convert the powders into frits (rapidly water-cooled glass powders) and also to manufacture glazed ceramic tiles that have beneficial abrasion resistance, conductivity, electro-magnetic field absorption, and aesthetic properties.
RESULTS
LIFE ReTSW-SINT developed new processes for the production of ceramic tiles and other ceramic products from thermal spraying waste. The new products had a high content of spent thermal spray powders. These new processes therefore take a hazardous waste that is currently disposed of in landfills, and turn it into a new resource for the ceramics sector.
The project partners established a pilot plant where spent powders were separated and sieved to obtain a material of sufficient purity and homogeneity for reuse. Refined powder batches were used in frit and glaze production and in spark plasma sintering (SPS) processes. The project team succeeded in replacing up to 50 % of raw zirconia (a material used in the production of frits) with recycled spent powders, and obtaining SPS products with almost 100 % spent powders content.
The project demonstrated the reuse of spent powders in the facilities of the commercial partners (ceramic and sintering sectors). At Turbocoating, almost 100 % of the waste produced by thermal spraying was reused (in the range of 1 000 to 2 000 kg/month). The waste generated was successfully separated at source, with no cross contamination of different waste streams (different spent powders). In addition, harmful contaminants (e.g. nickel compounds) in frits and glazes were immobilised, so avoiding their leaching into the environment.
In terms of greenhouse gases, carbon dioxide (CO2) emissions for frit production were reduced by about 10 %, in part due to a reduction of almost 100 % in transport impacts (local supply of spent powder instead of zirconia imported from Australia). The environmental load of frit production was reduced by about 14 %; though the environmental benefits are much less when considering the whole ceramic tile life (from cradle to grave) because most of the negative impacts occur during distribution, installation and use. A Life Cycle Assessment (LCA) of the frits/glazes/tiles production line using spent powders instead of raw zirconia, showed a reduction of up to 50 % in the use of raw zirconia for frits, without changing the energy required for the melting/firing phase. Fondovalle and the other project beneficiaries are interested in the industrialisation of the developed process and are looking to introduce a product to the market (based on the process) after additional research. Conclusions from the project suggest that the new product will have comparable production costs to a product made using the traditional process. Recycling of spent powders has continued beyond the project end (about 1-2 tonnes/month).
A number of socio-economic benefits could arise from the uptake of the project’s new technology, including a reduction in worker health and safety risks (calculated at about 18 % considering factors such as toxicity), the creation of new jobs and expertise, and increased market competitiveness at the European level.
The project’s results are relevant to the Waste Framework Directive (hazardous wastes and recycling of spent powders), the Industrial Emissions Directive (immobilisation of harmful compounds), the Energy Efficiency Directive (lower energy use with recovered powders compared to the embodied energy of raw materials such as zirconia), the EU Action Plan for the Circular Economy, and EU climate change mitigation policy.
Further information on the project can be found in the project's layman report and After-LIFE Communication Plan (see "Read more" section).
