Ceramic shell waste valorization: A new approach to increase the sustainability of the precision casting industry from a circular economy perspective

The problem of waste generation has grown because of the need to extract natural resources, obtain materials, and consume energy to meet current societal needs. Many studies have been conducted worldwide in favor of technological solutions for the valorization of industrial waste (IW) but few discussed relevant data for effective recovery. In this study, a case study of ceramic shell waste (CSW) was performed using, for the first time, a waste valorization system based on the classification, potentiality, quantity/viability, and applicability criteria (CPQvA) in a specific region (Brazil). CPQvA is a multicriteria decision-making system that acts as a guide to help managers and researchers connect the potential of IW with the feasibility of its application in a product or another process. Using the proposed systematic criteria, it was possible to demonstrate similarities and differences in waste applications. Thirteen possible products made from CSW were analyzed based on all the parameters of CPQvA. Ceramic filters and refractory aggregates were the most viable products. Creating public policies that encourage the use of waste as a raw material could make the precision casting industry process cleaner and the economy more circular.

Innovative thermal and acoustic insulation foam by using recycled ceramic shell and expandable styrofoam (EPS) wastes

Ceramic foams were produced using ceramic shell (mullite source), an industrial solid waste from the precision casting process, and expandable styrofoams, EPS (d₅₀ < 1 mm) as pore former, envisaging thermal and acoustic insulation applications. Physical, chemical, structural properties of the selected raw materials (wastes) were characterized. The influence of the amount and morphology of the EPS powder beads on the microstructure, thermal conductivity, acoustic absorption and compressive strength of ceramic shell foams were evaluated. Batches containing well mixed ceramic shell powder (d₅₀ < 2 µm), EPS beads, in different proportions (from 10 to 70 vol%), were added as pore forming agent, and BonderPlus® (Na₂SiO₃ solution) were uniaxially pressed at 20 MPa, dried and fired in controlled conditions. The experimental results showed that homogeneous microstructures of elongated and interconnected pores with sizes between 115 and 1200 µm can be obtained. These connections exhibit a significant impact on the thermal/sound absorption properties, as a consequence of the interaction between air molecules within the pores through the passage of the thermal/sound wave. Ceramic shell foams (containing 70 vol% of EPS powder beads) featured porosities up to 77%, thermal conductivity of 0.061 W/mK, sound absorption coefficient of ∼0.9 (3 kHz), and excellent compressive strength ∼5.4 MPa. In addition, the use of ceramic shells wastes for the manufacture of acoustic and thermal insulators with suitable microstructural characteristics is a great sustainable opportunity, since with the use of this refractory waste, is possible to avoid the release to the atmosphere of about 3.1 kg of CO₂ per kg of manufactured material.