Recycling of thermally treated cement-asbestos for the production of porcelain stoneware slabs

The directives of the European Commission Environment on the management of hazardous asbestos-containing materials (ACM) are pointing towards treatment and recycling other than disposal in landfills. KRY·AS is a secondary raw material obtained by the thermal transformation of cement-asbestos (CA) and can be inserted in the production line of e.g. concrete, clay bricks, ceramics, and plastic materials. This being a possible future solution to the huge “CA-emergency” in Italy, additional recycling options are sought. In this work, KRY·AS was used for the production of glass-ceramic frits destined for the manufacturing of porcelain stoneware slabs. Two novel frits were obtained by vitrifying KRY·AS together with minor amounts of natural raw materials as well as glass waste. The resulting frits were added in a ceramic body formulation (0, 1, 3, 5 wt.%). Phase composition, microstructure and technological properties of fired samples were evaluated and the results were compared to those obtained when using a standard commercial frit. According to water absorption tests, the novel products can be classified as BIa-type. Comparable or even improved technological properties were found between the standard body and the frit-bearing ones. More precisely, the addition of 5 wt.% of the novel frits led to better stain resistance as well as higher productivity due to reduction of the linear firing shrinkage. Improved mechanical strength (ca. 75 MPa compared to ca 60 MPa for the standard) was also obtained. The novel recycling route of KRY·AS supports a conclusive solution for the management of hazardous CA in Italy.