A novel mechanical process for CRT glass recycling

Dismantling of Cathode Ray Tubes (CRTs) represents a pressing environmental problem. Dismantled CRTs are generally used in the production of new CRTs in close-circuit recycling scheme, but in Europe, due to the technological changes towards flat panels, CRT technology is becoming obsolete, so new applications must be found. On the other hand, new legislation, such as the European Directive on Waste Electric and Electronic Equipment (WEEE), will require increased recycling and recovery rate, while landfilling should be more and more a residual option. CRTs contain mainly two types of glass (funnel and panel), welded together with a lead frit. In color equipments, the funnel contains a significant quantity of PbO (18–20% in weight), and present a carbon coating on the inside. The panel, instead, is characterized by high levels of BaO (9–11% in weight) and SrO (8–10% in weight) and it is coated with a matrix of thousands of tiny phosphor dots, constituted by chemicals which emit light when excited by a stream of electrons. Furthermore, a significant presence of iron characterizes CRT glass, which must be reduced to let glass recovery in open-circuit scheme. In-depth investigations need to evaluate the feasibility of open-circuit recycling scheme, considering technical features, quantities, environmental implications and economic considerations. In this study, a novel mechanical process for CRT glass has been tested at industrial scale to obtain a product able to meet the required market standard. The process consists of an attrition operation controlled by a screening unit. It has been monitored in order to set up the best working conditions in terms of fine particles production and quality control. The products (input, oversize and undersize) have been characterized by image and chemical analysis to determine morphologic, morphometric and compositional properties. For the input and oversize products, image analysis shows as particle morphology shifts to circularity after processing, presenting a more uniform shape. The analysis on the color intensity on the particle surface shows as the output product is characterized by a brighter color. These results could be related to the removal of the conductive coating on inside surface, composed by phosphor dots in the panel and by graphite and Fe oxide in the funnel. The analysis on under-size product allowed individuating the suitable rotational speed and water content to control fine particle production and decontamination.