## 1 Introduction
Furthermore, in the EU, new regulations and directives were posed concerning the environment, such as the waste frame Directive 2008/98/EC, which poses the priorities for handling the wastes, ordered as follows [12]: (a) prevention, (b) preparation for reuse, (c) recycling, (d) recovery, and (e) disposal. Even the increasing interests in the waste disposal of recycling spent refractories are a common approach worldwide for the management of spent refractories. Therefore, reuse and recycling become of higher importance and influence handling of the spent refractories. The decision to reuse or recycle the refractory waste depends on a set of parameters, the most important of which are (a) the quality of the spent refractories, (b) the previous use of the refractories and the substances deposited on their surface, (c) the type of refractory, (d) the composition of refractory materials which could contain potentially toxic elements posing a threat to human and ecosystems, and (e) the leachability of potentially toxic elements from refractories. Another significant parameter to be considered is the type of recycling process. The closed-loop process concerns the use of the spent refractories producing new refractories. This is the most attractive since the recycling of the spent refractories is focused on added-value products with high production cost as far as the required energy is concerned. The interest in reusing refractory spent materials with better environmental characteristics is expected to grow in the upcoming years. Therefore, it is crucial to evaluate the ecotoxicological potential of the refractory spent materials. The evaluation of potential ecotoxicity of products/materials has been applied in several works [13; 14]. The approach for evaluating the potential environmental risk of granular solid materials for ecotoxicological potential and landfilling was based on the Council Decision 2003/33/EC [15]. The appropriateness of the spent refractories for recycling is strongly dependent on the quality of the spent refractory and the clearness as far as the environmental impacts and health issues are concerned. The Council Decision 2003/33/EC discretized 15 components and their limits with respect to the content of the material used for which these can be characterized as inert, nonhazardous, and hazardous. In general, the proposed thresholds of concentration for the 15 components provide a guide for the acceptance for recycling of the wastes. A question is raised concerning the appropriateness of the spent refractories and the types of products of the recycling, and this decision is complicated related to (a) the kind of mineral of the refractory (chromite, dolomite, SiO\({}_{2}\), MgO, Al\({}_{2}\)O\({}_{3}\), etc. ), (b) the use of the recycling products in the industries whereby different qualities of refractories are used for different industries, and (c) the chemical and physical characteristics of the spent materials and, most importantly, their environmental appropriateness. However, there is no commonly accepted approach in the literature that evaluates and quantifies the environmental appropriateness of waste materials by considering the concentration of the 15 components together with expert judgment. This study aims to fill this gap and is focused on the development of a methodological approach for (a) the discretization of the spent refractories to those that can be recycled, and (b) the development of a measure for the identification of the environmental appropriateness of the spent refractories which can be used for recycling. The measure is based on a structured multicriteria decision aid (MCDA) approach described later on, which will support decisions concerning the kind of recycling that can be used for any type of waste. The paper is organized as follows: Section 1 includes the introduction which provides an overview of the current literature related to the specific topic.