## 1 Introduction  
Cork is a plant tissue that has always been used for multiple purposes, and it is considered a sustainable and environmentally friendly raw material [1]. It is composed of cells that, once dead, are replaced by air, creating an airy and light material that is elastic and compact [2]. Cork is also a natural material that is compressible and flexible, and it has very low thermal conductivity [3]. One of the various uses of cork is the manufacturing of caps for wine bottles, champagne, cognac, vinegar, etc. There are several advantages of using this material for bottle capping. A cap retains more CO2 than it releases during production (approximately 309 g absorbed against 300 g sold) [2]. In the production of corks, waste arises that must be managed; hence, the purpose of this research was to investigate this waste. In particular, we focused on the scrap produced by a company in northern Italy in the agglomerate cork trimming phase. This cork residue is about 80% wt. cork (imported from Portugal, which is the largest cork producer [4]) and 20% wt. additives (polyurethane glue, paraffin and others). There are currently agreements to return this residue to the Portuguese supplier involving high environmental and economic costs related to transport; therefore, an alternative valorisation on the territory would appear to be an interesting option. One possible recovery strategy, alternative to the one proposed in this work, was proposed in a study conducted in Portugal in 2017 [5]. It concerned the feasibility of gasification of industrial cork waste using a semi-batch fluidized bed reactor. The tests were carried out using air as an oxidizing agent and sand particles as the bed material at a bed temperature of 780-900 \({}^{\circ}\)C. Cork waste pelletization to allow its use as fuel for direct combustion or gasification was proposed by [PERSON] et al. [6]. The study presented here included an initial phase concerning the optimization of the cork-waste pyrolysis process, aimed at obtaining a carbon residue (char) to be included in the formulation of lightweight silicate matrix materials. The second phase corresponded to a feasibility study of the material realisation. To the best of the authors' knowledge, there are no previous scientific studies concerning the pyrolysis process involving the production of two kinds of porous ceramics for cork waste valorisation. Pyrolysis is an endothermic process where biomass is heated up in the absence of oxygen at temperatures in the range from 300-800 \({}^{\circ}\)C and thermal decomposition of large hydrocarbon molecules into smaller molecules in the forms of gases (such as CO and CO\({}_{2}\)), liquids and solids (char) takes place [7]. In this case, the objectives were the thermal degradation of the unwanted components and the reduction of the size and mass through the carbonization process. In addition, received cork powder (not yet pyrolysed) has previously shown unsatisfactory performances in the clayey matrix [8]. Char is the solid product of the pyrolysis process and has the ability to retain a part of the carbon that would be dispersed into the atmosphere in a solid form recalcitrant to decomposition for hundreds of years [9]. Furthermore, if char is returned to agricultural land, it can permanently increase the carbon content of the soil and create a carbon sink for atmospheric CO\({}_{2}\). However not all chars are suitable as soil amendments. Only a specific niche of chars, called biochars, can be used for agronomic applications. Biochars need to meet specific characteristics defined by the European Biochar Certificate or the International Biochar Initiative [10,11]. One of the key requirements consists in the absence of toxic impurities in the biomass [10,11]. In this work, the starting feedstock consisted of a blend of cork scraps containing organic additives (glues and adhesives) and virgin cork.