## 4 Conclusions  
Throughout the study, it has been possible to glimpse the environmental implications of the partial substitution of three natural clays for different wastes in the manufacture of lightweight ceramic aggregates. In order to determine the environmental impact of this product, the Life Cycle Assessment methodology was applied within the impact categories included in the framework of the CML 2000. Data extracted from laboratory, reference sources and databases such as Ecoinvent were used, processed by SimaPro and subsequently interpreted, always in accordance with the guidelines of the ISO 14040 standard.  
The results obtained in this research allow us to conclude that the addition of organic wastes (nutshells, paper sewage sludge, cork dust and coffee grounds) in the mix represents an improvement over the traditional aggregate (without residue) with which it is compared, although in some cases, this improvement is slight. Of the wastes analyzed, the aggregates with almond and hazelnut shells proved to be the option that would have the least impact on the environment, with reductions exceeding 30% in the most pronounced cases, but remaining at an average of 15%. This, together with coffee grounds, would be the wastes that have proven to be the most efficient in reducing the carbon footprint in the manufacture of ceramic materials under conditions of sintering at high temperatures and reduced times.  
Although one might expect that the addition of paper sewage sludge and paper cork dust would represent considerable improvements due to their high exothermic power, the overall calculation indicates that such improvements would be negligible. They present maximum values that barely reach a 3% improvement.  
The great worldwide abundance of waste such as coffee grounds could be partly diminished by their use in high-demand products. Pellets for consumption in boilers or lightweight aggregates, as we have observed in this study, would be an optimal end with which to seek energy efficiency. The positive change in direction that the world is experiencing towards awareness of sustainability and the reuse of waste materials opens up a range of possibilities with an interesting horizon.  
Conceptualization, T.C.-P. and C.M.-G.; methodology, M.U.-R. and A.B.L.-G.: software, M.U.-R.; validation, M.U.-R., A.B.L.-G., J.M.M.-M. and C.J.C.-C.; formal analysis, M.U.-R.; investigation, M.U.-R. and A.B.L.-G.; resources, M.U.-R.; data curation, M.U.-R. and A.B.L.-G.; writing--original draft preparation, M.U.-R.; writing--review and editing, M.U.-R., A.B.L.-G. and J.M.M.-M.; visualization, C.M.-G.; supervision, T.C.-P.; project administration, C.M.-G.; funding acquisition, T.C.-P. and C.M.-G. All authors have read and agreed to the published version of the manuscript.  
This research was conducted as a part of the ECO-MET-AL Project (PID2019-109520 RB-100). \"Can industrial and mining metalliferous wastes produce green lightweight aggregates? Applying the Circular Economy\" funded by the Spanish Ministry of Science, Innovation and Universities.  
Not applicable.  
Data Availability Statement: Data is contained within the article.  
This research was conducted as a part of the ECO-MET-AL Project (PID2019-109520 RB-100), \"Can industrial and mining metalliferous wastes produce green lightweight aggregates? Applying the Circular Economy\" funded by the Spanish Ministry of Science, Innovation and Universities and ERDF funds, framed in the \"Ayudas a 'Proyectos I + D + i' en el marco de los Programas Estatales de Generacion de Conocimiento y Fortalecimiento Cientifico y Tecnologico del Sistema de I + D + i y de I + D + i orientada a los Retos de la Sociedad, Convocatoria 2019\". The authors also gratefully acknowledge the technical and human support provided by CICT of the University of Jaen and the University of Malaga (UJA, MINECO, Junta de Andalucia, FEDER).  
The authors declare no conflict of interest.