**Acknowledgements**

The authors wish to acknowledge the financial support from the CDTI projects "Systems to recycle aqueous effluents with valorisation of contaminants and reduction of discharges. Total oxidation of contaminants in effluents by using Ecomaterials" (CDTI IDI-20091139), "Devel‐ opment of applications of glycerine sub product of biodiesel with catalysts made from Ecomaterials" (CDTI IDI-20121298) and "Design of sílica with controlled texture to be used in detergency using as raw material rice husk ash" (CDTI IDI-20143711-20143713) and the Spanish National Science Council for the projects "Valorisation of agriresidues for generation of biocompatible materials (Ecomaterials) to be used in dental implants" (INNPACT IPT-2011-1935-310000), "Preparation of materials from agro industrial residues for biomedical uses" (PIE CSIC 201480E103) and "Valorisation of Spanish agriresidues for advanced uses" (PIE CSIC 201460E105).
