Conversion of Plaster Molds Wastes Into the New Inorganic Products by Thermal Dehydration

Abstract

Solving the environmental issues by reducing the waste generated by the industries of building and ceramic materials is a global priority due to their impact on the human health and ecosystems. Recovery of plaster molds wastes from fine ceramic industry is an important topic to address in order to reduce the use of natural gypsum resources and address environmental issues generated by solid wastes from landfill disposal. The main objective of this paper is related to the thermal behaviour study of the calcium sulphate dehydrate during the calcination and to determine the kinetic parameters for the dehydration reactions. Also, the effects of different heating rates on the course of dehydration are investigated, pointing out that the general state of dehydration does not change, although at a given temperature the mass loss is the same for different heating rate. On the other hand, the increase in the heating rate displaces the reaction towards high temperatures. Thus, based on the kinetic study carried out, it was established that the dehydration process needs to take place approximately 50 minutes at a constant temperature of 373 K. Finally, the dehydrated waste is used to obtain a new inorganic material, which can be used for geopolymer preparation. For geopolymeric mortar, 5 % and 10 % from fly ash was replaced with gypsum. The solutions of NaOH 5M and sodium silicate were used to activate the geopolymer. The obtained results indicated a good geopolymer structure formation.