Estudo dos processos de secagem e queima de tijolos cerâmicos com adição de resíduos de diatomita.

Abstract

For the maintenance of industrial activities, humans extract a vast amount of raw materials from nature, a significant portion of which turns into waste or solid rejects. Among the materials that generate substantial volumes of waste/rejects is diatomite, which holds great importance in the industry as a filter and refractory material, in fertilizers, chemical catalysts, pesticides, and other applications. A significant volume of waste is also generated in the ceramic industry due to losses during the manufacturing process in the drying and firing stages, processes that can lead to increased costs when improperly dimensioned. With the aim of presenting an alternative for utilizing diatomite waste in the ceramic sector, the present study constitutes an experimental and computational research using Wolfram Mathematica software. Its primary objective is to conduct numerical and experimental studies of the drying and firing processes of test specimens related to six-hole hollow ceramic bricks manufactured with diatomite waste added to red clay. In the production of test specimens, diatomite waste was added in percentages of 5, 10, and 15%, and all the results were compared to reference compositions in which no waste was added. Drying was evaluated at temperatures of 50, 70, and 90 °C, and firing at 800, 900, and 1000 °C. The results indicate that moisture loss and temperature elevation are affected by the chemical composition of the brick. Higher percentages of waste led to greater water absorption, with the reduction of drying temperature contributing to a decrease in absorption after firing. In all the analyzed scenarios, water absorption remained within the range required by the Brazilian Association of Technical Standards, NBR 15270-1 (ABNT, 2017), which deals with requirements for ceramic components – blocks and bricks for masonry. The material's porosity exhibited a behavior similar to water absorption. Regarding compressive strength, only the samples with 5% of waste, dried at 90 °C, and subjected to firing up to 1000 °C at a heating rate of 2 °C/min, met the requirements of NBR 15270-1 (ABNT, 2017). The physical problem was addressed through a concentrated analysis, and the theoretical curves showed excellent correspondence with the experimental curves. This allowed for the determination of convective and diffusive mass transfer coefficients. These parameters increase as the temperature rises, and the relative humidity of the air decreases during the drying process. Furthermore, it was observed that the convective mass transfer coefficient on the outer surface of the test specimen was higher than that obtained on the inner surface, clearly indicating that the outer surface of the test specimen plays a central role in mass loss throughout the drying process.