Mining circular economy: Potential of rice husk ash as an alternative mineral source in the production of clay ceramics using simplex design

Abstract

To determine the feasibility of using rice husk ash (RHA) in clay ceramic production, a design of experiments (DoEs) method was employed to test 10 different formulations. The vertex formulations (from triaxial diagram) were tested to obtain their chemical (XRF), mineralogical (XRD), and thermal properties (DSC/TG). After obtaining the optimum lower and upper limits of the materials, all formulations were further evaluated in terms of particle size (>45 µm), plasticity (Atterberg), real density (helium gas pycnometry), drying shrinkage at various humidities (Bigot’s curve), and technological properties exhibited after thermal processing namely, total shrinkage, water absorption index, apparent density, and diametral mechanical strength. The integration of RHA into ceramic paste showed positive impacts on the drying process and dimensional control - higher RHA content decreases shrinkage and stabilizes the drying more quickly; however, it reduced the density and plasticity of the formulations. The use of RHA > 25% left the plasticity index < 10, impairing the workability of the paste. The results of the mixture design method indicated that RHA could only be used in a limited capacity of 15% by mass; higher RHA contents would make the water absorption index exceed the threshold established as per the technical standard (25%).