Sustainable Optimization of Lightweight Aggregate Production from Bauxite Residue via Nonlinear Programming

In this work, lightweight aggregates were developed from mixtures of bauxite residue and clay, using a nonlinear programming model to determine the optimum composition. The aggregates were characterized using TGA/DTG/DSC analysis, X-ray diffraction, scanning electron microscopy and physical tests of apparent density, porosity and water absorption, carried out on three samples (BR50, BR30.50 and BR0). The results showed that the bauxite residue favored the formation of amorphous and porous phases, reducing the density of the aggregates. A nonlinear programming model was developed to determine the optimal composition of a lightweight aggregate, resulting in a mixture containing 30.50% bauxite residue and 69.50% clay. This composition yielded a material with a density of 0.78 ± 0.03 g/cm³, porosity of 14.54 ± 1.13%, and water absorption of 14.05 ± 1.72%, confirming its classification as a lightweight aggregate. The reference sample, with 100% clay (BR0), had a density of 2.20 ± 0.02 g/cm³ and a more compact structure. The proposed model proved effective in maximizing density and porosity without compromising the integrity of the aggregate, indicating that the use of bauxite residue is a promising and sustainable alternative to produce materials for use in civil construction.