Viability of Belterra clay, a widespread bauxite cover in the Amazon, as a low-cost raw material for the production of red ceramics

Abstract The Amazon region has the largest bauxite reserves in Brazil, where their deposits are capped by a thick layer of clay material known as Belterra clay (BTC). Its extensive distribution and surface occurrence (and therefore accessibility) and the clayey nature of BTC were of interest for this study, which evaluated its technical viability for the production of red ceramics. BTC from the large bauxite deposits of Rondon do Para in the southeast region of Para state was selected for the study. BTC, yellow soil and clayey siltstone, these two last used as additives, were characterised by X-ray diffraction (XRD), X-ray fluorescence (XRF), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), inductively coupled plasma mass spectrometry (ICP-MS), scanning electron microscopy (SEM) and laser particle analysis (LPA). To determine the physical and mechanical properties, 12 different mixtures of specimens were produced with the samples of Belterra clay and 40% yellow soil or clayey siltstone. All mixtures were calcined at three different temperatures (900, 1000 and 1200 °C). Next, the following were measured: linear shrinkage, water absorption, apparent porosity, apparent density and flexural strength. The BTC essentially consists of kaolinite, which contains quartz, goethite, anatase and gibbsite as accessory minerals. The pure and simple BTC samples do not present favourable technological aspects for the manufacture of ceramic products; however, with the addition of yellow soil or clayey siltstone from the same region, the technological characteristics of BTC are significantly improved.