PRODUCTION OF INSULATING FIREBRICKS FROM HYDROMETALLURGICALLY-PROCESSED CLAYS

Abstract

The production of Insulating Firebricks from indigenous clay deposits for high temperature applications has been studied. Clays were obtained from five different notable deposits within south-west, Nigeria: Ifon in Ondo State, Igbara-Odo and Isan in Ekiti State, Ipetumodu in Osun State and Iseyin in Oyo State. The clays were separately washed and the deleterious particles removed by decantation. They were then drained in Plaster of Paris (P.O.P.) mould for effective removal of the water molecules contained there-in, sun-dried for three days and later in the oven at a temperature of 90 °C for 6 hours. The dried clays were then crushed and subsequently ground to finer size of 100 μm using the laboratory jaw crusher and Rawwley Sussex grinder respectively. The relative proportions of the constituent compounds, the morphology and the phase identification of the different clays were determined by X-Ray Fluorescence (XRF), Scanning Electron croscopy/Energy Dispersive Spectroscopy (SEM/EDS) and X-Ray Diffraction (XRD) analyses. These tests revealed that two of the deposits (Igbara-Odo and Isan clays) had the highest proportions of the most deleterious of the impurities (Fe2O3); 9.226% and 10.408% respectively. They were consequently dropped for the remaining three (Ifon, Ipetumodu and Iseyin clays) whose iron contents were 6.109 %, 5.652 % and 7.266 % respectively. The three samples were then prepared for hydrometallurgical purification using oxalic acid of different concentrations (0.4, 0.8, 1.2, 1.6 and 2.0 mol/dm3) at different times (30, 60, 90, 120 and 150 minutes), temperatures (30, 50 and 70 °C) and agitation speeds (120, 160, 200 and 240 rev/min). The results of the purification process as revealed by the Atomic Absorption Spectrophotometry (AAS) showed that the optimum condition of purification for each deposit is: sample 1(Ifon clay) – 1.2 mol/dm3 at 70 °C for 90 min and 240 rev/min, sample 2 (Ipetumodu clay) - 1.6 mol/dm3 at 70 °C for 150 min and 200 rev/min and sample 3 (Iseyin clay)- 1.2 mol/dm3 at 30 °C for 30 min and 200 rev/min. The bulk of the clays were therefore purified at the identified optimum conditions. The purified samples were again analysed using the XRF, XRD and SEM/EDS in order to confirm the extent of Fe2O3 removal. The results revealed that Fe2O3 was reduced by 53.40, 80.61 and 48.27 % for samples 1, 2 and 3 respectively. Sample 2 (Ipetumodu clay) which showed the best response to purification was therefore selected for refractory tests and the phase identification. Bulk of the selected clay was purified at the identified conditions of leaching and samples (5cm high by 5cm diameter) containing different quantities of alumina cement (5-20 %), and sawdust (1-5 %) were prepared, dried at 110 °C and subsequently fired at 900 °C, 1100 °C, 1300 °C and 1500 °C at the rate of 4 °C /min and soaked for 2 hrs. These samples were subjected to different refractory tests (permanent linear change, refractoriness under load, thermal shock resistance, modulus of rupture, bulk density, cold crushing strength and apparent porosity). For all the properties tested, 3 % sawdust and 10 % alumina cement gave the desired requirement for preparing good insulating firebricks with reliable phase integrity, as revealed by scanning electron microscopy (SEM).