Desenvolvimento de membrana nas cerâmicas tubulares obtidas a partir de um resíduo da produção de alumina.

Abstract

The Bayer process uses bauxite as raw material to obtain alumina. This process includes four stages: digestion, clarification, precipitation and calcination. The waste generated during the calcination step is a product with small particle size, known as ESP dust. This research aimed to develop tubular ceramic membranes using in its composition the ESP dust, an alumina powder from electrostatic precipitator, and a bentonite clay. Initially, the characterization of the precursors was performed. Two samples were studied, one from crude residue and other from calcined residue at 1200°C. These samples showed a high content of alumina in chemical compositions. The gibbsite and α-alumina phases were identified in crude residue and after calcination gibbsite was completely transformed into α-alumina. Were observed no significant changes in particles size and morphology after calcination, but during this process, the particles become porous, probable due changes in crystalline phase of alumina and the water outlet of crystals. Among twenty different formulations tested to produce ceramic membranes, four compositions showed better results with regard to the extrusion processing: two compositions with crude residue and two with calcined residue. In this paper, tubular membranes produced from alumina residue and bentonite clay were sintered at 900, 1000 and 1100°C. It was observed that the produced membranes had surfaces with distributed pores. The apparent porosity was between 47.70% (composition with 60% of calcined residue and 40% of bentonite clay sintered at 1000°C) and 58.40% (composition with 70% of crude residue and 30% of bentonite clay sintered at 1000°C). Tangential flow tests were performed with deionized water at pressures of 1.0; 1.5 and 2.0 Bar. Higher permeate flow rate (909,24L/h.m2) was observed for membranes made of a composition containing crude residue (70%) and bentonite clay (30%) sintered at 1100°C, applying pressure of 1 bar.