Red ceramics enhancement by hazardous laundry water cleaning sludge

Abstract

Permanently increasing number of industrial and municipal wastes accumulated in the dumps, inevitably leads to contamination of soils, surface waters and subterranean waters, the atmosphere and is a perceptible factor of climate change on our planet.This paper is one more proof that waste utilization, as a valuable source of components for new materials production, is environmentally and economically the best way for their management.The purposes of the research were the next: to develop eco-friendly ceramics that include and immobilize hazardous laundry sludge after cleaning of extremely polluted industrial uniforms with high contents of As, Ba, Cd, Pb, Cr, Hg, Cu, Zn and grease, oil, resin, tar, paints, organic volatile compounds, etc.; to improve the mechanical properties of red ceramic, using laundry sludge; to demonstrate a possibility of natural raw materials extraction decrease, partially replacing them with laundry sludge. This sludge was introduced in the traditional clay-sand mix in the amount of 0, 3, 5, 7, 10, 15 and 20 wt. %. After sintering of these composites at temperatures 1000°, 1050°, 1100°, 1150 °C the maximum values of flexural strength resistance of the ceramics was 15.6 MPa, values of linear shrinkage ranged from 4.5 to 14.1%, water absorption values – from 13.0 to 20.3%, and density values ranged from 1.65 to 1.83 g/cm3. All these characteristics of the mechanical properties of the developed materials significantly exceed the properties of ceramics from traditional clay-sand mixes without laundry sludge. The leaching and solubility values of the heavy metals immobilized within these ceramics are hundreds of times lower than threshold levels set by the national standards of Brazil. This study showed that industrial laundry sludge can be safely used as additive to ceramics in proportions of 10–20% wt. %, enhancing the mechanical properties of the materials and constituting an ecological way to manage these wastes.