Highly porous ceramics production using slags from smelting of spent automotive catalysts

Abstract

Spent automotive catalysts are the most crucial secondary resources of platinum group metals (PGMs). Currently, the iron-capturing method is one of the most promising technologies for PGMs recycling. The residual smelting slags contain large amounts of CaO, Al2O3, MgO, SiO2, Na2O, and the trace of heavy metals (e.g. Cr, Pb, Ni), which are classified as solid waste or even hazardous waste, which are typically treated by landfills, and poses severe threats to the environment. In this paper, based on the specific chemical composition of smelting slags, ceramic foams with high porosity, low density and good thermal insulation were fabricated by particle-stabilized foams method, where long-chain surfactant hexadecyltrimethylammonium chloride served as the hydrophobic modifier of slag particles and colloidal silica as binding agent. Herein, the influence of sintering temperature and the amount of smelting slag on the physical properties of obtained porous ceramics were systematically investigated. The results showed that porous ceramics with a bulk density of 0.40–0.64 g/cm3, open porosity of 74.7–83.4%, thermal conductivity of 0.10–0.21 W/(m∙K) and compressive strength of 1.04–4.01 MPa can be obtained with the mass ratio of slag: colloidal silica of 2:1, 3:1 and 4:1 sintered at 1000°C for 2 h. The porous ceramics with these unique properties are promising to be applied as thermal insulation materials. This convenient, facile and versatile approach is also expected to fabricate porous ceramics by using other solid waste as raw materials.