Orimulsion fly ash in clay bricks. Part 1: composition and thermal behaviour of ash

A bitumen-in-water emulsion (Orimulsion) is currently used as a fuel in several thermal power plants worldwide. Orimulsion combustion produces a fly ash rich in S, Mg, V and Ni, which is processed to recover metals. In order to assess the feasibility of a recycling in clay brick production, a characterization of the physico-chemical and thermal properties of ash was performed by ICP-OES, XRPD, SEM, BET and TGA-DTA techniques. Orimulsion ash resulted to be fine-grained (aggregates of submicronic particles), highly hygroscopic, constituted mainly of magnesium sulphate, vanadyl sulphates and magnesium and nickel oxides, and thermally instable in the usual brick firing conditions. These features can affect the brickmaking process, particularly the plasticity of the clay body and its drying and firing behaviour; furthermore, a mobilization of sulphates could occur, promoting the formation of efflorescence and/or the SOx release during firing.