A concise analytical strategy applied to waste treatment technology

Studying the mechanisms at work in waste technologies, such as waste-immobilisation, reactive barriers for waste containment, waste–waste neutralisation, etc., requires an integral characterization of materials. Materials before and after processing should be characterised in terms of (a) proportions of phases (liquids and solids), (b) composition and homogeneity of phases, (c) grain-size distribution (ideally per phase), and (d) large-scale compositional gradients within the system. Novel techniques can be applied successfully such as Rietveld-analysis of powder-XRD patterns to determine the modal proportions of fine-grained solids and laser-ablation–ICP–MS to determine trace element distributions on a ≈10-μm scale. Mathematical mass-balance and diffusion models provide checks for consistency in the characterization of materials. A case study is presented on a geochemical engineering treatment of red mud, the waste product of bauxite processing.