Alkalis are highly corrosive towards materials associated with syngas processing and utilisation, including ceramic particulate filters and metallic components. The removal of alkali species, consequently, is an important step in the cleaning of coal and biomass-derived syngas. The origins of the alkali contaminant govern the ability of specific sorbents to remove these species via chemical means. Alkali salt removal is dependent on the formation of an acid halide species, a reaction, which in the absence of H2O, involves hydrogen and carbon dioxide. This reaction becomes increasingly unfavourable above 1000 °C, but below this temperature, equilibrium conversion approaches 100%. The fluxing of a gasifier slag, which is often necessary to reduce viscosity to a level that allows tapping, reduces its ability to absorb alkali halides. This effect however was not observed with oxide-based alkalis, which shows strong affinity for gasifier slag regardless of fluxing, up to 1600 °C. Furthermore, there is a potential for removal of boron and phosphorous contaminants using these same sorbents. In a complete high-temperature, dry gas cleaning sequence, alkali removal would ideally be undertaken prior (or simultaneously to) halide removal and prior to sulfur removal. © 2011 Curtin University of Technology and John Wiley & Sons, Ltd.