Method of treating reflux lyes containing various halides

Aqueous effluent liquors such as those derived from the ash-slagging of coal are treated to remove halide, eg. chloride ions by heating the liquor to 400°C to 500° C and contacting the vapor with, for example, a fixed or fluidised bed of calcium carbonate maintained at the reaction temperature. During the heating, the temperature is increased at a rate of at least 50° C sec-1 over the range 100° C to 300° C. The treated liquor may be used as a reactant in the ash-slagging gasification of coal.