There is provided a method of producing a mixed metal compound comprisingat least Mg2+ and at least Fe3+having an aluminium content of less than 10000 ppm,having an average crystal size of less than 20nm (200A)comprising the steps of:(a) combining a Mg2+ salt and a Fe3+ salt with Na2CO3 and NaOH to produce a slurry, wherein the pH of the slurry is maintained at from 9.5 to 11 , and wherein the Na2CO3 is provided at an excess of 0 to 4.0 moles than is required to complete the reaction(b) subjecting the slurry to mixing under conditions providing a power per unit volume of 0.03 to 1.6kW/m3(c) separating the mixed metal compound from the slurry, to obtain a crude product having a dry solid content of at least 10 wt%(d) drying the crude product either by(i) heating the crude product to a temperature of no greater than 150°C and sufficient to provide a water evaporation rate of 0.05 to 1.5 kg water per hour per kg of dry product, or(ii) exposing the crude product to rapid drying at a water evaporation rate of 500 to 50000 kg water per hour per kg of dry product.
