A procedure for obtaining hydromagnesite is described. The process involves the formation of a Mg(HCO3)(2) solution by carbonation of a MgO-containing residue slurry and further precipitation of hydromagnesite by addition of pure magnesium oxide as the precipitating agent. The solid residues generated can be landfilled and the water effluents discharged or reused at the plant. The optimum parameters for the precipitation were established, and the kinetic data were examined according to the equation for diffusive control. The activation energy diagram suggests a transition from diffusive to mixed control of the reaction rate. Under certain experimental conditions, an undescribed crystalline structure was obtained, and its stability and structural transformation into hydromagnesite were also investigated.