A method for processing MgCl2 solutions including the steps of: providing an aqueous solution including 5-25 wt. % of MgCl2 and optionally organic contaminants to a step, wherein water and present, organic components are evaporated; withdrawing aqueous solution with a MgCl2 concentration of 25-35 wt. % from an evaporation step and providing it to a preconcentrator where it is contacted with a HCl containing gas stream at least 300° C.; providing aqueous solution with a MgCl2 concentration of 35-45 wt. % resulting from the preconcentrator to a thermohydrolysis reactor, being at at least 300° C.; withdrawing MgO from the thermohydrolysis reactor in solid form, and withdrawing a HCl containing gas stream from the thermohydrolysis reactor, said HCl-containing gas stream at least 300° C.; providing the HCl-containing gas stream with at least 300° C. to the preconcentrator; withdrawing a HCl-containing gas stream with a temperature of at most 150° C. from the preconcentrator.