A process for preparing magnetic activated carbons including the steps of a) treating an aqueous solution having a biomass hydrothermally at autogenic pressure at a temperature 180 and 250° C., under acidic conditions in the presence of iron ions, to obtain a precursor product, b) activating the precursor product obtained in step a) by mixing an activating agent at elevated temperatures between 550 and 850° C., for a period up to 9h. The disclosure also relates to magnetic activated carbon prepared according to the process and use of the carbon for separation and storage of gases and purification of liquids. A method for separation of particles from a liquid and/or a gas, and method for regenerating magnetic activated carbon by heating using an oscillating electromagnetic field are also disclosed.