The invention relates to a combined process for the adsorption of metals in a liquid and for the neutralisation of metal-containing waste acids. The adsorption material used in the process is in the form of a geological mineral containing at least one alkali metal and/or alkaline earth metal, e.g. wollastonite (CaSiO.sub.3) , magnesite (MgCO.sub.3) or burnt magnesite (MgO). The spent adsorption material that has been used in the adsorption process is thereafter used as neutralisation agent for the neutralisation of waste acids, such as spent pickling baths. The application moreover relates to an adsorption material comprising a geological mineral containing at least one alkali metal and/or alkaline earth metal, which mineral has been concentrated by crushing, milling and shake sieving in a dry state.