The invention refers to a process to separate silicates and alkaline earth metal carbonates implementing at least one hydrophobically modified polyalkyleneimine, wherein: i) the polyalkyleneimine is hydrophobically modified by replacement of all or part of the hydrogens of their primary and/or secondary amino groups by functional group R, where R comprises a linear or branched or cyclic alkyl and/or aryl group and contains 1 to 32 carbon atoms; ii) prior to modification, the polyalkyleneimine has at least 3 alkyleneimine repeat units and a molecular weight of between 140 and 100 000 g/mol; iii) modification of the polyalkyleneimine results in an increase in the atomic C amount, relative to the unmodified polyalkyleneimine, of between 1 and 80%.