[en] The aim of this study is to determine for which conditions humic substances modify the migration, and in particular the retention of actinides onto mineral surfaces and under relevant geochemical conditions (pH, ionic strength, presence of competing cations). For this purpose, the behaviour of humic substances towards mineral phases is important to know, and particularly the formation of an organic film. The objective of the present work is to study the retention of humic acids onto hematite as a function of physico-chemical parameters (pH, ionic strength, humic concentration) and to appreciate the effect of this phenomenon onto the actinides retention onto mineral surfaces. In the framework of this study we choose a system consisting of hematite (α-Fe₂O₃), one of the major component of the colloidal matter contained in natural waters, Aldrich humic acids and thorium(IV). Cromieres et al. already quantified the interaction of Th(IV) with hematite colloids using non electrostatic and diffuse double layer surface complexation models, and the hydrolysis constants recommended by Baees and Mesmer. The objectives of this work are to study the influence of humic acids upon the sorption of a tetravalent actinide upon hematite. (orig.)