The solid-liquid extraction of lanthanum(III), europium(III), and lutetium(III) by mesostructured silicas doped with 1-phenyl-3-methyl-4-stearoyl-5-pyrazolone (HPMSP, bearing one chelating site) or with 1,12-bis(1'-phenyl-3'-methyl-5'-hydroxy-4'-pyrazolyl)-dodecane-1,12-dion e (HL-10-LH, bearing two chelating sites) has been studied and compared to the analogous solvent and micellar extractions in terms of the stoichiometry of the extracted complex and of the extraction efficiency. The solid-liquid extraction order in the lanthanoid series is La < Eu < Lu; it is the usual liquid-liquid extraction order obtained with acidic extractants. A theoretical model is used to determine the stoichiometries of the extracted complexes and the extraction yield is measured as a function of the pH, of the extractant/metal ratio (S/M) and of the volume ratio of the two phases (phi). For HPMSP, the extracted complexes involve three ligand molecules for one metal. For HL-10-LH, the complex stoichiometries are found to be either Ln(L-10-L)(L-10-LH) (Ln = La, Eu) or Lu-2(L-10-L)(3) for S/M = 25, or Eu-2(L-10-L)(3) for S/M = 5. For the first time, the synergistic solid-liquid extraction is studied after a successful attempt at simultaneously immobilizing both extractants HL-10-LH and 2,4,6-tri(2-pyridyl)-1,3,5-triazine, "TPTZ", into silica; the complex extracted in this case differs from the one obtained in solvent extraction.