The present work describes the sorption of Cs⁺, Sr²⁺, La³⁺ and Th⁴⁺ on Fe₃O₄ nanoparticles (NPs). The selection of metal ions was done on the basis of different charges to see its effect on sorption. Experiments were carried out at two different pH, 6 and 9 and in presence of NaCl salt to see the effect of these factors on metal ion removal rate. Interestingly no sorption of metal ions were observed at pH ∼ 6 while at pH ∼ 9 only Sr²⁺ and La³⁺ ions can be selectively sorbed on NPs surface. Experiments in presence of high concentration of salt suggest that the presence of salt does not have an appreciable effect on sorption suggesting the formation of an inner sphere complex of these metal ions on NPs surface. Sr²⁺ and La³⁺ sorption over NPs surface facilitates the enhancement of settlement of NPs. NPs settlement rate was monitored in presence of different metal ions and interestingly was found to vary with metal ions. The results were explained on the basis of DLVO theory, HSAB (hard soft acid base) principle, hydrogen bonding and different charges on metal ions.