In this study, inverse spinel cubic ferrites MFeO (M = Fe, and Co) have been fabricated for the high-capacity adsorptive removal of Hg(II) ions. The PXRD analysis confirmed ferrites with the presence of residual NaCl. The surface area of FeO (Fe-F) and CoFeO (Co-F) material was 69.1 and 45.2 m g, respectively. The Co-F and Fe-F showed the maximum Hg(II) adsorption capacity of 459 and 436 mg g at pH 6. The kinetic and isotherms models suggested a spontaneous adsorption process involving chemical forces over the ferrite adsorbents. The Hg(II) adsorption process, probed by X-ray photoelectron spectroscopy (XPS), confirmed the interaction of Hg(II) ions with the surface hydroxyl groups via a complexation mechanism instead of proton exchange at pH 6 with the involvement of chloride ions. Thus, this study demonstrates a viable and cost-effective solution for the efficient remediation of Hg ions from wastewater using non-functionalized ferrite adsorbents. This study also systematically investigates the kinetics and isotherm mechanism of Hg(II) adsorption onto ferrites and reports one of the highest Hg(II) adsorption capacities among other ferrite-based adsorbents.