This research uses co-precipitation to synthesize cobalt nickel ferrite as a heavy metal absorbing material from natural iron sand. The co-precipitation method was applied with temperature calcination of 700 °C for 2 h. Characterization of crystal structure using X-ray diffraction (XRD), characterization of magnetic properties using Vibrating Sample Magnetometer (VSM), and characterization of particle morphology using Field Emission Scanning Electron Microscopes (FE-SEM). Characterization of adsorption capacity of samples using Atomic Absorption Spectrophotometer (AAS). From the characterization results, it is known that cobalt nickel ferrite is a hard magnet and has a cubic crystal structure. The magnetic hysteresis curve shows a coercivity of 715.68 Oe and a remanent magnetization of 18.38 emu/g. The absorption capacity obtained from Cu and Cr removal efficiency was 96.26%, with an adsorption capacity of 10.83 mg/L.