Activated carbon (AC) was magnetized with Fe₃O₄ nanoparticles (AC–Fe₃O₄-NPs) and loaded with Au nanoparticles (AC–Fe₃O₄–Au-NPs), and was fully characterized using different techniques such as XRD, XPS, VSM, TEM and SEM. 2-((2,4-Dichloro-benzylidene)-amino)-benzenethiol (DBABT), a complexing agent, was synthesized and characterized using ¹H-NMR, ES-MS and FT-IR analysis. Subsequently, AC–Fe₃O₄-NPs was modified with DBABT and applied for the ultrasound-assisted removal of Cd²⁺, Pb²⁺, Cr³⁺ and Ni²⁺ ions via complexation with DBABT. The influences of variables such as reaction time and adsorbent mass (equilibrium) were optimized simultaneously. The method under optimum conditions was set at pH 5, concentrations of 5, 15, 25 and 25 mg L⁻¹ for the Cd²⁺, Pb²⁺, Cr³⁺ and Ni²⁺ ions, respectively, 0.02 g for the adsorbent mass, 5 min sonication time and 6 mg L⁻¹ for the concentration of DBABT, producing removal percentages of 80.59, 93.85, 68.52 and 81.68 for Cd²⁺, Pb²⁺, Cr³⁺ and Ni²⁺ ions, respectively. Analysis of real experimental equilibrium data at various concentrations of analytes reveals the efficiency of the Langmuir model for good representation of experimental data, with maximum mono-layer adsorption capacities of 185.22, 135.14, 188.70 and 133.34 mg g⁻¹ for Cd²⁺, Pb²⁺, Cr³⁺ and Ni²⁺ ions respectively. The experimental data at various real times reveal that in most situations the systems reach equilibrium at contact times lower than 20 min, while the data fitted well to a combination of a pseudo second order kinetic model and intraparticle diffusion.