Synthesis and application of a ternary composite of clay, saw-dust and peanut husks in heavy metal adsorption

The adsorption of a multi-component system of ferrous, chromium, copper, nickel and lead on single, binary and ternary composites was studied. The aim of the study was to investigate whether a ternary composite of clay, peanut husks (PH) and saw-dust (SD) exhibited a higher adsorption capacity than that of a binary system of clay and SD as well as a single component adsorbent of PH alone. The materials were used in their raw state without any chemical modifications. This was done to retain the cost effective aspect of the naturally occurring adsorbents. The adsorption capacities of the ternary composite for the heavy metals Fe²⁺, Cr³⁺, Cu²⁺, Ni²⁺ and Pb²⁺ were 41.7 mg/g, 40.0 mg/g, 25.5 mg/g, 41.5 mg/g and 39.0 mg/g, respectively. It was found that the ternary composite exhibited excellent and enhanced adsorption capacity compared with both a binary and single adsorbent for the heavy metals Fe²⁺, Ni²⁺ and Cr³⁺. Characterization of the ternary composites was done using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and thermogravimetric analysis (TGA). Kinetic models and adsorption isotherms were also studied. The pseudo second order kinetic model and the Langmuir adsorption isotherm best described the adsorption mechanisms for the ternary composite towards each of the heavy metal ions.