[Adsorption Characteristics and Mechanism of Cadmium in Water by Alkali and Magnetic Composite Modified Wheat Straw...

Wheat straw biochar (BC) was modified by KOH and magnetics to generate composited modified biochar (FKC). Based on characterization by scanning electron microscopy-energy dispersive spectrometry (SEM-EDS), Brunauer-Emmett-Teller (BET), Fourier transform infrared (FT-IR), X-ray diffraction (XRD), and magnetic (VSM) techniques, the adsorption characteristics and mechanisms of Cd²⁺ in water and the effects of temperature, pH value, and dosage on the adsorption characteristics of FKC were studied. The results showed that the modified biochar was loose and porous. The specific surface area of FKC increased by 19.11 times, the number of aromatic and oxygen-containing functional groups such as O-H, C=O, and C=C increased, and a new functional group Fe-O formed compared to the BC. FKC is magnetic, and its magnetization is 8.43 emu·g^-1, which can be recycled and reused. The adsorption of Cd²⁺ by FKC fitted well with the pseudo-second-order kinetic model and the Langmuir model, indicating that chemical adsorption is the main adsorption mechanism. The theoretical maximum equilibrium adsorption capacity of FKC is 23.44 mg·g^-1, which is 1.47 times that of BC. The thermodynamic parameters suggested the adsorption of Cd²⁺ by FKC was a spontaneous and endothermic process. The adsorption capacity increased with an increase of pH in the region 2-8, and a biochar dosage of 10 g·L^-1 was used. After three cycles of adsorption-desorption-adsorption, the adsorption capacity of Cd²⁺ by FKC still reached 17.71 mg·g^-1, indicating that FKC has good reusability. These results can provide a theoretical basis for the application of KOH and magnet-modified biochar from wheat straw to remove heavy metals from contaminated wastewater.