Adsorption of Cd²⁺ by Potassium-Permanganate-Modified Wheat Straw

Heavy metal ions Cd²⁺ were adsorbed by potassium-permanganate-modified wheat straw. The modified wheat straw was characterized by scanning electron microscopy, zeta potential, and Fourier transform infrared spectroscopy. The effects of pH, adsorption time, solid-liquid ratio, and temperature of the solution and desorption on Cd²⁺ adsorption were also studied. Four different concentrations of potassium-permanganate-modified wheat straw were observed. Results show that, compared with the surfaces of other concentrations, the surface of 0.05 mol·L^-1 potassium-permanganate-modified wheat straw appeared smoother and had more negative charges. These outcomes were beneficial to improving the adsorption performance of Cd²⁺. Moreover, the adsorption reached equilibrium at 300 min and fitted the pseudo two-order kinetic equation. The best adsorption effect was obtained when the pH of the modified wheat straw was 6, and the solid-liquid ratio was 1:300. According to the Langmuir isothermal adsorption equation, the adsorbents prepared using the modified adsorbents of 0.05 mol·L^-1 had the largest adsorption capacity for Cd²⁺ (30.21 mg·g^-1) far larger than the optimum adsorption capacity of the unmodified wheat straw (5.7 mg·g^-1). The adsorbent has been found to have good stability for Cd²⁺ adsorption.