Preparation and Characterization of Magnetic Walnut Shell Adsorbents

In this paper, the magnetic walnut shell adsorbent was prepared by the composite modification of acidification and magnetization with agricultural waste solid waste walnut shell as raw material. Response surface method (RSM) and analysis of variance (ANOVA) were used to optimize the preparation conditions of the modified walnut shell adsorbent. The influence of parameter changes and the interaction between parameters were evaluated. The walnut shell before and after modification was characterized by SEM, FT-IR, BET, elemental analysis and magnetization curve. After the magnetization of the walnut shell, the morphology of the sample changed. The stretching vibration peak of the oxygen-phosphorus bond was increased at 1300 cm⁻¹, and the combined frequency of the stretching vibration peak of N–H and the stretching vibration peak of hydroxy-group appeared at 3398 cm⁻¹. The specific surface area of the magnetic walnut shell was 2.7375 m²/g, and the pore volume was 0.012479 cm³/g. The average pore diameter was 16.3854 nm, and the results of elemental analysis and magnetic response could determine the successful preparation of walnut shell adsorbent. Magnetic walnut shells can effectively remove Cr⁶⁺ from simulated wastewater. When the reaction temperature is 57℃, the reaction time is 40min, and the ion ratio n (Fe³⁺): n (Fe²⁺) is 2.52:1, the removal rate of Cr⁶⁺ from the magnetic walnut shell can reach 94%. All these prove that magnetized walnut shell has a good adsorption effect on Cr⁶⁺.