Adsorption Behaviors of Lignophenol Compounds and Their Dimethylamine Derivatives Prepared from Rice and Wheat Straws for Some Precious Metal Ions

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Lignophenol based adsorbents were prepared from rice and wheat straws, and further modified by immobilization of dimethylamine group. The adsorption behavior of these adsorbents for metal ions was studied in hydrochloric acid solution. The adsorbents adsorbed Au(III) selectively over the whole range of hydrochloric acid concentration tested and have shown no affinity for base metal ions. Adsorption of Au(III), Pd(II) and Pt(IV) on the adsorbents modified with dimethylamine was found to be unaffected by base metal ions. The adsorption isotherms followed Langmiur model in all cases of Au(III), Pd(II) and Pt(IV) while the highest loading capacity was observed for Au(III) for all adsorbents. Reduction of Au(III) to Au(0) was proposed to be the major process for its highest loading capacity. The electrostatic interaction between amine groups and anionic chloride complexes of Pd(II) and Pt(IV) in acidic chloride media was concluded as the main mechanism for their adsorption.