Adsorption Behavior of Lignophenol Compounds and Their Dimethylamine Derivatives Prepared from Rice and Wheat Straws for Precious Metal Ion

Lignophenol-based adsorbents were prepared from rice and wheat straws and further modified by immobilization of dimethylamine groups. The adsorption behavior of the substrates for various metal ions in hydrochloric acid solution was studied. The lignophenol adsorbents selectively adsorbed Au(III) over the entire range of hydrochloric acid concentrations tested but showed no affinity for base metal ions. Adsorption of Au(III), Pd(II), and Pt(IV) on the dimethylamine-modified adsorbents was also unaffected by the presence of base metal ions. The highest loading capacity was observed for Au(III) in the case of all adsorbents; this could be primarily explained by the facile reduction of Au(III) to Au(0). The electrostatic interactions between protonated amine groups and anionic chloro complexes of Pd(II) and Pt(IV) in acidic chloride media was proposed as the main adsorption mechanism.