Alkali-treated straw and insoluble straw xanthate as low cost adsorbents for heavy metal removal – preparation, characterization and application

Heavy metal removal using alkali-treated straw (ATS) and insoluble straw xanthate (ISX) is reported. Insoluble straw xanthate consisting of 4.1% total sulfur is also applied for the removal of various metal ions simultaneously. Potentiometric data of alkali-treated straw and xanthated straw indicated polyfunctionality of these materials. Diffuse Reflectance IR (DRIFT) spectra of ISX exhibited peaks characteristic of xanthate groups on straw. Removal of Cr3+ from aqueous solutions using ATS and ISX followed the Langmuir adsorption model and both the materials have shown significant chromium removal efficiencies (>80%). In the case of chromate and dichromate, pore adsorption preceded the surface adsorption. Detailed spectroscopic (DRIFT & EPR) and sodium release studies conducted using ISX suggest that Cr3+ is removed through the adsorption-exchange mechanism involving alkoxide or xanthate groups. Xanthate groups bind Cr3+ aqua complex through unidentate monosulfur chelation.