Adsorption behavior of modified rice straw to thorium

Background: Agricultural wastes are widely applied in heavy metal wastewater treatment, and became a hot point in this field. Purpose: The aim is to study modified rice straw with significant removal ability of thorium. Methods: The rice straw modified with butanedioic acid was used to remove Th⁴⁺ from aqueous solution. And its influence factors such as adsorbent dosage, pH, adsorption time and reaction temperature were investigated through dynamic tests. Results: The optimal conditions were found to be 0.50 g of modified rice straw, pH=3.5, 0.5 h of adsorption time and 10 mg∙L^-1 of initial thorium concentration at 65 ℃. Under these conditions, the removal rates reach 96%. Fourier transform infrared spectroscopy (FTIR) analysis shows some new adsorption peaks such as carboxyl, ester and hydroxyl has added to modified rice straw. The adsorption behavior of Th⁴⁺ could be fitted well by the Freundlich adsorption isotherms and the quasi-second order kinetics equation. Conclusion: Its absorptive property enhancement might attribute to expose more internal porous structure of lignin and cellulose and add special functional groups by the modifying process.