Removal of heavy metal ions from aqueous solution using rice husks-based adsorbents

Abstract

This study reports on the preparation and characterization of rice husks-based adsorbents and their application in the removal of heavy metal ions from aqueous solution. Three different adsorbents were developed: rice husks ash (RHA), rice husks ash-derived silica (RHS) and triaminopropyl-silica hybrid (TSH-R). The prepared materials were characterized by acid titration, Attenuated Total Reflectance Fourier Transform Infrared (ATR-FTIR) spectroscopy, Scanning Electron Microscopy-Energy Dispersive X-ray (SEM-EDX) spectroscopy and nitrogen physisorption analysis. Results from the ATR-FTIR analysis indicated that pure silica was obtained from RHA and that after surface modification the triaminopropyl group was successfully attached onto the silica framework with a loading of 2.15 mmol per g silica. The RHA, RHS, TSH-R had average particle sizes of 336.8, 296.4 and 1054.1 nm and BET surface areas of 17.8, 20.2 and 5.7 m²/g, in the same order. Adsorption studies of Ni²⁺, Zn²⁺, Pb²⁺, Cu²⁺ and Co²⁺ ions showed that RHA and TSH-R were good adsorbents with an average maximum adsorption of 99 and 95 % for RHA and TSH-R, respectively when 1.0 g of adsorbent and initial metal ions concentration of 21 - 27 mg/L at pH 4 were employed. Both Langmuir and Freundlich isotherms indicated that the adsorption was favorable.

 Keywords: Triaminopropyl-silica hybrids, rice husks ash, rice husks silica, adsorption