Biosorptive Removal of Hexavalent Chromium by Rice Husk Ash and Silica from Aqueous Solution

Etim Ee ,E F Aikhoje ,Adelagun Roa ,A E Kamba ,O A Ushie

doi:10.7176/cmr/13-1-02

Abstract

Hexavalent chromium ion removal by adsorption using rice husk ash and silica prepared from rice husks obtained locally from rice mill as biosorbents was evaluated as low cost wastewater treatment in this study. Batch equilibrium isotherm experiments were performed as well as effect of dosage and initial chromate solution pH to determine the potentials of the sorbent to remove hexavalent chromate ion from synthetic fed wastewater. Equilibrium isotherm experimental data isotherms were tested with isotherm models (Langmuir, Freundlich and Tempkin models), being best represented by the Langmuir model. Optimum conditions were: dosage = 0.5 g / 200 ml at room temperature and pH o > 6. The equilibrium between adsorbate in the solution and on the adsorbent surface was practically achieved in 2 h. The monolayer sorption capacity was 67.45 mg/g for rice husk silica and 55.98 mg/g for rice husk ash. Estimation of energy of the sorption process revealed chemisorption as the prevailing means of interaction between the adsorbents and adsorbates moieties. The abundance and affordable (cheap) cost of rice husks justifies its use as a precursor in the preparation of rice husk ash and silica as effective adsorbents for chromium removal from industrial effluents. Keywords :Hexavalent chromium, Biosorption, Isotherm, Rice husk ash, Rice husk silica DOI: 10.7176/CMR/13-1-02 Publication date: January 31 st 2021

Highlights

Biosorptive treatment of wastewater involves the use of biological materials via a metabolically - mediated physicochemical pathways to accumulate and sorb the inherent pollutants
The experimental data of the equilibrium isotherm studies of chromium ion sorption onto the two adsorbents used in this study (RHA and RHS) were fitted into three common equilibrium isotherm models namely, Freundlich, Langmuir and Tempkin equations
The Freundlich isotherm model regarded as an empirical isotherm with no theoretical basis, hints that the adsorption occurs on a heterogeneous adsorbent surfaces and sites of varying affinities and binding strength

Summary

Introduction

Biosorptive treatment of wastewater involves the use of biological materials via a metabolically - mediated physicochemical pathways to accumulate and sorb the inherent pollutants This technique is an environmental cleanup practice used by Scientists and Water Engineers to provide an economical alternative for removing toxic wastes including heavy metals, pesticides and other organic compounds which can be toxic to wildlife and humans in small concentration from industrial effluents. During controlled firing and proper conditions, 1⁄4 (w/w) of the husk is usually converted to rice husk ash made up of about 90 % amorphous silica of a very high purity Advantages such as low cost, abundance, availability and possibility of regeneration and reuse have greatly favoured the application of rice husk in the removal of pollutants including heavy metals in aqueous solution in recent times (Viere et a.l,2010; Gibb et al, 2009). The acidic condition of pH 5 indicates approximately the complete precipitation of silica from sodium silicate by the following reaction: SiO2 + 2NaOH →

Sodium Silicate

Isotherm Model

Rice Husks

Conclusion