This study compares the ability of Natural Rice Husk (NRH) and fly ash in removing Cr (III) ion from aqueous solution and industrial wastewater. Batch studies were conducted to characterize the adsorption process. The influence of three parameters (solution pH, initial metal concentration in solution and adsorbent dosage) on the adsorption or removal process of Cr (III) ion by NRH and fly ash conducted at 28 ± 2 °C were studied. From the batch studies, the removal percentage of Cr (III) ion by NRH was found to be 99.71% for aqueous solution containing 50 ± 2 mg/L of Cr (III) ion using 0.50 g adsorbent. Fly ash was found to have 95.27% removal of Cr (III) ion for an aqueous solution containing 50 ± 2 mg/L of Cr (III) ion using 0.10 g adsorbent. The optimum pH of the adsorption process for NRH and fly ash was 5.5 and 2.0, respectively. The removal of Cr (III) ion from industrial wastewater sample with a concentration of 50 ± 2 mg/L by NRH and fly ash was 92.78% and 85.24%, respectively. The adsorption of Cr (III) ion using NRH followed Langmuir's adsorption model, while the adsorption of Cr (III) ion using fly ash followed both Langmuir and Freundlich's adsorption model. Based on the Langmuir constants, fly ash was found to have a higher adsorption capacity (13.37 mg/g) for the adsorption of Cr (III) ion as compared to NRH (2.33 mg/g).
Heavy metals in industrial wastewater are toxic to aquatic life and can contaminate potable water sources. Heavy metals such as chromium are found in natural water as well as in various industrial wastewaters, such as chromium plating, wood treatment, chrome tanning of leather, electroplating, dyes and pigments manufacturing.
The commonly used methods for removal of trivalent chromium are chemical precipitation, ion exchange, reverse osmosis, electrochemical reduction and activated carbon adsorption. Most of these methods involve high capital cost with recurring expenses which cannot be afforded by small and medium-scale industries. Studies on treatment of wastewater bearing heavy metals have revealed adsorption to be a highly effective, cheap and easy method among the physico-chemical treatment processes.
The adsorption process makes use of an "adsorbent"—a solid that binds molecules or particles to a surface by physical attractive forces and chemical binding. The design is simple, sludge-free and can be considered a low cost investment. The adsorbents that are commonly recommended for removal of heavy metals are alumina, silica, iron oxide and activated carbon. These adsorbents are relatively expensive (Corapcioglu and Huag, 1987; Viraraghavan and Rao, 1991; and Weng and Huang, 1994). In recent years, there has been a rapid growth in the use of natural absorbents for controlling the soluble metal ions concentration in heterogeneous systems. Agricultural wastes and industrial byproducts, in particular, have received attention as economical adsorbents for removing heavy metals from wastewater. Among these are rice husk from the rice production process and fly ash from a wood combustion process. Rice husk and fly ash have received particular attention as economical adsorbents for removing heavy metals from aqueous solution because they can be easily obtained in large quantities at low price. But little observation of the potential of fly ash for removal of heavy metals from industrial wastewater, especially from tannery wastewater, is available. |
