Abstract
This study was carried out to evaluate the efficiency of metal ions removal from aqueous solution using silica adsorbent. Silica was extracted from rice husk using sol-gel method. The silica was modified with 1.0 M of nitric acid. Using batch adsorption technique, the effects of temperature, pH, contact time and adsorbent dosage on adsorption process of Cu (II), Zn (II), Mn (II) and Pb (II) ions were studied using standard solutions of their salts. Percentage removal of the metals ions studied decreased as the temperature was varied between 28°C and 43°C. Percentage removal of metal ions studied showed an increase at different pH varying from 4 to 8 and decreased after the pH 8. The variation of contact time between 2 and 8 hours showed a sharp increase in metals removal from 2 to 6 hours but a slow increase after 6 hours. The percentage removal of metal ions increase as the adsorbent dosage increased between 0.5 g and 2.0 g. The maximum percentage removal of metal ions was found to be 99.48%. The general observed trend of efficiency being Cu>Pb>Zn>Mn. The experimental data was also tested using adsorption isotherm models of Langmuir and Freundlich and Langmuir model was found to be the best fit for the data.
Highlights
Rice husk, an outer cover of rice grain, is a by-product of the rice milling industry
The rice husk ash was treated with 200 mL portions of 1 M NaOH and heated at 80°C in 250 mL Erlenmeyer flasks for 1 h with constant stirring
The results of the effect of temperature, pH, contact time and adsorbent dosage are presented in Tables 1, 2, 3 and 4 respectively
Summary
An outer cover of rice grain, is a by-product of the rice milling industry. There are various methods of removing heavy metal ions, and they include chemical precipitation, membrane process, ion exchange, solvent extraction, electrodialysis, and reverse osmosis These methods are non-economical and have many disadvantages such as incomplete metal removal, high reagent and energy consumption, and generation of toxic sludge or other waste products that require disposal or treatment [8]. In the recent years many biosorbent materials of agricultural based have been utilied for heavy metal biosorption These include coconut husk and shell, sea weeds, bagasse ash, hazelnut shell, peanut hull, tree fern, black gram husk, maize leaf, maize fibre, sun flower waste, coffee beans, Ficus religiosa leaves, wheat bran, almond shell, tea waste [9]. It may occur due to electrostatic attraction [11]
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