Removal of Rhodamine B from aqueous solution using silica extracted from rice husk

Abstract

Global annual production of rice husk is approximately 120 million tons. It doesn’t easily biodegrade, resulting in disposal problems. This paper therefore, investigated the use of silica obtained from the burning of the raw rice husk in open air (RHSA) and in a Muffle Furnace at 540 °C (RHSO). The efficiency of the two silica samples in removing Rhodamine B (RB) from aqueous solution was tested using different process parameters. 89% silica was obtained from either method. The removal of RB was more possible on RHSA than on RHSO. This was revealed by calculated Langmuir RL values of 0.152 for RHSA and 0.558 for RHSO. This was also supported by the obtained Temkin isotherm equilibrium constants values of 3.379 and 0.677 L/mg for RHSA and RHSO respectively. Langmuir monolayer capacities of 6.0 and 6.87 mg/g were obtained for RHSA and RHSO respectively. Increased in mass of RHSA or RHSO greatly enhanced RB removal (65% with 0.05 g to 98% with 0.5 g for RHSA). Optimal removal conditions on each sample were; temperature 27 °C, mass adsorbent 0.5 g, pH 7.05, contact time 24 h and 10 mg/L of RB initial concentration. The RB removal was negatively affected by ionic strength, decreasing from 84 to 46% for RHSA and 60–41% for RHSO with increase in ionic strength from 0.00 to 2 M. The two adsorbents are efficient in RB removal and easily regenerated as it is purely a physical process.