Comparative analysis of removal of crude oil and some refined petroleum products from the environment using rice husk: Adsorption isotherm and kinetic studies

Abstract

Rice husk a low cost agricultural waste was assessed for its efficiency as an oil spill sorbent by comparing its oil (crude oil, diesel and kerosene) uptake with that of a standard conventional synthetic sorbent mat used in oil spill clean-up. The sorption process of crude oil, diesel and kerosene onto rice husk and the standard was studied using Langmuir, Freundlich, Elovich, Temkin and Dubinin – Radushkevich adsorption models while the sorption kinetics was studied using Lagergren pseudo-first-order, pseudo-second-order, intraparticle diffusion and liquid film diffusion models. Suitable environmental applicability of both sorbents was also studied. The result of the study shows that rice husk sorbed3.30± 0.23g of crude oil, 2.50± 0.81 g of diesel and 1.95± 0.72g of kerosene per unit mass while the standard sorbed11.50± 0.54g of crude oil, 10.34± 0.77g of diesel and 8.20± 0.93g of kerosene per unit mass. About 2.46± 0.17g of sorbed crude oil, 1.60± 0.64g of sorbed diesel and 1.57± 0.11g of sorbedkerosene were recovered from a unit mass of rice husk, while, 9.67± 0.36g of sorbed crude oil, 8.40± 0.95g of sorbed diesel and 6.50± 0.49g of sorbed kerosene were recovered from a unit mass of synthetic sorbent mat. The amount of the sorbed oils retained by a unit mass of rice husk is about 0.84± 0.22g of crude oil (25 % of sorbed crude oil), 0.90± 0.97g of diesel (36 % of sorbed diesel), and 0.38± 0.90g of kerosene (20 % of sorbed kerosene), while, 1.83± 0.33g of crude oil (15 % of sorbed crude oil), 1.94± 0.97g of diesel (19 % of sorbed diesel) and 1.70± 0.89g of kerosene (20 % of sorbed kerosene) were retained by a unit mass of synthetic sorbent mat. The result of the study indicates that the standard is a better sorbent for oil removal than rice husk. Rice husk has the ability to retain sorbed oil which makes it a good sorbent when oil recovery is not required, but disposal. The sorption process for both sorbents follows the Langmuir isotherm. Intraparticle diffusion model and liquid film diffusion model were parts of the rate determining steps of the sorption process of the oils onto rice husk and the standard.

Keywords: Rice husk, adsorption isotherm, adsorption kinetics, crude oil, refined petroleum products.