Study of Hg(II) removal from aqueous solution using lignocellulosic coconut fiber biosorbents: equilibrium and kinetic evaluation

Abstract

Lignocellulosic coconut wastes such as pith and fiber, which are abundantly available and cheap, have the potential of being used as low-cost biosorbents for heavy metal ion removal. In this study, pristine (CF-Pristine) and NaOH-treated (CF-NaOH) coconut fibers were used as a biosorbent for Hg(II) removal from an aqueous solution. The coconut fiber biosorbent (CFB) was characterized by scanning electron microscopy (SEM) and Fourier transform-infrared (FTIR) spectroscopy. The Hg(II) sorption capacities obtained for CF-Pristine and CF-NaOH were 144.4 and 135.0mg/g, respectively. Both the equilibrium and kinetic data of Hg(II) sorption onto CFB followed the Langmuir isotherm model and a pseudo-second-order kinetic model, respectively. A further analysis of the kinetic data suggested that the Hg(II) sorption process was governed by both intraparticle and external mass transfer processes, in which film diffusion was the rate-limiting step. These results demonstrated that both pristine- and alkali-treated coconut wastes could be potential low-cost biosorbent alternatives for the removal of Hg(II) from aqueous solutions, such as water containing Hg(II) produced in the oil and gas industry.