Khairiraihanna Johari

The coconut pith biosorbents were prepared by modifying coconut pith (CP) with sodium hydroxide and bis(triethoxysilylpropyl) tetrasulfide to enhance its sorption capacity and selectivity toward silver ion [Ag(I)]. It was found that the Ag(I) sorption capacity of pure CP, CP modified with sodium hydroxide, and CP modified with bis(triethoxysilylpropyl) tetrasulfide was 0.50, 0.48, and 0.62 mmol/g, respectively. The Ag(I) equilibrium data were best fitted to the Langmuir isotherm model, whereas the kinetic data obeyed the pseudo-second-order kinetic model with the anticipation of the film diffusion as the rate-limiting step. The sorption process was generally governed by a combination of physical and chemical sorption mechanisms. The Ag(I) sorption capacity and selectivity of coconut pith biosorbents were low as compared with other metal ions.

This article presents the biosorption potential of rice residues for Hg(II) removal from aqueous solution and oilfield produced water. Rice husk and rice straw were selected and functionalized with sulfur group from carbon disulfide in alkaline condition. The raw and modified biosorbents were characterized by using scanning electron microscopy, fourier transform infrared spectroscopy, energy dispersive X‐ray, and X‐ray photoelectric spectroscopy. Batch biosorption experiments were carried out to evaluate the effects of pH, initial ion concentration, contact time, and temperature on the removal process. It was found that the biosorption of rice residues showed a significant improvement in Hg (II) biosorption performance after the functionalization treatment. The maximum Hg(II) capacity of sulfur‐functionalized rice straw (RSS) and sulfur‐functionalized rice husk (RHS) obtained under present experiment condition was 119 and 92 mg/g, respectively. The equilibrium data were best‐fitted to Langmuir isotherm model, while the kinetic data followed the pseudo‐second‐order kinetic model. The biosorption process was endothermic, feasible and spontaneous in nature. The biosorbents showed good selectivity towards Hg(II) biosorption from the oilfield produced water. © 2015 American Institute of Chemical Engineers Environ Prog, 34: 1298–1310, 2015

The mercerized coconut fiber (CF-NaOH) was prepared by treating the pristine coconut fiber (CF-Pure) with NaOH solution. The morphology and chemical composition of CF-Pure changed after mercerization process. The maximum Ag(I) adsorption capacity of the CF-Pure and CF-NaOH was 0.502 and 0.612 mmol/g, in which the equilibrium data fitted to the Freundlich and Langmuir isotherm models, respectively. The Ag(I) adsorption rate also increased by using CF-NaOH and the kinetic data of both CF-Pure and CF-NaOH obeyed the pseudo-second order kinetic model. The enhancement of Ag(I) adsorption selectivity from photographic waste solution was also observed for the CF-NaOH.

The preparation of chars and activated carbon as low-cost elemental mercury adsorbents was carried out through the carbonisation of coconut husk (pith and fibre) and the activation of chars with potassium hydroxide (KOH), respectively. The synthesised adsorbents were characterised by using scanning electron microscopy, Fourier transform infrared spectroscopy and nitrogen adsorption/desorption analysis. The elemental mercury removal performance was measured using a conventional flow type packed-bed adsorber. The physical and chemical properties of the adsorbents changed as a result of the carbonisation and activation process, hence affecting on the extent of elemental mercury adsorption. The highest elemental mercury (Hg°) adsorption capacity was obtained for the CP-CHAR (3142.57 µg g⁻¹), which significantly outperformed the pristine and activated carbon adsorbents, as well as higher than some adsorbents reported in the literature.

Rasped pith sago residue (RPSR) was used as a biosorbent for inorganic (Hg(II)) and organic (CH₃Hg(I)) mercury removal from aqueous solutions. In biosorbent preparation, the RPSR having particle size range of 0.06–0.10 was washed with deionized water repeatedly to eliminate impurities, dried in an oven at 50°C for two days, followed with drying in a vacuum oven for 3 h. The performance of RPSR as a novel biosorbent for removing mercury was evaluated in batch adsorption. The adsorption of mercury ions was found to highly dependent on the pH of the solutions. The Hg(II) adsorption was high at pH > 4, while the CH₃Hg(I) adsorption was found higher at pH < 5. The higher adsorption capacity for Hg(II) and CH₃Hg(I) was 0.288 and 0.213 mmol/g, respectively. Both mercury adsorptions equilibrium and kinetics were fitted to the Langmuir isotherm model and pseudo‐second‐order kinetic model, respectively. These results indicate the RPSR has a potential to be a low‐cost biosorbent for mercury removal process from aqueous solutions.