Adsorption of Ni(II), Zn(II) and Fe(II) on modified coir fibres

The potential of a cheap lignocellulosic fibre, coir was assessed for removal of heavy metal ions like Ni(II), Zn(II) and Fe(II) from their aqueous solutions. The fibre was also chemically modified by oxidising it with hydrogen peroxide for use as adsorbent. Langmuir type adsorption was followed by the coir fibres. The modified coir fibres gave higher metal ion uptake as 4.33, 7.88 and 7.49 mg/g for Ni(II), Zn(II) and Fe(II), respectively, against 2.51, 1.83 and 2.84 mg/g for the unmodified coir fibres. The metal ion uptake values decreased with lowering of pH. The desorption efficiency, regenerative and reuse capacity of these adsorbents were also assessed for three successive adsorption–desorption cycles. The adsorptive capacity was retained only when regeneration with dilute NaOH solution is carried out as an intermediate step after desorption. An ion-exchange mechanism has been proposed for the enhanced metal ion uptake on modified coir.