Removal of Zinc from Aqueous Solution by Adsorption using Coir Dust (Residue and Extract)

Abstract

The adsorption behaviour of Zn (II) ions onto unmodified coconut coir dust residue and NaCl treated coconut coir dust extract (UCCR, UCCE, NaCCE and NaCCR) was investigated at 30oC and pH of 7.0. The trend in the percentage adsorption of the adsorbate on the adsorbents decreased in the following descending: UCCR NaCCE>NaCCR> UCCE. There was justification in modifying the coir dust extract since this enhanced its adsorptive capacity. However, modification of the coir residue decreased its adsorptive capacity and not justifiable. The sorption data were also subjected to Langmuir, Freundlich and Flory-Huggins adsorption isotherm models. The adsorption of Zn(II) ions on NaCl treated coir residue (NaCCR) conform to the Langmuir isotherm model with high correlation value R2 > 0.90. This indicated monolayer surface coverage of the Zn(II) ions on these adsorbents. The data for the adsorption on NaCl treated coir residue (NaCCR) and NaCl treated coir residue (NaCCR) at 50oC fitted well to the Freundlich isotherm model implying a heterogeneous surface coverage of the adsorbents. All the adsorptions of Zn(II) ions on these adsorption did not fit the Flory-Huggins model. The adsorption increased with increase in temperature indicating an endothermic process. The negative value of ?Go signifies that the adsorption reaction was spontaneous process. The result indicate that the coir dust residue and modified coir dust extract could be employed as low-cost alternative for the removal of Zn(II) ions from solution. Keywords: Adsorption, coir dust residue, isotherm, NaCl treated coir extract, zinc.