Peat as an Adsorbent for Water Purification in Developing Countries
Figure 8: Change in percentage of metal ions removed in a competitive environment
Figure 9: Hydrated radius of various cations and anions
Figure 8 shows the adsorption of both metal ions in a competitive environment. This corresponds with the results in 3.4 which also shows that a long time period is required for the adsorption of zinc ions as compared to lead(II). However, the percentage of zinc ions remained constantly lower than that of lead(II) up till the 30 minute mark. Hence, we can conclude from this graph that Lead(II) ions adsorb faster and the percentage of ions removed remained higher as compared to zinc ions. We hypothesise that this is due to the hydrated radius of the ion when in water. As shown in Figure 9, Lead(II) ions has a smaller hydrated radius than zinc ions. Thus, there are less water molecules that are form coordinate bonds with a lead (II) ion which makes it easier to form co-ordinate bonds with the hydroxyl groups in peat. The difference in hydrated radius can be used to explain the difference in the adsorption of peat.
Figure 10: Adsorption of lead(II) ions in competitive and non-competitive environments
Figure 11: Adsorption of zinc ions in competitive and non-competitive environments
Figures 10 and 11 shows the graphs of the percentage removal of both metal ions. We can observe that there is a greater percentage of lead(II) ions removed in the presence of both metal ions as compared to a non-competitive environment. However, the reverse is true for zinc ions. There is a greater percentage of zinc ions adsorbed in a non-competitive environment compared to a competitive one. A Mann-Whitney U test was also conducted to determine whether there was a significant difference between the percentages of metal ions removed during competitive adsorption as compared to zinc ions. At a 5% level of significance, we can conclude that there is a significant difference in the amount of zinc ions adsorbed during competitive adsorption as compared to normal adsorption. However, there is insufficient evidence to show whether there is a significant change in lead(II) ions adsorbed as there are varying p-values.