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The Randles–Sevcik Equation (at 25 °C) (Sato et al. 1996) was used to calculate the concentrations of the labile Zn and Pb ions from the peak height currents. The diffusion coefficients of various labile ions used for the concentration computations are shown in Table 1. The differences in concentrations of the labile Zn and Pb ions in the presence of Ca and Mg (attributed to competitive binding to the organic ligands used) were also measured (Tables 2 and 3).

Table 1

Diffusion coefficients (D) of selected hydrated cations in water, at T = 298.15 °K and infinite dilution (Buffle et al. 2007)

Hydrated metal ionD (10−10 m2s−1)Hydrated metal ionD (10−10 m2s−1)
Fe3+ 6.04 Ca2+ 7.92 
Mg2+ 7.06 Cd2+ 7.19 
Mn2+ 7.12 Co2+ 7.32 
Ni2+ 7.05 Cr3+ 5.95 
Pb2+ 9.45 Cu2+ 7.14 
Zn2+ 7.03 Fe2+ 7.19 
Hydrated metal ionD (10−10 m2s−1)Hydrated metal ionD (10−10 m2s−1)
Fe3+ 6.04 Ca2+ 7.92 
Mg2+ 7.06 Cd2+ 7.19 
Mn2+ 7.12 Co2+ 7.32 
Ni2+ 7.05 Cr3+ 5.95 
Pb2+ 9.45 Cu2+ 7.14 
Zn2+ 7.03 Fe2+ 7.19 
Table 2

Concentration of labile Pb after complexation equilibration using humic acid, tannic acid and catechol as chelating ligands (in the presence and absence of Ca)

MatrixPeak concentration (ppm) at pH 4Peak concentration (ppm) at pH 8Significance at 0.1Significance at 0.05
Pb + HA 1.134 3.19 Values significantly different (P = 0.0944, RMSE = 5.9) Values not significantly different (P = 0.0944, RMSE = 5.9) 
Pb + CAT 1.32 14 
Pb + TA 2.64 19.6 
Pb + Ca + HA 2.9 1.26 Values not significantly different (P = 0.7118, RMSE = 4.7) Values not significantly different (P = 0.7118, RMSE = 4.7) 
Pb + Ca + CAT 6.61 4.69 
Pb + Ca + TA 5.4438 13.5 
MatrixPeak concentration (ppm) at pH 4Peak concentration (ppm) at pH 8Significance at 0.1Significance at 0.05
Pb + HA 1.134 3.19 Values significantly different (P = 0.0944, RMSE = 5.9) Values not significantly different (P = 0.0944, RMSE = 5.9) 
Pb + CAT 1.32 14 
Pb + TA 2.64 19.6 
Pb + Ca + HA 2.9 1.26 Values not significantly different (P = 0.7118, RMSE = 4.7) Values not significantly different (P = 0.7118, RMSE = 4.7) 
Pb + Ca + CAT 6.61 4.69 
Pb + Ca + TA 5.4438 13.5 

RMSE = root mean square error.

Table 3

Differences in Pb and Zn complexing concentrations (in ppm) in humic acid (represented as HA), tannic acid (represented as TA) and catechol as a function of Ca influence

SolutionpH = 4
pH = 8
PbZnPbZn
HA 1.77 2.68 1.94 3.74 
TA 5.59 −2.49 6.15 1.50 
Catechol 2.8 6.27 9.31 1.07 
SolutionpH = 4
pH = 8
PbZnPbZn
HA 1.77 2.68 1.94 3.74 
TA 5.59 −2.49 6.15 1.50 
Catechol 2.8 6.27 9.31 1.07 

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