Kinetics, thermodynamics and competitive adsorption of lead and zinc ions onto termite mound|
Abdus-Salam, N. & Bello, M. O.
The elemental composition of termite mound
was determined by XRF which revealed K, Ti and Mn as
minor constituents while Ca and Fe as major constituents.
The dominant functional groups of termite mound are Fe–
OH, Fe–O and O–H. The Pb(II) and Zn(II) adsorption capacities
(mg g-1) are in order of Pb(II) (13.07)>Zn(II)
(12.40)>Pb(Pb/Zn) (11.72)>Zn(Pb/Zn) (7.62). The
Langmuir adsorption isotherm fitted the adsorption data
better than Freundlich isotherm. The adsorption process
was best described by pseudo-second-order kinetic model
for single and binary solutions, and the rate constants k2
(g mg-1 min-1) are 0.036, 0.016, 0.024 and 0.015, and the
calculated value of qe (mg g-1) is 12.33, 12.25, 11.52 and
7.84 for Pb(II), Zn(II), Pb(Pb/Zn) and Zn(Pb/Zn), respectively.
The regression coefficient, R2 values, for these solutions
ranged between 0.9966 and 0.9978. The
ΔH (kJ mol-1) values were positive for single and binary
solutions in the order Pb(II) (32.0)>Pb(Pb/Zn)
(30.8)>Zn(Pb/Zn) (28.0)>Zn(II) (19.0), while
ΔS (kJ mol-1 K-1) are in the order of Pb(II) (0.103)>
Pb(Pb/Zn) (0.097)>Zn(Pb/Zn) (0.082)>Zn(II) (0.06).
The ΔG value for Zn(II) is positive in both single and
binary systems, while that for Pb(II) was positive between
313–333 and 323–333 K for single and binary systems,
respectively. The data show that the use of neglected termite
mound for Pb(II) and Zn(II) removal from aqueous
solutions is economically significant in wastewater
Termite mound; Competitive adsorption; Kinetics; Thermodynamics; Binary solution