In mono-component systems, biosorption rapidly increased in the first 30 min, after which slowly
approached equilibrium. At this time about 50% of copper, 80% of nickel and 100% of zinc have
been removed, when compared with the total amount removed at equilibrium. In mono-component
systems, zinc reached equilibrium after 1 h, and nickel and copper after 2 h. Other researchers (Zhu
et al., 2008) obtained similar results for copper removal by the same material. The same equilibrium
times were observed in tri-component system, however the amount removed of each metal was lower.
The Lagergren’s (1898) pseudo-first and Ho’s (1995) pseudo-second order models were fitted to the
experimental data. The model parameters and their statistics are presented in Table 1. The Fisher’s
test indicates that for copper the models are statistically equivalent for mono-component system
and, considering their high determination coefficients, any model could be used; for the tricomponent
system, the best fit was obtained for the pseudo-second order model; this kinetic model
was proposed for the same system by Zhu et al. (2008).
The pseudo-second order model was also the best for nickel in mono component system; for the
same metal, in tri-component system, the models are statistically equivalent, however presenting
lower determination coefficients than for copper.
For zinc, only the mono-component system data could be fitted; the models are statistically
equivalent but the determination coefficients are not high.
Pseudo-second order kinetics was followed in general. Other researchers also report the same
kinetics for metals removal by agricultural wastes (Aydin et al., 2008).
From Table 1, it can be calculated that the total sorption of metals (0.041 mmol g-1) was similar to
the maximum capacity obtained in mono-component system (0.038 mmol g-1 for zinc).