Abstract
The chromium(VI) biosorption onto guava seeds, as an alternative method for Cr
6+
removal from aqueous solutions, was investigated. The parameters affecting kinetics and equilibrium of Cr
6+
adsorption onto guava seeds were studied. An external mass-transfer diffusion coefficient k and intra-particle diffusion coefficient k
i
were determined to measure the rate-limiting step of adsorption. A single external mass-transfer diffusion model and intra-particle diffusion models were used. The effects of initial pH, sorbent mass, and initial Cr
6+
concentrations on mass-transfer coefficients were investigated. The external mass-transfer coefficient has an average value of 7.2×10
−3
cm s
−1
, while the intra-particle mass-transfer diffusion coefficient was 0.34 mg g
−1
min
−0.5
. This indicates that external diffusion to the guava seeds surface and intra-particle diffusion are both involved in the sorption process. The isotherm equilibrium data were well fitted by the Langmuir and Freundlich models with an average correlation coefficient R
2
=0.98. The maximum removal of Cr
6+
was obtained at pH 1 (about 100% for adsorbent dose of 15 g l
−1
and 25 mg l
−1
initial concentration of Cr
6+
). The results indicated that the guava seeds exhibit acceptable sorption capacity.