Ni (II) and Cr (VI) sorption kinetics by Microcystis in single and multimetallic system

The kinetics of Ni (II) and Cr (VI) sorption by Microcystis, was studied in single and multimetal systems. External mass transfer and intraparticle diffusion data suggested that Microcystis resembles a physical sorbent and therefore holds great potential for employment as a substitute (but requires revalidation at large scale) of physical sorbents in wastewater treatment. Microcystis showed better Ni (II) sorption efficiency than Cr (VI) in a single metal system at pH 6.4 +/- 0.1 and 6.0 +/- 0.3. However, in a multimetal system Ni (II) showed an insignificant difference from Cr (VI) due to a competitive effect. Sorption of Ni (II) and Cr (VI) was dependent on their initial concentration. The initial sorption rate showed non-proportionality with initial concentration (Co), and intraparticle diffusion rate parameters (K-i) which were not directly related to initial concentration (K-i = (Co)(n) where n = 0.5). This suggests that neither external mass transfer rate nor intraparticle diffusion was a rate limiting factor. On fitting the experimental data both in first and second order equations, the regression analysis of second order equation gave a better r(2) value. Thus, external mass transfer and intraparticle diffusion together are involved in the sorption process and pseudo second order equation provides an appropriate description than the first order equation. (C) 2001 Elsevier Science Ltd. All rights reserved.