Removal of hexavalent chromium from aqueous environments using adsorbents (Lemna and Azolla): An Equilibrium and Kinetics Study

Introduction: Chromium is among the important heavy metals which is found in most
industrial wastes and is associated with both health and environmental risks. Therefore,
this study tries to analyze the efficiency of lemna and azolla powders in removing
hexavalent chromium from aqueous solutions.
Methods: As an experimental trial, this study was conducted experimentally in the lab
scale. Initially, lemna and azolla were collected and washed three times with distilled
water. They were desiccated in a dry heat, set on 105°C, for 24 hours and then were
sieved with a 10-30-mesh sieve. Variation in pH, adsorbent dose, contact time, and initial
metal ion concentration were investigated and the remaining concentration was analyzed
using spectrophotometer (540 nm). [Equilibrium] Adsorption data were explained using
the adsorption isotherms and kinetics.
Results: The results of the study indicated that increasing adsorbent dose and contact time
will increase adsorption efficiency with both adsorbents (azolla and lemna), whereas the
adsorption capacity will be decreased; also, efficiency of [chromium] removal was
decreased with decreasing the initial concentration of chromium and the best pH that can
be used for removing chromium was found 3. For adsorbents used in this study, the best
type of isotherm was Langmuir and the best reaction kinetics was second order kinetics.
Conclusion: Generally, the adsorbents considered in this study, as inexpensive
adsorbents, can be used successfully for treating industrial wastes and aqueous solutions.