Cr(III) removal by a microalgal isolate, Chlorella miniata: effects of nitrate, chloride and sulfate

In the present study, nitrate, chloride and sulfate anion systems were used to investigate the presence of anions on the removal of Cr(III) by Chlorella miniata. Kinetic studies suggested that the equilibrium time of Cr(III) biosorption was not affected by the presence of different sodium salts, even at the concentration of 1.0 M, and all reached equilibrium after 24 h. Equilibrium experiments showed that the effects of different anions on Cr(III) biosorption varied, and the inhibitory order was SO4 (2-) > Cl(-) > NO3 (-). Langmuir isotherm indicated that the maximum sorption capacity of C. miniata increased with the increase of pH under different anion systems. The strongest inhibition effect of the sulfate system was attributed to the formation of Cr(OH)SO4 aq. and the decrease of Cr(OH)(2+) and Cr(3+) in solution, while the difference of inhibitory effect in the other two anion systems could be accounted by the formation of the inner-sphere surface complex in the nitrate system and the outer-sphere surface complex in the chloride system. The present study suggested that the presence of anions greatly affected the removal of Cr(III) on C. miniata and thereby their transport in the environment.