Comparison of Mn, Zn, and Cr removal in fluidized- and fixed-bed reactors by using clinoptilolite

Natural minerals are used as sorbents in ion-exchange processes due to their high exchange capacity and their relatively low cost. In the present study the use of natural zeolite as filling medium in fixed- and fluidized-bed reactors for the removal of heavy metals from aqueous solutions is investigated. The major objective is to compare the removal efficiency of heavy metals by the two processes—fluidized and fixed bed. Fixed and fluidized bed experiments were conducted in order to examine the Mn2+, Zn2+, and Cr3+ uptake by natural clinoptilolite, using the same critical experimental conditions: particle size (90–180 μm), volumetric flow rate of 12.48 BV/h, total normality of 0.01 N, initial pH value equal to 4, and ambient temperature (25°C). The fluidized bed process was conducted in an experimental 50 cm long plexiglass column of 4.4 cm internal diameter and fixed bed experiments in 70 cm long plexiglass columns of 2 cm internal diameter. The fluidized bed breakthrough curves for Mn2+ and Zn2+ are very similar with Cr to give the best results in terms of removal efficiency. In fixed bed the breakthrough curves are similar for all three metals, with Cr exhibiting slightly lower removal efficiency. Furthermore, the breakthrough points are shifted to the left (0–5 BV) in comparison to the fixed bed experiments (10 BV) for all metals. Comparing the two processes, it is concluded that fixed bed operation exhibits better results than the fluidized bed most probably due to better hydrodynamic conditions in the former.