Removal of Cu(II) in fixed bed and batch reactors using natural zeolite and exfoliated vermiculite as adsorbents

The ability of natural zeolite (clinoptilolite) and exfoliated vermiculite to remove copper from aqueous solutions was studied in fixed bed column and batch reactors. The effect of agitation speed (0, 100, 200, 400 rpm), temperature (25, 45, 60°C), and particle size [2.5-5.0 mm, dust (<0.25 mm)] and solution pH (1.00–4.00) on the removal of heavy metals was studied. Fixed bed experiments were conducted, using three different volumetric flow rates of 5–7–10 BV (Bed Volumes)/h, under an initial normality of 0.01 N (317.7 mg/L), at initial pH of 4.00 and ambient temperature (25°C). Vermiculite was found to be more effective for the removal of copper in batch mode reactors under all the tested conditions, while the removal efficiency follows the order: vermiculite > clinoptilolite dust > clinoptilolite 2.5–5.0 mm. The removal of Cu(II) using vermiculite reached 67.6%, at ambient temperature and at the agitation speed of 400 rpm, while it was approximately 42.5% at 60°C with no agitation. The highest removal level in the case of clinoptilolite use reached the percentage of 37.3% at the temperature of 60°C without agitation; the same removal efficiency was obtained at ambient conditions with an agitation speed of 400 rpm. Clinoptilolite dust is found to be more efficient than granular clinoptilolite under all the conditions that were tested. Agitation and temperature also affect the uptake of the specific ions. Finally, the acidity of the aqueous solution influences the removal of copper by minerals. In column studies, the decrease of the flow rate resulted in the increase of the removal efficiency.

This work has studied the effect of both vermiculite and zeolite in the removal of copper from solutions in batch reactors as well as in bed columns under a variety of operating conditions. In conclusion, the series of the tests performed in this work shows that • Vermiculite was found to be the most effective mineral for the removal of Cu2+ in aqueous solutions, while granular clinoptilolite was the least effective one under all operating conditions. The % removal of copper follows the order: vermiculite > clinoptilolite dust > clinoptilolite 2.5–5.0 mm. • The usage of vermiculite resulted in the removal of Cu2+ by 67.6% at ambient temperature and 400 rpm agitation and the respective removal was approximately 42.5% at 60°C without agitation. The highest removal level reached by clinoptilolite was 37.0%. • High agitation speeds and high temperatures enhance the ion exchange processes by the minerals. The highest efficiencies were observed at high agitation speeds (400 rpm) at room temperatures and the second highest removal efficiencies were observed at high temperatures (60°C) with no agitation. At a future study it is interesting to examine the effect of combined high agitation speeds and temperatures. • Acidity of the aqueous solutions also influences the removal of ions by the minerals. The pH value of 4.00 seems to give better results than lower pH values. • In column studies the decrease of the flow rate resulted in the increase of the removal efficiency. However, there is a need to balance between very low flows which are not practicable and high flows that reduce removal efficiencies.