Abstract:
Adsorption by volcanic rocks is investigated as a possible alternative to the conventional method of Cr(VI)
removal from polluted waters. In this work, adsorption of Cr(VI) onto pumice (VPum) and scoria (VSco)
has been studied by using a batch method at room temperature. The following factors affecting sorption of
Cr(VI) were investigated: solution pH, contact time, type and size of adsorbents, adsorbent dose and initial
metal ion concentration. The maximum adsorption yield, 77% for VSco and 80% for VPum, was obtained
at low pH of about 2. The applicability of the Langmuir as well as Freundlich adsorption isotherms for
the present system is tested. The batch sorption kinetics has been mathematically described using the
Lagergren pseudo-first order, pseudo-second order equations and equations for intra-particle and liquid
film diffusion. For both VPum and VSco, the entire kinetic data fitted well with pseudo-second-order
reaction rate model. In the case of VSco, the rate constant was the highest (338 × 10−3 kg mg−1 h−1) and
the VPum gave the lowest (7 × 10−3 kg mg−1 h−1). The experimental results inferred that electrostatic
attraction and surface complexation are the major adsorption mechanisms for binding Cr(VI) ions to the
macro and micro-vesicular volcanic rocks. The two volcanic rocks tested have potential for an inexpensive
and suitable method for removal of Cr(VI) from polluted waters.
