Illegal discharges are of great concern among industry activities, since they occur under
uncontrolled conditions. In most cases, effluents are acidic and the concentrations of heavy
metals are very high. With this in mind, the main goal of this study was to evaluate the
sorption of two of the most toxic heavy metals, Cr(VI) and Pb(II), in those conditions.
A loamy sand soil was collected in Oporto, Portugal. Batch equilibrium and kinetic sorption
experiments were performed using both metals solutions, with concentrations among 50 mg
L-1 and 200 mg L-1, at pH 2 and 5, between 2 h and 288 h.
To evaluate the sorption equilibrium, eight isotherm models were fitted. Better adjustments
were observed for the Redlich-Peterson and Khan models for the adsorption of chromium (R2
= 0.99), and of lead (R2 = 0.99), respectively. The sorption kinetics was evaluated using three
models – Elovich, Pseudo first order and an empirical power function. The retention of lead
was almost instantaneous and the empirical power function described better the sorption
kinetics of chromium (0.89 < R2 < 0.99).
In addition, flow experiments were performed with effluents of both metals (50 mg L-1) at pH
2 and 5, for about 90 h. Results revealed a high retention of chromium, and a weak retention
of lead, for low pH values. FTIR analyses to the columns samples revealed that clay minerals
have an important role in the retention of both metals
