The dyestuff solution was prepared dissolving 120 mg L1 of alizarin red (Carlo Erba Reagents) used without further purification in bi-distilled water, using 0.05 M Na2SO4 (Carlo Erba Reagents) as supporting electrolyte. The physicochemical
properties of alizarin red are reported in Table 1. Heptahydrated ferrous sulphate was of analytical grade supplied by Carlo Erba Reagents. Solution pH was adjusted to the desired value by addition of H2SO4 or NaOH. pH was measured using a Schott Gerate CG822 pH-meter.