Cadmium adsorption onto and desorption from sodium alginate and sodium alginate with poly(vinyl alcohol) (PVA) were studied. Intraparticular diffusion was demonstrated to limit adsorption kinetics during the first 20 min of process. The Deff value was dependent on adsorbent chemical composition and ranged from 3.35 ´ 10-10 m2/s to 1.86 ´ 10-10 m2/s for the 1.5% alginate with 0.5% PVA and for the 2% alginate with 5% PVA, respectively. At equilibrium the adsorption was more effective onto the 2% alginate and was lower for the alginate sorbent containing poly(vinyl alcohol). The dimensionless separation factor RL increased from 0.26 to 0.68 for the 2% alginate and the 2% alginate + 5% PVA, respectively. The maximum adsorption capacities in Langmuir isotherm for both the 2% and 1.5% alginate with 0.5% PVA were similar and were 176 and 178 mg/g dry weight, respectively. However, the adsorption capacity decreased to 48 mg/g dry weight for the 2% alginate with the 5% PVA (in proportion to the polymer amount increase in the adsorbent). Cadmium desorption was more effective for nitric acid than for sulfuric and hydrochloric acids (desorption pH 2.2). More cadmium was desorbed from 2% alginate with 5% PVA than from 2% alginate or 1.5% alginate with 0.5% PVA.
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