Influence of pH and ionic strength on cadmium sorption by some biosorbents

To study the effect of pH and ionic strength on the sorption behavior of cadmium by biosorbents، a batch experiment was conducted with various initial concentration of Cd2+ (0 – 200 mg. L-1) with two biosorbents (sunflower stalks and apple pruning residues) in two pH (4، 8) and two ionic strength (0. 1 and 0. 03 M). Sorption data were fitted to Langmuir، Temkin and Freundlich equations. Results showed that both pH and ionic strength (IS) had significantly effect on Cd sorption. Langmuir maximum mono layer adsorption (qmax) and binding energy value (KL(increased with increasing pH by two biosorbents and sorption coefficients of Freundlich (KF، n) and Temkin (KT، A) showed similar trends as well. But by increasing IS (from 0. 03 to 0. 1 M) all sorption parameters significantly decreased; in the case of sunflower stalks with increasing ionic strength، on average qmax decreased from 8505 to 8150 mg/kg and KL from 0. 14 to 0. 08 L/mg; for apple pruning residues، qmax decreased from 7550 to 7300 mg/kg and KL from 0. 09 to 0. 06 L/mg، respectively.