Th(ІV) biosorption from a three-component feed solution by Ca-pretreated Cystoseria indica alga in a fixed-bed column: Experimental tests and modeling

Abstract

In this work, Th(ІV) biosorption by Ca-pretreated Cystoseria indica alga from a three-component feed solution containing Th(ІV), V(V), and Fe(ІІІ) ions was studied in a fixed-bed column at various bed heights (3.5–7 cm), and Th(ІV) concentrations (10–90 mg/L) with constant concentrations of 40 and 20 mg/L for V(V) and Fe(ІІІ), respectively. The results showed a minimum Th(ІV) biosorption capacity (54.15 mg/g) by increasing bed height and a maximum Th(ІV) biosorption capacity (104.6 mg/g) by increasing Th(ІV) concentration. Also, the results showed the effect of V(V) and Fe(ІІІ) ions at low Th(ІV) concentrations on breakthrough curve is more significant, and the binding sites on the surface of Cystoseria indica alga have a stronger affinity towards Th(ІV) ions compared to V(V) and Fe(ІІІ) ions. The breakthrough curves were analyzed by empirical models such as Bohart Adams, Belter, modified dose-response, and Clark models. Furthermore, a new empirical model was proposed to improve the breakthrough curves prediction. Also, using this new empirical model, the Th(ІV) biosorption capacity was presented as separate functions of bed height and Th(ІV) concentration. Moreover, mass transfer models include internal and external mass transfer, biosorption on active sites, and Henry models were used to determine the rate-limiting step and mass transfer mechanism. The results showed that the Henry model performed better, and it was concluded that the equilibrium in the biosorption process is instantaneous and occurs rapidly.