Kinetics of desorption of heavy metals and their mixtures from immobilized activated sludge

Abstract

In order to use biosurfactants to desorb metals from biosorbents without changing their adsorption capacity, there is a need to determine conditions of process. In this study, we examined the kinetics of desorption of cadmium, zinc, and copper and their mixtures from activated sludge immobilized in 1.5% sodium alginate with 0.5% polyvinyl alcohol. Metals leaching from immobilized biomass were analyzed with the use of three biosurfactants—saponin, JBR 515, JBR 425, and nitric acid. Desorption effectiveness of single metals and their mixtures was also investigated as influenced by different desorption parameters such as pH, contact time, and dose of desorbents. The obtained values of kinetic constants of pseudo-first-order (k₁) and pseudo-second-order (k₂) showed that in case of all analyzed desorbents, the process of metals leaching from immobilized activated sludge proceeded according to the pseudo-second-order reaction as indicated by the R² values. Out of the analyzed desorbents, saponin and nitric acid proved to be the most effective in leaching both individual metals and their mixtures from the biosorbent. Saponin showed high leaching effectiveness in a pH range of 1–5, whereas the optimal conditions for nitric acid were at pH 1–2. The effectiveness of metals desorption from biosorbent using saponin reached 94.8% (Zn), 86.6% (Cu), and 51.2% (Cd) (a solution of single metal) and 92.7, 73.6, and 43.1%, respectively, for a solution of metal mixture. These results show that saponin is an attractive and environmentally friendly desorbent for the removal of metals and their mixtures from biosorbent.

Keywords:

• Biosorption
• Desorption
• Heavy metals
• Biosurfactants

Acknowlegments

This research was financially supported by the grant: KBN N N523 452936 (Poland). The present study was carried out at Warmia and Mazury University in Olsztyn in Poland in the years 2011–2012.