Removal of silver and copper ions by biosorption onto residue of solid-liquid extraction of alginate from seaweed

Author(s)

Geovani Rocha de Freitas

• Document type: Master's Dissertation
• Press: Campinas, SP.
• Institution: Universidade Estadual de Campinas (UNICAMP). Faculdade de Engenharia Química
• Defense date: 2018-06-18

Examining board members

Meuris Gurgel Carlos da Silva; Marcelino Luiz Gimenes; Liliane Maria Ferrareso Lona

• Advisor: Meuris Gurgel Carlos da Silva; Melissa Gurgel Adeodato Vieira

Abstract

Copper and silver are two toxic metals commonly found in effluents from ore and electroplating industries. Due to their several negative effects, environmental agencies have developed strict legislation that limits the concentration of these two metals in effluents before being dumped into receiving water bodies. In this regard, biosorption appears as a low cost and high efficiency alternative in the treatment of wastewater contaminated by toxic metals in low concentrations, but still above the value established by environmental legislation. The use of biosorbents of low or no commercial value, such as industrial wastes, is essential for biosorption to become economically attractive. In the process of alginate solid-liquid extraction from seaweed, a residue is produced, but it still maintains properties that enable the uptake of toxic metals. Thus, this work aims to evaluate the applicability of the residue of this process obtained from the brown alga Sargassum filipendula as biosorbent in the removal of copper and silver ions in dilute aqueous solutions. The study of the biosorption in monocomposite conditions of these two metals was developed in batch and fixed bed systems. The yield of alginate and residue was 25% and 46%, respectively. After alginate extraction, the biosorbent was pre-treated using nitric acid, at which stage a mass loss of around 20% occurred. Kinetic experiments showed that there was a small reduction in copper biosorption capacity after acidification, whereas for silver, the biosorption capacity increased. It was necessary an average time of 60 and 300 minutes for copper and silver biosorption to reach equilibrium, respectively. Kinetic models indicated that biosorption may be described by pseudo-second order kinetics and that external film resistance is the dominant resistance in the process. Isotherm experiments using the acidified biosorbent resulted in a higher biosorption capacity of copper (3.580 mmol.g-1) at the highest temperature of this work (40 ºC), whereas for silver, this capacity was higher at 20 °C (2.916 mmol.g-1). The D-R model was the most predictive among the isotherm models used. Thermodynamic analysis of the process indicated that the copper biosorption presented a positive enthalpy (22.91 kJ.mol-1) and entropy (114.98 J.mol-1.K-1) changes, suggesting endothermic nature with dissociative mechanisms, whereas in silver biosorption, the enthalpy (-21.35 kJ.mol-1) and the entropy (-48.94 J.mol-1.K-1) changes were negative, suggesting exothermic nature with associative mechanisms. Experiments to evaluate the ion exchange mechanism showed that sodium and calcium ions are the light metal ions most released in copper and silver biosorption. Fixed bed experiments at the lowest flow rate (0.5 mL.min-1) and the lowest initial concentration (1.0 mmol.L-1) resulted in a higher percentage of copper and silver removal. The Yan et al. (2001) model was the most predictive among the breakthrough curve models used. FTIR spectra indicated that the main groups involved in the process of removal of copper were carboxylic and alcoholic, whereas in the silver removal, the carboxylic, alcoholic and amine groups were the main responsible for the biosorption of this metal. SEM micrographs showed that the surface of the biosorbent became smoother after acidification. The biosorbent porosity decreased from 40.16% to 37.07% and 39.93% after copper and silver biosorption, respectively, indicating that a higher amount of copper ions filled the empty pores of the acidified biosorbent (AU)

• FAPESP's process: 16/06173-2 - Removal of silver and copper ions by biosorption residue of marine alginate extraction
• Grantee: Geovani Rocha de Freitas
• Support Opportunities: Scholarships in Brazil - Master