Effect of solution temperature, pH and ionic strength on dye adsorption onto Magellanic peat

Abstract

The aim of this research was to study the effect of the solution temperature, pH and ionic strength on the adsorption of the Basic Blue 3 (BB3) and Acid Black 1 (AB1) dyes in Magellanic peat. The peat used was physically characterized as fibrous, of low decomposition level, without the presence of crystalline material and with a highly porous morphology. The functional groups with major concentration in the surface adsorbent were the carboxylics and phenolics, with values of 0.91 and 0.47 mmol/g, respectively. The results of the batch assays showed that the adsorption of the AB1 dye was strongly dependent of electrical charge density on the surface, contrary to what occurred to the BB3 dye, because the interactions between the dyes and carboxylic groups of the peat could be either electrostatic or non-electrostatic. The Langmuir, Freundlich and Sips isotherm models were fitted to the experimental data; among them, the Sips model presented the best adjustment quality. The maximum adsorption capacities for BB3 and AB1 dyes were 33.1 and 33.7 mg/g, respectively. The adsorption of BB3 dye onto Magellan peat has an exothermic behaviour, obtaining an adsorption enthalpy of –3.44 kJ/mol. Contrarily the adsorption of AB1 has an adsorption enthalpy of 56.76 kJ/mol.

Keywords:

• adsorption
• dyes
• peat
• isotherm
• ionic strength
• pH