Carboxylic acids-modified palm stones as sorbents for metal ions using single and multi-metal aqueous solutions

Abstract

Natural palm stone has been modified in order to enhance its sorption capacity for different metal ions. The palm stone (PS), or date-pits, was treated with different carboxylic acids, namely carboxylic acid (CA), tartaric acid (TA), salicylic acid (SA), oxalic acid (OA), mandelic acid (MND) and malic acid (MA). Batch sorption tests were carried out using single, binary or tertiary metal systems composed from copper, zinc and cadmium. In single metal systems, the sorption of metal ions by modified date-pits stone was always higher than that of the unmodified date-pits. The best sorbents used in this work for the removal of Cu, Zn and Cd from their individual solution are SA-PS, CA-PS and MA-PS, respectively. For multi-metal systems, OA-PS and TA-PS can be considered as the best candidates for metal removal. Equilibrium is achieved in a contact time of about an hour. The amount adsorbed was dependent on the process conditions; it increased with an increase in pH, initial metal concentration and amount of sorbet. The Freundlich model agreed very well with the equilibrium isotherm experimental data.