Removal of Lead(II) Ions from Industrial Waste Water using Biomaterials of Terminalia ivorensis Plant and its Composite with Fe-Alginate Beads as Adsorbents

Abstract

Three effective adsorbents are developed for the removal of lead ions from industrial effluents based on stem powder of Terminalia ivorensis (TISP), its active carbon (TIAC) and a composite of Fe-alginatebeads doped with the active carbon (TIAC-beads). The beads are synthesized by crosslinking the Na-alginate with Fe3+ instead of conventional Ca2+, with an aim to improve its adsorptivity. The conditions for obtaining the uniform beads with good morphology are established. These sorbents are investigated for their adsoptivity for Pb2+ ions with respect to various extractions conditions and are optimized for the maximum removal of Pb2+. The sorption capacities are found to be: 34.0 mg/g for TISP, 39.0 mg/g for TIAC and 49.0 mg/g for TIAC-beads. The higher sorption of TIAC-beads may be due to the cumulative sorption nature of active carbon assisted by iron-alginate beads towards Pb2+. The optimum conditions are: for TISP: pH: 5, sorbent dosage: 2.0g/and, eqi. time: 120 min; for TIAC: pH: 7, sorbent dosage: 1.5 g/L; eqi. time: 90 min; and for TIAC-beads: pH: 6, sorbent dosage: 1.0 g/L and eqi. time: 60 min. Substantial removal of Pb2+ is noted in a range of pHs: 4 to 9 for TIAC-beads; 4 to 8 for TISP and 6 to 8 for TIAC. This permits the applicability of the sorbents in neutral as well as less acidic and basic solutions and it is a good feature as Pb2+ containing industrial effluents are inconsistent in their pHs. Three fold excess of co-ions marginally interfered. Thermodynamic studies reveal that the adsorption is endothermic and spontaneous. The high ΔH values, > 30.0 KJ/mol, emphasizes the chemical nature of binding between Pb2+ and surface functional groups of sorbent and is increasing in the order: TISP (32.385 KJ/mol) < TIAC (35.531 KJ/mol) < TIAC-beads (42.480 KJ/mol). This is supported by symmetrical humps with in the curves of pH vs. % removal. Positive ΔS values reflect disorder at the solid-liquid interface-an ideal condition for Pb2+ ions to cross the surface barrier existing at the solid/liquid interface, resulting in good adsorptivity. Negative ΔG values indicate the spontaneity of the sorption process. Spent TISP/TIAC/TIAC-beads can be regenerated and reused for 2 cycles for TISP, 3 cycles for TIAC and 3 cycles for TIAC-beads. The sorbents are successfully applied to remove Pb2+ form industrial effluents.