Recovery of lead and cadmium ions from metal-loaded biomass of wild cocoyam (Caladium bicolor) using acidic, basic and neutral eluent solutions

Michael Horsfall Jnr*
Department of Pure and Industrial Chemistry
University of Port Harcourt
P. O. Box 402, Choba
Port Harcourt, Nigeria
Tel: 234 803 507 9595
E-mail: horsfalljnr@yahoo.com

Fred E. Ogban
Department of Chemistry
Delta State University
P. M. B 1, Abraka
Delta State, Nigeria
Tel: 234-8025434425

Eyetemi E. Akporhonor
Department of Chemistry
Delta State University
P. M. B 1, Abraka
Delta State, Nigeria
Tel: 234-8035501947

*Corresponding author

The influences of acidic, basic and neutral reagents on the recovery of Pb²⁺ and Cd²⁺  from metal-loaded biomass of wild cocoyam (C. bicolor) were investigated in this study. Over 94% Pb²⁺ and 74% Cd²⁺ of the initially adsorbed metals were recovered by 0.01 M HCl, while < 20% of both metals was recovered by basic reagent. Distilled water recovered less than 9% of both metal ions from the biomass.

Introduction

Regeneration of spent biosorbent is crucially important to keeping the process costs of remediation down and to opening the possibility of recovering the metal(s) extracted from the liquid phase. A number of studies have demonstrated the feasibility of using plant biomass to remove heavy metal ions from aqueous solutions (cassava waste; Abia et al. 2003, Medicago sativa (Alfalfa); Gardea-Torresdey et al. 1998; and Spagnum Moss Peat; Ho et al. 1995) just to mention a few. However, very little has appeared in the literature as a major study on the recovery of adsorbed metals from the biomass (Gardea-Torresdey et al. 1998; Zhou et al. 1998; Chu and Hashim, 2001). Again, most biomass in its native form may not be suitable for process applications as they may disintegrate under the harsh conditions of wastewater processing, especially in cases where the biomass is exposed to a stronger reagent to recover the adsorbed metal ions and regenerate the biomass for reuse. Hence, this study examined the influence of acidic, basic and neutral eluents in the recovery of Pb²⁺ and Cd²⁺ from biomass of wild cocoyam (C. bicolor).

Materials and Methods

C. bicolor (Wild cocoyam) biomass was used in this study. The preparation and estimation of the surface characteristics of the biomass has been reported elsewhere (Horsfall and Spiff, 2004; Horsfall and Spiff, 2005). The finely divided biomass was analyzed to determine their functional groups using a Fourier Transform Infrared Spectroscopy (Shimadzu IR Prestige - 21, FTIR - 84005). Batch adsorption experiments were first conducted to load the C. bicolor biomass with metal ions separately and found to be 49.53 mg/g and 48.20 mg/g for Pb²⁺ and Cd²⁺respectively.

In the batch recovery experiment, some amount of metal-laden C. bicolor biomass were placed in several flasks containing 50 mL of recovery reagents. The flasks were shaken for specified time at 29ºC and agitated on a mechanical shaker at 150 rpm. At the end of each contact time the suspensions were centrifuged. For each fixed time interval, five cycles of recovery equilibrium experiments were conducted to asses the reusability of the biomass. The solutions from the five cycles were combined and evaporated gently to decrease the final volume and metal content (Pb²⁺ and Cd²⁺) measured using Flame Atomic Absorption Spectrometry after digestion.

Results and Discussion

The surface area was determined to be 32.91 ± 1.22 (m² g^-1), while the bulk density, porosity and pore volume were 1.63 ± 0.11 (g cm^-1), 59.31 ± 1.14 (%) and 0.61 ± 0.03 (cm³ g^-1) respectively. Furthermore, the cation exchange capacity (25.69 ± 0.58; meq g^-1) and surface charge density (0.78 ± 0.04; meq m^-2) were also determined. The FTIR spectra reveals the presence of the following peaks at wave no. 3400 cm^-1 representing - OH stretching frequency; several  peaks at wave no 1650 cm^-1 and 1050 cm^-1 representing - C = N of amides and C - O of alcohol, and peak at 1709 cm^-1 for C = O group of ketones. The peak at 2300 cm^-1 represents a C - H saturated hydrocarbon of chain. On the overall the spectra indicated the presence of hydroxyl, carboxyl, amide and possibly carbonyl group.

The recovery data as obtained indicates that, the recovery of Pb²⁺ and Cd²⁺ is time dependent and was relatively rapid with equilibrium recovery achieved within the first 15 - 25min of contact time and remained constant thereafter. From the metal-laden biomass, over 90% and 75% of Pb²⁺ sorbed were recovered by acidic media concentrations of 0.01 M HCl and 0.1 M HCl respectively, while the amount of Cd²⁺ recovered at the same acidic media concentrations were 80.52 and 78.15% respectively. In the case of recovery in basic media, a rapid phase of recovery was observed followed by a relatively slow phase before apparent recovery equilibrium was reached. The fast region occurred during the first 20min of contact time. However, at the end of the 20 min recovery, only about 12.11% (Pb²⁺); 23.44% (Cd²⁺) and 13.64% (Pb²⁺); 26.13% (Cd²⁺) were recovered from the metal-laden biomass in the basic media with concentrations of 0.01 M NaOH and 0.1 M NaOH respectively. A poor recovery was also observed for distilled water in which less than 3% of sorbed Pb²⁺ and Cd²⁺ were recovered from the metal-laden biomass. The highest metal recovery from the metal-laden C. bicolor biomass was observed in acidic media. This is because in acidic medium the carboxyl, carbonyl or hydroxyl groups in the biomass become protonated and does not attract the positively charged metal ions and therefore releases the metal ions into recovery solution. Again, in acidic medium, the protons in solution replaces the metal ions on the biomass surface, while the apparent poor recovery  of less than 20% observed in basic media such as NaOH, may be due to the coordinating ligands being deprotonated, hence bound-metal ions finds it difficult to be detached from the biomass. A control experiment using distilled water at pH 7.0 demonstrated negligible metal recoveries within the entire contact time tested in this study. The data in this investigation revealed that, on a comparative basis, recovery of bound metal ion from the biomass is greater for Pb²⁺ than Cd²⁺ in all the recovery media investigated. and subsequently releases greater amount into recovery media upon slight agitation.

References

ABIA, A.A.; HORSFALL, M. Jr. and DIDI, O. The Use of Chemically Modified and Unmodified Cassava Waste for the Removal of Cd, Cu and Zn ions from Aqueous Solution. Bioresource Technology, December 2003, vol. 90, no. 3, p. 345-348. [CrossRef]

CHU, K. H. and HASHIM, M.A. Desorption of copper from polyvinyl alcohol-immobilized seaweed biomass. Acta Biotechnologica, November 2001, vol. 21, no. 4, p. 295-306. [CrossRef]

GARDEA-TORRESDEY, J.L.; GONZALEZ, J.H.; TIEMANN, K.J.; RODRIGUEZ, O and GAMEZ, G. Phytofiltration of Hazardous cadmium, chromium, lead and zinc ions by biomass of Medicago sativa (Alfalfa). Journal of Hazardous Materials, January 1998, vol. 57, no. 1-3, p. 29-39. [CrossRef]

HO, Y.S.; JOHN WASE, D.A. and FORSTER, C.F. Batch Nickel Removal from Aqueous Solution by Sphagnum Moss Peat. Water Research, May 1995, vol. 29, no. 5, p.1327-1332. [CrossRef]

HORSFALL, Michael Jnr. and SPIFF, Ayebaemi I. Studies on the Effect of pH on the Sorption of Pb²⁺ and Cd²⁺ ions from aqueous solutions by Caladium bicolor (Wild Cocoyam) Biomass. Electronic Journal of Biotechnology [online]. 15 December 2004, vol. 7, no. 3. Available from Internet: http://www.ejbiotechnology.info/content/vol7/issue3/full/8/index.html. ISSN 0717-3458.

HORSFALL, Michael Jnr. and SPIFF, Ayebaemi I. Kinetic Studies on the sorption of lead and cadmium ions from aqueous solutions by Caladium bicolor (Wild Cocoyam) Biomass. Bulletin of Chemical Society of Ethiopia, June 2005, vol. 19, no. 1, p. 89-102.

OKIEMEN, F.E.; MAYA, A.O. and ORIAKHI, C.O. Sorption of cadmium, lead, and zinc ions on sulphur-containing chemically modified cellulosic materials. International Journal of Environmental Analytical Chemistry, 1987, vol. 32, p. 23-27.

ZHOU, J.L.; HUANG, P.L. and LIN, R.G. Sorption and Desorption of Cu and Cd by macroalgae and microalgae. Environmental Pollution, 1998, vol. 101, no. 1, p. 67-75. [CrossRef]