Removal of Heavy Metals Using Coconut Husks

Topics: Adsorption, Zinc, Activated carbon Pages: 12 (4105 words) Published: May 15, 2012
Biochemical Engineering Journal 36 (2007) 174–181

Removal of heavy metal from industrial wastewater using modified activated coconut shell carbon O.S. Amuda a,∗ , A.A. Giwa a , I.A. Bello b
Environmental/Analytical Chemistry Unit, Department of Pure and Applied Chemistry, Ladoke Akintola University of Technology, Ogbomoso 210001, Nigeria b Physical Chemistry Unit, Department of Pure and Applied Chemistry, Ladoke Akintola University of Technology, Ogbomoso 210001, Nigeria Received 1 September 2006; received in revised form 11 February 2007; accepted 12 February 2007 a

Abstract The present study was undertaken to develop a cost effective biosorbent and to study the biosorption process involved in the adsorption of heavy metal-contaminated industrial wastewater using the developed biosorbent. Coconut shell carbon was modified with chitosan and/or oxidizing agent (phosphoric acid) to produce composite adsorbent. The adsorption efficiency of the adsorbent was evaluated by measuring the extent of adsorption of zinc (II) in synthetic beverage industrial wastewater. Operational parameters such as pH, agitation time and adsorbent concentration, initial ion concentration and particle size were also studied. Adsorption data fitted well with the Langmuir and Freundlich models. However, Langmuir isotherm displayed a better fitting model than Freundlich isotherm because of the higher correlation coefficient that the former exhibited, thus, indicating to the applicability of monolayer coverage of the zinc (II) on the surface of adsorbent. Desorption studies were carried out with NaOH and quantitative recovery of the metal was evident. The dominant sorption mechanism is ion exchange. The use of agricultural waste (coconut shell) and aquatic waste (chitin) to produce activated carbon potentially leads to the production of a highly effective adsorbent generated from less expensive raw materials that are from renewable resources. © 2007 Elsevier B.V. All rights reserved. Keywords: Coconut shell; Chitosan-coated carbons; Heavy metals; Industrial wastewater; Adsorption isotherms

1. Introduction Rapid industrialization has led to increased disposal of heavy metals into the environment. The tremendous increase in the use of the heavy metals over the past few decades has inevitably resulted in an increased flux of metallic substances in the aquatic environment. The metals are special because of their persistency in the environment. At least 20 metals are classified as toxic, and half of these are emitted into the environment in quantities that pose risks to human health [1]. The ability of a water body to support aquatic life as well as its suitability for other uses, however, depends on many trace elements. Trace concentrations of zinc (Zn) are important for the physiological functions of living tissue and regulate many biochemical processes. However, just like other heavy metals, when Zn is discharged into natural waters at increased concentrations

Corresponding author. Tel.: +234 8034402907. E-mail address: (O.S. Amuda).

in sewage, industrial wastewater or from mining operations it can have severe toxicological effects on humans and aquatic ecosystems [2]. A similar experience is the minamata mercurypoisoning episode in Japan [3]. Hence, it is essential to remove Zn from industrial wastewaters before transport and cycling into the natural environment. A number of technologies have been developed over the years to remove heavy metals from industrial wastewater. The most important technology includes coagulation/flocculation [4,5]. Other conventional chemical methods include precipitation, ion-exchange, electrochemical processes and membrane technology. All the chemical methods have proved to be much costlier and less efficient than the biosorption process [6]. In addition, chemical methods increase the pollution load on the environment. Biosorption, a biological method of environmental control can be an...
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