Naoki Kano

Additional information is available at the end of the chapter http://dx. doi. org/10.5772/51 164

1. Introduction

Contamination of toxic metals in the aquatic environment is one of the most debated problems in the world with industrial development. Thus, the minimization and recovery of harmful pollutants such as heavy metals in natural environment is very significant [1]. Various treatment technologies such as ion exchange, precipitation, ultrafiltration, reverse osmosis and electrodialysis have been used for the removal of heavy metal ions from aqueous solution [2]. However, these processes have some disadvantages, such as high consumption of reagent and energy, low selectivity, high operational cost, and difficult further treatment due to generation of toxic sludge [3].

Among environmentally friendly technologies for the removal of heavy metals from aquatic effluent, biosorption has attracted increasing research interest recently [4-5]. The major advantages of biosorption are its high effectiveness in reducing the heavy metals and the use of inexpensive biosorbents [6]. Biosorption studies using various low cost biomass as adsorbents have been currently performed widely for the removal of heavy metals from aquatic effluent [7-18].

Among many biosorbents, marine seaweed can be an excellent biosorbent for metals because it is well known to concentrate metals [19-20]. Seaweeds are reported to accumulate hydrocarbons (as well as metals); and they are exposed to the ubiquitous presence of organic micropollutants and can work as suitable biomonitors [21]. Furthermore, it is considered that the shell (usually treated as waste material) can be also an promising adsorbent. The shell has an internal structure comprised of three distinct layers. The innermost layer (i. e., hypostracum) consists of aragonite; the middle layer (i. e., ostracum), which is the thickest of the three, consists of various orientations interbedded with protein molecules (conchiolin); and the outermost layer (i. e., periostracum) consists of chitin, which is represented as (C8H13NO5)n [22]. Particularly, it is considered that protein (called

© 2013 Kano, licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons. org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

"conchiolin") including amino acid group play an important role for collecting trace metal in shell [23].

Biosorption studies have been mainly focused on toxic elements such as Cd, Pb, Cu, As and Cr for subject elements [24]. In our research, the objective elements are mainly rare earth elements (REEs) from the viewpoint of resources recovery, although REEs do not represent a common toxic threat.

Rare earth elements (REEs) find wide range of applications as functional materials in agriculture and as other industrial products, then the demand of REEs in modern technology has increased remarkably over the past years [25-26]. These elements and their compounds have found a variety of applications especially in metallurgy, ceramic industry and nuclear fuel control [27]. For example, current applications of lanthanum as a pure element or in association with other compounds are in super alloys, catalysts, special ceramics, and in organic synthesis [28]. However, the shortage of trace metals including REEs (and the problem of stable supply for these metals) has been a concern in recent years. Therefore, the establishment of the removal or recovery method for trace metals is important from the viewpoint of resources recovery.

It is known that alginate is an exopolymer extracted mainly from brown algae (and various bacteria) that has been used both as immobilization material and as biosorbent of several heavy metals [29]. Then, biosorption studies using seaweed have been generally concentrated on brown algae so far [30-31]. Green and red algae as well as brown algae were also used for biosorbent of REEs in the present work.

Considering the above-mentioned, laboratory model experiments for confirming the efficiency of marine biomass (seaweed and shell) as sorbent for REEs was designed in present work. Furthermore, the surface morphology of the marine biomass used in this work was determined by SEM (Scanning Electron Microscope) before and after metal adsorption.

The crystal structure, and the specific surface area of the shell biomass were also determined by by XRD (X-ray powder diffraction), and BET (Brunaeur, Emmet and Teller) and Langmuir method, respectively.