Biosurfactant Complexation of Metals and Applications for Remediation - Biosurfactants: Research Trends and Applications - page 278

Mine Tailings ................................................................................................ 295
Industrial Waste ............................................................................................ 296
Summary ...................................................................................................... 296
Phytoremediation .............................................................................................. 297
Remediation of Cocontaminated Systems ........................................................ 298
Liquid Media ..................................................................................................... 299
Recovery of Metal from Biosurfactant-Metal Complexes ................................ 301
Conclusion ............................................................................................................. 301
References .............................................................................................................. 302
INTRODUCTION
Humanity's ability to access and manipulate metals was the keystone to our advance-
ment from the Stone Age to today's technologically advanced society. While this
keystone drove technological innovation and societal development, it simultaneously
resulted in unprecedented alterations of natural biogeochemical cycles and, arguably
for the first time, affected the environment on a global scale. Indeed, paleopollution
archaeology is a field of study devoted to evaluating this human impact by analyz-
ing metal deposits in polar ice caps, bogs, and aquatic sediments to document and
understand mining and smelting practices of ancient civilizations, such as the Roman
Empire, as long as 2000 years ago (Nriagu, 1996). This analysis has shown that our
utilization of metal resources is having local and global effects on human and envi-
ronmental health. Practical, effective, and economical remediation technologies are
needed to address large-scale metal contamination; microbially produced surfactants
(biosurfactants) meet these requirements, and may be the basis for developing green
remediation technologies. The goal of this chapter is to provide a brief introduction
of metals and environmental metal contamination,* followed by an in-depth exami-
nation of metal interactions with biosurfactants. The chapter will conclude with a
discussion of potential remediation techniques and technologies based on metal-
biosurfactant interactions.
METALS AND METAL CONTAMINATION
In general, metals are lustrous solids (except Hg), usually ductile and malleable,
capable of conducting both electricity and heat and forming alloys (Kotz et al.,
2006). On the periodic table (Figure 11.1), they can be found to the left of the diago-
nal line drawn from B to At, excluding Ge, Sb, and H. Elements that display some
physical characteristics of metals are defined as metalloids and include B, Si, Ge,
As, Sb, and Te (Kotz et al., 2006). The two common terms used to describe metals,
especially those of concern environmentally, are “trace elements”—elements in the
Earth's crust at or below 100 mg kg −1 , for example, Zn, Ni, Cu, Co (Essington,
2004)—and “heavy metals”—elements with densities greater than 5 g cm −3 , for
example, Cu, Co, Fe, Mn (Callender, 2003); these terms are used synonymously
for the purpose of this chapter.
* For a more extensive review, see Nriagu (1990) and Callender (2003).