Environmental Engineering Reference
In-Depth Information
aqueous solutions. Loaded metal ions could be stripped off by acid washing.
Selective separation of different metal ions was achieved by controlling the
solution pH. Magnetic nanocomposites particles with reactive functional
groups have great potential applications in industrial, biological, and pharma-
cological processes.
Keywords Magnetic nanocomposite particles
industrial effluent treatment
heavy metal removal
molecular self-assembly
direct silanization
two-step
silica coating
mesoporous silica coating
molecular templating
sol-gel
reaction
templates removal
surface functionalization
6.1 Introduction
The problem of disposing industrial wastes is as old as industry itself. Industrial
wastes often cause serious water, air, and soil pollution. Heavy metals are
frequently found from chemical manufacturing, petroleum, fossil fuel combus-
tion, painting and coating, mining, extractive metallurgy, nuclear, and many
other industries [1, 2]. The heavy metals most often implicated in accidental
human poisoning are lead, mercury, arsenic, and cadmium. Some heavy metals,
such as zinc, copper, chromium, iron, and manganese, are required by the body
in trace amounts, but these same elements can be toxic at higher concentrations
in human body. In addition to impair fetuses development, poisoning of heavy
metals generally can cause the damage of kidneys, brain, blood, livers, central
nervous, digestive, and skin system. These toxicities have been well established
in scientific literature. Heavy metals can enter ground water aquifer by direct
industrial and consumer waste disposal or released from soils, other industry
solid wastes as a result of acid rain leaching.
The regulated levels of various heavymetal ions in drinking water are extremely
low. For example, the World Health Organization has set a maximum guideline
concentration of 0.01 mg/L for As in drinking water [3] and the US Environ-
mental Protection Agency (EPA) has set a maximum limit of 0.005 mg/L for Pb
and 0.65 mg/mL for Cu in drinking water [4]. It is a big challenge to remove
these metal ions to such a low level from large volume, low concentration
effluents in a cost effective manner. Discharge of metals to the environment
not only causes serious health concerns but also is a waste of dwindling and
valuable resources. Moreover, financial benefit could be gained by recovering
these metals while detoxifying the water for recycling or soft disposal. Recovery
of metals from effluent streams is thus in line with the principles of sustainable
development.
Growing concerns about the environmental pollution, economic impact, and
the potential threat that these heavy metals pose to human being stimulated
increasingly stringent control on the discharge of industrial wastes. Consider-
able efforts have been devoted to developing fundamental understandings and
viable technologies to reduce environmental consequences of industrial wastes,
