Chemistry Reference
In-Depth Information
inorganic solids may partially replace the minerals used. Ashes are incorporated to the clinker. Therefore,
this procedure saves and sustains non-renewable natural resources. Unfortunately, co-processing presents
many restrictions. For example, mercury, cadmium fluorine and chlorine compounds are to be avoided.
Therefore, the waste generated in an industrial or laboratory site must be separated to avoid placing
undesirable waste for co-processing. Mercury, cadmium and fluorine compounds must be passivated via
precipitation to be disposed of in industrial dumps. However, it is much better to avoid their use in industrial
and laboratory procedures, replacing them by other green alternatives.
Organic wastes containing low concentrations of heavy metals can be treated by a biological process,
producing ground fertilizer (composting).
Recycling is a logical option for non-biodegradable materials, such as metals, plastic and glass. Selective
collecting is essential to ensure a successful recycling program. Laboratory waste, which falls under this
category, must be clean before sending to a recycling site.
However, a great tendency is to use waste as a raw material for other processes [127]. For example, food
waste and compost are used for production of biofuels, mitigation of green house gases and in agriculture.
Waste fibers from the tannery industry may be employed for removal of pollutants from water. Even remediation
of contaminated soils or other environmental sites may be performed using appropriate waste [126].
The physico-chemical characterization of the waste determines its possible use in other industrial processes.
Despite this impressive aspect, true green chemistry means no generation of wastes. Waste remediation in
a short-term measure is necessary but must not be regarded as the final solution.
22.5
Green environmental analysis applied for atmospheric samples
Historically, atmospheric compounds were measured by wet chemical methods. For instance, ozone present
in an air sample was bubbled through an acidic solution containing iodide ions. The I
2
formed was determined
using wet chemical techniques [130].
These classical wet methods were subjected to much potential interference. In the example given above,
SO
2
presents a negative interference (it reduces I
2
to I
−
), whereas NO
2
gives a positive interference (it also
oxidizes I
−
to I
2
). As a result, these methods were abandoned, being replaced by instrumental methods of
analysis. These are used in both tropospheric and stratospheric analyses [130].
22.5.1 Gases
Instrumental methods for gas analysis include the following: (1) optical spectroscopic techniques, such as
chemiluminescence, fluorescence, infrared spectroscopy (multi-pass cells, FTIR, tunable diode laser
spectroscopy (TDLS), non-dispersive infrared spectroscopy (NDIR), matrix isolation spectroscopy (MI), and
ultraviolet-visible absorption spectroscopy (UV-vis); and (2) mass spectrometry. In these circumstances, the
sample is introduced to the instrument without the aid of any reagent [130]. These methods usually offer real-
time measurements and require low quantities of sample.
Some compounds, particularly those at very low concentrations in the air [130-133], can be collected
from gas streams for subsequent quantification by analytical techniques (HPLC, GC, GC-MS, colorimetric
methods, etc.). The media available are filters, denuders, transition flow reactors, mist chambers and
scrubbers. The sample must be passed for sufficient periods of time to collect measurable amounts of the
substance to be analyzed [130, 132]. Volatile organic compounds (hydrocarbons, carbonyl compounds,
etc.) are typical examples of compounds collected from air samples prior to analysis [130, 133]. This
analysis may be via spectroscopy or derivatization methods [130, 132, 133]. These may employ toxic
reagents, such as 2,4-dinitrophenylhydrazine (DNPH), for determination of aldehydes and ketones [130].
