Geology Reference
In-Depth Information
remobilization.
119,121
The increasing sophistication of the DGT technique is
now also permitting comparisons of measured metal speciation in fresh-
waters with model (e.g. WHAM, ECOSAT) predictions.
122,123
Finally, it should be noted that sediment cores continue to be used to
investigate historical perspectives of environmental contamination by
anthropogenic organic compounds, such as organochlorine pesti-
cides,
124,125
polychlorinated biphenyls,
124,125
polychlorinated naphtha-
lenes,
126
polycyclic aromatic hydrocarbons,
124,127,128
aliphatic hydro-
carbons,
128,129
polychlorinated dibenzo-p-dioxins,
130
polychlorinated
dibenzofurans,
130
and polybrominated diphenyl ethers
125,131
in environ-
ments as diverse as the Great Lakes
124,129-131
and Washington
128
in
North America, Esthwaite Water
126
in England, remote mountain
lakes
127
in the Pyrenees and Alps in Europe and Greenland.
125
3.3.3.3 Onondaga Lake. Onondaga Lake, near Syracuse, New York
State, has been called 'one of the world's most polluted lakes' and
provides a textbook case of the impact of industrial processes on the
environment.
132
Rich natural resources, especially the local brine
springs, made the Syracuse region an ideal location for chemical
manufacturing. Unfortunately, the exploitation of these, despite the
implementation of significant technological advances and, for the time,
environmentally responsible operation of factories had a devastating
impact upon the chemistry of the lake.
The Solvay Process, which was introduced for the manufacture of the
industrially important chemical, 'soda ash', i.e. sodium carbonate
(Na
2
CO
3
), along the west shore of Onondaga Lake in 1884, was cheaper
and less polluting than the existing Leblanc Process. Essentially, it made
use of two cheap and plentiful naturally occurring substances in the area
- NaCl from the deep brine springs and CaCO
3
from limestone out-
croppings - in a simple reaction, which yielded two useful products.
CaCO
3
þ
2NaCl
Na
2
CO
3
þ
CaCl
2
"
(3.105)
In practice, this overall reaction required a series of individual reactions
and chemical intermediates, one of the most important involving
ammonia in a step to separate NaHCO
3
from NH
4
Cl by fractional
crystallization at 273 K.
NH
3(g)
þ
CO
2(g)
þ
NaCl
(ag)
þ
H
2
O
(1)
"
NaHCO
3(s)
þ
NH
4
Cl
(aq)
(3.106)
The NaHCO
3
was subsequently heated to yield Na
2
CO
3
while NH
3
,the
most expensive compound used, was regenerated from the decomposition
of NH
4
Cl. So the very ecient Solvay Process, one of the first industrial
