ENVIRONMENTAL CHEMISTRY

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ENVIRONMENTAL CHEMISTRY Chem. 3030
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The two terms environmental chemistry and
pollution often seem to go together, yet
environmental chemistry is much more than the
study of chemical effects of pollution. It is a
multidisciplinary science of chemical phenomena
in the environment involving chemistry, physics,
life science, public health, engineering, etc.
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THE COURSE OUTLINE
Stratospheric chemistry and the ozone layer
principles of photochemistry, light absorption by
molecules, noncatalytic and catalytic process of
ozone distraction, free radicals, Cl and Br as X
catalysts, the ozone hole and its consequences,
chlorofluorocarbons (CFCs). Ground-level
(tropospheric) air chemistry ground-level ozone
and photochemical smog, oxidation of methane,
hydrocarbons and atmospheric SO2, acid rain,
ecological effects of outdoor air pollutants,
indoor air pollution formaldehyde, NO2, CO,
tobacco smoke, asbestos, radioactivity from radon
gas. The greenhouse effect and global warming
energy absorption, the major and minor greenhouse
gases CO2, water vapour, methane, N2O,
CFCs. Environmental consequences of energy use
CO2 emissions, solar energy, conventional and
alternative fuels, nuclear energy. The chemistry
of natural waters acid-base chemistry,
CO2/carbonate system, ion concentations,
alkalinity, seawater, redox chemistry in natural
waters, oxygen demand, the pE scale, sulphur and
nitrogen compounds, ion complexes,
stratification, precipitation. Soil chemistry
soil components, weathering process, aerobic,
anaerobic soils, water-sediment-soil system.
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Reading References W. vanLoon, S. J. Duffy
Environmental Chemistry, a Global Perspective,
2nd ed. Colin Baird Environmental Chemistry TG
Spiro, WM Stigliani Chemistry of the
Environment Course notes
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WATER
WATER IS THE ELEMENT OF SELFLESS CONTRAST IT
PASSIVELY EXISTS FOR OTHERS WATERS EXISTENCE
IS,THEREFORE, AN EXISTING-FOR-OTHERS ITS FATE
IS TO BE SOMETHING NOT YET SPECIALIZED AND
THUS IT SOON CAME TO BE CALLED THE MOTHER OF
ALL THAT SPECIAL Hegel, Philosophy of
nature (1817)
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WATER
PROPERTY MAGNITUDE CONSEQUENCE
HEAT CAPACITY Exceptionally high
a). Slows down temp.changes. 4.19 kJ / kg
K b). Heat transported around
the globe by
ocean currents.
c). Influences climate
LATENT HEAT OF Exceedingly high
Stops the water temp. from changing FUSION
333 kJ/ kg rapidly when is around zero
additional energy required to freeze
the water.
LATENT HEAT OF Highest of all substances Low
water and heat loss to the EVAPORATION 2260
kJ/kg atmosphere
DENSITY Maximum density at 40C
Ice floats, insulating the water below
Decreases with from
cold. increasing salinity.
Stratification of non-flowing waters
SURFACE Highest of all liquids
Controls the size of raindrops, sea TENSION
73 mN/m waves, sprays, etc.
DISSOLVING Exceptionally good
Dissolves nutrients and transports POWER
them to plants.
TRASPARENCY Relatively large
Absorbs in the ultraviolet and
infrared but transmits the
visible
radiation required for photosynthesis
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STRATIFICATION
EPILIMNION warmer, lower density, aerobic CO2
H2CO3 HCO3- SO42- NO32--
Fe(OH)3 THERMOCLINE HYPOLIMNION cooler, more
dense, anaerobic CH4 H2S NH3 NH4
Fe2(ag) bacteria SEDIMENTS
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THE ACDITY OF WATER
THE ACIDITY OF WATER AND ANY AQUEOUS SOLUTION
MEASURE OF CONCENTRATION OF HYDRONIUM IONS pH
pH -log H3O or simply pH -log
H
Autoprotolisis of water 2H2O ? H3O OH- K
H3O OH- / H2O 1.8 x 10-16 (250C)
What is the concentration of water in water?
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ACIDITY OF THE SOLUTION

• IDENTIFY THE SPECIES IN SOLUTION
• ex. sol. NaCl in water sol. HCl in water
• HOW CONCENTRATIONS OF IONS DEPEND ON EACH OTHER
• ex. Ka, Kb, Kw for HCl and NaOH sol.
• MASS BALANCE
• ex. For the fixed volume V ? m c
• CHARGE BALANCE
• ve ve-
• SOLUBILITY OF GASES
• X(g) X(aq)
• KH X(aq) / px - Henrys Law

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ACID-BASE CHEMISTRY IN NATURAL WATERS
THE CO2 / CARBONATE SYSTEM CO32- ?
H2CO3 moderately
weak strong
base acid CO2 H2O ?
H2CO3 ? 2H CO32- LIME ROCKS SOURCE
OF CARBONATE IONS
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The proportion of the carbonate present in all
its possible forms
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NATURAL AIR,WATER,ROCK SYSTEM
CO2
H20
Ca2
CaCO3
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EQUILIBRIUM WATER / CaCO3
1. CaCO3 ? Ca2 CO32- Ksp
Ca2 CO32- 4.6 X 10 9 (250C)
Ca2 CO32- S - solubility, Ksp
S2, S (Ksp)1/2 6.8x 10-5M
2. CO32- H2O ? HCO3- OH- K
HCO3- OH- / CO32-
3. (1 2) CaCO3 H2O ? Ca2
HCO32- OH- and KT Ksp K Ka
(HCO3-) 4.7 x 10-11 and Ka x Kb
KW 10-14 Kb (CO32- ) KW / Ka 2.1
x 10-4 conjugate base KT
Ca2 HCO3- OH- and S Ca2
HCO3- OH- KT S3 9.7 x 10-13
? S 9.9 x 10-5 GREATER SOLUBILITY BECAUSE
CO32 REACTS WITH WATER
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EQUILIBRIUM WATER / CaCO3 / CO2 (ATMOSPHERIC)
CaCO3 CO2 H2O ? H2CO3 ? Ca2
2HCO3- with K Ksp x Ka x Kb x KH/ KW
1.5 x 10-6 M3/L3atm ?
? and K
Ca2 HCO3-2 / p CO2 S x (2S)2 / p
CO2 p CO2 partial pressure of atmospheric CO2
0.00036 atm S3 1.3 X 10-10 and
S 5.1 x 10-4 M / L
Compare water with CO2 without CO2
Ca2 ? 5.1 x 10-4 M / L 9.9 x 10-5
M / L
WATER WITH DISSOLVED CO2 MORE READILY DISSOLVES
CaCO3
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ACIDITY OF NATURAL WATERS normal and acid rain
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ACIDITY OF NATURAL WATERS sea water
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ACIDITY OF NATURAL WATERS - seawater
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METAL COMPLEXES IN NATURAL WATERS
APPLICATION OF CHEMISTRY OF SIMPLE METAL -
LIGAND SYSTEMS TO MUCH MORE COMPLEX
ENVIRONMENTAL SYSTEMS
EX Inorganic Hg complexes in sea
water Conditions pH 8.4 OH- , major anion Cl-
Large number of equilibrium reactions are
occurring in water
In order to assess the environmental impact of
trace metals in water body predictions have to
be made as to which species are present in
solution.
Solutions Complicated computer modeling
and/or graphical representations
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THE MAJOR COMPLEXES OF TRACE METALS IN WATERS
FREE IONS
FREE IONS
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ELEMENTS PREDICTED TO HAVE SIMILAR SPECIATION IN
FRESH AND SEAWATER
ELEMENTS PREDICTED TO HAVE DIFFERENT SPECIATION
IN FRESH AND SEAWATER
FRESHWATER BOTH SEAWATER
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REDOX CHEMISTRY IN NATURAL WATERS
The concentration of electrons control redox
processes in the environment pE -log e-
Most common measure of electron activity is EH,
the electrode potential measured against SHE
The natural limits of redox in natural waters
pE and EH are linearly related pE (F/
2.3RT) EH
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REDOX AND ACIDITY CONDITIONS IN NATURAL WATERS
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pE pH (or EH - pH) DIAGRAMS (Pourbaix
diagrams)
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pE pH (or EH - pH) DIAGRAMS (Pourbaix
diagrams)
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WATER CHEMISTRY... AND SOIL
Soil composition
1. Inorganic mineral matter (defined as soil
material made up mostly of oxygen, silicon, and
aluminum (many other metals in small quantities
may be included) 2. Organic mineral matter
(defined as soil material having derived mostly
from plant residues and made up mostly of carbon,
oxygen, and hydrogen) 3. Solutes (refers to the
portion of soil composed of water and mostly
dissolved salts (plant nutrients) 4. Air (refers
to the gaseous portion of soil composed of the
same gases found in the atmosphere (oxygen,
nitrogen, and carbon dioxide) but in different
proportions)
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WATER CHEMISTRY... AND SOIL Soil modifies water
chemistry or quality through the processes
of 1. Surface-exchange hydrolysis 2. Dispersion
by monovalent metal ions 3. Soil's catalytic role
in many chemical and/or electrochemical
reactions 4. Precipitation reactions of heavy
metals through hydroxylation 5. Oxidation
reactions of organics and inorganics 6.
Hydrolysis reactions of organics and
inorganics 7. Condensation reactions of
organics 8. Physical adsorption of metals and
metalloids 9. Chemical reactions with
metalloids 10. Soil-dissolution
reactions Overall, soil systems behave as
complex biomolecular sieves.
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Soil polymeric structures of silicates
extended networks Si4 can be replaced by
Al3 Other major cations H, K, Na, Mg2,
Ca2, Fe2
Structural units in silicate minerals
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ION EXCHANGE EQUILIBRIA ON THE SURFACE OF
SOIL-CLAY PARTICLE
Clay minerals particles lt2µm. They bond
electrostatically cations natural ion exchangers
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Organic matter humus decompose by organisms
plant material in forms of cellulose and
hemicellulose undecomposed protein and lignin
and its polimerized and partly oxidized forms
containing carboxylic groups COOH fulvic and
humic acids
Fulvic acid soluble in alkaline and acidic
solution Humic acid - soluble in alkaline, not
soluble in acidic solution
Humic materials have great affinity to heavy
metal cations and extract them from waters by ion
exchange process formation of complexes by
COOH groups in fulvic and humic acids
CEC Cation Exchange Capacity quantity of
cations that are reversibly adsorbed per unit
mass of a dry soil number of moles of positive
charge
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WEARTHERING PROCESS
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DISSOLUTION AND DEPOSITION PROCESSES
THE INTERCHANGE OF MATERIAL BETWEEN SEDIMENTS AND
WATER
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SOIL CHEMISTRY TRRESTIAL CHEMISTRY WATER-SOIL
CHEMISTRY BIOGEOCHEMISTRY
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• DISSOLUTION AND DEPOSITION PROCESSES
• SOLUBILITY AND PRECIPITATION
• CHEMICAL WEATHERING
• - BY HYDROLISIS (SILICATES)
• - BY OXIDATION (IRON MINERALS, S2-)
• COLLOIDS AND THEIR AGGREGATION
• - HYDROPHILIC COLLOIDS (LARGE MOLECULES
• WHICH INTERACT STRONGLY WITH WATER)
• - HYDROFOBIC COLLOIDS (INTERACT LESS STRONGLY
• BUT ARE STABLE BECAUSE PARTICLES REPEL EACH
  OTHER
• - ASSOCIATION COLLOIDS (MICELLES)

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CONCENTRATION OF IONS IN SOIL SOLUTIONS IS
DETERMINED BY MANY PROCESSESS DEPENDENT ON EACH
OTHER
REDUCTION
DESORPTION
PRECIPITATION
OXIDATION
ACID-BASE REACTION
COMPLEX FORMATION
ADSORPTION
OTHER CONNECTIONS.?
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REMOVING COLLOIDAL MATERIAL ? TO AGGREGATE
COLLOIDS ? TO DESTABILIZE COLLOIDS ?
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ACID MINE DRAINAGE
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ACID MINE DRAINAGE
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• The pollution associated with AMD is
  characterized by
• Seeping from mines acidified water and
  rust-coloured iron hydroxide
• The concentrated acid liberate toxic heavy metals
  from their ores in the mine, further adding to
  the pollution.

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CHEMICAL SPECIATION OF HEAVY METALSTHE NEED FOR
SPECIATION

• DISTRIBUTION, MOBILITY AND BIOLOGICAL
  AVAILABILITY OF CHEMICAL ELEMENTS DEPENDS NOT
  SIMPLY ON THEIR CONCENTRATIONS BUT, CRITICALLY,
  ON THE CHEMICAL AND PHYSICAL ASSOCIATIONS WHICH
  THEY UNDERGO IN NATURAL SYSTEMS.
• CHANGES IN ENVIRONMENTAL CONDITIONS (NATURAL AND
  ANTHROPOGENIC) CAN STRONGLY INFLUENCE THE
  BEHAVIOUR OF BOTH ESSENTIAL AND TOXIC ELEMENTS BY
  ALTERING THE FORMS IN WHICH THEY OCCUR.
• THE MOST IMPORTANT CONTROLING FACTORS INCLUDE pH,
  REDOX POTENTIAL, AND AVAILABILITY OF REACTIVE
  SPECIES SUCH AS COMPLEXING LIGANDS (ORGANIC AND
  INORGANIC), PARTICLE SURFACES FOR ADSORPTION, AND
  COLLOIDAL MATTER.
• SPECIATION SCIENCE SEEKS TO CHARACTERISE, AT
  LEAST SOME OF, THE MOST IMPORTANT FORMS OF AN
  ELEMENT, IN ORDER TO UNDERSTAND THE
  TRANSFORMATIONS BETWEEN FORMS WHICH CAN OCCUR,
  AND TO INFER FROM SUCH INFORMATION THE LIKELY
  ENVIRONMENTAL CONSEQUENCES.

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CLASSES OF CHEMICAL SPECIATION
SCREENING SPECIATION (identification and
quantification of different species of an
element, e.g. free ions, complexes)
REDOX SPECIATION (identification and
quantification of different oxidation states of
an element)
ISOTOPIC SPECIATION (mostly for medical purposes
or to trace sources of contaminants)
DISTRIBUTION SPECIATION (e.g. biological uptake,
transport in soils, distribution in water
column)
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CHEMICAL SPECIATION OF HEAVY METALSFUTURE
DEVELOPMENTS AND REQUIREMENTS

• STANDARIZATION OF SPECIATION SCHEMES
• DEVELOPMENT OF NEW IN SITU ANALYTICAL METHODS FOR
  SPECIES DETERMINATION
• DEVELOPMENT OF INTELLECTUAL TOOLS NECESSARY TO
  FILL THE GAP BETWEEN THE MOLECULAR AND THE
  MACROSCOPIC LEVELS
• IMPROVEMENT OF THE IDENTIFICATION AND
  QUANTIFICATION OF ORGANIC MATERIALS
• STUDY OF THE BEHAVIOUR AND PROPOERTIES OF
  COLLOIDAL MATTER
• STUDY OD THE ROLE PLAYED BY LIVING ORGANISMS IN
  TRACE METAL CONTROL
• DEVELOPMENT OF CHEMICAL SPECIATION SCHEMES WHICH
  CAN BE DIRECTLY RELATED TO MEASURES OF
  BIOAVAILABILITY

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CHEMICAL SPECIATION OF HEAVY METALSGENERAL
STRATEGIES FOR SPECIATION

• DISTURBANCE OF EQUILIBRIUM STATE
• SAMPLING
• PREPARATION STEPS
• STORAGE
• SEPARATIONS
• DIRECT METHODS FOR DETERMINATION
• INDIRECT METHODS FOR DETERMINATION
• SPECIATION BASED ON CALCULATION METHODS
• SOLUTION OF MULTIPLE SIMULTANEOUS EQATIONS
• COMPETING CHEMICAL EQUILIBRIA
• MASS BALANCE RELATIONSHIPS ASSUMPTIONS
• NUMBER OF SPECIES
• BEST VALUES OF THE VARIOUS EQUILIBRIUM
  CONSTANTS
• COMPUTER MODELING
• SIMULATIONS
• PREDICTIONS
• EXPERIMENTAL vs CALCULATION METHODS

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THE MODELING OF SPECIATION REACTIONS IN NATURAL
SYSTEMS

• PRINCIPLES OF CHEMICAL THERMODYNAMICS THAT CAN BE
  USED TO PREDICT THE SPECIATION OF A GIVEN
  ELEMENT
• COMPLEX EQUILIBRIA
• PRECIPITATION AND DISSOLUTION
• ADSORPTION AND MINERAL PHASES
• ACTIVITY COEFFICIENTS AND INTERFERENCES
• ACIDITY AND ELECTRON BALANCE (pH, pE)
• PHYSICAL PROPERTIES (TEMP. PRESSURE, UV, ETC.

THE RESULTS OF MODELLING ARE ONLY AS GOOD AS THE
ANALYTICAL DATA USED FOR CALCULATIONS!