ENVIRONMENVIRONMENTAL ENTAL CHEMISTRYCHEMISTRY

Chem. 3030Chem. 3030

The two terms ‘environmental chemistry’ and The two terms ‘environmental chemistry’ and ‘pollution’ often seem to go together, yet ‘pollution’ often seem to go together, yet environmental chemistry is much more than the environmental chemistry is much more than the study of chemical effects of pollution. study of chemical effects of pollution.

It is a multidisciplinary science of chemical It is a multidisciplinary science of chemical phenomena in the environment involving phenomena in the environment involving chemistry, physics, life science, public health, chemistry, physics, life science, public health, engineering, etc.engineering, etc.

THE COURSE OUTLINETHE COURSE OUTLINEStratospheric 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.

Reading References: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

THREE MAJOR ENVIRONMENTAL MEDIA: SURFACE WATERS, SUBSURFACE THREE MAJOR ENVIRONMENTAL MEDIA: SURFACE WATERS, SUBSURFACE WATERS (SOIL AND GROUND WATER), AND THE ATMOSPHEREWATERS (SOIL AND GROUND WATER), AND THE ATMOSPHERE

Each medium has its own distinct characteristics but they have also many similarities.Each medium has its own distinct characteristics but they have also many similarities.Few chemicals are restricted in their movement to one medium only – Few chemicals are restricted in their movement to one medium only –

chemical exchange must be considered.chemical exchange must be considered.

WATERWATER

WATER IS THE ELEMENT OF SELFLESS CONTRAST –WATER IS THE ELEMENT OF SELFLESS CONTRAST –IT PASSIVELY EXISTS FOR OTHERSIT PASSIVELY EXISTS FOR OTHERS

… … WATER’S EXISTENCE IS,THEREFORE, AN EXISTING-FOR-OTHERSWATER’S EXISTENCE IS,THEREFORE, AN EXISTING-FOR-OTHERS

……ITS FATE IS TO BE SOMETHING NOT YET SPECIALIZEDITS FATE IS TO BE SOMETHING NOT YET SPECIALIZED

… … AND THUS IT SOON CAME TO BE CALLEDAND THUS IT SOON CAME TO BE CALLED

‘‘THE MOTHER OF ALL THAT SPECIAL’ THE MOTHER OF ALL THAT SPECIAL’

Hegel, Hegel, Philosophy of nature (1817)Philosophy of nature (1817)

WATERWATER

PROPERTY PROPERTY MAGNITUDEMAGNITUDE CONSEQUENCECONSEQUENCE

HEAT CAPACITYHEAT CAPACITY Exceptionally highExceptionally high a). Slows down temp.changes. a). Slows down temp.changes. 4.19 kJ / kg K4.19 kJ / kg K b). Heat transported around the globe b). Heat transported around the globe

by ocean currents.by ocean currents. c). Influences climatec). Influences climate

SURFACE SURFACE Highest of all liquidsHighest of all liquids Controls the size of raindrops, sea Controls the size of raindrops, seaTENSIONTENSION 73 mN/m73 mN/m waves, sprays, etc. waves, sprays, etc.

DISSOLVING DISSOLVING Exceptionally goodExceptionally good Dissolves nutrients and transports Dissolves nutrients and transportsPOWERPOWER them to plants. them to plants.

TRASPARENCYTRASPARENCY Relatively largeRelatively large Absorbs in the ultraviolet and Absorbs in the ultraviolet and infrared but transmits the visible infrared but transmits the visible radiation required for photosynthesisradiation required for photosynthesis

LATENT HEAT OFLATENT HEAT OF Exceedingly highExceedingly high Stops the water temp. from changing Stops the water temp. from changingFUSION FUSION 333 kJ/ kg333 kJ/ kg rapidly when is around zero – rapidly when is around zero –

additional energy required to freeze additional energy required to freeze the water.the water.

LATENT HEAT OFLATENT HEAT OF Highest of all substancesHighest of all substances Low water and heat loss to the Low water and heat loss to the EVAPORATIONEVAPORATION 2260 kJ/kg2260 kJ/kg atmosphere atmosphere

DENSITY DENSITY Maximum density at 4Maximum density at 400CC Ice floats, insulating the water below Ice floats, insulating the water below Decreases withDecreases with from cold. from cold. increasing salinity.increasing salinity. Stratification of non-flowing waters Stratification of non-flowing waters

Model of water moleculeModel of water molecule Ice crystalIce crystal

The model of hydration The model of hydration sphere of sodium – an inner sphere of sodium – an inner rigid water shell, an outer, rigid water shell, an outer,

somewhat rigid floating in the somewhat rigid floating in the sea of ‘free’ watersea of ‘free’ water

Polymers of water molecules Polymers of water molecules demonstrating the ‘flickering demonstrating the ‘flickering

clusters’ modelclusters’ model

STRATIFICATIONSTRATIFICATION

EPILIMNIONEPILIMNIONwarmer, lower density, aerobicwarmer, lower density, aerobic

COCO2 2 HH22COCO3 3 HCOHCO33- - SOSO44

2- 2- NONO33

2-2-- - Fe(OH)Fe(OH)33

THERMOCLINETHERMOCLINE

HYPOLIMNIONHYPOLIMNIONcooler, more dense, anaerobiccooler, more dense, anaerobic

CHCH4 4 H H22S NHS NH3 3 NHNH44+ + FeFe2+2+(ag) bacteria(ag) bacteria

SEDIMENTSSEDIMENTS

THE ACDITY OF WATERTHE ACDITY OF WATER

THE ACIDITY OF WATER AND ANY AQUEOUS SOLUTION –THE ACIDITY OF WATER AND ANY AQUEOUS SOLUTION –

MEASURE OF CONCENTRATION OF HYDRONIUM IONS = pHMEASURE OF CONCENTRATION OF HYDRONIUM IONS = pH

pH = -log [HpH = -log [H33OO++] or simply pH = -log [H] or simply pH = -log [H++] ]

Autoprotolisis of water: Autoprotolisis of water: 2H2H22O O H H33OO+ + + OH+ OH--

K = [HK = [H33OO++] [OH] [OH--] / [H] / [H22O] = 1.8 x 10O] = 1.8 x 10-16 -16 (25(2500C)C)

What is the concentration of water in water?What is the concentration of water in water?

1000g (1L) / 18g = 55.56 mol/L1000g (1L) / 18g = 55.56 mol/L

K = [HK = [H33OO++] [OH] [OH--] / 55.56 ] / 55.56

or or K x 55.56K x 55.56 = [H = [H++] [OH] [OH--] = 10] = 10-14 -14 (25(2500C)C)

KKW W

andand pK pKw w = pH + pOH = 14= pH + pOH = 14

ACIDITY OF THE SOLUTIONACIDITY OF THE SOLUTION

IDENTIFY THE SPECIES IN SOLUTIONIDENTIFY THE SPECIES IN SOLUTION

ex. sol. NaCl in water sol. HCl in water

HOW CONCENTRATIONS OF IONS DEPEND ON EACH OTHERHOW CONCENTRATIONS OF IONS DEPEND ON EACH OTHER

ex. Ka, Kb, Kw for HCl and NaOH sol.

MASS BALANCEMASS BALANCE

ex. For the fixed volume V m ~ c

CHARGE BALANCECHARGE BALANCE

ve+ = ve-

SOLUBILITY OF GASESSOLUBILITY OF GASES

X(g) = X(aq)

KH = [X(aq)] / px - Henry’s Law

ACID-BASE CHEMISTRY IN NATURAL WATERSACID-BASE CHEMISTRY IN NATURAL WATERS

THE COTHE CO2 2 / CARBONATE SYSTEM/ CARBONATE SYSTEM

COCO332- 2- H H22COCO33

moderately weakmoderately weak

strong base acidstrong base acid

COCO2 2 + H+ H22O O H H22COCO3 3 2H 2H+ + + CO + CO332-2-

LIME ROCKS – SOURCE OF CARBONATE IONSLIME ROCKS – SOURCE OF CARBONATE IONS

The proportion of the carbonate present in all its possible formsThe proportion of the carbonate present in all its possible forms

AIRAIR

WATERWATER

ROCKROCK

SOILSOIL

SEDIMENTSSEDIMENTS

COCO22

CaCOCaCO33

HH22COCO3 3 HCO HCO33- - + H+ H++

COCO332- 2- + H+ H22O HCOO HCO33

- - + OH+ OH--

HH2200

++CaCa2+2+

NATURAL AIR,WATER,ROCK SYSTEMNATURAL AIR,WATER,ROCK SYSTEM

EQUILIBRIUM: WATER / CaCOEQUILIBRIUM: WATER / CaCO33

3. = (1 + 2) 3. = (1 + 2) CaCOCaCO3 3 + H+ H22O O CaCa2+ 2+ + HCO+ HCO332- 2- + OH+ OH- -

and Kand KT T = = Ksp + K

Ka (HCOHCO33--) = 4.7 x 10) = 4.7 x 10-11-11 and and Ka x Kb = KW = 10-14

Kb (COCO332-2-

) = ) = KW / Ka = 2.1 x 10-4

conjugate base

KT = [CaCa2+2+] [HCO] [HCO33--] [OH] [OH- - ] and S = ] and S = [CaCa2+2+] = [HCO] = [HCO33

--] = [OH] = [OH- - ] ]

KT = SS3 3 = 9.7 x 10= 9.7 x 10-13 -13 S = 9.9 x 10S = 9.9 x 10-5-5

GREATER SOLUBILITY BECAUSE COGREATER SOLUBILITY BECAUSE CO332 2 REACTS WITH WATERREACTS WITH WATER

2. CO2. CO332- 2- + H+ H22O O HCO HCO33

- - + OH+ OH- -

K = [HCOK = [HCO33--]] [OH[OH- - ] / [CO] / [CO33

2-2- ]]

1. CaCO1. CaCO3 3 Ca Ca2+ 2+ + CO+ CO332-2-

Ksp = [CaCa2+2+] [CO] [CO332-2-

] = 4.6 X 10 ] = 4.6 X 10 –9–9 (25 (2500C)C)

[CaCa2+2+] = [CO] = [CO332-2-

] = S - solubility, ] = S - solubility, Ksp = S2, S = (Ksp)1/2 = 6.8x 10-5M

EQUILIBRIUM: WATER / CaCOEQUILIBRIUM: WATER / CaCO33 / CO / CO2 (ATMOSPHERIC)2 (ATMOSPHERIC)

CaCOCaCO33 + CO + CO2 2 + H+ H22O O H H22COCO3 3 Ca Ca2+2+ + 2HCO + 2HCO33--

with K = Kwith K = Ksp sp x x Ka x Kb x KH/ KW = 1.5 x 10-6 M3/L3atm

and K = [CaCa2+2+] [HCO] [HCO33--]]2 2 / p / p CO2CO2 = S x (2S) = S x (2S)2 2 / p / p CO2CO2

p p CO2 CO2 – – partial pressure of atmospheric COCO2 2 = 0.00036 atm= 0.00036 atm

SS3 3 = 1.3 X 10 = 1.3 X 10-10 -10 and S = 5.1 x 10and S = 5.1 x 10-4 -4 M / LM / L

Compare:Compare: water with water with COCO22 without COwithout CO22

[CaCa2+2+] ] 5.1 x 10 5.1 x 10-4 -4 M / L 9.9 x 10M / L 9.9 x 10-5 -5 M / L M / L

WATER WITH DISSOLVED COWATER WITH DISSOLVED CO2 2 MORE READILY DISSOLVES MORE READILY DISSOLVES CaCOCaCO33

ACIDITY OF NATURAL WATERS – normal and acid rainACIDITY OF NATURAL WATERS – normal and acid rain

pH = 5.6pH = 5.6

(1)(1)

(1)(1)

ACIDITY OF NATURAL WATERS – sea waterACIDITY OF NATURAL WATERS – sea water

1122334455

66

77

22

55

AC

IDIT

Y O

F N

AT

UR

AL

WA

TE

RS

- s

ea

wa

ter

AC

IDIT

Y O

F N

AT

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WA

TE

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ea

wa

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11

pH = 8.4pH = 8.4

METAL COMPLEXES IN NATURAL WATERSMETAL COMPLEXES IN NATURAL WATERS

APPLICATION OF CHEMISTRY OF SIMPLE METAL - LIGAND SYSTEMS

TO MUCH MORE COMPLEX ENVIRONMENTAL SYSTEMS

EX: Inorganic Hg complexes in sea waterEX: Inorganic Hg complexes in sea water

Conditions: Conditions: pH = 8.4 – OHpH = 8.4 – OH- - , major anion Cl, major anion Cl--

ClCl- - HgHg2+ 2+ + Cl+ Cl-- HgCl HgCl++

HgClHgCl+ + + Cl+ Cl-- HgCl HgCl22

andand HgClHgCl33-- HgClHgCl44

2-2-

OHOH-- HgClHgCl+ + + OH+ OH- - HgOHCl HgOHCl

and and HgOHHgOHxxClClyyzz

Large number of equilibrium reactions are occurring in water Large number of equilibrium reactions are occurring in water

In order to assess the environmental impact of trace metals in water body 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. predictions have to be made as to which species are present in solution.

Solutions: Complicated computer modeling and/orSolutions: Complicated computer modeling and/orgraphical representations graphical representations

THE MAJOR COMPLEXES OF TRACE METALS IN WATERSTHE MAJOR COMPLEXES OF TRACE METALS IN WATERS

FREE IONSFREE IONS FREE IONSFREE IONS

COMPLEXESCOMPLEXES

ADSORBEDADSORBEDNaNa

KK

NiNi

AgAg

PbPbCuCuHgHg

FRESHWATERFRESHWATER

COMPLEXESCOMPLEXES

ADSORBEDADSORBED

NaNaKK

NiNi

AgAg

PbPb

CuCu

HgHg

SEAWATERSEAWATER

ELEMENTS PREDICTED TO HAVE ELEMENTS PREDICTED TO HAVE SIMILAR SPECIATION IN FRESH AND SEAWATER SIMILAR SPECIATION IN FRESH AND SEAWATER

ELEMENTS PREDICTED TO HAVE ELEMENTS PREDICTED TO HAVE DIFFERENT SPECIATION IN FRESH AND SEAWATER DIFFERENT SPECIATION IN FRESH AND SEAWATER

ELEMENTELEMENT MAJOR SPECIESMAJOR SPECIES

FRESHWATERFRESHWATER BOTH BOTH SEAWATERSEAWATER

REDOX CHEMISTRY IN NATURAL WATERSREDOX CHEMISTRY IN NATURAL WATERS

The concentration of electrons control redox processes in the environmentThe concentration of electrons control redox processes in the environment

pE = -log [epE = -log [e--]]

Most common measure of electron activity is EMost common measure of electron activity is EHH, ,

the electrode potentialthe electrode potential measured against SHEmeasured against SHE

The natural limits of redox in natural watersThe natural limits of redox in natural waters

The oxidation of waterThe oxidation of water

HH22O = OO = O2 2 + 4H+ 4H+ + + 4e+ 4e- - log K = - 83.1log K = - 83.1

K = pK = pO2 O2 [H[H++]]4 4 [e[e--]]44

and pE = 20.75 -pHand pE = 20.75 -pH

pEpE

pHpH

The reduction of waterThe reduction of water

2H2H+ + + 2e+ 2e- - = H= H2 2 log K =0log K =0

K = pK = pH2H2/ [H/ [H++]]2 2 [e[e--]]22

and pE = -pHand pE = -pH

pEpE

pHpH

pE and EpE and EH H are linearly are linearly relatedrelated: pE = (F/ 2.3RT) E: pE = (F/ 2.3RT) EHH

REDOX AND ACIDITY CONDITIONS IN NATURAL WATERS

pE – pH (or EpE – pH (or EH H - pH) DIAGRAMS (Pourbaix diagrams)- pH) DIAGRAMS (Pourbaix diagrams)

pE – pH (or EpE – pH (or EH H - pH) DIAGRAMS (Pourbaix diagrams)- pH) DIAGRAMS (Pourbaix diagrams)

1. Inorganic mineral matter (defined as soil material made up mostly of oxygen, 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)silicon, and aluminum (many other metals in small quantities may be included)

2. Organic mineral matter (defined as soil material having derived mostly from 2. Organic mineral matter (defined as soil material having derived mostly from plant residues and made up mostly of carbon, oxygen, and hydrogen)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 3. Solutes (refers to the portion of soil composed of water and mostly dissolved salts (plant nutrients)salts (plant nutrients)

4. Air (refers to the gaseous portion of soil composed of the same gases found 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 in the atmosphere (oxygen, nitrogen, and carbon dioxide) but in different proportions)proportions)

WATER CHEMISTRY... WATER CHEMISTRY... AND SOILAND SOIL

Soil compositionSoil composition

WATER CHEMISTRY... AND SOILWATER CHEMISTRY... AND SOIL

Soil modifies water chemistry or quality through the processes of:Soil modifies water chemistry or quality through the processes of:

1. Surface-exchange hydrolysis1. Surface-exchange hydrolysis2. Dispersion by monovalent metal ions2. Dispersion by monovalent metal ions3. Soil's catalytic role in many chemical and/or electrochemical 3. Soil's catalytic role in many chemical and/or electrochemical reactionsreactions4. Precipitation reactions of heavy metals through hydroxylation4. Precipitation reactions of heavy metals through hydroxylation5. Oxidation reactions of organics and inorganics5. Oxidation reactions of organics and inorganics6. Hydrolysis reactions of organics and inorganics6. Hydrolysis reactions of organics and inorganics7. Condensation reactions of organics7. Condensation reactions of organics8. Physical adsorption of metals and metalloids8. Physical adsorption of metals and metalloids9. Chemical reactions with metalloids9. Chemical reactions with metalloids10. Soil-dissolution reactions10. Soil-dissolution reactions

Overall, soil systems behave as complex biomolecular sieves. Overall, soil systems behave as complex biomolecular sieves.

Structural units in silicate mineralsStructural units in silicate minerals

Soil – polymeric structures of Soil – polymeric structures of silicates – extended networkssilicates – extended networks

SiSi4+4+ can be replaced by Al can be replaced by Al3+3+

Other major cations: Other major cations:

HH++, K, K++, Na, Na++, Mg, Mg2+2+, Ca, Ca2+2+, Fe, Fe2+2+

ION EXCHANGE EQUILIBRIA ON THE SURFACE OF SOIL-CLAY PARTICLEION EXCHANGE EQUILIBRIA ON THE SURFACE OF SOIL-CLAY PARTICLE

Clay minerals – particles <2Clay minerals – particles <2µm.µm.

They bond electrostatically cations – natural ion exchangersThey bond electrostatically cations – natural ion exchangers

Organic matter – humus:Organic matter – humus:

decompose by organisms plant material in forms of cellulose and decompose by organisms plant material in forms of cellulose and hemicellulosehemicellulose

undecomposed –protein and lignin and its polimerized and partly undecomposed –protein and lignin and its polimerized and partly oxidized forms containing carboxylic groups –COOH: fulvic and oxidized forms containing carboxylic groups –COOH: fulvic and humic acidshumic acids

Fulvic acid – soluble in alkaline and acidic solutionFulvic acid – soluble in alkaline and acidic solution

Humic acid - soluble in alkaline, not soluble in acidic solutionHumic acid - soluble in alkaline, not soluble in acidic solution

Humic materials have great affinity to heavy metal cations and Humic materials have great affinity to heavy metal cations and extract them from waters by ion exchange process – formation extract them from waters by ion exchange process – formation of complexes by –COOH groups in fulvic and humic acidsof complexes by –COOH groups in fulvic and humic acids

CEC – Cation Exchange Capacity – quantity of cations that are CEC – Cation Exchange Capacity – quantity of cations that are reversibly adsorbed per unit mass of a dry soil – number of reversibly adsorbed per unit mass of a dry soil – number of moles of positive chargemoles of positive charge

WEARTHERING PROCESSWEARTHERING PROCESS

DISSOLUTION AND DEPOSITION PROCESSESDISSOLUTION AND DEPOSITION PROCESSES

WATERWATER

BOTTOMBOTTOM

SEDIMENTSSEDIMENTS

DISSOLUTIONDISSOLUTION

SEDIMENTATIONSEDIMENTATION

SUSPENDED SUSPENDED

SEDIMENTSSEDIMENTS

RESUSPENSIBLE RESUSPENSIBLE

BOTTOMBOTTOM

SEDIMENTSSEDIMENTS

THE INTERCHANGE OF MATERIAL BETWEEN SEDIMENTS AND WATERTHE INTERCHANGE OF MATERIAL BETWEEN SEDIMENTS AND WATER

SOIL CHEMISTRYSOIL CHEMISTRY

TRRESTIAL CHEMISTRYTRRESTIAL CHEMISTRY

WATER-SOIL CHEMISTRYWATER-SOIL CHEMISTRY

BIOGEOCHEMISTRYBIOGEOCHEMISTRY

DISSOLUTION AND DEPOSITION PROCESSES:DISSOLUTION AND DEPOSITION PROCESSES:

SOLUBILITY AND PRECIPITATIONSOLUBILITY AND PRECIPITATION

CHEMICAL WEATHERINGCHEMICAL WEATHERING - - BY HYDROLISIS (SILICATES)BY HYDROLISIS (SILICATES) - BY OXIDATION (IRON MINERALS, S- BY OXIDATION (IRON MINERALS, S2-2-))

COLLOIDS AND THEIR AGGREGATIONCOLLOIDS AND THEIR AGGREGATION- - HYDROPHILIC COLLOIDS (LARGE MOLECULES HYDROPHILIC COLLOIDS (LARGE MOLECULES WHICH INTERACT STRONGLY WITH WATER)WHICH INTERACT STRONGLY WITH WATER)- HYDROFOBIC COLLOIDS (INTERACT LESS STRONGLY - HYDROFOBIC COLLOIDS (INTERACT LESS STRONGLY BUT ARE STABLE BECAUSE PARTICLES REPEL EACH OTHERBUT ARE STABLE BECAUSE PARTICLES REPEL EACH OTHER- ASSOCIATION COLLOIDS (MICELLES)- ASSOCIATION COLLOIDS (MICELLES)

CONCENTRATION OF IONS IN SOIL SOLUTIONS IS DETERMINED CONCENTRATION OF IONS IN SOIL SOLUTIONS IS DETERMINED

BY MANY PROCESSESS DEPENDENT ON EACH OTHERBY MANY PROCESSESS DEPENDENT ON EACH OTHER

REDUCTIONREDUCTION

COMPLEX COMPLEX FORMATIONFORMATION

PRECIPITATIONPRECIPITATION

DESORPTIONDESORPTION

OXIDATIONOXIDATION

ADSORPTIONADSORPTION

ACID-BASEACID-BASEREACTIONREACTION

OTHER CONNECTIONS….?OTHER CONNECTIONS….?

REMOVING COLLOIDAL MATERIAL REMOVING COLLOIDAL MATERIAL TO AGGREGATE COLLOIDS TO AGGREGATE COLLOIDS TO TO DESTABILIZE COLLOIDS DESTABILIZE COLLOIDS

ACID MINE DRAINAGEACID MINE DRAINAGE

ACID MINE DRAINAGEACID MINE DRAINAGE

The pollution associated with AMD is characterized by:The pollution associated with AMD is characterized by:

1.1. Seeping from mines acidified water and rust-coloured iron hydroxideSeeping from mines acidified water and rust-coloured iron hydroxide

2.2. The concentrated acid liberate toxic heavy metals from their ores in the The concentrated acid liberate toxic heavy metals from their ores in the mine, further adding to the pollution.mine, further adding to the pollution.

This reaction is catalyzed by bacteria.This reaction is catalyzed by bacteria.

CHEMICAL SPECIATION OF HEAVY METALSCHEMICAL SPECIATION OF HEAVY METALS

THE NEED FOR SPECIATIONTHE 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, SPECIATION SCIENCE SEEKS TO CHARACTERISE, AT LEAST SOME OF, THE MOST IMPORTANT FORMS OF AN ELEMENT, IN ORDER TO THE MOST IMPORTANT FORMS OF AN ELEMENT, IN ORDER TO UNDERSTAND THE TRANSFORMATIONS BETWEEN FORMS WHICH CAN UNDERSTAND THE TRANSFORMATIONS BETWEEN FORMS WHICH CAN OCCUR, AND TO INFER FROM SUCH INFORMATION THE LIKELY OCCUR, AND TO INFER FROM SUCH INFORMATION THE LIKELY ENVIRONMENTAL CONSEQUENCES.ENVIRONMENTAL CONSEQUENCES.

CLASSES OF CHEMICAL SPECIATION CLASSES OF CHEMICAL SPECIATION

REDOX SPECIATION

(identification and quantification

of different oxidation states

of an element)

CHEMICALCHEMICAL

SPECIATIONSPECIATION

SCREENING SPECIATION

(identification and quantification

of different species of an element,

e.g. free ions, complexes)

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)

CHEMICAL SPECIATION OF HEAVY METALSCHEMICAL SPECIATION OF HEAVY METALSFUTURE DEVELOPMENTS AND REQUIREMENTSFUTURE 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

CHEMICAL SPECIATION OF HEAVY METALSCHEMICAL SPECIATION OF HEAVY METALSGENERAL STRATEGIES FOR SPECIATIONGENERAL STRATEGIES FOR SPECIATION

DISTURBANCE OF EQUILIBRIUM STATEDISTURBANCE OF EQUILIBRIUM STATE

SAMPLINGSAMPLING

PREPARATION STEPSPREPARATION STEPS

STORAGESTORAGE

SEPARATIONSSEPARATIONS

DIRECT METHODS FOR DETERMINATIONDIRECT METHODS FOR DETERMINATION

INDIRECT METHODS FOR DETERMINATIONINDIRECT METHODS FOR DETERMINATION

SPECIATION BASED ON CALCULATION METHODSSPECIATION BASED ON CALCULATION METHODS

SOLUTION OF MULTIPLE SIMULTANEOUS EQATIONSSOLUTION OF MULTIPLE SIMULTANEOUS EQATIONS

# # COMPETING CHEMICAL EQUILIBRIA COMPETING CHEMICAL EQUILIBRIA

## MASS BALANCE RELATIONSHIPS ASSUMPTIONS MASS BALANCE RELATIONSHIPS ASSUMPTIONS

# # NUMBER OF ‘SPECIES’ NUMBER OF ‘SPECIES’

## ‘BEST VALUES’ OF THE VARIOUS EQUILIBRIUM CONSTANTS ‘BEST VALUES’ OF THE VARIOUS EQUILIBRIUM CONSTANTS

COMPUTER MODELINGCOMPUTER MODELING

# # SIMULATIONS SIMULATIONS

# # PREDICTIONS PREDICTIONS

EXPERIMENTAL vs CALCULATION METHODSEXPERIMENTAL vs CALCULATION METHODS

THE MODELING OF SPECIATION REACTIONS IN NATURAL SYSTEMSTHE 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 THE RESULTS OF MODELLING ARE ONLY AS GOOD AS THE ANALYTICAL DATA USED FOR CALCULATIONS!AS THE ANALYTICAL DATA USED FOR CALCULATIONS!