Species in natural freshwater · -0,1-0,2-0,3-0,4-0,5 First Component S e c o n d C o m p o n e n t...
Transcript of Species in natural freshwater · -0,1-0,2-0,3-0,4-0,5 First Component S e c o n d C o m p o n e n t...
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Species in natural freshwater
Central equilibriums in natural water samples KJM MEF 4010
Module 19
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Compilation, calculations and QC of data
After the analysis the data must be: compiled reckoned in terms of
equivalent charge and
quality controlled by ion balance and agreement between measured and calculated conductivity
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Statistical analysis
Correlation matrix Identify parameters
that are directly correlated or co-variate
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Multivariate statistics How to interpret information in a data
matrix of 1000 samples with typically 20 – 30 parameters
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Cluster analysis
Organizing parameters that co-variate in clusters Identify
• Links between parameters and groups of parameters
• Identify key explanatory factors
• General patterns
NO3-K+Cl-
Na+HCO3
Mg2+
Ca2+
Free P
O4SO
42-
DOCSAR
sUVa
H+
25,00
50,00
75,00
100,00
Variables
Sim
ilari
ty
DendrogramComplete Linkage; Correlation Coefficient Distance
DNOM Geology Agriculture Seasalts
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Principal Component Analysis Makes an n-dimential graph of your
n parameters Identifies the greatest variation in the swarm of data
points and draws the PC1 through its axis.
Identifies the next PC perpendicular to the previous
Produce loading plots that are projections of the points to the PC plane 0,40,30,20,10,0-0,1-0,2-0,3
0,2
0,1
0,0
-0,1
-0,2
-0,3
-0,4
-0,5
First Component
Seco
nd C
ompo
nent
HCO3
Free PO4
Cl-
NO3-
SO42-
K+Na+
Mg2+
Ca2+
DOCSAR
sUVa
H+
Loading Plot of H+; ...; HCO3
Acid Alkaline
Organic
Inorganic
45,3%
29,3
%
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43210-1-2-3
3
2
1
0
-1
-2
First Component
Seco
nd C
ompo
nent
Nesøytjernet
Kolbotnvann
Årungen
Gjersjøen
Østensjøvannet
Lutvann
Sværsvann
Akerselva
Maridalsvannet
Score Plot of H+; ...; DOP
Dystrophic
Soft dilute
Hard alkaline
Eutrophic
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0
500
1000
1500
2000
2500
3000
ueq/
L
Org. charge PO43- Tot-F Cl- NO3- SO42- HCO3- H+ K+ Na+ Mg2+ Ca2+
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Challenges with simultaneous equilibrium
Speciation programs (MINEQL)
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Inorganic complexes
Major cations in natural waters H+, Ca2+, Mg2+, Na+, K+
Common ligands in natural systems: HCO3
-, SO42-, NO3
-, Cl-, F- & organic anions In anoxic environment: HS- & S2-
Dominating species in aerobic freshwater at pH 8 are:
Metal ion Dominating species % Mn+aq of
total amount of M
Mg(II) Mg(H2O)62+ 94
Ca(II) Ca(H2O)62+ 94
Al(III) Al(OH)2(H2O)4+, Al(OH)3(H2O)3
0, Al(OH)4(H2O)2- 1•10-7
Mn(IV) MnO2(H2O)20 -
Fe(III) Fe(OH)2(H2O)4+, Fe(OH)3(H2O)3
0, Fe(OH)4(H2O)2- 2•10-9
Ni(II) Ni(H2O)62+, NiCO3(H2O)5
0 40 Cu(II) CuCO3(H2O)2
0, Cu(OH)2(H2O)20 1
Zn(II) Zn(H2O)42+, ZnCO3(H2O)2
0 40 Pb(II) PbCO3(H2O)4
0 5
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Hydrolysis
85.22 H4Al(OH)OH4Al
25.17 H3Al(OH)OH3Al
55.10 H2Al(OH)OH2Al
954 H Al(OH) OH Al
6.5 HAl(OH)OHAl(OH)
75.6 HAl(OH)OHAl(OH)
6.5 HAl(OH)OHAl(OH)
954 HAl(OH)OHAl
43214aq
42aq3
3213aq 0
32aq3
212aq22aq3
11aq2
2aq3
4aq42aq0
3
3aq0
32aq2
2aq22aq2
1aq2
2aq3
=+++=+↔+
=++=+↔+
=+=+↔+
==+↔+
=+↔+
=+↔+
=+↔+
=+↔+
+−+
++
+++
+++
+−
++
+++
+++
pKpKpKpKp
pKpKpKp
pKpKp
.pKp
pK
pK
pK
.pK
β
β
β
β
In aqueous systems, hydrolysis reactions are important Hydrolysis reactions are controlled by {H+}
• The higher the pH, the stronger the hydrolysis of metal cations
• E.g. Aluminium
• Al3+aq denotes Al(H2O)6
3+
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Distribution of dissolved Fe3+ species Two total Fe concentrations, FeT = 10-4M and FeT = 10-2M
FeT = 10-4 M
%Fe
0
20
40
60
80
100
FeT = 10-2 M
pH1 2 3 4
%Fe
0
20
40
60
80
100
Fe3+
FeOH2+
Fe(OH)2+
Fe2(OH)24+
Fe3+
FeOH2+
Fe(OH)2+
8
10
12
14
160 2 4 6 8 10 12 14
pHp
X
pFe
pFe(OH)
pFe(OH)2
pFe(OH)3
pFe(OH)4
Distribution diagrams
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Dissolved Organic Matter Low molecular weight (LMW)
< 1000Da (e.g. C32H80O33N5P0.3) E.g.:
High molecular weight 1000 - > 100 000Da Humic substance
• Very complex and coloured substances
Measured by
TOC/DOC Or by
UV absorbency or colour
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Speciation with different ligands present In aqueous solution, containing a number of metal cations and
ligand anions, there are several simultaneous equilibriums Important ligands in natural water systems
• Basic: CO32-, OH-, Org-, Cl-
• Acid: F-, SO42-, Org-, Cl-
The distribution of species will depend on factors such as ligand concentrations, temperature, pH and ionic strength
The calculations become very complex where a metal cation have the opportunity to bind to more than one type of ligands Multiple iterations of the calculations are necessary
For such calculations we apply computer programs as MINEQL+, ALCHEMI or PHREEQ-C
E.g. simple system with only Al3+ and F-
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Relevant balanced equilibrium reactions
Definition of unknown
Equilibrium expressions Mass balance
Charge balance
No of unknown <
No of equations
Solve equations
Are assumptions justified?
No
Yes
No
Yes
Scheme for chemical equilibrium calculations
1 2 and 3
Approximations are commonly done by assuming the concentration of specific species are 0 Molar
Only mass balance and charge balance equations can be simplified
Approximations
New Approximations
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Set of expressions 1. Equilibrium expressions
– KW, KSP, KA, KB, βn, KREDOX, Kd
2. Mass (read: concentration) balance – Set the equilibrium molarities (MX)
up against each other (MX vs. MY) and against the analytical molarity (MX vs. cX) – Analytical concentration is the concentration of a substance dumped
into a solution. It includes all the forms of that substance in the solution.
3. Charge balance – Σ eqv./L positive charge = Σ eqv./L negative charge
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1. Equilibrium expressions • KW, KSP, KA, KB, βn, KREDOX, Kd
K H O OHW = + −[ ][ ]3
K Ba SOSP = + −[ ][ ]2
4
2
K H O CH COOCH COOHA =
+ −[ ][ ][ ]3 3
3
K OH CH COOHCH COOB =−
−
[ ][ ][ ]
3
3βn
n
n
n
Ni CNNi CN
=−
+ −
[ ( ) ][ ][ ]
2
2
K Mn FeMnO Fe HdOksRe
[ ][ ][ ][ ] [ ]
=+ +
− + +
2 3 5
4
2 5 8K
IId
org
aq
=[ ][ ]
2
2
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2. Mass balance • Ex.1: BaSO4 in HCl solution
– We see from the molecular formula that: So that:
The hydroniumion (H+) has two sources:
HCl (=cHCL) and the auto-proteolysis of water (=[OH¯]):
• Ex.2: Ag2CrO4 solution – We see from the molecular formula that : So that :
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3. Charge balance • The law of physics demand that
– Number of positive charge is equal to number of negative charge Charge contribution of a specie
= Valens · Molar concentration
Ex. 1: – In neutral pH solutions one can disregard the H+ and OH- ions
Ex. 2: – No new information
Σ Σn X m Yn m⋅ = ⋅+ −[ ] [ ]
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Metal hydrolysis The hydrolysis is described by a set of equilibrium reactions
{Fe3+} is determined by replacing each of the other parts of the mass equation with their equilibrium expression expressed by {Fe3+} :
Then the other species can be determined from the {Fe3+} and β E.g.;
}{Fe(OH)}{Fe(OH)}Fe(OH){}{Fe(OH)}{Fe
7.22 H4Fe(OH)OH4Fe
8.13 H3Fe(OH)OH3Fe
31.6 H2Fe(OH)OH2Fe
05.3 H Fe(OH) OH Fe
4
032
23
43214aq
42aq3
3213aq 0
32aq3
212aq22aq3
11aq2
2aq3
−+++
+−+
++
+++
+++
++++=
=+++=+↔+
=++=+↔+
=+=+↔+
==+↔+
C
pKpKpKpKp
pKpKpKp
pKpKp
pKp
β
β
β
β
2
32
2 }{}{)( +
++ =
HFeOHFe β
2
32
2
3
22
2
aq22aq3
}H{}{Fe}{Fe(OH)
}{Fe}H{}{Fe(OH)
H2Fe(OH)OH2Fe
+
++
+
++
+++
=
•=
+↔+
β
β
++++= ++++
+4
43
32
213
}{H}{H}{H}{H1}{Fe ββββC
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Speciation programmes MINEQL+ is a chemical
equilibrium model capable of calculating aqueous speciation solid phase saturation precipitation-dissolution adsorption.
An extensive thermodynamic database is included in the model
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Speciation; Shortcomings The equilibrium model is based on a choice of
complexes and their stability constants, which makes the results questionable
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Tutorial
Start out by choosing components that define your system
Find thermodynamic constants in database in ”Scan Thermo”
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Tutorial
The Calculation Wizards Tool is a collection of 5 input options to describe the chemistry of the system
Running the
calculation
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Tutorial Multirun manager
Titration 2 way analysis Field data
Output manager Types of Output
• The Header • The Log • The MultiRun Table • Component Groups • Special Reports
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Tutorial
Graphics manager Bar and X-Y plots
Run through the 4 problems
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Report
The report (~ 3p) should include the following paragraphs Abstract Introduction Material and methods Results Discussion Conclusion