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JORD310 - Soil Pollution and Sustainability > Trace elements > Flashcards

Trace elements Flashcards

(80 cards)

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1
Q

What is Exchangeable sodium percentage (ESP)

A

Measures the proportion of cation exchange sites occupied by sodium

Sodic soils: ESP > 6
Highly sodic: ESP > 15

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2
Q

What is sodic soils?
Why is it problematic?

A

High sodium levels relative to other cations

Low soil permeability
Compacted or hard soil:
Crusting

Nutrient imbalance (Na2+ competes)
Osmotic stress
Toxicity

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3
Q

SAR

A

Sodium adsorption ratio

High SAR values = high concentration of sodium

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4
Q

Hvilket ion av antimon (Sb) er mest giftig?

A

Sb (III) > Sb (V)

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5
Q

Hvilket ion av krom (Cr) er mest giftig?

A

Cr (VI) > Cr (III)

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6
Q

In which mineral do one find Cr (III) naturally? Why is this problematic for the production of concrete?

A

Limestone

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7
Q

What defines a trace element?

A

Elemenst with low concentrations in
- Soils
- Plants
- Water

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8
Q

Which elements are abundant in the earths crust, but still considered trace elements?

A
  • Ti (titanium)
  • Al (aluminium)
  • Fe (iron)
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9
Q

“Heavy metals” have a density higher than:

A

> 5.0 g/cm3

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10
Q

What are “man made soils” called?

A

Technosols

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11
Q

Examples of oxyanions

A

Cr(III): Cr(OH)₃
Cr(VI): CrO₄²⁻ ☣️

As(III): AsO₃³⁻ ☣️
As(V): AsO₄³⁻

Sb(III): Sb(OH)₃ ☣️
Sb(V): Sb(OH)₆⁻
(Antimon)

Se(IV): SeO₃²⁻ ☣️
Se(VI): SeO₄²⁻

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12
Q

Examples of 7 cationic metals

A

Al²⁺
Cd²⁺
Cu²⁺
Fe³⁺
Ni²⁺
Pb²⁺
Zn²⁺

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13
Q
A
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14
Q

What are sorces for trace elements from human activites

A
  • Mining
  • Tailings
  • Acid mine drainage
  • Landfill leachate
  • Industry
  • Urban runoffs
  • Amendments
    • Sewage sludge/biosolids
    • Inorganic fertilizers (rock)
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15
Q

One common sorces of “natural” contaminations in Norway

A
  • Black shale
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16
Q

What is the process that causes cation exchange?

A

Sorption ⇆ Desorption

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17
Q

How do trace elements come from primary and secondary minerals?

A

Dissolution

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18
Q

How are secondary minerals made?

A
  • Precipitation
  • Chemical weathering
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19
Q

What the process when (trace) elements are locked up in organisms?

A

Immobilization

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20
Q

What is it called when elements are made available from organic matter?

A

Mineralization

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21
Q

At what pH does led (Pb) have the lowest solubility?

A

pH 10

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22
Q

At what pH are trace elements normal least soluble?

A

pH 6-10

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23
Q

At what pH is iron (Fe) least soluble?

A

pH 8

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24
Q

What is the difference between activity and concentration of a trace element?

A

Concentration is how much of a trace element is present.

Activity is how much that element is able to do or react in a situation, often in relation to other substances.

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25
What is the redox state of ground water?
Reduced
26
How low is the pH at Foldal?
pH 1.8
27
What is Coprecipitation, and why does this happen with ironhydroxides?
Coprecipitation is when different substances, like metals, get stuck together as they form a solid. Iron hydroxides are good sorbants, and can trap other elements while precipitating.
28
What does USA use to make Pb²⁺ less soluble, and why is this problematic?
PO₄³⁻ causes Pb²⁺ to precipitate as secondary mineral PO₄³⁻ → Sb(OH)₆⁻ more soluble PO₄³⁻ → Antimon (V) more soluble
29
What is a complex?
An **ion** that is formed when combining: - Cations - Anions - And molecules
30
How does complexation affect mobility of elements?
Enhances mobility
31
What are ligands?
Things that trace elements combine with to make complexes
32
Name 6 inorganic ligands?
Cl⁻ – Chloride CO₃²⁻ – Carbonate HCO₃⁻ – Bicarbonate (or Hydrogen carbonate) OH⁻ – Hydroxide PO₄³⁻ – Phosphate SO₄²⁻ – Sulfate
33
Which trace elements are important when testing?
As – Arsenic Cr – Chromium Cd²⁺ – Cadmium(II) ion Cu – Copper Hg²⁺ – Mercury(II) ion Ni²⁺ – Nickel(II) ion Pb²⁺ – Lead(II) ion Zn²⁺ – Zinc(II) ion
34
Law of mass action
- How the speed of a chemical reaction depends on the concentrations Slower < [trace element ]= faster reaction (up to a point) It helps predict how chemical reactions will behave. Used in chemistry to understand equilibrium and reaction rates.
35
DOC-ions at low pH
R-COH₂⁺ R-COOH₂⁺
36
DOC-ions at neutral pH
R-COH R-COOH
37
DOC-ions at high pH
R-CO⁻ R-COO⁻
38
What types of OM are good at sorbing Pb and Cu?
- Peat - Compost
39
Three ways trace elements can sorb to surfaces:
- Surface complexation - Ion exchange - Specific binding
40
Which soil colloids/particles have **permanent charge** and which do not?
2:1 Silicate clay minerals Not - 1:2 Silicate clay minerals - Humus - (Hydr)oxides
41
Which soil colloids/particles have **variable charge**?
- 1:2 Silicate clay minerals - Humus - (Hydr)oxides
42
Which clay minerals have high activity (CEC)? Why? Which do not?
2:1 Silicate clay minerals - ↓ weathered - ↑ effective surface area 1:1 Silicate clay minerals - ↑ weathered - ↓ effective surface area
43
Which clay minerals have low activity (CEC)? Why?
44
How are clay minerals produced?
Chemical weathering of aluminosilicates
45
How can clay be used when it comes to pollutants? What side effects do we have to consider?
- Add clay to sorb cations - Makes soil more dense
46
What is the process called were clay minerals become permanently charged?
Isomorphic substitution
47
Which ions usually replace silicon when clay minerals undergo isomorphic substitution?
Al³⁺ Fe²⁺ Mn²⁺
48
Which two clay minerals are common in Norway?
- Illite (2:1) - Chlorite (2:1:1)
49
English and norwegian name for "brunleir"
- Dry cross clay - Tørrskorpeleire
50
Information about "brunleir"
- Leire over grunnvann - Mer forvitret - Mer oksidert
51
Information about "blåleir"
- Leire under grunnvann - Mindre forvitret - Mer redusert
52
What is filter press?
When soil is washed with water to separate the bigger pieces, you’re left with a fine, sticky clay. This clay is called filter press clay because it's collected during the washing process.
53
Which elements form (hydr)oxides?
Al Fe Mn
54
iron (hydr)oxides at: - low pH - "neutral" pH - high pH
Low: Fe(OH₂⁺)₃ Fe(OH)₃ High: Fe(OH⁻)₃
55
Why is Cr a problem in concrete production?
Naturally occuring in limestone Concrete have high pH → Cr(VI) Cr(VI) = Bad and needs to be reduced to Cr(III)
56
Amphotheric feature
something that **can act like both an acid and a base**, depending on the situation.
57
Which sorbants have amphoteric features?
(hydr)oxides
58
Two types of iron (hydr)oxides What can be said about these
- Hematite (oxide) - Geothite (hydroxide) These are "free iron" that gives soil red/yellow colour
59
Total iron =
Free iron (hydr)oxides - Discrete particles - Isolated or linked to surface of other particles (eg. clay) Structural iron: - Trapped in silicates crystal lattice
60
Outer-sphere complex
- Non specific bound - Not a stable sorption - Weak forces - forming a loose connection between trace elements and surface of metal oxides,
61
Inner-sphere complex
- Specific bound - Covalent bond - forming a stronger, more stable connection between trace elements and metal oxides
62
Which two forms of complexes do metal oxides form?
Inner-sphere complex Outer-sphere complex
63
Which one forms stronger connections between trace elements and metal oxides? Outer-sphere complex Inner-sphere complex
Inner-sphere complex
64
Adsorption edge
The point where the amount of a trace element sticking to a surface suddenly jumps. This happens when the pH of the solution changes, making the surface (like soil or metal oxide) more likely to attract and "stick" the trace element.
65
Information about soil organic matter as sorbants
- Large molecules - Reactive functional groups - Negative charge at pH 7 - Good sorbents for cations & organic pollutants - Low affinity for anions
66
4 reasons redox state is important
- Determines speciation (some are toxic, others aren't) - Fate of trace elements due to leaching - Precipitation of trace elements - Controlling geochemistry of natural waters
67
Do sulphides have high or low solubility?
Low
68
The link between: - Electron activity - Redox potential
- How many electrons are available or free to participate in a redox reaction. - A measure of how likely those available electrons are to actually undergo a certain redox reaction, due to a substances tendency to gain/lose electrons.
69
High electron activity
- More reducing conditions - More free electrons for reduction
70
Low electron activity
- Oxidizing conditions - Fewer free electrons, more chance for oxidation
71
High redox potential
- Oxidizing conditions - More likely to lose electrons
72
Low redox potential
- Reducing conditions - More likely to gain electrons
73
Biotransformation
Lliving organisms change the chemicals they come into contact with A substance is broken down, modified, or transformed by a living organism - Usually involves enzymes
74
75
How to spot oxidized manganese in soil
- Dark purple spots - Soft masses - Pore linings
76
How to spot iron oxides in soil
Colour: Yellow, orange, brown, black, red - Soft masses - Pore linings - Coatings - Concretions
77
In waterlogged soils, which elements are: - Decreasing - Increasing Why?
Decreasing **O₂** → H₂O **NO₃⁻** → NO₂⁻ **SO₄²⁻** → S²⁻ **OM** → CO₂ Increasing: Mn⁴⁺ → **Mn²⁺** Fe³⁺ → **Fe²⁺** SO₄²⁻ → **S²⁻** OM → **CH₄**
78
At what pH is iron (Fe) least soluble?
pH 8
79
How does complexation affect mobility of elements?
Enhances mobility
80
Inner-sphere complex
- Specific bound - Covalent bond - forming a stronger, more stable connection between trace elements and metal oxides

JORD310 - Soil Pollution and Sustainability (15 decks)

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