Envr 403 introduction to environmental chemistry
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ENVR 403 Introduction to Environmental Chemistry. Philip C. Singer Department of Environmental Sciences and Engineering [email protected] 919-966-3865 April 2010. Topics. 1. Chemistry of Natural Waters 2. Purification of Water. 1. Chemistry of Natural Waters. Redox Equilibria

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ENVR 403 Introduction to Environmental Chemistry

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Envr 403 introduction to environmental chemistry

ENVR 403Introduction to Environmental Chemistry

Philip C. Singer

Department of Environmental Sciences and Engineering

[email protected]

919-966-3865

April 2010


Topics

Topics

1. Chemistry of Natural Waters

2. Purification of Water


1 chemistry of natural waters

1. Chemistry of Natural Waters

Redox Equilibria

-speciation

-dissolved oxygen resources

Acid-Base Equilibria

-speciation

-the carbonate system and alkalinity

Solubility Equilibria

-metal solubility

-aqueous lead (Pb) solubility


Ph and pe as master variables

pH and pE as Master Variables

H2CO3 = HCO3- + H+Ka1

pH = pKa1 + Log [HCO3-]/[H2CO3]

NO3- + 10H+ + 8e- = NH4+ + 3H2OKred

pE = -1/8 (pKred) + 1/8 (Log [NO3-] [H+]10/[NH4+])

pEo = -1/n (Log Kred)

pE = pEo + 1/n Log [Ox]/[Red])

Analogous to Nernst Equation

EH = EoH + 2.3 RT/nF (Log [Ox]/[Red])


Envr 403 introduction to environmental chemistry

After M. Benjamin, 2002


Envr 403 introduction to environmental chemistry

After M. Benjamin, 2002


Envr 403 introduction to environmental chemistry

After M. Benjamin, 2002


Envr 403 introduction to environmental chemistry

After M. Benjamin, 2002


Electroneutrality equation charge balance for natural waters

Electroneutrality Equation (Charge Balance) for Natural waters

Major Cations: Na+, K+, Ca2+, Mg2+

Major Anions: Cl-, SO42- , NO3-, HCO3-, CO32-

Charge Balance

[Na+]+ [K +] + 2[Ca2+] + 2[Mg2+]+ [H +] = [Cl- ]+ 2[SO42-]+ [NO3-] + [HCO3-] + 2[CO32-]+ [OH-]

Cb-Ca = Acid neutralizing Capacity = Alkalinity =

[HCO3-] + 2[CO32-]+ [OH-] – [H +]


Envr 403 introduction to environmental chemistry

What is the pH of pure rainwater?

Pure rainwater contains only dissolved CO2 in equilibrium with the atmosphere.

H2CO3 = KH PCO2 ~ 10-5M

What is the pH of a 10-5M solution of H2CO3?

Cb-Ca = Alkalinity = 0

[H+] = [HCO3-] + 2[CO32-] + [OH-] = K1[H+]C/D + 2 K1K2C/D

where D = [H+] 2 + K1 [H+] + K1K2

Answer: pH 5.65


Envr 403 introduction to environmental chemistry

If a body of water has a pH of 7.5 and an alkalinity of 2x10-3 equivalents/L, what is the equilibrium pH of the water if 10-3 eq./L of acid is added to the water?

Use initial pH and given alkalinity to find total carbonate concentration C

C = (Alkalinity + [H+] - [OH-]) /((K1[H+]/D) + 2K1K2/D) = 2.12x10-3 M

Added acid consumes alkalinity

New alkalinity = 2x10-3 – 10-3 = 10-3 eq/L

Find new pH from alkalinity expression

Alkalinity = [HCO3-] + 2[CO32-]+ [OH-] – [H +]

10-3 = ((K1[H+]/D) + 2K1K2/D) 2.12 x10-3 + [OH-] – [H +]

Find pH = 6.35


Envr 403 introduction to environmental chemistry

After M. Benjamin, 2002


Solubility of caco 3 s

Solubility of CaCO3(s)

  • Kso = [Ca2+][CO32-]

  • [Ca2+] = Kso/[CO32-] = Kso/α2[TOTCO3]

  • Solubility of Ca increases with decreasing pH


Lead in drinking water

Lead in Drinking Water

Pb(II) Pb(IV)

OCl-

Cl-

Particulate

CO32-, PO43-

CO32-, PO43-, Cl-

Pb2+

Pb 2+

Pb(IV)O2, Pb3(CO3)2OH2, PbCO3, Pb5(PO4)3OH

Lead Pipe Pb(0)

  • Lead pipe (Pb0) develops scales of corrosion products.

  • The products formed (oxides, carbonates, and phosphates) depend on the water chemistry.

  • Changes in distribution system water chemistry can destabilize corrosion products.

  • Optimization of water chemistry can mitigate lead release to solution.


Solubility of potential lead containing phases

Solubility of Potential Lead-containing Phases

Hydrocerussite

(Pb3(CO3)2(OH)2)

with 50 mg/L DIC

Hydroxylpyromorphite

(Pb5(PO4)3OH)

with 1 mg/L P

Plattnerite (PbO2)

-2

-3

Litharge (PbO)

-4

(M)

-5

diss

-6

Log[Pb]

15 ug/L Pb

-7

-8

-9

4

5

6

7

8

9

10

11

pH


Conventional and waterfree urinal

Conventional and Waterfree Urinal


Operation of falcon waterfree cartridge

Operation of Falcon Waterfree cartridge

Urine in

Source: Falcon Waterfree


Envr 403 introduction to environmental chemistry

Falcon—6 months

Fed Ex Global Health Building (highuse)


Chemical composition of urine udert et al 2003

Chemical Composition of Urine (Udert et al. 2003)


Underlying chemical theory hydrolysis of urea

Underlying Chemical Theory: Hydrolysis of Urea

  • NH2(CO)NH2+2H2O2NH4++CO3-2

  • Urease is urea-hydrolyzing enzyme

  • Urease decomposes urea into ammonium and carbonate, causing the pH to increase

  • Increase in pH and addition of ammonium and carbonate leads to over-saturation with respect to several different minerals, including struvite (MgNH4PO4) and calcium hydroxyapatite Ca5(PO4)3(OH)2.


Envr 403 introduction to environmental chemistry

Comparison of XRD patterns with struvite reference pattern.


Envr 403 introduction to environmental chemistry

O

P

Mg

Ca

SEM Results for RDU Terminal A Composition Similar to Struvite, MgNH4PO4 (s)


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