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Calcium Carbonate Saturation. WQT 134 Aquatic Chemistry II Standard Methods 20 th ed #2330 Calcium Carbonate Saturation. Week 5 Objectives . Reading assignment:

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calcium carbonate saturation

Calcium Carbonate Saturation

WQT 134

Aquatic Chemistry II

Standard Methods 20th ed

#2330 Calcium Carbonate Saturation

week 5 objectives
Week 5 Objectives

Reading assignment:

American Public Health Association (APHA), American Water Works Association (AWWA) & Water Environment Federation (WEF). 1999.  Standard Methods for the Examination of Water and Wastewater, 20th edition

  • Understand the function of the marble test

2. Understand the role of calcium carbonate saturation in corrosiveness.

3. Understand how to measure calcium carbonate saturation (SM #2330)

calcium carbonate saturation3

Calcium Carbonate Saturation

WQT 134

Environmental Chemistry II

STM. 20th edition. #2330

calcium carbonate marble test experimental design

Calcium Carbonate “Marble Test” Experimental Design

Part 1 Standardization of Titrant (Sulfuric acid)=purchased from Hach!

Part 2 Titration for Total Alkalinity

determine p alkalinity

determine T Alkalinity mg/L as CaCO3/L

Part 2 ADD 0.5 g CaCO3 + redue!

pH above 8.3 = P alkalinity

color change

0.02 N Sulfuric acid

P alkalinity

200 ml of sample + 5 drops Phenolphthaleinindicator no color change Palkalinity =0 or titrate to pH 8.3

Blue Color change after addition of Bromcresol green/methyl red

pH 4.5 = T alkalinity

red color change endpoint

T alkalinity

+ 5 drops Mixed bromcresol green-methyl red titrate to pH 4.5

pH Met4er

stir bar

stir plate

calcium carbonate saturation 2330

Calcium Carbonate Saturation #2330

  • What is Calcium carbonate saturation?
  • The sample pH and total alkalinity are determined. Then the sample is saturated with calcium carbonate and the procedure is repeated. A comparison of the before and after values is done by subtraction to determine if the system is under saturated, saturated, or in equilibrium with calcium carbonate.
  • Why do we care?
  • This test helps to determine how much lime or soda ash are needed to keep a distribution system in good operating condition
calcium carbonate saturation 23306

Calcium Carbonate Saturation #2330

  • Why is it important in wastewater industry?
  • the corrosiveness of the water leaving the plant.
  • Why is it important in water industry?
  • Aesthetic taste of water and to prevent corrosiveness of lines.
calcium carbonate saturation 23307

Calcium Carbonate Saturation #2330

  • What are some assumptions in procedure?
  • View procedure as a qualitative guide to the behavior of CaCO3 in aqueous systems
calcium carbonate saturation 23308

Calcium Carbonate Saturation #2330

  • What are some interferences in procedure?
  • Deposition from oversaturated waters is inhibited by the presence of phosphates (particularly polyphosphates), certain naturally occurring organics, and magnesium
calcium carbonate saturation 23309

Calcium Carbonate Saturation #2330

Calculations and Formulas?

Step 1 Calculate pH(1) of original sample

Step 2 Calculate alkalinity alk (1) of original sample

Alk(1) T Alkalinity mg/L as CaCO3/L=

(ml of acid to 8.3=colorless+ ml to reach pH 4.5=pink)(Normality)(50mg/meq CaCO3)(1000 ml)

ml of original sample volume

Step 3 Calculate pH(2) of 0.5 g spiked CaCO3 sample

Step 4 Calculate alk(2) of 0.5 gspiked CaCO3 sample

(ml of acid to 8.3=colorless+ ml to reach pH 4.5=pink)(Normality)(50mg/meq CaCO3)(1000 ml)

ml of original sample volume

slide10
Calcium Carbonate Saturation

Calculations and Formulas?

Step 5 A= samples prior to saturation

B= samples after saturation

Eq 1: A-B= Stability Index

Eq 2: Alk(1)-Alk(2)= +, -, 0

Eq 3: pH(1) – pH(2)= +, -, 0

A>B- water is supersaturated with respect to carbonate and may forma precipitate scale

A

A=B water is in equilibrium with respect to carbonate constituents

calcium carbonate saturation 233011

Calcium Carbonate Saturation #2330

  • Tips and Suggestions?
  • Use ample sample volume (300 ml); its trial and error
  • Leave the lime behind
  • Add H2SO4 slowly!
  • Keep track of H2SO4added each time!
  • Rely solely on indicators or can use pH probe!
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