alkalinity, hardness, & lime/soda ash softening alkalinity, hardness, & lime/soda ash...

Alkalinity, Hardness,Alkalinity, Hardness,& Lime/Soda Ash Softening& Lime/Soda Ash Softening

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Douglas Rittmann, Ph.D., P.E.Douglas Rittmann, Ph.D., P.E.Water/Wastewater ConsultantWater/Wastewater Consultant

Presented toPresented to

CE 5345CE 5345

OnOn

Sept., 2006Sept., 2006

General ConsiderationsGeneral Considerations

1. Its capacity to neutralize acids or its buffering capacity.

2. 3 major classes of materials

A. Bicarbonates, HCO3- - pH 4.0 ≤ pH

8.3 B. Carbonates, CO3

- - >pH 8.3 < pH 10

C. Hydroxide, OH- - > pH 10.0

Sanitary SignificanceSanitary Significance

1. Lime/Soda Ash Softening1. Lime/Soda Ash Softening

2. Effects on Coagulant Dosing

3. Total Dissolved Solids compliance

4. Industrial Wastes Discharges

5. Calcium Carbonate Stability

Method of AnalysisMethod of Analysis

Acrobat Document

1. Phenolphthalein Alkalinity

A. Phenolphthalein indicator

B. pH 8.3 endpoint of titration

2. Total Alkalinity

C. Measures Carbonates and Hydroxide ions

A. Bromcresol green or Methyl Orange indicator

B. pH 4.5 endpoint of titration

C. Measures Bicarbonates

Methods of ExpressingMethods of Expressing

1. Phenolphthalein Alkalinity as CaCO1. Phenolphthalein Alkalinity as CaCO33

P. Alk. = ml 0.02N sulfuric acid (1000/ml sample) = mg/L as CaCO3

2. Total Alkalinity as CaCO3

T. Alk. = ml 0.02N sulfuric acid X (1000/ml sample) = mg/L as CaCO3

3. Hydroxide, Carbonate, and Bicarbonate Alkalinity as CaCO3

Alkalinity Alkalinity RelationshipsRelationships

Titration Titration ResultResult

OHOH--

Alkalinity as Alkalinity as CaCOCaCO33

COCO33--

Alkalinity as Alkalinity as CaCOCaCO33

HCOHCO33--

Alkalinity as Alkalinity as

CaCO3CaCO3

P = 0P = 0 00 00 TT

P<1/2 TP<1/2 T 00 2P2P T-2PT-2P

P=1/2 TP=1/2 T 00 2P2P 00

P>1/2 TP>1/2 T 2P – T2P – T 2(T- P)2(T- P) 00

P = TP = T TT 00 00

Standard SolutionsStandard Solutions

General ConsiderationsGeneral Considerations

1. Saves Time in calculating results1. Saves Time in calculating results

2. Selection of Proper Normality is convenient2. Selection of Proper Normality is convenient

* 1 mg/ml or 1000mg solution * 1 mg/ml or 1000mg solution

* 1/eq.wt., example: Alkalinity as CaCO3 = * 1/eq.wt., example: Alkalinity as CaCO3 = 0.02 N0.02 N

3. Preparation of Solution of Proper Normality3. Preparation of Solution of Proper Normality

* Material of Known purity is weighed & * Material of Known purity is weighed & transferred to transferred to volumetric flask volumetric flask

* Purchase Solutions of known Normality* Purchase Solutions of known Normality

Preparation of 1N Acid Preparation of 1N Acid SolutionSolution

* Sulfuric acid used for Alkalinity Test* Sulfuric acid used for Alkalinity Test

1 GMW = 98 g pure H2SO4 = 2.016 g H+

1 GMW/2 = 49 g pure H2SO4 = 1.008 g H+

Acid is 96% pure, then 49/0.96 = 51 g = 1.008 g H+

Make 5% stronger = 51 X 1.05 = 53.5 g

Procedure: Weigh about 53g of conc. acid into a small beaker on Trip balance. Place 500 ml of distilled water in 1-liter graduated cylinderAnd add the acid to it. Rinse the contents of the beaker into the cylinderWith distilled water, and add water to the 1-liter mark. Mix by pouringBack and forth from the cylinder into a large beaker. Cool to room temp.

Primary StandardPrimary Standard

* Sodium Carbonate is a convenient primary standard* Sodium Carbonate is a convenient primary standard

MW = 106 of Na2SO3

1EW or 1N = 53g/L when reacting with H2SO4 to pH 4.5, T. Alk endpoint

Preparation of 0.02 N Acid or N/50 can be made from 1N based onml X N = ml X N

Example: ml X 1.0 = 1000 X 0.02 ml = 20

Introduction To Introduction To HardnessHardness

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CE 5345CE 5345

OnOn

Sept., 2006Sept., 2006

Introduction to Introduction to HardnessHardness

** Causes & Sources of HardnessCauses & Sources of Hardness

Cations causing Cations causing hardnesshardness

AnionsAnions

CaCa++++ HCOHCO33--

MgMg++++ SOSO44==

SrSr++++ ClCl--

FeFe++++ NONO33--

MnMn++++ SiOSiO33==

* Source – Rain contact with soil and rock formations

Sanitary SignificanceSanitary Significance

* * Reasons to SoftenReasons to Soften

1. Reduce Soap Consumption1. Reduce Soap Consumption

2. Improve Aesthetics of Water2. Improve Aesthetics of Water

3. Hot Water Heaters last longer3. Hot Water Heaters last longer

* Reasons not to Soften* Reasons not to Soften

1. Expensive Process1. Expensive Process

2. May be less healthy2. May be less healthy

3. Competes with health related costs3. Competes with health related costs

Method of AnalysisMethod of Analysis

* EDTA – Ethylenediaminetertraacetic Acid Method* EDTA – Ethylenediaminetertraacetic Acid Method

* EDTA complexes Ca & Mg

* Eriochrome Black T serves as an indicator when EDTA is in excess of the complexed hardness ions.

* Color change is from red to blue

Types of HardnessTypes of Hardness

* Calcium and Magnesium Hardness* Calcium and Magnesium Hardness * Total Hardness – Calcium Hardness = Magnesium Hardness* Total Hardness – Calcium Hardness = Magnesium Hardness

* Carbonate and Noncarbonate Hardness* When alkalinity < Total Hardness, CO3 Hardness = T. Alkalinity

* When alkalinity ≥ Total hardness, CO3 Hardness = T. Hardness

* CO3 hardness removed by boiling or lime (Temporary Hardness)

* Noncarbonate Hardness (permanent) = T. Hardness – CO3 Hardness

* Pseudo-Hardness* Associated with Na+ which causes soap consumption but not considered part of hardness.

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CE 5345CE 5345

OnOn

Sept., 2006Sept., 2006

Effective Lime/Soda Ash Effective Lime/Soda Ash Water SofteningWater Softening

I. IntroductionI. Introduction

A. Reasons to SoftenA. Reasons to Soften

1. Reduce Soap Consumption1. Reduce Soap Consumption

2. Improve Aesthetics of Water2. Improve Aesthetics of Water

B. Reasons not to Soften B. Reasons not to Soften

1. Expensive Process1. Expensive Process

2. May be less healthy2. May be less healthy

3. Hot Water Heaters last 3. Hot Water Heaters last longerlonger

Water SofteningWater Softening

3. Competes with health related costs3. Competes with health related costs

II. What is Hardness? II. What is Hardness?

C. Carbonate Hardness as CaCOC. Carbonate Hardness as CaCO33 = T. Alkalinity as CaCO = T. Alkalinity as CaCO33

D. Non-Carbonate Hardness = T. Hardness – T. Alkalinity D. Non-Carbonate Hardness = T. Hardness – T. Alkalinity


a. Removed by Boilinga. Removed by Boiling

b. Removed by Limeb. Removed by Lime

a. Unaffected by boilinga. Unaffected by boiling

b. Removed by Soda Ashb. Removed by Soda Ash

B. T. Hardness, mg/L, as CaCOB. T. Hardness, mg/L, as CaCO33 = (Ca X 2.5) + (Mg X 4.12) = (Ca X 2.5) + (Mg X 4.12)

(MW=100) (40 X 2.5 = 100) (24.3 X 4.12 = 100)(MW=100) (40 X 2.5 = 100) (24.3 X 4.12 = 100)

A. Hardness ClassificationsA. Hardness Classifications

a. Soft Water = 0 to 70 mg/La. Soft Water = 0 to 70 mg/L

b. Moderate Hardness = 71 to 150 mg/Lb. Moderate Hardness = 71 to 150 mg/L

c. Hard Water = > 150 mg/Lc. Hard Water = > 150 mg/L


III. Methods of SofteningMethods of Softening

A. Lime-Soda Ash ChemistryA. Lime-Soda Ash Chemistry1. 11. 1stst Stage Treatment (Lime only) Stage Treatment (Lime only)

* CO* CO22 + Ca(OH) + Ca(OH)22 CaCOCaCO33 + H + H22OO

* Ca + 2HCO* Ca + 2HCO33 + Ca(OH) + Ca(OH)22 2CaCO2CaCO33 + 2H + 2H22O(pH 8.3-9.4) O(pH 8.3-9.4)

* Mg + 2HCO* Mg + 2HCO33 + Ca(OH) + Ca(OH)22 CaCOCaCO33 + Mg + CO + Mg + CO33 + 2H + 2H22O(pH >10.8)O(pH >10.8)

a. Carbon Dioxide Removal (< 8.3 pH)a. Carbon Dioxide Removal (< 8.3 pH)

b. Carbonate Hardness Removal b. Carbonate Hardness Removal

c. Magnesium Hardness Removal (>pH 10.8)c. Magnesium Hardness Removal (>pH 10.8)

* Mg + CO* Mg + CO33 + Ca(OH) + Ca(OH)22 CaCOCaCO33 + + Mg(OH)Mg(OH)22

* Mg + SO* Mg + SO44 + Ca(OH) + Ca(OH)22 Ca + SO Ca + SO44 + + Mg(OH)Mg(OH)22

* Ca + SO* Ca + SO44 + Na + Na22CO3 NaCO3 Na22SOSO44 + + CaCOCaCO33

2. 22. 2ndnd Stage Treatment Stage Treatment (Soda Ash) (Soda Ash)

* Ca + Cl* Ca + Cl22 + Na + Na22COCO33 CaCOCaCO33 + 2NaCl + 2NaCl

AnalysesAnalyses Water #1Water #1 Water #2Water #2 Water #3Water #3

Total HardnessTotal Hardness 300300 300300 300300

Calcium Calcium HardnessHardness

200200 200200 200200

Mg HardnessMg Hardness 100100 100100 100100

Total AlkalinityTotal Alkalinity 150150 250250 350350InterpretationsInterpretations Water #1Water #1 Water #2Water #2 Water #3Water #3

Calcium Calcium AlkalinityAlkalinity

150150 200200 200200

Mg. AlkalinityMg. Alkalinity NoneNone 5050 100100

Sodium Sodium AlkalinityAlkalinity

NoneNone NoneNone 5050

Ca N.C. Ca N.C. HardnessHardness

5050 NoneNone NoneNone

Mg. N.C. Mg. N.C. HardnessHardness

100100 5050 nonenone

A. Calcium Alkalinity = Ca Hardness or T. Alkalinity whichever is smallerA. Calcium Alkalinity = Ca Hardness or T. Alkalinity whichever is smaller

B1. Magnesium Alkalinity = Mg. Hardness if T. Alkalinity > or = than total hardnessB1. Magnesium Alkalinity = Mg. Hardness if T. Alkalinity > or = than total hardness

B2. Magnesium Alkalinity = Total Alkalinity – calcium hardness if total alkalinity is > thanB2. Magnesium Alkalinity = Total Alkalinity – calcium hardness if total alkalinity is > than calcium hardness but less than total hardness.calcium hardness but less than total hardness.

C. Sodium alkalinity = total alkalinity – total hardnessC. Sodium alkalinity = total alkalinity – total hardness

IV. Chemical Analyses InterpretationsIV. Chemical Analyses Interpretations

D. NCH = Total Hardness – Total Alkalinity ( If Mg Alkalinity present then no Ca NCH)D. NCH = Total Hardness – Total Alkalinity ( If Mg Alkalinity present then no Ca NCH)


Example: Calculate the hydrated lime (100%), soda ash, and carbon dioxide requirement to Example: Calculate the hydrated lime (100%), soda ash, and carbon dioxide requirement to Reduce the hardness of a water with the following analysis to about 50 to 80 mg/L by the excessReduce the hardness of a water with the following analysis to about 50 to 80 mg/L by the excessLime-soda ash process.Lime-soda ash process.

Analyses: Total Hardness = 280 mg/L as Analyses: Total Hardness = 280 mg/L as CaCO3CaCO3 Mg++ = 21 mg/L Mg++ = 21 mg/L Alkalinity = 170 mg/L as CaCO3Alkalinity = 170 mg/L as CaCO3 Carbon Dioxide = 6 mg/LCarbon Dioxide = 6 mg/L

Lime Requirement: Carbon Dioxide = (6) (56) / (44) = 8 Lime Requirement: Carbon Dioxide = (6) (56) / (44) = 8 Alkalinity = (170) (56) / (100) = 95 Alkalinity = (170) (56) / (100) = 95 Mg ++ = (21) (56) / (24.3) = 48Mg ++ = (21) (56) / (24.3) = 48

Excess Lime = = 35Excess Lime = = 35 Total CaO required = Total CaO required = 186mg/L186mg/L

Soda Ash Requirement: NCH = 280 – 170 = 110 mg/LSoda Ash Requirement: NCH = 280 – 170 = 110 mg/L Soda Ash (Na2CO3) = (110) (106) / (100) = Soda Ash (Na2CO3) = (110) (106) / (100) = 117 mg/L117 mg/L

A. Theoretical Solubility of Ca & Mg: A. Theoretical Solubility of Ca & Mg: Mg(OH)2 = 9 mg/L SolubilityMg(OH)2 = 9 mg/L Solubility CaCO3 = 17 mg/L SolubilityCaCO3 = 17 mg/L Solubility Total = ~ 26 mg/L SolubilityTotal = ~ 26 mg/L Solubility

B. Practical Minimum Total Hardness = 50 to 80 mg/LB. Practical Minimum Total Hardness = 50 to 80 mg/L

V. Theoretical versus PracticalV. Theoretical versus Practical

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