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1 CHEMICAL PRECIPITATION: WATER SOFTENING Submitted to: Dr. Hashsham Research Complex Engineering Department of Civil and Environmental Engineering Michigan State University East Lansing, MI 48824 Authors Dipa Dey Amanda Herzog Vidya Srinivasan ENE 806 May 2, 2007 i

2 Acknowledgement aluable guidance and We are grateful to Dr. Syed A. Hashsham for his inv support during the course of this project. We would also like to thank Mr. Joseph Nguyen for his assistance and cooperation. Dipa Dey May 2, 2007 Amanda Herzog Vidya Srinivasan ii

3 CONTENTS Caption Page No. Title page i ii Acknowledgement iii Contents iv List of Figures and Tables Abstract 1 Introduction 2 3 Chemistry of Hardness Removal Process Objective 5 Methods and Materials 5 Results and discussion 6 8 Conclusions 9 References 10 Appendix -1 10 RAW DATA Appendix-2 11 11 Sample Calculation to Determine the Lime Dosage Appendix-3 13 13 Water Softening and alkalinity Protocol Appendix-4 16 16 Pictures iii

4 LIST OF FIGURES AND TABLES Caption Page No. Variation of hardness, alkalinity and pH for varying lime 6 Figure 1: dosages (run1) Figure 2: Variation of hardness, alkalinity and pH for varying lime 7 dosages (run2) Figure3: Comparison of replicate runs 8 16 Setup and Samples with lime dosages 16 Floc. Formation 16 Filtration Setup 16 Samples After Filtration Before Titration 16 Mid-Titration 16 End of Titration 16 Table 1: : Run1 for varying lime dosages 10 Table2: Run2 for varying lime dosages 10 iv

5 ABSTRACT ve soap consumption. Hard water can cause many problems including scaling and excessi In the United States, hard water is mostly found in the mid west ern and western states. It ranges between 120-250 mg/L as CaCO or beyond 250 mg/L as CaCO for very hard 3 3 waters. The acceptable water hardness range is between 60-120 m g/L as CaCO . A water 3 softening experiment was conducted in replicate to observe the changes in parameters such as total hardness, calcium hardness, magnesium hardness, alkal inity and pH with varying dosages of lime. A lime dosage range of 30-180% of the st oichiometric amount was chosen for the experiments. The sample used was groundwater fr om an East Lansing . Results indicated that an increase well which had a total hardness of 332 mg/L as CaCO 3 in lime dosage upto 90% caused a decrease in total hardness, alkalini ty, magnesium hardness and calcium hardness concentrations. However, for a lime dosage beyond 120%, the total hardness, alkalinity, and calcium hardness concentrations increased while magnesium hardness concentration decreased to lower values. The pH continually increased for a lime dosage between 30% and 180%. 1

6 INTRODUCTION Hard water is the most common water quality problem reported by consumers throughout ground water and hard the United States. More than 60 percent of the Earth’s water is water is found in more than 85% of the country. The water travels t hrough rocks and soil d water. picking up minerals including calcium and magnesium, ions which produce har (Water Review, Consumer report, 1990). Hard water interferes with almost every cleaning task from laundering and dishwashing to bathing and personal grooming (IANR, Water Quality 1996). Clothes lau ndered in hard water may look dingy and feel harsh and scratchy. Dealing with hard water problems in the home can be a nuisance. In addition, hard water affects the amount of soap and detergent necessary for cleaning. Soap used in hard water combine s with the minerals to form a sticky soap curd. Some synthetic detergents are less e ffective in hard water because the active ingredient is partially inactivated by har dness, even though it stays ky soap curd on the dissolved. Bathing with soap in hard water leaves a film of stic skin. The film may prevent removal of dirt and bacteria. Soap cur d interferes with the return of skin to its normal, slightly acid condition, and may lead to i rritation. Soap curd on hair may make it dull, lifeless and difficult to manage. Hard water also contributes to inefficient and costly operation of water treatment equipment. Heated hard water forms a scale of calcium and magne sium minerals that can contribute to the inefficient operation or failure of water treat ment equipment . Pipes can become clogged with scale which reduces water flow and ultimately results in pipe replacement. Hard water is not a health hazard. In fact, the National Resea rch Council (National Academy of Sciences) states that drinking hard water generally contributes to the total calcium and magnesium needs in humans. Water utilities struggling with source water that contains hi gh amounts of calcium and/or magnesium often turn to lime softening to remove hardness. Raising treatment pH above 9.6 converts soluble calcium bicarbonate hardness to insoluble calcium c arbonate. An increase in pH beyond 10.6 converts soluble magnesium bicarbonate to insoluble treatment pH of magnesium hydroxide. Aggressive magnesium removal often requires a 11 or higher, a process known as excess lime softening (Jones, C; et.al. 2005). 2

7 Chemistry of Hardness Removal Process During precipitation softening, calcium is removed form water in the form of CaCO 3 precipitate and magnesium is removed as Mg(OH) precipitate (Frederick W. Pontius). 2 The carbonic acid concentration present and the pH play an important rol e in the by the addition of precipitation of these two solids. Carbonate hardness can be removed hydroxide ions and raising the pH by which the bicarbonate ions are conve rted to carbonate form having a pH above 10. Due to the increase in carbonate concentration, precipitates of calcium carbonate is formed. The remaining ca lcium, i.e. non carbonate hardness, cannot be removed by simple adjustment of pH. Therefore, soda as h (sodium calcium. Magnesium is carbonate) must be externally added to precipitate this remaining removed due to the precipitation of magnesium hydroxide. In the lime soda ash process, lime is added to raise the pH while sodium carbonate is added to provide a source of carbonate ion. H CaCO OH Ca H O (1) 2 ) ( + → + CO 2 2 3 2 3 Eq.(1) is the neutralization reaction between CO carbonic acid and lime. This equation 2 that for each mg/L of does not result any net change in water hardness. This also suggest carbonic acid expressed as CaCO present, 1mg/L of lime expressed as CaCO will be 3 3 required for neutralization by knowing the stoichiometric ratios. 2 + − ( CaCO OH Ca HCO Ca (2) 2 2 ) O ) ( 2 + → + + H s 3 2 2 3 shows that for each Eq.(2) presents the removal of calcium carbonate hardness. It also ormed by increasing molecule of calcium bicarbonate present, two carbonate ions can be f the pH. This also suggest that for each mg/L of calcium bicarbonat e present, 1mg/L of lime expressed as CaCO will be required for its removal by knowing the stoichiometric 3 ratios between them. 2 2 − −     SO SO 4 4 2 + + (3) CaCO + Ca → + Na CO + + 2 Na     3 2 3 − − Cl 2 Cl 2         Eq.(3) reflects the removal of calcium noncarbonated hardness. The stoi chiometric hardness present, 1mg/L coefficient suggest that for each mg/L of calcium noncarbonate of sodium carbonate expressed as CaCO will be required for its removal. 3 3

8 + 2 + OH Mg CaCO OH Ca HCO Mg O (4) + s 2 ) ( ) ( 2 ) ( 2 2 H + → + 3 2 2 2 3 Eq. (4) is similar to eq.(2). If the magnesium bicarbonate and lim e are expressed as CaCO , then the stoichiometric ratios suggest that for each mg/L of ma gnesium 3 bicarbonate hardness present, 2 mg/L of lime expressed as CaCO will be needed for its 3 removal. 2 2 − −     SO SO 4 4 2 + + (5) + + + → + ( ( Mg ) ( ) ) Ca s OH Mg OH Ca     2 3 − − Cl 2 2 Cl         Eq. (5) represents the removal of magnesium noncarbonate hardness. If the magnesium noncarbonate hardness and lime are expressed as CaCO , stoichiometric ratios suggest 3 mg/L of lime that for each mg/L of magnesium noncarbonate hardness present, 1 expressed as CaCO will be needed for its removal. Here no net change in the hardness 3 level resulted as for each magnesium ion removed calcium ion is added. Thus to complete the hardness removal process, sodium carbonate required to be added to precipitate the calcium as presented in the equation below. 2 − 2 −     SO SO 4 4 2 + + (6) + → + + + 2 ) CO ( Na Na s CaCO Ca     2 3 3 − − Cl 2 2 Cl         4

9 OBJECTIVE the effects of varying The objective of the water softening experiment was to determine lime dosages on parameters such as total hardness, calcium hardnes s, magnesium hardness, alkalinity and pH. METHODS and MATERIALS Very hard ground water was obtained from a well located in East La nsing provided by Joseph Nguyen. Initial sample characteristics such as pH, alkal inity, and total hardness are provided in Appendix 2. A lime, Ca(OH) , stock solution of 10mg/mL was prepared 2 for dosing the sample with 30, 60, 90, 120, 150 and 180 percent of the stoichiometri c amount of lime. The jar test was executed with the conventional apparatus with s ix 2-liter ime for 20 beakers (Appendix-2) mixing the groundwater with the various amounts of l min at 30 rpm. The samples were then filtered through 0.45μ m filter and then titrated for sium hardness total hardness, calcium hardness, and alkalinity. In addition pH and magne were noted down. This experiment was done in replicate to compare results and determine the degree of experimental error. Detailed protocols for this experiment, including titrations and calculations, are available in the appendix. 5

10 RESULTS and DISSCUSSION Run 1: Water Softening pH for varying Lime dosages Replicate 1: Variation of Hardness, Alkalinity and 350 13 300 3 12 250 pH 11 200 Total Hardness 10 pH 150 Alkalinity 9 100 Magnesium Hardness Calcium Hardness 8 Concentartion, mg/L as CaCO 50 7 0 180 140 120 100 80 60 40 160 0 20 Lime dose, % Stoichiometric Amount Figure 1: Variation of Hardness, Alkalinity and pH for varying Lime do sages (Run1) Replicate runs for the water softening experiment evaluated par ameters such as alkalinity, hardness and pH in response to varying lime dosages from 30% to 180% of t he ue of stoichiometric amount. In Run 1, the total hardness reached a minimum val approximately 160 mg/L as CaCO for a lime dosage of 90% (fig.1). The calcium 3 CaCO hardness first decreased in concentration to a minimum of 35mg/L as for a lime 3 dosage of 90% and then after that continued to increase in concentration with an increase of lime dosage. This increase in calcium hardness was observed due to the addition of excess lime and the absence of alkalinity caused by carbonat es. The plateau between 60% and 90% of lime is due to the presence of extra alkalinity. Any ex cess lime added in this region converts bicarbonates to carbonates and those carbonates combine w ith the free calcium ions to form precipitates. Magnesium hardness concentration decreased with the increasing dos age of lime. Alkalinity decreased to a minimum at approximately 90% of lim e and increased thereafter. This is due to the addition of lime and the precipit ation of species, which e dosages higher than 120%, consumes alkalinity that causes the initial decrease. At lim y addition of lime, free alkalinity increases due to an addition of excess lime. For ever 6

11 - - ions are released, therefore an increase in OH ions is responsible for an increase in OH pH. Run 2: Water Softening Replicate 2: Variation of Hardness, Alkalinity and pH for various Lime dosages 400 13 3 12 300 11 pH 200 10 pH Total Hardness Alkalinity 9 100 Magnesium Hardness Concentration, mg/L as CaCO 8 Calcium Hardness 7 0 80 60 140 160 0 180 100 40 20 120 Lime dose, % Stoichiometric Amount Figure 2: Variation of Hardness, Alkalinity and pH for varying Lime do sages (Run2) y 160 mg/L as In Run 2, the total hardness reaches a minimum value of approximatel CaCO tion first for a lime dosage of 120% (fig.2). The calcium hardness concentra 3 decreases to a minimum of 35 mg/L as CaCO for a lime dosage of 60% and then starts to 3 increase above a lime dosage of 90%. This result was due to the addit ion of excess lime and the absence of alkalinity caused by carbonates. The plateau bet ween 60% and 90% of lime was because of the presence of extra alkalinity. Any excess lime added in this region converts bicarbonates to carbonates and combine with the free c alcium ions to form precipitates. Magnesium hardness decreases with an increase in lime dosag e and reaches a concentration of 30mg/L as CaCO , for a lime dosage of 180%. This concentration 3 ddition alkalinity indicates an approximate solubility limit of magnesium ions. In a . The trends decreased to a minimum around 90% of lime but increases thereafter observed in Run1 and Run2 were in good correlation with each other. 7

12 ng Comparative Study of Replicate Runs : Water Softeni 400 y = 1.0797x 2 R = 0.8977 350 300 250 200 Run 2 150 Magnesium Hardness, mg/L as CaCO 3 100 Alkalinity, mg/L as CaCO 3 Total Hardness, mg/L as CaCO 3 50 Calcium Hardness, mg/L as CaCO 3 Linear Trendline 0 400 300 200 100 0 Run 1 Figure 3: Comparison of Replicate Runs This plot is a comparative study of the data obtained from run 1 and run2. The data from 2 each run have an R correlation of 0.90 for the parameters of this study. Hence, the experiment is reproducible and the trends observed for each parameter in response to varying lime dosages are in agreement with the expected trends. CONCLUSIONS This experiment yielded the following conclusions: • Calcium hardness concentrations decreased with an increase in lime dosage but concentrations increased at dosages higher than 90%. • specially when Magnesium hardness decrease with an increase in lime dosage, e calcium hardness was increased (dosage higher than 90%) Alkalinity decreased to a minimum value of approximately 135 mg/L as CaCO at • 3 a lime dosage of 90% and increased thereafter due to the addition of excess lime. - • pH increased with an increase in lime dosage due to the gen eration of free OH ions. thereby The replicate runs conducted were in correlation with each other, • demonstrating reproducibility. 8

13 REFERENCES 1. IANR, Water Resources management, Water Quality, 1996. 2. Jones, C; Corriagn,T; Graham, D.B; McMullen, L.D, 2005. “Reduced Lime Fee d: Effects on Operational Costs and water Quality”. 3. Syed Hashsham. Chemical Precipitation: Water Softening. Lab Report, 1993 4. Water Quality and Treatment: A Handbook of Community Water Supplies . American Water Works Association. Fourth edition, 1990 5. Water Review, Consumer Report, Vol.5,No.1. 1990. A publication of the water quality research council 6. Water Treatment Principles and Design. MWH. Second edition, 2005 9

14 APPENDIX 1 – RAW DATA Table1: Run 1 pH Mg Alkalinity Total Ca Alkalinity Total Lime Ca Hardness (Titrant hardness Hardness Hardness dose hardness volume) (Titrant (Titrant (%) Volume) Volume) 5 8.3 31.1 200 332 311 132 7.7 0 240 3.1 24 124 268 6.7 144 8.4 30 4.2 1.1 150 15 44 168 60 124 9.3 90 0.9 13.5 36 148 135 112 11 3.7 120 4.1 13 68 164 130 96 11 1.7 150 3.7 4.6 15 148 184 150 36 12 225 180 6.3 22.5 232 252 5.8 20 12 Table2: Run 2 pH Mg Alkalinity Total Ca Alkalinity Total Ca Lime Hardness Hardness Hardness (Titrant hardness hardness dose volume) (Titrant (Titrant (%) Volume) Volume) 5 31.1 200 332 311 132 7.7 0 8.3 2.9 272 23.6 116 30 236 156 8.4 6.8 0.9 4.4 14.4 36 176 144 140 10 60 10 0.9 90 140 4.4 13.5 36 176 135 120 4.1 13.7 64 164 137 100 11 1.6 12 3.7 5.2 14.9 148 208 149 60 150 180 12 8.5 9.2 21.4 340 368 214 28 10

15 APPENDIX 2 – Sample Calculation to Determine the Lime Dosage Ground water Sample: pH= 7.72 2+ Ca = 200 mg/L 2+ = 132 mg/L Mg 0 Temperature= 20 C Alkalinity= 311 mg/L Total Hardness= 332 mg/L Carbonate Hardness= Alkalinity = 311 mg/L CaCO 3 Non Carbonate hardness = Total hardness- Alkalinity = 21 mg/L CaCO 3 From the above values we know that it is an excess lime soda –ash process 332 200 0 2+ 2+ Mg Other Cations Ca Other Anions HCO 3 311 0 Step1: Assume pH=7, so all alkalinity is in the bicarbonate form 61 1 1 -3 a) [HCO ]=311 mol/L ( ) ( × × × ) = 6.22 x 10 ) ( 3 50 1000 61 14.8435- 3404.71 /293 – 0.032786 (293) b) =10 K 1 -7 K = 4.26 x 10 1 6.498- 2909.39/293-0.02379(293) = 10 K 2 -11 = 3.97 x 10 K 2 1 c) = α 1 7 − 7 − 1/ K × K × 10 + 1 1 + / 10 1 2 1 = − − 7 11 7 7 − − 26.4/ × 10 + + × × 1 10 × 10 1 97.3 10 1/ = 0.81 11

16 22.6 − × 10 3 3 − × d) mol/L 10 = C .7 679 = T 0 . 81 -3 -3 * -3 = 1.477 x 10 ]= 7.679 x 10 mol/L -6.22 x 10 [HCO e) 3 -3 * ]= 1.477 x 10 mol/L x 62 g/mol = 0.0915 g/L= 91.5 mg/L [HCO 3 * ]= 147.7 mg/L CaCO [HCO 3 3 332 147.7 0 200 Other Cations 2+ 2+ Mg Ca H CO = 2 3 147.7 - Other Anions HCO 3 0 311 147.7 Step2: Total Hardness= 332 mg/L 2+ Ca Carbonate Hardness = 200 mg/L 2+ Non Carbonate Hardness = 0 mg/L Ca 2+ Carbonate Hardness = 311-200 = 111 mg/L Mg 2+ Mg Non Carbonate Hardness= 332-311= 21 mg/L Step3: Lime Dosage: 147.7 + 200 +2(111) +21= 590.7 mg/L as CaCO 3 590.7 X (37/50) = 437.118 mg/L as Ca(OH) 2 Soda Ash dose: =0+21=21 mg/L as CaCO 3 53 Soda ash dose = 21 × 22.26 mg/L as Na CO = 2 3 50 12

17 APPENDIX 3 - Water Softening and alkalinity Protocol Water Softening Protocol TRIAL RUN: 1. Prepare a Lime stock of 10 mg/mL Prepare 0.1 M EDTA stock 2. Using ground water samples measure Total hardness, Calcium hardness , 3. Magnesium hardness, Alkalinity, pH and Temperature a. Total hardness, Calcium hardness and Alkalinity protocols attached at the end of this document. Determine the appropriate water softening process: 4. a. i.e. East Lansing well water= excess lime soda-ash 5. Calculate and add lime dosage for 100% stoichiometric amount to a lit er of ground water Use AWWA equations for dosage calculation a. 2. Conduct flocculation for 20 min at 30 RPM 3. Filter the entire sample through 0.45 uL filter (smooth side of filter facin g down in the funnel) 4. Collect supernatant and measure Alkalinity, Calcium and Total hardness and pH 5. Calculate Magnesium hardness RUN 1 & 2: 1. Calculate and add lime dosage for 30, 60, 90, 120, 150, and 180% of the stoichiometric amount to a liter of ground water. a. Use AWWA equations for dosage calculation 2. Conduct flocculation for 20 min at 30 RPM 3. Filter the entire sample through 0.45 uL filter (smooth side down in the funnel) 4. Collect supernatant and measure Alkalinity, Calcium and Total hardness and pH 5. Calculate Magnesium hardness Repeat experiment to determine degree of experimental error 6. 13

18 ALKALINITY PROTOCOL: 1. Use pH 7.0 buffer and adjust the pH meter to 7.0. Use pH 4.0 buffer and adjust the pH meter to 4.0. 2. Titrate 100 mL of sample with 0.02 N H2SO4 to obtain pH 4.5 by vigorously stirring towards the end of the titration step. This is done in order to break the surface and to obtain rapid equilibrium between CO2 in soluti on and CO2 in the atmosphere. 3. Total Alkalinity is measured as CaCO3 in mg/L= (ml of titrant) X 10 To prepare 0.02N H2SO4, Use the following formula: Nf*Vf=Ni*Vi Where: Nf: Final normality desired Vf: Final total volume Ni: Initial normality Vi: Initial volume TOTAL HARDNESS: 1. Take 25mL of sample and add 25 mL of DI water 2. Add 1 mL of hardness buffer and measure pH • Ideal pH for reaction is above 10 3. Add a scoop of Erichrome Black T indicator • The solution will turn pink 4. Titrate 0.1M EDTA until a permanent blue color appears ++ ++ • This is when Ca and Mg ions complex w/ EDTA Total Hardness= Volume of titrant*1*(1000/vol. of sample) 5. 14

19 ++ Ca HARDNESS: 1. Take 25mL of sample and add 25mL of DI water 2. Add 2mL 8N NaOH solution and measure pH • pH ideally above 10, usually 12 or 13 3. Add a scoop of Erichrome Blue Black R indicator • The solution will turn pink 4. Titrate 0.01 N EDTA until a permanent blue color appears Calcium Hardness=Volume of titrant*1*(1000/vol. of sample) 5. ++ ++ Hardness + Mg Hardness Total Hardness= Ca Carbonate Hardness=Alkalinity Non-carbonate Hardness=Total Hardness – Alkalinity 15

20 APPENDIX 4 - Pictures Setup & Samples with Lime Dosage Floc. Formation Filtration Setup Samples After Filtration End of Titration Before Titration Mid-Titration 16

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