Lime, a generic term encompassing ground limestone (calcium carbonate), hydrated lime (calcium hydroxide), and burned lime (calcium oxide), plays a crucial role in various environmental and water treatment applications. Its versatility stems from its ability to alter pH, remove pollutants, and contribute to coagulation and flocculation processes.
1. Ground Limestone (Calcium Carbonate):
2. Hydrated Lime (Calcium Hydroxide):
3. Burned Lime (Calcium Oxide):
Advantages of Using Lime:
Considerations:
Conclusion:
Lime, in its various forms, is a critical component of many environmental and water treatment processes. Its versatility, effectiveness, and relatively low cost make it a valuable tool for improving water quality, protecting ecosystems, and ensuring sustainable practices. By understanding the different types of lime and their specific applications, we can harness its potential to create a cleaner and healthier environment.
Instructions: Choose the best answer for each question.
1. Which of the following is NOT a form of lime used in environmental and water treatment? a) Ground limestone (calcium carbonate) b) Hydrated lime (calcium hydroxide) c) Burned lime (calcium oxide) d) Quicklime (sodium hydroxide)
d) Quicklime (sodium hydroxide)
2. What is the primary application of ground limestone in water treatment? a) pH adjustment b) Softening c) Coagulation and flocculation d) Filter media
d) Filter media
3. Hydrated lime is commonly used for which of the following in wastewater treatment? a) Removal of dissolved organic matter b) Removal of phosphorus c) Removal of heavy metals d) All of the above
d) All of the above
4. Which of the following is a major consideration when using lime in water treatment? a) The cost of lime b) The availability of lime c) The potential for sludge production d) The effectiveness of lime
c) The potential for sludge production
5. What is a key advantage of using lime in environmental and water treatment? a) It is a highly selective treatment agent. b) It is a readily available and relatively inexpensive material. c) It has a high solubility in water. d) It does not produce any byproducts.
b) It is a readily available and relatively inexpensive material.
Scenario: A small water treatment plant uses lime to adjust the pH of incoming water before disinfection. The plant receives water with a pH of 6.5, and the desired pH for disinfection is 7.5. The plant uses hydrated lime (Ca(OH)2) for this purpose.
Task:
Hint: You may need to research the chemical reactions involved and consider the following factors:
**1. How Lime Affects Water pH:**
Hydrated lime (Ca(OH)2) is a strong base. When added to water, it dissociates into calcium ions (Ca2+) and hydroxide ions (OH-). The hydroxide ions react with hydrogen ions (H+) in the water, reducing their concentration and increasing the pH. This reaction can be represented as follows:
Ca(OH)2 (s) + 2H+ (aq) → Ca2+ (aq) + 2H2O (l)
**2. Calculating the Amount of Lime Needed:**
1. **Determine the initial and final [H+] concentrations:**
pH = -log[H+]
Initial [H+]: [H+] = 10^-6.5 = 3.16 x 10^-7 mol/L
Final [H+]: [H+] = 10^-7.5 = 3.16 x 10^-8 mol/L
2. **Calculate the amount of H+ removed:**
3.16 x 10^-7 mol/L - 3.16 x 10^-8 mol/L = 2.84 x 10^-7 mol/L
3. **Calculate the amount of Ca(OH)2 needed:**
From the balanced chemical equation, 1 mole of Ca(OH)2 reacts with 2 moles of H+. Therefore, for 2.84 x 10^-7 moles of H+, we need (2.84 x 10^-7 mol H+)/2 = 1.42 x 10^-7 moles of Ca(OH)2.
4. **Convert moles of Ca(OH)2 to grams:**
(1.42 x 10^-7 moles Ca(OH)2) * (74.09 g Ca(OH)2 / 1 mole Ca(OH)2) = 1.05 x 10^-5 g Ca(OH)2
5. **Scale up for 1 million liters:**
(1.05 x 10^-5 g Ca(OH)2 / 1 L) * (1,000,000 L) = 10.5 g Ca(OH)2
Therefore, approximately 10.5 grams of hydrated lime is needed to raise the pH of 1 million liters of water from 6.5 to 7.5.
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