EC Assignment 1

 

Q 1: Discuss the Zeolite method for water purification with suitable diagram, reaction and procedure.  

Ans: Zeolites are naturally occurring sodium aluminum silicates having different amounts of water of crystallization. They are represented as Na2O.Al2O3.xSiO2.yH2O where x and y varies from 2 to 10 and 2 t 6 respectively. They have the property of exchanging their Na ions for hardness causing ions like Ca⁺⁺  and  Mg⁺⁺ 

Ca(HCO3)2+Na₂Ze→CaZe+2NaHCO3  

MgSO4+Na2Ze→MgZe+Na2SO4 

CaCl2+Na₂Ze→CaZe+2NaCl 

where Ze represents zeolite. 

The Ze mineral gets exhausted when all the Na⁺ are replaced by Ca⁺⁺ and Mg⁺⁺ ions. Now Ze can be regenerated by passing Nacl solution, 

CaZe+2NaCl→CaCl₂+Na₂Ze 

MgZe+2NaCl→MgCl₂+Na₂Ze 

The regenerated Ze can now be used for replacing Ca⁺⁺and Mg⁺⁺ from hard water. Zeolite softening is carried out in large cylindrical tank as shown, holding ze material on a perforated platform. The tank has two inlets for feeding raw water and passing saturated NaCl solution.

Limitations- 

1) Raw material must be free from turbidity and suspended impurities. 

2) Highly acidic water is not suitable as it affects mineral. 

3) Zeolites of iron and manganese cannot be easily regenerated by passing NaCl solution. Hence iron and manganese impurities in the water to be treated must be minimum. 

Advantages- 

1) Water of about less than 15 ppm is obtained. 

2) The process automatically adjusts for different hardness of incoming water. 

3) Water obtained is quiet clear. 

4) The equipment is compact and requires less space. 

5) It requires less skill in maintenance as well as operation. 

Q 2: Define: Hard water, Soft water, Caustic embrittlement, Scale & Sludge. 

Ans: Hard water: Hard water is a term that denotes water having a very high mineral content (the term is the opposite of ‘soft water’). As water percolates into deposits of calcareous, gypsum or chalk that are primarily composed of carbonates of magnesium or calcium, bicarbonate and sulphates, hard water is formed. 

Soft water: Soft water can be defined as surface water that contains relatively low ion concentrations and is low in calcium and magnesium ions. Soft water naturally occurs where rough, impermeable and calcium-poor rocks are responsible for the formation of the runoff and the drainage basin of rivers. 

Caustic embrittlement: Caustic embrittlement is a phenomenon that occurs in boilers where caustic substances accumulate in boiler materials. It also can be described as the cracking of riveted mild steel boiler plates. This occurs at temperatures of 200°-250°C as a result of local deposition of concentrated hydroxide. 

Scale: Scale is hard mineral coatings and corrosion deposits made up of solids and sediments that collect on or in distribution system piping, storage reservoirs and household plumbing. 

Sludge: Sludge is a water-formed sedimentary deposit which may include all suspended solids carried by the water and trace elements in solution in the water. 

Q 3: What are the essential requirements of boiler feed water? Discuss the boiler problems due to using impure water in detail. 

Ans: Boiler feedwater is the water that is supplied to a boiler for generating steam. The essential requirements of boiler feedwater are as follows:  

1. Purity: Boiler feedwater should be free from impurities such as suspended solids, dissolved minerals, organic matter, and gases. The presence of impurities can cause scale formation, corrosion, and fouling, leading to reduced efficiency and safety hazards. 

2. pH: The pH of the feedwater should be within a specific range to prevent corrosion and scale formation. Typically, the pH range for boiler feedwater is between 8.5 and 9.5. 

3. Hardness: Hardness in water is caused by the presence of dissolved minerals such as calcium and magnesium. Hardness can cause scaling in the boiler, reducing its efficiency. The recommended maximum hardness for feedwater is 0.2 parts per million (ppm) as calcium carbonate.  

4. Alkalinity: Alkalinity is the capacity of water to neutralize acids. High alkalinity in boiler feedwater can lead to the formation of scale and foaming. The recommended maximum alkalinity is 700 ppm as calcium carbonate.  

5. Oxygen: Oxygen in boiler feedwater can cause corrosion of metal surfaces. The recommended maximum oxygen concentration is 0.007 ppm. 

Q 4: 0.5g of CaCO3 was dissolved in dil. HCL and then diluted up to 250 ml. 50ml of this solution requires 50ml of EDTA solution for titration. 50ml of hard water sample require 25 ml same EDTA solution for titration. 50ml of same hard water sample on boiling and filtering consumed 15ml of EDTA for titration. Calculate total, carbonate and non-carbonate hardness. 

Ans: 0.5g of CaCO3 was dissolved in dil. HCL and then diluted up to 250 ml 

Concentration of sample of hard water = 0.5g/250ml CaCo₃ 

                                                                        = 0.002g/ml = 2mg/ml 

Now, 50ml of same hard water sample required 50ml EDTA. 

1ml EDTA Solution = 50/50 = 1ml CaCO3 

Equivalent Hardness 

Now, 50ml water sample = 25ml EDTA 

Hardness of sample = 25*(50/50) mg CaCo₃ = 25 mg CaCo₃ 

Hardness per liter of sample = 25*(50/50)*1000 mg/l  = 500 mg/L

50 ml water sample after boiling = 15ml EDTA solution 

Permanant 1 non carbonate hardness of sample = 15*(50/50) mg CaCo₃  = 15 mg CaCo₃ 

Permanant hardness of one liter = 15*(1000/50) mg CaCo₃  = 300 mg/l of CaCo₃ 

Temporary hardness = Total – permanent = 500 – 300 = 200 mg/l of CaCo₃ 

Q 5: Discuss the complexometric method for estimation of hardness in water. 

Ans: The complexometric method is a common method used for the estimation of hardness in water. The method involves the formation of a complex between the metal ion present in the water and a complexing agent, also called a chelating agent. The complexing agent used is usually ethylenediaminetetraacetic acid (EDTA), which has a high affinity for metal ions. The steps involved in the complexometric method for estimation of hardness in water are as follows:  

1. Sample Collection: Collect a water sample to be tested for hardness. The sample should be representative of the water source being tested.  

2. Sample Preparation: Adjust the pH of the sample to around 10 using a buffer solution. This is done to ensure that the metal ions present in the sample are in their free ion form, which is necessary for the complexation to occur.  

3. Titration: Add a small amount of indicator solution to the sample. The indicator used is usually a dye called Eriochrome Black T, which changes color from blue to wine red when it forms a complex with the metal ions. Then, add a standardized solution of EDTA to the sample until the color of the indicator changes from blue to wine red. The volume of EDTA solution required to reach the end-point is noted.  

4. Calculation of Hardness: The hardness of the water sample is calculated using the formula:  

Hardness (in mg/L) = (Volume of EDTA x Normality of EDTA x 1000)/Volume of Sample  

The normality of EDTA is known, and the volume of the sample is measured. The hardness of the water sample is expressed in terms of milligrams per liter (mg/L) of calcium carbonate (CaCO3) equivalent.