Do chemical pH adjusters cause treated water pH fluctuations?

Do chemical pH adjusters cause treated water pH fluctuations? We have some instances when Soda Ash (Sodium Carbonate) after being used to correct the pH of the treated water and the pH value measured immediately after correction kept increasing slightly as time increased at constant temperature (in the stored water). This does not happen when Caustic Soda (Sodium Hydroxide) or Hydrated lime (Calcium Hydroxide) is used.

Any explanation or advice for this? The water quality is within WHO limits.

Thanks

Taxonomy

• Chemical Treatment
• Biological & Chemical Quality
• Quality
• Chemical Analysis
• Water Quality Management
• Carbonates
• Chemical Materials
• Chemical Engineering

10 Answers

1. The CO2 concentration in natural waters will also change throughout the day due to algae activity: photosynthesis during daylight / respiration at night. More pronounced during summer.

2. It depends due to the atmosphere your Plant located. Like our Sui Gas Purification is in Sui where Acid gas(H2s& Co2) is flared in the atmosphere and due to that sometimes when wind direction is towards plant the Ph of water drops sharply so in that case we immediately stop dosage of Sulphuric Acid to Control Ph of Basin water which provides cooling water to Heat-exchangers etc.

    

3. Soda Ash is Sodium Carbonate, not Calcium Carbonate as commented by Ahmed Soorma.

   Answer by Steve Oxtoby is correct due to

   Na2CO3 + CO2 +H2O2NaHCO3

   NaHCO3 + H2O H2CO3 + NaOH (pH goes up)

   1 Comment

   1. THEY ARE RELATED. REFER TO YOUR periodic table. not a matter of fluency and crammed work.

4. Due to equilibrium shifts CO2 goes to the gas phase  and the pH goes up. 

5. All details from all Expertise are correct and very clear on my opinion. But at present day some supplier have told me about sopecial clay which can be used in stead of PAV+Polymer. Does anyone khow in more details and posibility because I try to ask them in China but I get no information.

   AGGIE

6. By adding carbonate with the sodium carbonate you are increasing the carbonate alkalinity of the water. This has a buffering effect as it dissociates to hydroxide and CO2. If the CO2 is removed say by being aerated or an elevated temperature to buffering will act to balance this by creating more CO2 but will also create hydroxide and elevate the pH. 

7. Soda Ash is Sodium Carbonate, not Calcium Carbonate. Its disassociation  will be Hydroxyl ion and Carbonate ion. The makeup water composition will decide which way these ions aggregate to the ions in it.

   1 Comment

   1. Thanks Ahmed for the correction. It was a mistake which has been edited and corrected.

8. as Ca(OH)2 and NaOH do not disassociated further, the effect seen with soda ash is absent for above. Rather here the effect after some time seen is decrease in pH because hydroxide ion takes up carbon dioxide from atmosphere and get converted to carbonate

9. Soda ash is Na2CO3. On hydrolysis it first disassociates to carbonate/ bicarbonate and then hydroxide ion. hydroxide ion has  higher pH value.

10. CALCIUM CARBONATE CaCO3(s) HAS A WEAKER BOND BETWEEN THE CARBONATE MOLECULE AND THE CALCIUM ATOM HENCE ALWAYS HAS UNSTABLE TENDENCY IN COMBINATIONS. HOWEVER THE EXCESS IN SALT CONTENT FOR STABILITY WILL ALSO DEPEND ON THE +-ERRORS VOLUMES IN TITRATIONAL TREATMENT OF VOLUMES OF WATER AND TITRATE. refer to the periodic table.