greg-cws
12-10-2008, 02:14 PM
This question comes up rather frequently in the Intermountain West:-
"What is the waxy blue/green buildup that I'm finding when I drain my water heater/clean my aerators ?"
This buildup is Aluminum Hydroxide, a byproduct of the decomposition of an aluminum sacrificial anode in a water heater. It is waxy hen wet, and dries into crushable "sandy" granules.
If you read the literature from Water Heater manufacturers, you'll learn more about it:
http://www.hotwater.com/BULLETIN/bulletin14.pdf
Water heater manufacturers point out that this only occurs when the ph is high (8+). While this statement is generally accurate, there are other complicating factors to consider, as the reaction can occur when the pH is low also (<7.5).
Aluminum hydroxide is amphoteric - a substance that can behave as either an acid or base, depending on the associated chemistry at the time of reaction.
Dried Aluminum hydroxide is referred to as activated alumina, a chemical compound used by cities to treat various water contaminants at a municipal level.
High pH waters usually contain calcium carbonate (CaCo3). It is the carbonate that reacts with the Aluminum anode to begin the precipitation of aluminum hydroxide.
Extremely hard water (pH >7gpg) has significant quantites of Calcium Carbonate hardness. When this kind of water exhibits a low pH, it is usually because of entrained dissolved CO2 gas in the water, which creates carbonic acid - lowering the pH.
Another complicating factor is the presence of sodium in softened water. Sodium Hydroxide (NaOH) can exist in the heated softened water, which is a direct precursor to the development of Aluminum Hydroxide.
Regardless of how your Aluminum hydroxide was formed, the remediation process is usually simple:-
1. Install appropriate pH neutralization media before any softening if the water pH is <7.5 or > 8.3
2. Calibrate the softener to ensure regeneration occurs properly and that no NaCl residual escapes the system. Hydrolyte 525-3 media works the best here.
3. If activated alumina is used by the local water authority, install appropriate media to lower the aluminum level in the water.
4. Install an MBR (Microbubble Resorber) after any treatment equipment and at the inlet to the water heater. This will remove as much entrained CO2 as possible.
Aluminum hydroxide can sometimes be difficult to diagnose, but if you take a systematic approach, remediation is usually easy.
"What is the waxy blue/green buildup that I'm finding when I drain my water heater/clean my aerators ?"
This buildup is Aluminum Hydroxide, a byproduct of the decomposition of an aluminum sacrificial anode in a water heater. It is waxy hen wet, and dries into crushable "sandy" granules.
If you read the literature from Water Heater manufacturers, you'll learn more about it:
http://www.hotwater.com/BULLETIN/bulletin14.pdf
Water heater manufacturers point out that this only occurs when the ph is high (8+). While this statement is generally accurate, there are other complicating factors to consider, as the reaction can occur when the pH is low also (<7.5).
Aluminum hydroxide is amphoteric - a substance that can behave as either an acid or base, depending on the associated chemistry at the time of reaction.
Dried Aluminum hydroxide is referred to as activated alumina, a chemical compound used by cities to treat various water contaminants at a municipal level.
High pH waters usually contain calcium carbonate (CaCo3). It is the carbonate that reacts with the Aluminum anode to begin the precipitation of aluminum hydroxide.
Extremely hard water (pH >7gpg) has significant quantites of Calcium Carbonate hardness. When this kind of water exhibits a low pH, it is usually because of entrained dissolved CO2 gas in the water, which creates carbonic acid - lowering the pH.
Another complicating factor is the presence of sodium in softened water. Sodium Hydroxide (NaOH) can exist in the heated softened water, which is a direct precursor to the development of Aluminum Hydroxide.
Regardless of how your Aluminum hydroxide was formed, the remediation process is usually simple:-
1. Install appropriate pH neutralization media before any softening if the water pH is <7.5 or > 8.3
2. Calibrate the softener to ensure regeneration occurs properly and that no NaCl residual escapes the system. Hydrolyte 525-3 media works the best here.
3. If activated alumina is used by the local water authority, install appropriate media to lower the aluminum level in the water.
4. Install an MBR (Microbubble Resorber) after any treatment equipment and at the inlet to the water heater. This will remove as much entrained CO2 as possible.
Aluminum hydroxide can sometimes be difficult to diagnose, but if you take a systematic approach, remediation is usually easy.