CHELATORS & SEQUESTRANTS

[tacoma5050]

I found this on-line informaton about CHELATORS & SEQUESTRANTS very helpful. (attached below)

My question is: For control of iron from a pool heater. Which type of control is better; CHELATORS or SEQUESTRANTS?

And what are what are some product name examples or ingredients for each.

Thanks.....

Info from http://www.redspools.com/PoolCare.asp
CHELATORS & SEQUESTRANTS

The word CHELATE is derived from the Greek word for "claw". In pool and spa chemistry chelate means a chemical treatment to control or "coat" soluble metal ions and prevent their oxidation into unwanted colored precipitates. A chelator attaches to a metal ion like copper or iron and wraps around it like a claw.

There are many types of chelators available in the market. Among the most widely used is a group of organic acids called "amino polycarboxylic acids". These chemicals are usually formulated into liquids that quickly attach to copper or iron ions and deactivate them. Please note that chelators will not react with metals such as finely divided iron shavings and they react very slowly with metals that are already oxidized or precipitated.

Sequestrants differ from chelators in the way they "coat" or react with mineral ions. Sequestrants generally have a few active sites on each molecule allowing it to control two or more metal ions at a time. Because of this, sequestrants are often more powerful as stain removers and are often sold with specific stain removal directions.

FACTS ABOUT CHELATORS & SEQUESTRANTS

Many chelators and sequestrants have metal ION PREFERENCES called "displacements". This means that certain metal ions will be coated before others. The usual preference is iron, then copper, then manganese, then calcium, then magnesium. There are chelators that favor calcium first.

The EFFECTIVENESS of chelators and sequestrants to coat undesired metal ions depends on the concentration of the ions to be chelated. For example, it is easier to control 1 ppm of copper and 1 ppm of iron in soft water (50 ppm of calcium) than in hard water (350 ppm of calcium). The presence of 350 ppm of calcium in water, for example, will occupy a large portion of the chelator intended to control the copper and iron. With this in mind it is advisable to chelate or sequester undesired metal ions before adding calcium to the water.

The AMOUNT of chelator or sequestrant needed depends on the type of metal ions present. For example, copper, iron, and manganese all require about the same amount of chelator whereas calcium requires 50% more chelator. Reactions to control metal ions occur within seconds in most cases.

Chelators and sequestrants are PH AND OXIDIZER sensitive. Very low pH, occurring in a "pocket" of water where acid has been added, can cause loss of chelation. Very high pH, again a "pocket" effect, can also cause chelation failure and precipitation of copper or iron. Because most chelators and sequestrants are organic molecules, they are subject to attack by high levels of oxidizers and "wear off' over time. This is the reason that most product labels state that continued additions may be necessary to control metals. With this in mind, it is obvious that shock treatments should not be performed directly after chelators or sequestrants have been added.

TEMPERATURE and TDS (Total Dissolved Solids) have slight effects on chelation. According to manufacturer studies, high temperature and high TDS increase the amount of chelator or sequestrant needed.

 

[duraleigh]

I'm not sure I know the correct answer to your original question but would offer this:

pH needs to be adjusted if your putting metals into your water thru the heater. Most heat exchangers contain little or no iron so the common metal that occurs in a pool from the heater is copper.....again, only at very low pH.

 

[JasonLion]

For swimming pools you most commonly use a sequestrant. There are many many brands, though not so many different chemicals they can contain. A few of the popular brands include Jack's Magic Blue, Purple, and Pink Stuff, Metal Magic, Metal Free, Metal Kear, and on and on.

 

[tacoma5050]

I'm not sure I know the correct answer to your original question but would offer this:

pH needs to be adjusted if your putting metals into your water thru the heater. Most heat exchangers contain little or no iron so the common metal that occurs in a pool from the heater is copper.....again, only at very low pH.

Hi, My heater is a 15-20 year old Raypak VERSA 185. It has copper heater coils and cast iron headers on each end of the copper coils. The newer non-commercil Raypak heaters have some sort of hi-temp plastic headers on each end of the copper coils. Thanks for the info on ph! If I keep my ph away from the low side will that help reduce iron from my heater as well as cooper?

Someone suggested to bury a zinc block in the ground and electricaly attach it to the iron headers and that would act as a sacrifical anode and slow or stop any rust. I guess they use these on bridges or metal structures in contact with water. Not sure if I will try this or not.

 

[duraleigh]

pH is the key. Keep it 7.2 or above and your other parameters in line and you'll have no problems with metals in your pool water from this point forward.

You still have to deal with what's there but it won't get any worse.

The iron fittings are not too badly rusted, I hope. If they are, they may have to be replaced...pH won't fix that.

 

[Guest]

To answer your question the only chelating agent that is commonly used in pools is EDTA (an amino polycarboxylic acid derivative) as found in Natural Chemistry's MetalFree, for example. The majority of products on the market for metal are sequesterants based on HEDP or other phosphonic acid derivatives (NOTan amino polycarboxylic acid derivative) .
Phosphonic acid based sequesterants are MUCH more effective than EDTA and the only reason EDTA is pushed is because it will not be converted to orthophosphates. Orthophosphates are what all the phophate removers on the market (which are in most cases not needed) remove from your pool. It's interesting that NaturalChemistry's main product line consists of phosphate removers and enzymes so it only makes sense that they would have a no phosphate metal sequesterant. BTW, all chelating agents are sequesterant but not all sequesterants are chlelating agents...chelating compounds have a ring structure (this is just what it sounds like, the atoms are arranged in a ring shape except it is broken and not complete so it can 'clamp' onto the metal ions...sequesterant might or might not have one, but they both will 'deactivate' a metal ion so it does not react with other substances in the water .
The preference that different sequesterants have for various metal ions is called it's 'chelation index'. The majority of products have the highest chelation index for iron and then copper but there are some (such as Jack's Magic Blue Stuff) that are optimized for copper removal and there are several products on the market, often labeled calcium hardness reducers or stain and scale removers that have a high chelation index for calcium (yes, calcium is a metal!)