Sequestering Agent for Softening
Sequestering Agent for Softening
(OP)
I'm familiar with ion exchange softening. How does the sequestering agent work? Apparently the Ca and Mg doesn't precipitate out? It just stays "sequestered" in the water, thereby not causing the normal problems associated with hardness? Is there a hardness limit when this is an option in lieu of ion exchange? Thanks in advance.





RE: Sequestering Agent for Softening
Gary Schreiber, CWS VI
The Purolite Co.
RE: Sequestering Agent for Softening
RE: Sequestering Agent for Softening
There are limits to the effectiveness of sequestering agents based upon the water quality. At high mineral levels, the agents are not very effective. With long detention times in your storage, they are also not very effective. Testing should be performed to determine if they work.
RE: Sequestering Agent for Softening
If you are interested, please contact me through www.orendatech.com.
Orenda
RE: Sequestering Agent for Softening
Any other unbiased discussion/description? I'm mostly interested in how it works/how effective it is. I saw a small plant yesterday that was using a sequestering agent and it was referred to by the plant operator as "softener."
bimr, where you at?
RE: Sequestering Agent for Softening
Gary Schreiber has answered your question regarding sequestering agents not being "water softeners".
Semo has answered your question about the functioning of sequestrants.
To restate my earlier comment that our seqestering agent can "handle" up to 7,000 ppm calcium/magnesium hardness, please substitute "sequester" for "handle".
Virtually all of these products, regardless of their specific chemistry, function at a less-than-stoichiometric (threshold) treatment level. In general, these materials are effective at inhibiting hardness deposition, providing consideration is given to the water chemistry and hardness composition.
If you are looking for commercial users of these products for good/bad recommendations, contact any manufacturer utilizing large volumes of water, particularly for cooling and/or process purposes. The odds are good that they will have the experience you seem to be looking for.
If you continue to have a problem with this subject, I suggest you pick up a Betz or Nalco water treatment handbook as either will provide you with authoritative answers to your questions.
Orenda
RE: Sequestering Agent for Softening
Here are a few select passages from the book so you know what to expect.
“Much misinformation exists about the mechanisms of action of many of the inhibitor formulations. For example, the sequestration of ferrous iron to prevent red-water formation is often interpreted as “corrosion inhibition,” but in fact, it is only mitigating the symptom of the corrosion. Many polyphosphate chemicals will convert one form of corrosion to another, for example, alleviating tuberculation and replacing it with uniform corrosion. That is not corrosion inhibitions.”
“The way in which sodium silicate acts to form a protective film is still not completely understood, but there is evidence it sorbs on or reacts with existing oxide, hydroxide, or carbonate pipe deposits.” The effectiveness of sodium silicate as a corrosion inhibitor depends on water quality properties such as pH and bicarbonate concentrations. It is also more effective under higher-velocity flow conditions.”
“Silicate has been found to be effective when used in combination with chlorination to sequester iron in groundwater and allow control of copper and lead levels by pH adjustment.”
“Orthophosphate is known to have significant effect on the aggregation behavior of ferric hydroxide.”
“Orthophosphate usually forms insoluble passivating films on the pipe, reacting with the metal pipe itself (particularly with lead, iron and galvanized steel) in restricted pH and dosage ranges.”
RE: Sequestering Agent for Softening
"Although not yet comprehensively investigated, polyphosphates when mixed with orthophosphate, may assist in the formation of orthophosphate films by complexing calcium and magnesium in hard waters that otherwise could cause unwanted orthophosphate complexation or precipitates."
The chemical treatment suppliers such as Betz typically operate cooling tower cooling systems at high temperatures and high calcium concentrations using chemical treatment programs that involve the addition phosphate chemicals to the cooling water. Note that these chemical treatment programs are always done in combination with pH and alkalinity control.
This chemical treatment scheme will not work in a municipal water distribution system because the cost of the treatment chemicals will be too expensive.
RE: Sequestering Agent for Softening
No rep can say their product will work 100% of the time, especially without knowing about the water and system being treated. Also notice that Orenda said "inhibit" not "prohibit" hardness deposition. This goes back to Gary's comment that sequestering agents are not a sub for softening.
As I mentioned and Bimr reiterated, if you are really interested in chemicals do a pilot test. And, I'll also mention, jar testing does not suffice. The total water quality and system variables affect the performance.
RE: Sequestering Agent for Softening
RE: Sequestering Agent for Softening
If you will be at the WQA Convention in March in Las Vegas, stop by our booth.
Gary Schreiber, CWS VI
The Purolite Co.