Calgon as a Dispersing Agent

[kevgeotech]

In the past I have always made my despersing agent using 40 g of sodium hexametaphosphate per liter of distilled water as stated in ASTM D422. I have recently started working for a company that uses Calgon as the dispesing agent.

I know that hexamataphosphate is the active ingredient in Calgon. What I would like to know and can not find is:

Does the calgon have to be diluted into a solution? If so, to what ratios. If not, does the "pure" Calgon get added to the hydrometer at the same volume as ASTM D422 state the Hexameta... solution is added.

 

[woofar]

Hi Kev,

Calgon is sodium hexametaphosphate that has been chemically and mechanically altered to make it instantly water soluble.

CAN it be used to replace sodium hexametaphosphate solution as a laboratory reagent?
Well, in all likelyhood, yes it probably can. 30 years ago it was the industry standard over here.

SHOULD it be used to replace sodium hexametaphosphate solution as a laboratory reagent?
No, never, you should follow the appropriate procedures PRECISELY, even if those procedures are flawed.
If the procedures are flawed then you can attempt to get them changed. But until they are changed you should just keep following those procedures.

Here in Australia, we use a stock solution of 33g of sodium hexametaphosphate and 7g of sodium carbonate to 1 litre of water. The solution has a use by date of 1 month. We then toss it out and mix up a new brew.

Cheers
Michael

 

[theCorkster]

kevgeotech:

Many years ago (mid-1980's) there was a change in the formula of Calgon. The laboratory I was involved with used Calgon regularly, until the change was discovered.

You question could more properly be addressed by an analytical laboratory; while I suspect Calgon wants to maintain their mixture a secret, you might contact them as well.

 

[fattdad]

It seems like decades since I've thought of the Calgon v. sodium-hex topic. I'd like to see a comparative study just to see just how much difference there'd be in the results.

I'm not trying to argue with the sound wisdom of others suggesting that you use actual sodium-hex. I'm just wondering. . .

f-d

¡papá gordo ain’t no madre flaca!

 

[Dirtguy4587]

I know in undergrad labs (10 years ago-ish), we used Calgon, and to be perfectly honest, since I haven't done any dispersion tests since, I thought people still used Calgon.

 

[woofar]

Hi to all, just to expand a little,

As Fattdad said, I would like to see some comparitve testing done. All we are really doing is trying to disperse the clay and silt particles. Warm to hot water does this better than sodium hex or Calgon. Dishwashing detergent also does a very good job.

Unfortunately, it is the Chemists and Physicists that lead us in this area. They tell us that these other methods change the chemical structure of the soil. Whilst I don't doubt them or their science, I do doubt their conclusions in this particular instance. From a practical point of view these other methods work very well.

Having said that, I must also repeat what I said earlier.
Whatever the current procudures are, just follow them.

Cheers
Michael

 

[fattdad]

Just for the record, I'm thinking from the perspective of hydrometer testing. Not sure that warm to hot water would disperse clay and silt to the partical size for this application. Then again. . .

f-d

¡papá gordo ain’t no madre flaca!

 

[woofar]

You are right fattdad, my claim about warm to hot water is rather rash. From personal experience, I do believe it to be true, however I have nothing better than my word to back it up. This forum is definitely not the right place to express such opinions, unless they are properly quantified.

Cheers
Michael

 

[vulcanhammer]

From EM 1110-2-1906 (Appendix V, p. V-13, 20 Aug 86):

"The chemical product Calgon available in grocery stores shall not be used as a dispersing agent as it no longer contains sodium hexametaphosphate."

That was one of the revisions made to EM 1110-2-1906 made in 1986. I don't know if Calgon has changed yet again since.

http://www.pz27.net

 

[WHEngineer]

Calgon no longer contains sodium hexametaphosphate. Calgon's website indicates that Calgon is phosphate-free, meaning no sodium hexametaphosphate. The phosphates were removed back in the 1980's due to municipalities banning phosphate detergents and the like in order to minimize phosphate loading in the wastewater stream. Unfortunately, Calgon is still referenced in many publications, including a soil mechanics laboratory manual that I recently reviewed that is used by a number of major universities.