Phosphate scaling

[Swampwoman]

Yeah, I may have to call them. I was hoping to just boil water today with acid to test

I also need to find out if my trucked water had contained flouride or not. Obviously, my well doesn't, but even if I've added 60" this year (I likely have) I assume the flouride would just concentrate, since most of my water exchange is sponsored by evaporation, much moreso than by backwashing, which is rare.

At Nova's site, where the sell the taylor kit, K-1584, Taylor Drop Test Kit, Phosphonate, 1 drop = 0.8 ppm PBTC they say this:

K-1584 is a drop-count titration that employs chrome azurol S indicator instead of XO indicator. At the appropriate pH for the reaction, the addition of thorium nitrate titrating solution produces a distinct peach-to-purple color change at the endpoint. This test is appropriate for nonfluoridated process cooling waters that contain PBTC in the chemical treatment blend. Conversion factors also are provided for ATMP, Na5ATMP, HEDP, and HPA.

Note: Iron causes negative interference with the XO method, positive with the CAS method. With either method, orthophosphate and polyphosphate can cause positive interference; fluoride is an additional positive interference for the CAS method.

 

[Swampwoman]

I am posting this here for my own future reference

8.2 Hydrolyzable Phosphorus
8.2.1 Add 1 mL of H2SO4 solution (8.3) to a 50 mL sample in a 125 mL Erlenmeyer flask.
8.2.2 Boil gently on a pre-heated hot plate for 30-40 minutes or until a final volume of about 10 mL is reached. Do not allow sample to go to dryness. Alternatively, heat for 30 minutes in an autoclave at 121°C (15-20 psi). Cool, dilute to approximately 40 mL and filter.

To make solution: Sulfuric acid, 11 N: Slowly add 310 mL of conc. H2SO4 to approximately 600 mL distilled water. Cool and dilute to 1000 mL.

https://www.epa.gov/sites/production/files/2015-08/documents/method_365-3_1978.pdf

 

[JoyfulNoise]

Well, the good thing is you have an accurate photometer for measuring the Pi (shorthand for inorganic phosphate) levels. So you should be able to get a decent background measurement.

I would definitely call Taylor and try to find out what the strength of the interference is. I doubt you have much fluoride in the water and your iron levels are fairly low. If you give Taylor a rough estimate of your water quality, then I’m sure one of their chemists should be able to advise on the best testing strategy.

I’m sure I don’t have to tell you this but - please be careful with sulfuric acid! In its concentrated form, it’s very dangerous to get on your skin (it will burn you very badly). I only ever used it in a controlled fume hood with full PPE’s on. It has a huge heat of hydration and can easily cause water to boil on mixing. Treat it with respect.

 

[Swampwoman]

Yes, SwampHubby and i have determined that my experiment will be outdoors, gloved and goggled, using the hotplate with tongs when they come in, together with flask and beakers. There is to be NO kitchen DIY

He did consider aiding and abetting this afternoon in that he pondered extracting battery acid from his old jag and reducing it, then thought better of the plan given my notorious "left-handedness". We were equally hestitant about grabbing drain cleaner as the purest we found was 93% sulphuric acid but had additives we suspected would skew (anti-corrosives). As you know from my previous posts, SwampHubby can generally be relied upon to save me from myself

Instead, I ordered Hach's prepared sulphuric acid N5 solution/reagent (I think its approx 26%) and found their instructions for hydrolyzing polyphosphonates, which I will follow to the letter and report back in a few days. I was really happy to dig that up because its written in a way to do the process then follow with any type of po4 testing.

 

[JoyfulNoise]

See here - Drop Test, Phosphonate, Thorium Nitrate/Chrome Azurol S (uses pH test paper 2.5-4.5),1dr=0.8ppm PBTC

So the orthophosphate interference is when your levels are above 5ppm (5000ppb). Your metal levels are going to be small and I doubt you have fluorides. Polyphosphates are a non-issue.

In that case, the instructions say you can dilute your sample water to get the orthophosphates below 5ppm and then test the sample for phosphonates knowing the dilution factor. By diluting the sample, you'll also greatly reduce any metal or fluorine interference.

 

[JoyfulNoise]

Given you're at ~16,000ppb PO4, a dilution of 3:1 (DI water : Pool Water) should get you to 4000ppb and be under the interference threshold.

 

[Swampwoman]

Hey Matt, my solutions and flasks arrived today but my hotplate has gone MIA so I can't test til the weekend now.

I'm going to follow Hach's method, but it calls for de-ionized water for a rinse and top up of the 25 mil sample after is boiled for a half hour with the 5.25 n sulphuric acid.

I only have distilled on and. Do you think distilled water would skew my results in any way? Or do I need to track down DI water?

( I have to get this test nailed pdq and get the pool sorted with a final treatment as next week I need to be o.o.t to be with my sib whose having brain surgery...unexpectedly and semi-urgently. I'll be up against the hard deadline of hired help coming on the 9th to co-install the dome.)

 

[JoyfulNoise]

Distilled and de-ionized are technically different beasts.

Distilled water is typically filtered water that is boiled and vaporized and then cooled in a steam reformer. This produces water with very low trace minerals. It will have very low CH & TA and be fairly close to a pH of 7. It can still have some sodium ions in it and volatile organics if there wasn’t proper pretreatment with a GAC (granular activated charcoal) filter.

DI water is distilled water that is usually post-processed in an RO filtration system to remove all minerals (sodium & potassium) as well as any residual organics. Some setups with also treat the DI water with a UV light source to destroy and viral particles that may have made it into the system. Normal DI water needs to be stored under a nitrogen blanket in order to keep atmospheric oxygen and carbon dioxide from being absorbed. Proper DI water will have a resistivity greater than 18 mega-ohm.

Typical chemical analysis labs use DI water for dilutions to avoid unwanted precipitation of minerals when samples are reduced by boiling. High temperatures and concentrated solutes can cause precipitation reactions to occur.

I’d try it with the distilled water and see what happens.

 

[Swampwoman]

Thanks!

 

[Swampwoman]

Fascinating Pre Experiment Test Result!

In preparation for my boiling-water-with-sulphuric-acid-to-determine-sequestrant-amount experiment today, I ran a full set of tests on the pool water, including another po4 test.

Since day 1 after the floc treatment, my phosphate level dropped by HALF again to 5,200 ppb from 10,900 ppb!!!

I had bought 15lbs more alum to do a second treatment today, but this result has me reconsidering....eg let the filter keep working another week and see what he leftover alum picks up!

- Theory...after vacing to waste twice, I had started up the filter and found no need to backwash as I didn't have much of a pressure rise. So any wee bits if alum left are in the filter. Since it can be used as a filter aid, I decided I wouldn't backwash until prepping for this treatment today.

The extra filtering out of po4 may be because I don't run it at 3450 at all, and for 12 hrs of the day, its only at 1850 rpm, plus another six at 3100. Slow filtering is believed to be more effective.

I should note that I've had no scale shedding since the floc.

----------

Sulphuric Acid Test:

Object - to convert HEDP into po4 in order to measure total phosphate minus baseline ortho-phosphate

Method - Using Hach's method for hydrolyzable phosphorous, which is to boil 25 mil sample with 2 ml n5.25 sulphuric acid in a erlenmeyer flask for 30 min.; concentrate to 20 ml, adding deionized water to maintain 20 ml; cool to room temp, add 2 ml 5.0 N sodium hydroxide

Note - safety goggles, gloves, ventilation recommended, avoid fumes etc. I used a small alcohol burning lamp on a screen stand circa high school lab

Right now my solution is cooling. I did substitute distilled water as no ready access to deionized water. I also rinsed out all the glassware with hcl and water per instructions.


Here are pics from my little outdoor lab, aka the bar



Will report back readings after a swim so it can cool!

 

[JoyfulNoise]

I like the alcohol Bunsen burner...very retro. You just need some metal glassware stands and holders to complete “the look”.

And don’t forget - real chemists pipette by mouth...we no need no steenkin’ suction bulbs!

 

[Swampwoman]

Yes, but clearly I'm not a "real" chemist because my results are not at all what we expected

So, I wondered about adding so much distilled water as it boiled away but I did exactly what the instructions said.

AND ended up with a po4 level LOWER than my 5200 ppb base reading -- 3500, which is impossible!

I'm rerunning a test right now.

Here are my error theories:

1. Rate of dilution to keep solution at 20 mil for 30 min required at least 15 ml addition...can po4 possibly evaporate n steam?

2. Adding the sodium hydroxide somehow interfered with my Hanna reagents (molybdenum and presumably ascorbic acid?)

3. There is still trace alum in the water complexing in the low ph with the HEDP?

4. Problem in Chair, Not In Flask...I somehow contaminated the sample? Misapplied the mollyb? BFOM.

I will see if second reading cross referenced to aquarium kit sheds any light on the situation. Theories welcome

UPDATE:

Rerun with my Hanna meter gave me 6100 ppb

Cross test with hubby's aquarium kit gave us greater than 5,000 ppb.

Don't have enough solution left to run a diluted test, so I'll have to start over to make more ;(

 

[JoyfulNoise]

My first guess - you are precipitating some of the phosphate when you boil it down as your water may just be getting too hot. Distilled water plus pool water will still have quite a bit of calcium in it. So you may just be losing some to calcium phosphate scale.

 

[Swampwoman]

Yes, I just started a double batch, hoping that the larger volume of water slows it down a bit

I also retested straight pool water to restore confidence in my meter and method...got 5100, so 100 ppb less which is within a reasonable error rate.

So I'm still thrilled about that -- and the fact I'm still reading 0.0 iron..,so even if attempt #2 is a bust without deionized water, I'll call it a good day.

Okay, so five minutes in it boiled over! Good grief...

 

[Swampwoman]

Final Inexplicable Result:

This time, I boiled 50 ml pool water with 4 ml sulphuric acid and allowed it to concentrate to 20 ml (not without some boil overs.)

I only diluted it with flask-wash to bring it back up 5 mil after adding and swirling sodium hydroxide.

I'd re-read the instructions that said to use a bank of the boiled solution in the meter...so I did.

This TME, the Hanna Meter read 6100 -- 1000 more PpB than pool sample.

SwampHubby simultaneously read a 50% dilution of same sample water and ndependently arrived at "a shade over 6,000."

So there is testing concordance.

Which doesn't necessarily mean I'm down to a mere 1 ppm (aka 1000 ppb differential) HEDP - though it MIGHT mean that.

Hubby thinks the Alum may well have taken it down, or it breaks down faster in swg than we've previously thought, etc.

My sister's surgery has been moved up a day or I'd try a bucket test of my 0 ppm iron pool water to see if I could oxidize any iron but it takes too many days to break down. I guess I could do Ben's bucket test and see when I get back next weekend.

An oxidizing bucket test would tell e if I have sequestrant sequestering, or whether the HEDP is really gone.

At this point, I have not even the faintest stains on step, and its been I think at least a month since I've added any sequestrant at all.

 

[JoyfulNoise]

I say next time you use the persulfate/UV oxidation approach to digesting the phosphonates...no boiling beakers of acid to worry about. Hach has a write up for it.

 

[Swampwoman]

I will check that out, though I do love rockin the old school alcohol burner

I had a conversation with Hanna this week, asking if their persulphate reagents from the hydrolyzable phosphorous test would work in tandem with the high limit po4 test as a pre-treatment or whether there were contraindications. But that treatment only reads to 1600 ppb, which for my purposes, isn't likely useful. They were unsure.

We did discover that reagent A in my high limit test is sulphuric acid...so I in essence boiled with sulphuric acid, then for the high limit test, added 10 drops of sulphuric acid (concentration unknown).

Molybdenum requires a ph of 0-1 to form, I believe, so I assume that's why reagent A is sulphuric acid. I don't know enough chemistry to know if the twice-treated phenom skews or reduces somehow.

In my bucket test, though I'm resisting the temptation to read it early, there is no trace of iron discoloration whatsoever despite a half cup of bleach per 4 gallons and a half cup of washing soda. So maybe I "really" am somehow down to 0 iron...

I have to add salt back (from the alum vac to waste) before to dome goes back up and I almost hate to if trace iron will skew my musings further

I'll post a read on bucket for FE and pool for po4 and FE on Sunday when I get back.

If my theory is remotely accurate, my po4 would be lower again and my FE 0. I think trace alum in the sand filter could be making it filter more like a DE. My psi has been stable/normal at full speed.

 

[Swampwoman]

So, no wonder scientists I know drink copious amounts of scotch

Today's check of pool water shows 6700 ppb po4 -- more than last Sat by 1500...and 600 more THAN AFTER I BOILED WITH ACID.

This can only mean, for certain, that there is more HEDP in water than boiling allows to read.

I've not added any sequestrant at all.

ALSO, iron in pool now reads .33 ppm, from 0 last week.
Meanwhile, bucket test at super high FC and ph precipitated no visible iron and today read at .11 ppm after all that oxidization.

This suggests to me that .22 ppm of iron has entered the pool this week.

I DID add one 40 lb bag of salt. Don't have time to do the math and see if that's a probable cause, but it seems likely.

I will run the bucket test again Sunday to test for both FE and PO4, since same should be broken down by then.

 

[Swampwoman]

Its been a month since my last test.

My po4 today read 5200 - so a decrease.

My FE read 0.0 - so a big decrease.

The 5 gal bucket where I tried to oxidize iron is still clear, and if I test po4, the cuvette bubbles and overflows whn I add the reagent....so after a month, the high FC / washing soda is somehow still making it impossible to read

I've not added a single drop of sequestrant. My stairs are white as ever. My softened water spigot is reading 0 on iron as well.

I've not backwashed my filter since before the floc treatment as the psi is fine and it had seemed like whatever bits of alum were left in the filter continued to reduce the po4.

I actually think that's still happening with the low, slow filtering, (given the 1500 ppb drop this month) so I may hold off on adding the Seaklear lest I cause the need for a backwash

Most importantly, no scale coming from heater.

Weird but wonderful!

 

[JoyfulNoise]

Good update. Glad to see zero iron. Not surprised at the bubbling reagent - one of them is a very strong acid.

You’ll be pushing routine floc and phosphate remover use in the main threads in no time