Slippery Silicates

[kbd]

Greetings from London, England.

I hope that you can help me. I have discovered that I have high silicates in my tapwater, I estimate between 10 and 15 ppm using the Salifert test kit (diluting my sample with proven silicate-free DI).

I estimate that my RO reduces these to around 2 ppm, my DI has little additional impact. I am happy with the RO performance, but not realising the severity of my input, I have clearly bought the wrong membrane. It does what it says it should do.....

I use a generic TFS membrane made by Filmtec (MM-TFF 45/75), have good domestic water pressure and (the way it is plugged-in) usually warmish water. I use intermittantly.

My DI comprises separate columns, two litres each of cation/anion resin, I do not know the specifications. At around this volume I thought that I was safe ! My resin is not saturated at present (at least, not generally ! ). The cation resin is colour changing (brown to red), I replenish myself (resin is horrendously expensive in the UK).

Set out below (together with a recap of SiO2) is the performance measured in conductivity:-

...............................microS/cm....................ppm SiO2

Source Tap...............675.............................10 - 15
RO Output..................55................................2
DI Output.................. 1...............................1.5 - 2.0

I can improve DI output by reducing flow, but at 1 uS/cm I am probably beyond the precision of my probe, a Tunze, and don't bother.

As an experiment, I ran a closed loop thru' my DI, passing a sample several hundred times and only succeeded in reducing silicates to around 1 ppm. Does DI simply become "saturated" wrt silicates specifically while remaining active for other ions ?

I would like to reduce my silicates to comfortably below 1 ppm, allowing for the fact that source water may vary. At UK prices, I would prefer to use additional DI only if I can replenish it myself, but if I need to bite the bullet, so be it. In which case, given the expected RO output, would like to know the number of gallons I could reasonably expect before exhaustion.

I almost certainly need to import the kit....in the UK a high silicate rejection membrane costs about USD 200, a Kent Silica exchange module about USD 80 ! I do not joke......I weep.

Hope this sets out the problem I face and the result I seek. If you think that I should call you to discuss, then please post a number. Please don't be on the West Coast.....

Many thanks in advance for your advice, sorry for length of post but I wanted to set out all the info.

:)

kim

[SpectraPure]

Kim,

I have forwarded your questions to the Boss. Please give me a day or two to get an answer out of him!

Scott
SpectraPure, Inc.

[kbd]

Oops, I'm in trouble again.....

:eek:

Many thanks Scott !

kim

[kbd]

Friendly bump ^

:)

kim

[SpectraPure]

Kim,

I see ya'. Stand by....

Scott

[SpectraPure]

Kim,

We will try to help you without a phone call. Being in Arizona, we are only 1 hour away from the West Coast. We would always rather speak in person, 480-894-5437.

“Good domestic water pressure” can mean anywhere from 40 psi to 80 psi. We would like to know for sure.

Your membrane exhibits only 92% rejection of dissolved solids and only 80% rejection of SiO2. Both are way too low for adequate elimination of these impurities.

If you don’t have at least 98% rejection in your membrane, your silica rejection will be unacceptable; DI life will be very much shortened. The difference in product purity between 98% vs 92% is a factor of 4, not “just 6%”.

Calibrate your silica test kit against a sample of DISTILLED water (distilled water has low-ppb levels of silica). Often we find many of these test kits read “1” even in distilled water. We have found the Hach Low-Silicate Test Kit to be the best for accurate measurement of silica in the low-ppb range.

1 ppm SiO2 is 500 times more than 20 ppb; our more advanced DI systems produce silica levels in the 3-5 ppb range. By the time you read “1” microS/cm, it is already way too late.

You might try a 3-column DI system: first, all Anion; second, all Cation; third, all Anion. This arrangement will deal with your SiO2 problems most effectively. A 2-cartridge system would have our DI-SF-CI-10 followed by our DI-AR-CI-10, which is also a series of Anion-Cation-Anion resins.

The quality of the DI resin varies greatly. “Bargain Bulk” off the internet is a dice roll at best. We get resin from a limited number of SpectraPure-approved suppliers. Even then, we test every barrel that we receive, rejecting about 30% of it for not passing our QC. We send it back, what do you think they do with it? They sell it to someone else!

So, it looks like you need a new high-rejection membrane (MEM-S-90) and some DI resin to get back on track.

Hope this helps,

Scott
SpectraPure, Inc.

[kbd]

Many thanks.....will call tomorrow.

I agree that I have a problem ! As you will appreciate, would prefer not to throw away the kitchen sink immediately, although I am very happy to experiment if the costs are not prohibitive.

Looking fwd to a chat, and many thanks,

kim

[kbd]

Sorry not to be in touch. This is not a sign of reduced interest. I am trying to source a manoneter to check the pressure. Retailers don't seem to have in stock, the local plumber would come round for US$ 200......(plus cup of tea and an hour in front of cable TV).

Need a few days, will return,

kim