Generally, adding any ionic compounds to water increases the TDS (Total DISSOLVED solids). It can lower the electrical conductivity TDS reading but not TRUE TDS.  Conductivity is the common very easy method of measuring TDS but is really only an estimate of TDS based on electrical conductivity.

 

Lime (Calcium Carbonate) has limited solubility therefore can increase the TDS somewhat.

 

Calcium has an equivalent weight of about 20 (40/2 or Atomic weight divided by valence of 2).   If heavier cations with higher equivalent weights precipitates insoluble carbonate or hydroxide compounds, there can be a reduction in TDS .

 

In the unusual situation of sulfuric acid in high concentration, there can be a dramatic reduction of the TDS. This is because calcium sulfate is somewhat insoluble which precipate into a suspended solid and the acidity is neutralized by the carbonates gases off as carbon dioxide.

 

What is your goal?

 

Taoward Lee
Ecosystems, Inc.
Costa Mesa, CA 92627

If you are attempting to find a way to reduce TDS to comply with wastewater discharge limits, you need to find out if it is true TDS or EC (Electrical Conductivity usually in microseimens) or BOTH. 

 

Then as usual you have to know the chemical analysis of your wastewater.

 

Generally, the best way to control TDS in the wastewater is source reduction (preventing the chemical contamination of the wastewater in the first place)

 

Thank you Mr. Lee

 

I have a batch treatment for metal reduction in a parts dipping system before going thru an ion exchange for further metal reduction. The system was designed for 10,000 mg/l TDS and by the time it gets to the IE system the  TDS is 20,000 mg/l. I want to reduce the Tds so the IE unit will remove the copper better

 

Thanks

 

Doug

Doug,

 

Is you batch treatment for metal reduction a conventional hydroxide precipitation system?

 

What is the process(es) that causes the copper to be in the wastewater? Knowing the chemistry (water analysis) is important to deciding what to do.

 

How much water are you dealing with per day/week/month?

 

What is the TDS BEFORE batch treatment? Is most of the TDS caused by the batch treatment or are you dealing with a high TDS water to start?

 

If the only pollutant of concern is copper and your copper hydroxide sludge is a hazardous waste, have you considered electrowinning to make a non-hazardous?  Metallic copper (zero valence) is non-hazardous and has scrap value.

 

What is the copper discharge limit (ppm or mg/l)?  Which is more stringent the Federal discharge limits or the local discharge limits?

 

Yes, the high TDS interferes with the complete removal of small amount of metals.  This is normal for all IX resins.  I am sure that your engineer has chosen a chelating resin to minimize the issue of high TDS or high sodium.  Despite that I have been working with ion exchange and building IX systems for more that 32 years, you will get better advice about resin selection from resin experts like  Gary Schreiber, CWS VI from Purolite or Chub Michaud.  These guys are awesome.

 

My advice is to look upstream with a comprehesive look at the whole process to decide your best option.

 

Taoward Lee
Ecosystems, Inc.
Costa Mesa, CA 92627

Bill,

 

From my experience, I would recommend Purolite S930.  I believe this resin has a functionality similar EDTA and has exception metal removal in the presence of high levels of sodium and background TDS.

 

Remember the resin experts can give you the best opinion!

 

Taoward Lee
Ecosystems, Inc.
Costa Mesa, CA 92627

Bill,

 

If you are not already aware of this, I should remind you.  It is very important the the IX metal polisher be very selective for the metal you wish to remove.  AND it must have a greater selectivity (affinity) for the metal (copper in this case) than the common alkali metals, sodium, calcium and magnesium. 

 

Without a higher selectivity, you may waste ion exchange capacity on "tramp" ions especially calcium and magnesium.   For example: This will happen using a weak acid (carboxylic acid functionality) resin which picks up calcium and magnesium in preference to copper II.  When the calcium and magnesium starts to displace copper, the copper concentration can be MUCH HIGHER than the incoming copper concentration.  DO NOT MAKE THIS MISTAKE!!

 

Since this S930 is regenerated with a strong acid (HCl or sulfuric), converting it back to the sodium form before putting in to service will assure that you maintain a dischargeable pH. Otherwise, you will the resin in the Hydrogen form will lower the pH (at least initially) to lower than a dischargeable pH which is often a pH of 5 or 6.

 

I always recommend two chelating columns in series (lead-lag configuration) with sampling ports between the columns.  This minimizes the chance polluting by missing the endpoint.

 

If this information does NOT make sense, you need to hire a water treatment professional.

 

Good Luck.

 

Taoward Lee
Ecosystems, Inc.
Costa Mesa, CA 92627

Thanks for all the info

 

I am using a two column IX with purolite S930 PLUS

 

Doug

What is your flowrate (gpm per cubic foot)?  You need to assure enough retention time.  When the TDS and the copper concentration are BOTH high, you need the lowest flowrate per cubic foot (maybe 1 gpm/cu.ft. or less)

 

Thanks again Mr. Lee

 

The flow rate goin thru the IX is about 8 GPM

 

I will throttle it down