How can I reduce the hardness (Ca & K...I know that Magnesium Chloride
can be changed to a hydroxide with increase in ph) of seawater safely?
Urea may do it, but the release of ammonia after heating (150º F to
300º F) may be toxic to sealife.

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Request for Question Clarification by jenjerina-ga on 11 Sep 2002 16:42 PDT

Are you interested in reducing the hardness of seawater for an aquarium? How big?

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Request for Question Clarification by nellie_bly-ga on 17 Sep 2002 19:59 PDT

Hi-

I got this response from a bio-chemist friend who worked with a state
department of envrironmental protection and did a lot of ocean-related
work.

"The only way is to desalinate and then add the NaCl back in. 

 "Na is more active than the others so to get out the others Na goes
too.  There may be a selective catalyst of some sort but I don't think
so.  We ran into this problem when doing NO3 analyses of seawater --
the ions interfered with the spectro analysis so we had to get rid of
them without affecting the NO3 or NO2.  But since the Na, Mg, Ca, and
K were all more reactive than the NO3 and NO2 we could just do a
replacement.  But the water is then toxic to sea life.


"If there is another way to do it, one of the big salt water aquariams
would know what it is.  Most of the ones I have dealt with  (mostly
for culturing various sea critters) use a lot of reconstituted sea
water so they know exactly what is in it."


Does this answer your question? Or would you wish me to contact sea
water aquaria as suggested?

Nellie Bly

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Clarification of Question by gomex-ga on 18 Sep 2002 09:36 PDT

No, this is not for Aquariums. We are talking about a system that may
be anywhere from 42,000 to 200,000 gallons with continued influx of
seawater. Taking out the sodium would be an impossibility. I am
talking about oil and gas drilling fluids offshore. The hardness in
the water makes the filtrate to be excessive. Increasing the pH helps
by eliminating Magnesium Chloride, however, the pH will decrease down
hole under temperstures that may exceed 300º F. Oil base systems
eliminate the problem also, but they are not environmental
friendly...neither the synthetic fluids. But, water based systems have
continued problems with high temperature/high pressure filtrate loss
control. It can be controlled if you can control the hardness. How?

Hi gomex-ga,

Your description of the water system in question is not very detailed,
but the
best method for reducing hardness (Ca and Mg) in large volumes of
water is
by the cold lime softening process.  Lime (Ca(OH)2) reacts with Ca and
Mg to
form a precipitate of calcium carbonate and magnesium hydroxide.  This
also
reduces the alkalinity (carbonate and bicarbonate) of the water.  The
pH
increases to over 10, but can be adjusted after softening with
sulfuric or
hydrochloric acid.  Approximately 1 pound lime is required per 1000
gallons
of water treated.  Lime softening equipment is available to improve
the
efficiency of the process.

Typically, the calcium hardness is reduced to 35 ppm, but additional
softening can be achieved by supplemental use of soda ash (sodium
carbonate).

Many chemical additives are also available for down hole drilling
applications.

This is all what I remember from taking various chemistry courses over
the years.  For additional information you probably want to contact a
professional water chemistry consultant.  Harfst and Associates is one
such company.  They have a simple webpage here:

http://user.mc.net/~wfh/


I hope that helps,
dogbite-ga

The question was difficult and there may not be a quick answer. It
would not be feasible to attempt removing the sodium...perhaps
impossible. The problem is that most additive that may work also
present their own problems. A good example is soda ash, which was
mentioned, and been used for years in drilling fluids. I'm sorry, that
answer does not answer the question. I sincerely appreciate all those
who tried to answer it for me. However, within keeping of your stated
policy, if the question was not answered. I an entitled to a refund,
and requesting same.

this is further comment from the bio-chemist after I relayed your more
detailed information.

"well, the short answer is that there is no way that i can think of or
have heard of that will take it out aquatically w/out rendering the
seawater toxic or otherwise unfriendly.  this is because Na is higher
on the reative scale than the things that he wants to take out and
therefore the Na will go first (in simple terms).  Even if you ran it
through a reverse osmosis membrane system, the Na goes first.  And
that is simply not practical for this kind of an industrial operation.
 It is possible that there is some sort of a precipitating additive
like the ones used in sewage treatment that will cause the Mg and/or
Ca to drop out.  But I have never run across one in my travels .....
sorry i don't have a better answer

Nellie Bly