Dear Pier,
Thanks for your reply. I look forward to
seeing the Chapter you mention. Is there any possibility that I could see a
pre-publication copy?
My interest has been stirred by the
results of some experiments that I have conducted on the effect of reaction
temperature on the oxygen isotope composition of CO2 produced by the phosphoric
acid reaction. After a little investigation of the “phosphoric”
system it appears to me that the reaction is not between orthophosphoric acid and
carbonate, but pyrophosphoric acid (for acids with nominal H3PO4 concentrations
>90%). Since the reaction is exothermic I want to find out if there are any
consequences for the accuracy of the reaction temperature. Intuitively I would
expect that the reaction between “phosphoric” acid and carbonate at
25oC is so slow that any energy released by the reaction would be lost by
conduction before it was able to increase significantly the temperature of the
acid at the site of reaction. However, at high temperature the reaction is
almost instantaneous and there seems the possibility that the energy release
might be sufficiently fast to increase the real reaction temperature. If
temperature was increased by more than 1oC then this would start to have potentially
significant consequences for estimates of analytical uncertainty. It is this
effect that I wanted to investigate. Unfortunately my knowledge of the
chemistry in insufficient to allow me to place quantitative estimates on the
consequences with any confidence. I would be interested to know if this subject
is covered in your chapter.
Regards,
Steve
Department of Earth & Ocean Sciences
L69 3GP
0151 794 5163/5164
Remember:
"If there's anything that you want,
If there's anything that you need?
There's no need to be evasive,
Money talks, and it's persuasive."
Elvis Costello
From:
Sent: 23 April 2008 11:53
To: [log in to unmask]
Subject: Re: Reaction of
phosphoric acid with CaCO3
Dear Steve,
The acid digestion reaction of carbonates by phosphoric acid is more
complicated than it looks like. Work has been done on this matter, sure. If you
are a bit patient, second half of this year my handbook Vol-II will be
available, where in the chapter on O- and C-isotopes in carbonates (Chapter
4-5) a detailed description is presented on properties of phosphoric acid
(contributed to the chapter by Hilary Le Q Stuart-Williams), which will give
some more understanding of this system. Certainly, description of this system
cannot be done by just a simple thermodynamics calculation.
Not much of a help for now, but still I hope it gives some answer,
Best wishes,
Pier.
****************************************************************
Delta Isotopes
Consultancy
Dr. Pier A. de Groot
Pastoor Moorkensstraat 16
2400 Mol - Achterbos
Tel. +32 (0)14 326 205
e-mail: [log in to unmask] or
Associate editor for stable isotopes of eEarth on-line magazine
http://www.electronic-earth.net
Head of Isotopes in Geosciences of
the European Geoscience
EGU Home web-site: http://www.copernicus.org/EGU/EGU.html
Isotope program for the EGU2008 General Assemblee can be found at:
http://www.cosis.net/members/meetings/programme/view.php?m_id=49&p_id=316&PHPSESSID=1ad86b0d1b35d7bf9aee006f1e2f5cf4
Organization Committee member of BASIS (Benelux Association of Stable Isotope
Scientists).
http://www.basis-online.eu/
Visit my WEB-site about my “Handbook of Stable Isotope Analytical
Techniques”, with a link to the Elsevier web site on the handbook
(marked: ‘Order Now’):
http://users.pandora.be/handbook/index.html
last update: August 15, 2005
Volume I is available. Volume II is in press and will be available second half
of 2008.
****************************************************************
From: "
Reply-To:
Date: Wed, 23 Apr 2008 09:49:27
+0100
To: <[log in to unmask]>
Conversation: Reaction of
phosphoric acid with CaCO3
Subject: [ISOGEOCHEM] Reaction of
phosphoric acid with CaCO3
Dear Colleagues,
I would like to investigate aspects of the thermodynamics of the reaction of
CaCO3 with phosphoric acid. Unfortunately it has quickly become apparent that I
lack the necessary expertise to evaluate this chemical system with any
confidence. I wonder if anyone with a reasonable grasp of thermodynamics would
be interested in discussing this?
If so, please contact me directly. I don’t want to bore 99.99% of
ISOGEOCHEM users with this esoteric problem.
Regards,
Steve Crowley
Department of Earth
& Ocean Sciences
L69 3GP
0151 794 5163/5164