Reef Chemistry Question of the Day #172 Phosphate on Calcium Carbonate

Randy Holmes-Farley

Reef Chemist
View Badges
Joined
Sep 5, 2014
Messages
66,553
Reaction score
62,861
Location
Arlington, Massachusetts, United States
Rating - 0%
0   0   0
Reef Chemistry Question of the Day [HASHTAG]#172[/HASHTAG]

Phosphate is known to bind to the surface of calcium carbonate, and this binding to rock and sand can have significant implications for the phosphate cycle in reef aquaria.

Which arrangement of atoms is most likely to be holding phosphate to the calcium carbonate surface?

A. Calcium binding to phosphorus binding to oxygen
B. Calcium binding to oxygen binding to phosphorus
C. Carbon binding to phosphorus binding to oxygen
D. Carbon binding to oxygen binding to phosphorus
E. Oxygen binding to phosphorus binding to calcium
F. Oxygen binding to phosphorus binding to carbon

Good luck!
























.
 
Last edited:

Cory

More than 25 years reefing
View Badges
Joined
Oct 30, 2014
Messages
6,882
Reaction score
3,129
Location
Canada
Rating - 0%
0   0   0
Ive got little clue. Ill guess D because O and C are so abundant that it must be part of evolutionary result. Lol
 

Ryengoth

I wish I was in St John USVI
View Badges
Joined
Jun 17, 2015
Messages
456
Reaction score
213
Location
Wilmington, NC
Rating - 0%
0   0   0
Phos will bond to oxygen and carbon will bond easily with oxygen so I would say C to O and then CO to P or "D".
 

JimWelsh

Valuable Member
View Badges
Joined
Nov 5, 2011
Messages
1,547
Reaction score
1,679
Location
Angwin, CA
Rating - 0%
0   0   0
I think the nature of the bonding will be for PO4 (or some species of phosphate) to share an "O" with CO3, so the answer will be D.
 

Ontheway

Active Member
View Badges
Joined
Oct 11, 2015
Messages
145
Reaction score
43
Rating - 0%
0   0   0
No idea about the answer :)

Something else, If phosphate is able to bind calcium carbonate which is freely flowing in water column too, then will GFO collect phosphate 'and' alkalinity on its tail?
 

jaws789832

Active Member
View Badges
Joined
Oct 2, 2014
Messages
466
Reaction score
413
Location
New Mexico
Rating - 0%
0   0   0
Arent D and F the same thing? I am going to say F. Would think the phosphate if floating around and it binds to the carbon (because carbon wants to bind to everything by either giving 4 or getting 4 electrons).
 
OP
OP
Randy Holmes-Farley

Randy Holmes-Farley

Reef Chemist
View Badges
Joined
Sep 5, 2014
Messages
66,553
Reaction score
62,861
Location
Arlington, Massachusetts, United States
Rating - 0%
0   0   0
No idea about the answer :)

Something else, If phosphate is able to bind calcium carbonate which is freely flowing in water column too, then will GFO collect phosphate 'and' alkalinity on its tail?

Might an exposed phosphate on the surface of GFO bind a calcium on top of it, and might that then act as a nucleus for calcium carbonate? Possibly.

GFO seems to initiate precipitation of calcium carbonate, but since that happens both on the GFO and sometimes downstream of it, I think it is dissolved iron that initiates such precipitation (that is known in freshwater).

As to the GFO surface, some carbonate may bind, but generally, iron in seawater will form iron hydroxides which can then release water to form iron oxides (rust).
 
OP
OP
Randy Holmes-Farley

Randy Holmes-Farley

Reef Chemist
View Badges
Joined
Sep 5, 2014
Messages
66,553
Reaction score
62,861
Location
Arlington, Massachusetts, United States
Rating - 0%
0   0   0
And the answer is...B. Calcium binding to oxygen binding to phosphorus

Calcium looks like a little ball of positive charge.


Carbonate looks like:
https://en.wikipedia.org/wiki/Carbonate
where the red atoms are oxygen and grey is carbon. Each oxygen atom carries some negative charge (2/3 of a negative charge per oxygen).

200px-Carbonate-3D-balls.png


In calcium carbonate, the negative charges on the oxygen bind by electrostatics (ionic bonds) to the positive charge of the calcium. So in calcium carbonate, the binding is calcium to oxygen to carbon. At the calcium carbonate surface with water, there are both exposed calcium ions with a positive charge, and carbonate ions, with a negative charge.

Phosphate looks a lot like carbonate, with a central phosphorus atom surrounded by 4 oxygen atoms that each carry a partial negative charge.

images


So when phosphate comes up to a calcium carbonate surface, one of the negatively charged oxygen atoms binds ionically to a positively charged calcium ion. SO the bonding is calcium to oxygen to phosphorus (or the reverse).

While I drew the picture to show how GFO works, this might help folks understand in the analogous setting of phosphate binding to GFO:
http://reefkeeping.com/issues/2004-11/rhf/index.htm

Figure 2. Phosphate displacing hydroxide (OH-) and binding to a GFO surface.

Figure-2.jpg
 
Last edited:

Cory

More than 25 years reefing
View Badges
Joined
Oct 30, 2014
Messages
6,882
Reaction score
3,129
Location
Canada
Rating - 0%
0   0   0
"where the red atoms are oxygen and grey is phosphorus. Each oxygen atom carries some negative charge (2/3 of a negative charge per oxygen)."

Im confused. Are you describing the phosphorus picture or the carbonate picture? Sorry. :)
 
OP
OP
Randy Holmes-Farley

Randy Holmes-Farley

Reef Chemist
View Badges
Joined
Sep 5, 2014
Messages
66,553
Reaction score
62,861
Location
Arlington, Massachusetts, United States
Rating - 0%
0   0   0
"where the red atoms are oxygen and grey is phosphorus. Each oxygen atom carries some negative charge (2/3 of a negative charge per oxygen)."

Im confused. Are you describing the phosphorus picture or the carbonate picture? Sorry. :)

Not surprising you are confused. It should say carbon, not phosphorus. :D
 

Cory

More than 25 years reefing
View Badges
Joined
Oct 30, 2014
Messages
6,882
Reaction score
3,129
Location
Canada
Rating - 0%
0   0   0
Lol ok thanks. Love the pictures. :)
 
Back
Top