Sciencemadness Discussion Board

Calcium Oxide from sea shells

Little_Ghost_again - 17-9-2014 at 07:05

Hi,
I have been reading and came across a reference to calcium oxide in times gone by, being made from crushed sea shell's. As I live 4 miles from a deserted fabulous beach full of sea shells, this has me thinking.
Apparently the shells are crushed and heated to above 850C, the time of heating wasnt given however. We have a very small granite stone kiln we built outside last year, it has been used for melting lead for fishing weights and some Aluminum. The fuel source was dried pine cones (what else :D) that burn very hot and are fairly dense in a way similar to hard wood, they are also a renewable source.
The kiln is fanned from several small high powered 12V fans run from a leisure battery. I am confident I can reach and maintain the temperature but I am not sure for how long this needs to be done.
While I would wash the shells well in tap water, I am pretty sure any organic material would simply burn off or at most be converted to carbon. Calcium oxide looks like a neat desiccant and while not overly expensive 500 grams on ebay with postage is around £7.
So any idea how long the >850c needs to be held for? I might make a 2 KG batch and store in several smallish containers. I also need another crucible as the last one got broken.

DJF90 - 17-9-2014 at 08:49

Plante1999 has done this exact preparation and reported his results in the Prepublications forum.

Little_Ghost_again - 17-9-2014 at 08:54

Quote: Originally posted by DJF90  
Plante1999 has done this exact preparation and reported his results in the Prepublications forum.


Ok thank you I will go have a look :D

Magpie - 17-9-2014 at 09:13

Plante specifies 800°C for one hour. I have made CaO from garden lime [very cheap source of slaked lime, Ca(OH)2] a number of times. IIRC I used conditions very similar to that of Plante.

This makes a nice experiment for the use of a little chemistry math. Weigh your lime before and after heating. Then see if the weight loss matches the theoretical loss obtained by calculation using molecular weights.

metalresearcher - 17-9-2014 at 10:09

Quote: Originally posted by Magpie  
Plante specifies 800°C for one hour. I have made CaO from garden lime [very cheap source of slaked lime, Ca(OH)2] a number of times.


Indeed that worked for me too. Just a bag of garden (?) lime from the hardware shop. I heated 500g in a Kanthal furnace for an hour to 700C and I saw some plumes of water escape.

I used it for arcing it with bbq charcoal to make CaC2 whcih succeeded.

aga - 17-9-2014 at 10:41

Quote: Originally posted by metalresearcher  
I used it for arcing it with bbq charcoal to make CaC2 whcih succeeded.

Wow !

What arc did you use ?
A stick welding rig ?

Little_Ghost_again - 17-9-2014 at 12:04

Quote: Originally posted by Magpie  
Plante specifies 800°C for one hour. I have made CaO from garden lime [very cheap source of slaked lime, Ca(OH)2] a number of times. IIRC I used conditions very similar to that of Plante.

This makes a nice experiment for the use of a little chemistry math. Weigh your lime before and after heating. Then see if the weight loss matches the theoretical loss obtained by calculation using molecular weights.

Some of the shells like mussel and razor clam will have organic material, I could burn that off with a bunsen I guess.
But yes it will be interesting to see the results. A couple of questions that have arisen from a cryptic conversation with my dad........

I am assuming that shells are calcium carbonate, I mentioned this to dad and he smiled and asked if I was sure??? Looking at a shell under the microscope I think I am wrong. So working on an assumption I think there s some magnesium carbonate in there as well, there is definitely something other than calcium carbonate because I can see two crystal like structures that are different (mag Oil Immersion 1400x with phase contrast no stain).
So if I assume mag carbonate my question is there a test to distinguish magnesium and calcium carbonate?
Its not that I think it will matter, but I would like to know. Not sure what our home built stone kiln/roket stove can do temperature wise,but we have a IR thermometer that goes upto 1200C and it easily passes that! its pretty efficient on dry large pine cones, I burnt around 30Kg of cones last year melting a load of aluminum cans! Actually I ended up with 31Kg of aluminum! Mostly cans I picked up on our road verge and the lay by near us, also the beach had loads and the can recycle bank is full most days, so people just put bags of cans by the side. I pick them up and store until dad gets fed up falling over cans lol.
Anyway weighed the aluminum in and it paid for a new function generator :D.
All the ash that was left came to under 500g! The inside of the kiln is lined with lime and fire fibre mix (no idea what it is made of). I want to build a slightly bigger one this winter.

careysub - 17-9-2014 at 19:05

Quote: Originally posted by Little_Ghost_again  
Quote: Originally posted by Magpie  
Plante specifies 800°C for one hour. I have made CaO from garden lime [very cheap source of slaked lime, Ca(OH)2] a number of times. IIRC I used conditions very similar to that of Plante.

This makes a nice experiment for the use of a little chemistry math. Weigh your lime before and after heating. Then see if the weight loss matches the theoretical loss obtained by calculation using molecular weights.

Some of the shells like mussel and razor clam will have organic material, I could burn that off with a bunsen I guess.
But yes it will be interesting to see the results. A couple of questions that have arisen from a cryptic conversation with my dad........

I am assuming that shells are calcium carbonate, I mentioned this to dad and he smiled and asked if I was sure??? Looking at a shell under the microscope I think I am wrong. ...


Biological structural materials usually have nanostructure patterning that make them look different from minerals with similar composition - part of the evolutionary engineering that gives them superior physical properties .

If you are going to calcine them all of the organic materials (like chitins, proteins, etc) that may be incorporated into the structure are going to disappear.

Looking at one source that looked at the mineral composition of calcined mussel and oyster shells:
http://www.scielo.br/scielo.php?script=sci_arttext&pid=S...
we see that mussel shells are 95.6% CaO, with roughly similar amounts of seven other minerals (0.4 to 0.9%), while oyster shells are almost pure CaO - 98.2%.

Zyklon-A - 18-9-2014 at 06:20

Quote: Originally posted by aga  
Quote: Originally posted by metalresearcher  
I used it for arcing it with bbq charcoal to make CaC2 whcih succeeded.

Wow !

What arc did you use ?
A stick welding rig ?

You can read about it here:http://www.sciencemadness.org/talk/viewthread.php?tid=27475#...

Bert - 18-9-2014 at 06:48

If you are intending to re-create traditional building materials?

http://homescale.wordpress.com/makinglime/

Be sure to wash all the sea salt off the shells, especially if you're going to use steel mesh or bars in concrete work.

blogfast25 - 18-9-2014 at 10:09

Have a look at this for a better understanding of the relation between temperature and CO2 partial pressure, when calcining CaCO3 to lime and CO2:

http://en.wikipedia.org/wiki/Calcium_carbonate#Calcination_e...

Little_Ghost_again - 18-9-2014 at 10:15

Thanks guys for the links.
I dont want it to build with, I just thought it would be handy to have and a fun thing to do. It also gives me an excuse to fire up the kiln :D

Actinium - 18-9-2014 at 20:33

How fast does Ca(O) turn back into Ca(OH)2 ?
Doesn't it re-hydrate quite fast?

blogfast25 - 19-9-2014 at 04:05

Quote: Originally posted by Actinium  
How fast does Ca(O) turn back into Ca(OH)2 ?
Doesn't it re-hydrate quite fast?


Not if stored properly.

But the reaction between fresh quicklime (CaO) and actual water can be quite vicious and needs to be done carefully. It was in Roman times one of the less enjoyable jobs to turn quicklime into slaked lime, allegedly...

Bert - 19-9-2014 at 04:55
Quote:

the reaction between fresh quicklime (CaO) and actual water can be quite vicious


A Mason jar full of quick lime with a few small holes punched in the lid has been used for fishing by resourceful hillbillies without access to dynamite... Throw it in the water, it sinks to the bottom and water enters. As the lime slakes, it heats, water boils and the holes clog from bits of lime being forced against them from inside. The eventual steam explosion of the jar may be sufficient to stun fish.

macckone - 19-9-2014 at 06:32

Quote: Originally posted by Bert  

Quote:

the reaction between fresh quicklime (CaO) and actual water can be quite vicious


A Mason jar full of quick lime with a few small holes punched in the lid has been used for fishing by resourceful hillbillies without access to dynamite... Throw it in the water, it sinks to the bottom and water enters. As the lime slakes, it heats, water boils and the holes clog from bits of lime being forced against them from inside. The eventual steam explosion of the jar may be sufficient to stun fish.

Have you been spying on my fishing?

Actinium - 19-9-2014 at 13:14

Quote: Originally posted by Bert  

Quote:

the reaction between fresh quicklime (CaO) and actual water can be quite vicious


A Mason jar full of quick lime with a few small holes punched in the lid has been used for fishing by resourceful hillbillies without access to dynamite... Throw it in the water, it sinks to the bottom and water enters. As the lime slakes, it heats, water boils and the holes clog from bits of lime being forced against them from inside. The eventual steam explosion of the jar may be sufficient to stun fish.

My friend from W. Va will love this one:P
See Chemistry has very practical applications.

Now as far as drying the Ca(OH)2 > Ca(O) since I no longer have my kiln, will a torch suffice? If so I would use the bottom of a wine bottle so as not to ruin my precious glassware for this.

blogfast25 - 19-9-2014 at 14:08

Quote: Originally posted by Actinium  
Now as far as drying the Ca(OH)2 > Ca(O) since I no longer have my kiln, will a torch suffice? If so I would use the bottom of a wine bottle so as not to ruin my precious glassware for this.


It'll be borderline as the dehydration of slaked lime only starts at about 512 C.

Little_Ghost_again - 20-9-2014 at 03:36

Maybe you could use the fire bricks (slates) from inside something like a old broken wood burning stove.
Our MK2 kiln will use these to line inside the stone, we have no way to measure such high temps but I know the MK1 got extremely hot as the 1/2 inch steel sheet that the crucible was stood on melted!
The new Mk2 now under construction is going to use a fan from a kids small bouncy castle.
The air out put is very impressive, for control I am going to add a variac, this way I can control the amount of air going into the kiln.
Sone of the conifer trees in our wood produce huge 10" long pine cones (I use inches on here because most of you do, I prefer metric so if I get the sizes wrong sorry). When these cones are dry the are extremely dense, they make idea fuel for rocket stoves and kilns like this.
Our kiln designs have a burning chamber that is just behind the main flue, we place the object to be heated 6 inches up inside the flue. Just behind the fire chamber is the fuel box, this is where we put the cones, we can then poke them into the fire chamber and close the stone lid on the fire box.
What we found was as long as the flue (chimney) was 3 x the height as the fire box is long, then you get a massive updraft through the flue, this really gives a good draw on the fire. Add in extra air via a fan or whatever and you can get really high temperatures, most the rock around here is granite with marble here and there, we also have a area with lime stone but for the kiln we use the granite.
Everything is then rendered with cement and the fire fibre mix, then the fire bricks/tiles from wood burners go in front of this.
Hope that helps someone.

Refinery - 20-9-2014 at 14:05

Calcium hydroxide decomposes to oxide at 550-600C, while calcium carbonate needs 850-900C, but practically it is necessary to take the temp over 950-1000C to make the reaction fast. I have made CaO with electric furnace from calcium carbonate, and when temperature reached 1000C, the mass was fully decomposed to the extent I could measure it.

I made a furnace on a small 60 liter steel drum. I cut it about 1/3, put some pearlite clay on bottom of it, placed two firebricks on top of them, sat a plastic bucket in the middle and poured calcium sulfate plaster. When it dried, I made holes for nichrome wire and casted the 1/3 drum head full of plaster with couple of reinforcing bars that act as a handle too, mantled the whole setup in 150mm thick rockwool slab and dumped it into a 208l drum. It has to be heated very carefully at first time and ideally it should be placed into oven at 60C for 4-6 hours and then for 100C for another 4 hours, and then slowly heated to operational temperature to drive out the moisture contained in the plaster. It may still crack, but the drum keeps it together and once it's cracked, thermal expansion wont hurt it anymore. It can withstand 1300c temps continously.

Little_Ghost_again - 22-9-2014 at 08:43

Electric is expensive here, mostly we run from a diesel generator. Also I like the idea of running from a renewable fuel. We have a 8 acre commercial plantation of spruces etc as part of our woodland. Pine cones litter floor everywhere here! Dried out the are very dense and burn like a really good hardwood.
Add a good blast of air and 1000C is not hard to achieve. I like the idea of your electric one and if electric was cheap here I would tempted because I could combine it with my love of electronics to make a control system! But its just easier and cheaper for us to use a granite wood fired kiln.

blogfast25 - 22-9-2014 at 11:35

Quote: Originally posted by Little_Ghost_again  
Add a good blast of air and 1000C is not hard to achieve. I like the idea of your electric one and if electric was cheap here I would tempted because I could combine it with my love of electronics to make a control system! But its just easier and cheaper for us to use a granite wood fired kiln.


Fairly easy: lots of fuel and lots and lots of air. It'll melt copper quite easily if you push it.

But bear in mind that a wood or coal based fire will be quite rich in CO<sub>2</sub>, as one of the sources above indicated. This tends to push the equilibrium CaCO<sub>3</sub>(s) < === > CaO(s) + CO<sub>2</sub>(g) to left again (while temperature ushes it to the right).

Bert - 22-9-2014 at 12:15

Pine cones should make for a quite luminous fire- Perhaps you should explore harnessing that?

Reverberatory furnace

Traditional lime burning

[Edited on 22-9-2014 by Bert]

Little_Ghost_again - 22-9-2014 at 12:19

Quote: Originally posted by blogfast25  
Quote: Originally posted by Little_Ghost_again  
Add a good blast of air and 1000C is not hard to achieve. I like the idea of your electric one and if electric was cheap here I would tempted because I could combine it with my love of electronics to make a control system! But its just easier and cheaper for us to use a granite wood fired kiln.


Fairly easy: lots of fuel and lots and lots of air. It'll melt copper quite easily if you push it.

But bear in mind that a wood or coal based fire will be quite rich in CO<sub>2</sub>, as one of the sources above indicated. This tends to push the equilibrium CaCO<sub>3</sub>(s) < === > CaO(s) + CO<sub>2</sub>(g) to left again (while temperature ushes it to the right).


Now thats interesting! Does using charcoal lower the CO2? Although I am not too sure how easy it is to turn cones into charcoal!
Probably the best approach is to go for maximum heat. The other thing is the shells will be in a crucible rather than amongst the fuel, I doubt that is going to make any difference with CO2 though.

vmelkon - 25-9-2014 at 07:22

Quote: Originally posted by Little_Ghost_again  
Quote: Originally posted by blogfast25  

Fairly easy: lots of fuel and lots and lots of air. It'll melt copper quite easily if you push it.

But bear in mind that a wood or coal based fire will be quite rich in CO<sub>2</sub>, as one of the sources above indicated. This tends to push the equilibrium CaCO<sub>3</sub>(s) < === > CaO(s) + CO<sub>2</sub>(g) to left again (while temperature ushes it to the right).


Now thats interesting! Does using charcoal lower the CO2? Although I am not too sure how easy it is to turn cones into charcoal!
Probably the best approach is to go for maximum heat. The other thing is the shells will be in a crucible rather than amongst the fuel, I doubt that is going to make any difference with CO2 though.


Charcoal has a lot of carbon of course and as you burn it, it produces CO2. I imagine the ratio CO2 to H2O is higher for charcoal compared to wood which has moisture and carbohydrates and cellulose.

blogfast25 - 25-9-2014 at 09:23

Quote: Originally posted by Little_Ghost_again  
[ The other thing is the shells will be in a crucible rather than amongst the fuel, I doubt that is going to make any difference with CO2 though.


What makes you think keeping the shells in a crucible will make one iota of difference? You burn charcoal (or pine cones) and use the hot combustion gases, rich in CO<sub>2</sub>, to heat furnace and crucible in it. How can a crucible make a difference there/

[Edited on 25-9-2014 by blogfast25]

Little_Ghost_again - 25-9-2014 at 10:23

Quote: Originally posted by blogfast25  
Quote: Originally posted by Little_Ghost_again  
[ The other thing is the shells will be in a crucible rather than amongst the fuel, I doubt that is going to make any difference with CO2 though.


What makes you think keeping the shells in a crucible will make one iota of difference? You burn charcoal (or pine cones) and use the hot combustion gases, rich in CO<sub>2</sub>, to heat furnace and crucible in it. How can a crucible make a difference there/

[Edited on 25-9-2014 by blogfast25]


As I stated above, Nothing at all " I doubt that is going to make any difference with CO2 though"
It was more of I hope I am wrong and it will make a difference kind of thing :D.
Slight fly in the ointment at the moment, the last one used a leisure battery to power 12V air source, this one uses a 240V airblower from a bouncy castle, the problem is I have started building the MK2 15 meters too far for the power extension lead :D.
So I will have to drag the small petrol generator around the back when I want to use it :(

macckone - 26-9-2014 at 06:51

A crucible with a lid will keep contaminants out while allowing CO2 to escape. I mean do you really want to be picking
chunks of CaO out of ashes? It is more of a cleanliness thing.
The CaO doesn't care if it is in a crucible or not as it is formed.
In fact the crucible will slow down the reaction because the
heat must penetrate the calcium carbonate mass through
the crucible.

WGTR - 26-9-2014 at 07:56

One thing that I haven't seen mentioned so far is the effect of carbon monoxide on the equilibrium of the reaction. I've calcined small pieces of limestone in a charcoal kiln before. It was an updraft design, with forced air coming from below. The kiln was loaded with charcoal and lit. After everything heated up, more charcoal was loaded, and the limestone was placed on top of the charcoal. A lid was placed over the kiln, with a hole for the exhaust gasses. Most of the oxygen would get consumed at the bottom of the pile, with the heat and CO2 rising through the rest of the hot charcoal. The CO2 would be mostly CO by the time it got to the lime. This gas could be easily ignited at the exhaust vent. With the kiln insulated with fire brick, the atmosphere was glowing bright orange under the lid. With .25" pieces of limestone, they were calcined after about 15-20 minutes. For cool-down, more charcoal is loaded in the kiln, and the air holes plugged until things were no longer glowing, and the lime could be removed.

blogfast25 - 26-9-2014 at 09:15

Quote: Originally posted by macckone  
In fact the crucible will slow down the reaction because the
heat must penetrate the calcium carbonate mass through
the crucible.


Assuming equilibrium temperature is achieved fairly quickly the crucible will not hinder the process. It's only temperature that matters.

Quote: Originally posted by WGTR  
One thing that I haven't seen mentioned so far is the effect of carbon monoxide on the equilibrium of the reaction.


CO should not affect CaCO<sub>3</sub>(s) < === > CaO(s) + CO<sub>2</sub>(g)


[Edited on 26-9-2014 by blogfast25]

Little_Ghost_again - 26-9-2014 at 09:53

Thanks guys and thanks Blogfast for the equation, I have to redo the MK2 because of my lack of the whole measure twice cut once thing :D. I got switched the wrong way round lol.
yeah the crucible is mostly to keep it clean and out the ash, also I want powder the shells first, I found a really old Darkroom film developer machine in one the buildings. Dad says he had it a long time ago when he was into photography. A few mods and I should have a ball mill :D, my wrists are getting weaker so crushing things with a P&M hurts a fair bit.
My first batch of Ethanol got messed up today :(, so I have to get another batch going.

WGTR - 26-9-2014 at 10:10

My intended meaning, though poorly phrased, is that the presence of CO lowers the partial pressure of CO2, helping drive the reaction to the right. With the right kiln design and fuel loading, little CO2 should be exiting from the kiln.

blogfast25 - 27-9-2014 at 04:03

Quote: Originally posted by WGTR  
My intended meaning, though poorly phrased, is that the presence of CO lowers the partial pressure of CO2, helping drive the reaction to the right. With the right kiln design and fuel loading, little CO2 should be exiting from the kiln.


If you burn the fuel completely to CO then yes, the partial pressure of CO<sub>2</sub> will basically be that of air and the equilibrium will not be affected by the off gases.

But the combustion to CO runs less hot than to CO<sub>2</sub>:

C + 1/2 O<sub>2</sub> === > CO is less exothermic than ('all other things being equal'):
C + O<sub>2</sub> === > CO<sub>2</sub>


[Edited on 27-9-2014 by blogfast25]