# Sodium Silicate as a Precipitate



## Arrowood (Aug 6, 2011)

I just found some very interesting information on Sodium Silicate as a precipitate. According to Wikipedia,.. "Water glass (Sodium Silicate) was used in the Magic rocks toys invented in 1940. When waterglass was combined with a selection of different metals in solution, the waterglass would cause the metals to precipitate. Each metal would precipitate separately causing a different color stalagmite".

It seems like this could be a very good way to separate metals in solution to me. Has anybody heard of this being used in metal recovery?

Also according to Wikipedia,. Silicon dioxide (sand) dissolves in hot concentrated alkali or fused hydroxide, giving Sodium Silicate and water. This would be a very safe and easy way to make it (assuming you didn't spill any of the hot sodium hydroxide on you). 

SiO2 + 2 NaOH → Na2SiO3 + H2O.


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## Arrowood (Aug 6, 2011)

Heres some more information about "Magic rocks" from Wikipedia. "Magic Rocks, also sometimes referred to or marketed as Crystal Gardens or Chemical Gardens, are a novelty item for creating rock-like formations. A typical package of Magic Rocks contains an envelope of liquid sodium silicate and a small handful of colored "rocks" that are actually chunks of water soluble metallic salts. Some kits come with figurines to give the crystal garden a more exotic look. The "rocks" are placed into the liquid sodium silicate solution, and within several hours colorful crystal towers form. They were invented by two brothers named James and Arthur Ingoldbsy, in the Los Angeles area in 1940".

The following list details the various salt metals (could be hydrated) used for the different colored crystals:

white, calcium chloride (mineral, salt, dryer, laundry enhancer)
white, lead(II) nitrate (lead dye/paint stock, oxidizer, rodenticide)
red, cobalt(II) chloride (dampness marker, complex)
orange, iron(III) chloride (dross)
yellow, iron(III) chloride
green, nickel(II) nitrate (nickel stock)
blue, copper(II) sulfate (mineral, copper stock, oxidizer, algicide, fungicide, pesticide)
purple, manganese(II) chloride
magenta, manganese(II) chloride, (complex)

Here is how I would try to turn this toy into a practical process for separating metals in solution, as well as a way to do quantitative ore assays.

I would use a spot plate and put 1 gram of all the different metal salts (expanding the list above) in each of the spot plate wells. Then put this spot plate into my solution of metals (measuring the amount of ore used to make the solution first of course) and let the different metals precipitate out on the seed crystals. After the precipitation was finished I would remove the spot plate and measure the amount of crystals grown on each seed crystal. This would tell me how much of each metal was in the solution,. a quantitative assay in other words. Once I knew exactly what metals and how much of each was in my ore solution, the same process could be used to separate those metals in a bulk process just using the needed metallic salts.

Does this sound like a reasonable process?

If it works, this process appears to offer several advantages over other assaying procedures and separation techniques.

1) Absolute positive identification of the metals.
2) Much faster assays than testing for each metal individually.
3) Easier isolation of each metal type.
4) The metallic salts are easily recoverable for re-use.


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## butcher (Aug 6, 2011)

How are you going to selectively precipitate the metals? Or crystallize these metals? 

My thinking, metals which are very close in series may co-precipitate or one that crystallizes may plate another out of solution, this would be great for solutions with pure salts of metals, or if just two metals salts and the difference in their voltages in the reactivity series were far enough apart that they will not precipitate or plate out of solution.
Interesting Idea, but I would need to see it to believe it, call me a pessimist, I need you to convince me to become an optimist, if you do this experiment I would be very interested in your results.


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## Arrowood (Aug 6, 2011)

Thanks for the reply Butcher,.. I'm trying to understand how this process works myself. Its obviously partially dependent on the process of Nucleation, but the Nucleation process is not that well understood yet. The classical theory of nucleation has many problems, and only in the last 50 years has much research been done on the subject. The Magic Rocks toy was invented 20 years before that. 

I don't know how Sodium Silicate selectively isolates all the metal ions from the dissolved salts and precipitates them back in crystalline form where the different metallic salts were placed in the solution, but it does somehow. Sodium Silicate is a very unique substance. It is used for a great variety of purposes, including a flocculant. I think its flocculating properties may be partially responsible for it's selective isolation ability. Wikipedia says,.. "Waterglass binds to colloidal molecules, creating flocs of denser particles sinking to the bottom of the water. The microscopic negatively charged particles suspended in water interact with sodium silicate. Their electrical double layer collapses due to the increase of ionic strength caused by the addition of sodium silicate (doubly negatively charged anion accompanied by two sodium cations) and they subsequently aggregate." 

Maybe binding of the Sodium Silicate with the metals somehow prevents them from interacting with other ions until they reach the Nucleation site of Crystal formation? If the metal's double electrical layer collapses when bound to Sodium Silicate, perhaps it becomes encapsulated in the Sodium Silicate molecule and that prevents the other chemical interactions? Or maybe the aggregated metal has used up all its binding sights with the Sodium Silicate, and can't react with other metal particles until it reaches the crystal nucleation site and the bond with Sodium Silicate is broken? 

One potential problem I foresee in developing this process for metal recovery is that Sodium Silicate is only stable in neutral and alkaline solutions, and the solutions used by people in this forum are highly acidic. The metal solution would have to be neutralized before adding the Sodium Silicate. Maybe this wouldn't be a big problem,. I don't know yet, but I would appreciate some comments by some of the chemists here.

I think this needs to be researched more and some experiments done. When i get to the point where I can do some experiments with it, I will share the results of course.


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## butcher (Aug 6, 2011)

So you precipitate the metals from an acidic solution, and the make them into hydroxides to use this process? Maybe it would work for some metals, that easily make hydroxides, but for our more valuable metals, I think I will just stick with the conventional methods of refining for now.

Also just the sound of forming colloids in solution makes me shiver even thinking at trying to get my gold back, colloids are not good to deal with and clean separation of metal salts is harder from my experience with them.

Very interesting theory, but will it work practically? 
Well Einstein found many ways that a light bulb would not work.


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## Arrowood (Aug 6, 2011)

I don't know if you would need to precipitate the metals from an acidic solution first, and then make them into hydroxides or not. I hope not personally. I'm hoping I can just neutralize the acidic solution, add the Sodium Silicate and some seed crystals or metallic salts to help form seed crystals, and let the process begin. There is so much about chemistry we don't understand yet. Scientific discoveries sometimes come from unexpected sources however, and processes are often discovered before they are understood. I didn't know that Einstein found ways to make a light bulb dysfunctional, but it doesn't surprise me. He was a great man! 

I would definitely stick to your regular metal processes until you know there is a better way. Lol


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## butcher (Aug 6, 2011)

The acidic nature is what keeps metals in solution, when neutral they will precipitate, some metals will dissolve as hydroxides easily, and valuable metals would be much more difficult to dissolve as hydroxides.

Einstein spent more time on finding ways the light bulb would not work, until he thought of removing oxygen so the wire would not burn up, so most of his experiments was finding out what would not work, sometimes we see these inventions as something extra ordinary, I see a man who noticed something (hey if I put electricity to this wire it burns into, yes every body sees that, but Einstein saw a flash of light when it burnt up, and thought how can I keep it from burning up and keep its light glowing? and then he did not give up on his quest, burning up everything in sight to find his answer. even if he never found the answer at least he would know what would not work.

but then again you have to know when it is not feasible to try and reinvent the wheel, that has evolved thousands of years, but who knows you may be the one in a million to find a better wheel?

I still have not made up my mind if I think this one is better but it is different.
http://www.google.com/search?q=spokeless+wheel&hl=en&biw=988&bih=573&prmd=ivns&tbm=isch&tbo=u&source=univ&sa=X&ei=i8s9TqumHubRiAKDurnDBg&ved=0CBwQsAQ


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## Bellien (Aug 6, 2011)

The crystal growing kits use moderately concentrated sodium silicate and work via osmotic pressure. The metal salts aren't coming out of a mixed solution they are added as granules and go in and out of solution along their surfaces, which form bubbling growths as water moves back and forth between the salts and the sodium silicate. If the sodium silicate is too concentrated the whole volume will gel (neat polymer chemistry there). 

If you add sodium silicate to an acidic solution you get a silicon dioxide precipitate, this is how they make silica gel. Once you have a silica precipitate it would take hot NaOH or the-acid-which-must-not-be-named to get rid of it. 

Sodium silicate is the binder in useless furnace cement as well as fire place cement. It can be bought cheaply from most pottery supply stores and some hardware stores.

You might be able to get separated salts to grow into pretty growths, or you might just end up with a bucket full of porous glass with your values well trapped.


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## butcher (Aug 6, 2011)

http://en.wikipedia.org/wiki/Thomas_Edison
http://en.wikipedia.org/wiki/Albert_Einstein

just got email from one of our sharp forum members.

I have got these two mixed up, hope I spelled the name right.


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## Arrowood (Aug 7, 2011)

Ok,. thanks for the comments and info guys. If I understand you correctly Bellien, the reason the metal salts crystallize where they are placed in the solution, is because they dissolve and then crystallize at the same interface with the Sodium Silicate. That makes sense and explains the isolation of the different crystals. I still wonder about putting a seed crystal in the metal solution instead of starting with salts however. You would still have the exchange interface between the seed crystal and the Sodium Silicate, and metal ions in the solution to interact at that interface. 

Since I wouldn't be able to neutralize the acid however without precipitating a mixture of metals however, this idea probably only has the potential to work with metals that dissolve in alkaline solutions, so maybe its not such a good idea.

I'm very impressed by the versatility of Sodium Silicate. I did a Google Scholar search for "Sodium Silicate and metal recovery" and found all kinds of patents. People are using the stuff for metal recovery in lots of ways. Here is a selection of the variety of patents (and a few articles) I found just going through about 10 pages (out of 27,500 search results!) Some of them refer to recycling metals that may be interesting to some people in the forum too.

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Process for improved precious metals recovery from ores with the use of alkylhydroxamate collectors, DR Nagaraj - US Patent 5,126,038, 1992 - Google Patents

Solvent-in-pulp extraction, BH Lucas… - US Patent 3,969,476, 1976 - Google Patents

RECOVERY OF PRECIOUS METAL VALUES, US Patent 2,479,930, 1949 - Google Patents

Metal recovery and rejuvenation of metal-loaded spent catalysts, JS Yoo - Catalysis today, 1998 - Elsevier

LARGE PORE SILICA GEL CATALYSTS, DR Witt - US Patent 3,862,104, 1975 - Google Patents

Manufacture of shaped particles of hydrous alkali metal silicates, M Zb - US Patent 2,284,248, 1942 - Google Patents

Separation and recovery of reusable heavy metal hydroxides from metal finishing wastewaters, JM Frankard… - US Patent 4,680,126, 1987 - Google Patents

Fluorspar ore flotation, VV Mercade - US Patent 3,893,915, 1975 - Google Patents

The application of a sol-gel technique to preparation of a heavy metal biosorbent from yeast cells, J Szilva, G Kuncová, M Patzák… - Journal of sol-gel science …, 1998 - Springer

Recovery of gold, silver and platinum group metals with various leachants at low pulp densities, DR Butler - US Patent 5,215,575, 1993 - Google Patents

Process of recovering fluorine from phosphate rock, RJ Huvka - US Patent 2,954,275, 1960 - Google Patents

Evidence from alkali-metal NMR spectroscopy for ion pairing in alkaline silicate solutions, AV McCormick, AT Bell… - The Journal of Physical …, 1989 - ACS Publications

Flotation of heavy metal oxides, AP Mountains - US Patent 2,861,687, 1958 - Google Patents

HIGHLY ABSORBENT, LOW BULK DENSITY ALKALI METAL SODIUM SILICATES, PC Yates - US Patent 3,839,226, 1974 - Google Patents

Influence of sodium silicate addition on the adsorption of oleic acid by fluorite, calcite and barite, KI Marinakis… - International journal of mineral processing, 1985 - Elsevier

ALKALI METAL ALUMINO SILICATES, METHODS FOR THEIR PRODUCTION AND COMPOSITIONS THEREOF, JT Crockett - US Patent 3,582,379, 1971 - Google Patents

Method of increasing oil recovery, WS Fallgatter - US Patent 2,807,324, 1957 - Google Patents

Recovery of oil and sulfonate from filter cake, WH Tyson… - US Patent 4,501,670, 1985 - Google Patents

Bioadsorption composition and process for production thereof, VI Lakshmanan… - US Patent 5,084,389, 1992 - Google Patents

Production and recovery of metallic carbides from ores and concentrates, HG Brandstatter - US Patent 3,999,981, 1976 - Google Patents

Briquetting of foundry materials, JP Parsons - US Patent 3,316,083, 1967 - Google Patents

Bead for removing dissolved metal contaminants, BL Summers Jr… - US Patent 5,578,547, 1996 - Google Patents

Purification of clay by selective flocculation, VV Mercade - US Patent 3,701,417, 1972 - Google Patents

Composition for extraction of metal ions and oxanions, DW Darnall, MD Alexander, M Henzl… - US Patent …, 1991 - Google Patents

Alkali metal perborates, JH Young - US Patent 2,491,789, 1949 - Google Patents


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## Arrowood (Aug 7, 2011)

Wow,.. I like the Spokeles wheel Butcher! Putting the crank shaft inside the rim is a brilliant idea, and so is moving the seat inside the wheel to create a unicycle! Some people are very creative. :lol:


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