Sciencemadness Discussion Board

sequestering heavy metal oxides?

jgourlay - 7-5-2012 at 12:27

Gents, as part of a pottery hobby, I frequently have small amounts of 'glaze' left over containing some pretty shockingly poisenous stuff. Think "PbO" and V205 mixed with some nickel compound.

The amount is rarely larger than, say, about 4 cubic centimeters. This is not stuff i want to wash down the drain, or keep in a jar. Can I make this stuff safe to throw in the trash by mixing in some broken glass and firing the glass+toxins in a small clay dish during the glaze fire?

The thought being that the glass would lock up the stuff, thus rendering it disposable.

Pyridinium - 7-5-2012 at 13:22

The glass / pottery sequestration is actually a tried and true technique that has been used on some types of nuclear waste, at least in the past. I don't know if they're still doing it today.

I never thought of V2O5 as all that nasty, but the lead and nickel you wouldn't want to be throwing out (besides, what a waste). Metal oxides are poorly soluble as I'm sure you know, but of course the pH of the waters acting on them is of some concern.

If you want the safest, "environmentally friendly" way to deal with un-needed lead compounds, it requires a bit of chemistry. Precipitating the lead as PbS produces one of the most insoluble (low Ksp) compounds: galena. This occurs naturally, and many people live near (or on top of) huge galena deposits. (I often wonder how the de-industrializers and nanny staters are going to figure out how to eliminate those.)

blogfast25 - 7-5-2012 at 13:23

Yes, glassing is an extremely safe way to dispose of such waste but be careful not to breathe any fumes during the process. Once locked into the glass matrix the toxins are unlikely to be ever released to the environment. Make sure you use enough glass.

Endimion17 - 7-5-2012 at 13:39

It's a waste of time and relatively huge amount of energy. Seriously, melting glass just to get rid of PbO is not environmentally friendly. It's a huge overkill. Not to mention pretty much benign vanadium and nickel, or the ridiculously small amounts involved.

There's a reason why is vitrification, which is the proper term, used in high level waste management in nuclear industry. It's because the sheer radiotoxicity of the compounds involved are a good enough reason to do it.

If you really want to immobilize something that would be cool to play with in the lab, mix it into a concrete brick and throw the brick away. It will last for few thousands years in the dump.

BTW, "toxins" is an improper term. Toxins are biological poisons made by organisms.

Pyridinium - 7-5-2012 at 13:53

Quote: Originally posted by Endimion17  

If you really want to immobilize something that would be cool to play with in the lab, mix it into a concrete brick and throw the brick away. It will last for few thousands years in the dump.


This is a good point - Roman concrete is still around today. It's the steel reinforcing that makes cement crumble.

jgourlay - 7-5-2012 at 17:12

Thanks gents for confirming. Couple of thoughts. Maybe I over reacting on the V205, but the msds 'got my attention'. For me, the process isn't a waste of materials/energy. I'm good for a bottle of wine or two a month, and the 'charge' will go in the kiln with the glaze firing, so it's fundamentally free. Thanks again!

Hey, maybe it'll color the glass and make something pretty!

AJKOER - 7-5-2012 at 17:32

Oxalic acid attacks many metals forming insoluble Oxalates. However, avoid an excess of the H2C2O4 as with some metals a soluble complex can be formed (for example, with iron and cobalt).

In the particular case of nickel per "A system of chemistry ..." by Thomas Thomson, page 63 to quote:

"Oxalic Acid attacks nickel at a digesting heat, and a greenish white powder is deposited, which is the oxalat of that metal. The same salt is precipitated when oxalic acid is dropped into the solution of nickel in sulphuric, nitric, or muriatic acids. It is scarcely soluble in water, and is composed, according to Bergman, of two parts of acid to one of metal"

With respect to Pb, per the same source, to quote page 55:

"Oxalic Acid blackens lead, but it is scarcely capable of dissolving it; but it dissolves its deutoxide, and when nearly saturated deposites small crystalline grains of oxalat of lead. The same crystals are precipitated when oxalic acid is dropt into the nitrat, muriat, or acetat of lead dissolved in water. They are insoluble in alcohol, and scarcely soluble in water, unless they contain an excess of acid. They are composed, according to Bergman's analysis, of about 41.2 acid 58.8 oxide"

As such based on this reference, I would dissolve the Lead and Nickel in HCl and drop in Oxalic acid to form the insoluble Oxalates.

Link:
http://books.google.com/books?id=PzgwAAAAYAAJ&pg=PA63&am...

jgourlay - 7-5-2012 at 17:35

Thanks gents for confirming. Couple of thoughts. Maybe I over reacting on the V205, but the msds 'got my attention'. For me, the process isn't a waste of materials/energy. I'm good for a bottle of wine or two a month, and the 'charge' will go in the kiln with the glaze firing, so it's fundamentally free. Thanks again!

Hey, maybe it'll color the glass and make something pretty!

Pyridinium - 7-5-2012 at 19:04

Quote: Originally posted by jgourlay  
Thanks gents for confirming. Couple of thoughts. Maybe I over reacting on the V205, but the msds 'got my attention'. For me, the process isn't a waste of materials/energy. I'm good for a bottle of wine or two a month, and the 'charge' will go in the kiln with the glaze firing, so it's fundamentally free. Thanks again!

Hey, maybe it'll color the glass and make something pretty!


V2O5 does have a low TLV for airborne particles (0.05 mg/m3) according to the condensed chemical dictionary. In my edition of the CCD (1987) they were in that era where everything became "highly toxic". Then again if you check out J Toxicol Pathol. 2011 Sep;24(3):149-62, inhaled V2O5 dusts at > 1 mg / m3 apparently cause lung cancer in B6C3F1 mice, but I don't know enough about that phenotype; they could be extra susceptible to certain things (IIUC, they don't reject transplants.....)

in my searching around I also stumbled on two interesting things, unrelated to the present discussion ....

(A.) these B6C3F1 mice are pretty expensive (> 20 bucks apiece!) and

(B.) a study with B6C3F1 mice tends to support the concept of "a noisome and grievous sore" - see LeCalvez et al., Exp Tox Path 57: 255-265 (2006)... cross ref. with Revelation 16:2 (King James ver.) of course.

But anyway, if your glaze firing is already free, then yeah, vitrification might be worth it.







jgourlay - 8-5-2012 at 05:48

I looked up PbO as a 'reference': the exposure limits for V2O5 and PbO are the same.

Yrrrgh!!!