Fluxor
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proper disposal of ZnCl2
Hello everyone:
I finally carried out my first experiment (a demo really) - the generation of H2 by reacting Zn and HCL. I finished building my lab about two weeks
ago.
As I understand it, the reaction of the Zn and the HCL is:
Zn + 2HCL → H2 + ZnCl2
Anyway, here's my situation: I didn't calculate exactly how much HCL would be enough to react all of the acid without leaving any unreacted left over.
I just poured 30 mL of 36% HCL into an Ehrlenmeyer flask and dropped two pennies in. (I just wanted to demo the generation of H2 and then combust it
after capturing it in a balloon). So when it was time for disposal, I poured 300 mL of water into a 400 mL beaker in order to first dilute the
concentrated acid and ZnCl2. Then I proceeded to add little by little NaHCO3 until the fizzing stopped. I reasoned that the sodium bicarbonate would
neutralize both the leftover HCL and the ZnCl2, which is also highly acidic.
However, after the sodium chloride precipitated, I poured off the solution (water and ZnCl2) down the drain with plenty of water. What I want to know
is should the ZnCl2 solution (to which I added the sodium bicarbonate) been flushed down the drain like that? Or, because of its toxicity to aquatic
organisms, have been poured into a waste container to be taken to a hazardous waste collection site? At the time, because of the small amount
involved, I did not think pouring the ZnCl2 down the drain would be problematic, but would like your opinion as to the standard, safest way to both
neutralize it and dispose of it?
Thank you in advance.
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woelen
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Zinc is not a real problem in small quantities. Acid and base in the quantities and dilutions you have also is not a problem.
I have written a web-page about disposal of chemicals: http://woelen.homescience.net/science/chem/exps/rules.html
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Jor
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Zinc is very toxic to some organisms , but it much less of a problem than metals such as Hg, Cd, Pb, Ni, Cr, etc. So a few grams of it down the drain
is no problem, just don't do this everyday.
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aonomus
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If its a larger amount, if ZnCO3 is insoluble (many transition metal carbonates if not all are insoluble), convert to the carbonate, filter out and
wash, then heat until decomposition so it forms ZnO and becomes fairly safe to dispose in household waste (sunscreen contains some ZnO and probably
some people chuck out old stuff containing it). If its large enough to warrant disposing of it via hazardous waste disposal, perhaps it would be
easier to recover the metal?
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JohnWW
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You could use ZnCl2 as a water-soluble and colorless wood or fabric preservative. Or you could precipitate the Zn as ZnCO3 or preferably ZnO (but not
with an excess of NaOH, because ZnO is amphoteric), and after drying mix this with a suitable vegetable oil, like olive or peanut oil, for use as skin
sunscreen. The ZnCO3 or preferably ZnO could also be added to white paint to make it more ultraviolet-resistant.
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BromicAcid
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Metals that should never go down the drain are known in the industry as D-coded metals. There is a list of them here:
http://www.des.umd.edu/hw/rest/manual/codes.html
Although there are a number of rules for specific compounds, no soluble salts of these metals can go down the drain, into or on the ground, etc. This
is not a guideline for disposal, just one of the many rules.
[Edited on 4/4/2010 by BromicAcid]
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Fluxor
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proper disposal of ZnCl2
Everyone...Thank YOU for helping with this wealth of information! I can see that there is much to learn as I progress. I can see also that one can go
deeply using only a few chems and doing just a few experiments...but maybe I should really master the basics, stoichiometry, etc. at the same time
that I try new experiments and lab skills.
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Jor
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Here in the Netherlands, I have read an article in the laws of NL that wastes that can go down the drain (NOT in groundwater, it must be somewhere
wich goes to a water purification factory/facility) if they contain less than 0,01 mg Hg per liter, 0,1mg cadmium per liter, and less than 25mg of the
other heavy metals per liter (all together, so 10mg copper and 25mg lead may not be flushed, metals are Ni, Pb, Cu, As, Sb, Mn, Cr, etc).
But this rule is set even when tons are flushed, so I don't have problems flushing a gram or two of copper, zinc, Mn(II) or cobalt down the drain with
lots of water, per 2 weeks. But if the volume of solution isnt too large i keep the waste in my waste container.
Ni I only flush if very small amounts and relative large volume, but I hardly ever do this, Ni is carcinogenic. Hg, Pb and As, I never flush these,
not even milligrams, although this might be overreacting for lead.
Cr(III) is nontoxic for the environment, it doesn't even have a N symbol.
I don't think Zn is of much concern. it is also used in piping/roofing replacing lead, and because it is not very corroion resistant, i can imagine
losts getting into the environment when it rains!
It all matters how much you flush, and how often. I think I flush a total of 1-2g of metal per 2 weeks on average, as very dilute solutions (wich
would fill my entire waste bottle very quicly for a small amount of waste).
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woelen
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Zinc is not a real concern at all. Lots of zinc go down the drain and also in solid waste, due to zinc oxide based treatment of sore skin (think of
babies, treatment of red skin). Probably every household having babies or small children uses zinc-based treatment, so when you add a little amount of
zinc chloride then that is not a problem.
I also was very surprised to read how much of even toxic metals may be flushed down the drain. Most toxic ones are mercury, arsenic and cadmium,
immediately followed by lead. Natural or depleted uranium follows after lead (appr. ten times less toxic than lead) and after that many other metals
follow (e.g. cobalt, vanadium, nickel).
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