woelen
Super Administrator
Posts: 8012
Registered: 20-8-2005
Location: Netherlands
Member Is Offline
Mood: interested
|
|
Good source of arsenic?
I took a chance and ordered one of these:
https://www.ebay.nl/itm/Bulk-Lot-1-2-LB-Golden-Yellow-ORPIME...
The little parcel arrived unexpectedly fast and contained appr. 250 grams of orpiment (As2S3). I think it is natural material, found in mines. The
picture of the eBay seller accurately shows the appearance of my material. Quite a few pieces have a size of a few cm, other pieces are smaller. The
pieces look yellow/ochre, some pieces are somewhat darker and very shiny, most are yellow and look somewhat powdery, and some pieces have a thin
powdery white layer, which probably is some oxidized As2S3 (maybe it is As2O3?).
I was pleasantly surprised by the purity of my sample. I expected something with a little As2S3 and a lot of other minerals (stones). The pieces I
received, however, can be crushed easily and this process gives a yellow/ochre powder.
I carefully mixed some of the yellow powder with KClO3 and ignited the mix outside (with a firm breeze in my back in order to avoid inhalation of
smoke or dust). The mix burns very fast with a fairly bright greyish flame and produces white smoke. This shows that the material is not just some
stone with a little orpiment mixed in.
I also added some of the powder to 60% HNO3. The powder does not react with the cold acid, but when the acid is heated, then the powder slowly
dissolves, giving a nearly colorless solution and a brown mix of NO/NO2. I think that the colorless solution contains sulfuric acid and arsenic acid
as oxidation products of the orpiment.
This may be an interesting source of arsenic or arsenic compounds for other amateur chemists, which is easy to get. If you search for orpiment on
eBay, then you find lots of sellers in China, who sell small samples for just a few bucks and free shipping and somewhat larger amounts like the one,
which I posted here. You can also search for realgar, which is bright red As4S4, but this material is much more expensive than orpiment.
Is there anyone else over here, who has done experiments with orpiment?
If someone decides to buy this and experiment with it, please be careful. Although this is a natural mineral, it does not mean it is less
toxic. This stuff is an arsenic compound and hence it is toxic, very toxic! The mix with KClO3 is sensitive to ignition and the smoke from the burning
mix also is very toxic (it is a mix of mainly SO2, KCl and As2O3). Do not use it for pyrotechnic purposes, I made a small amount of the mix to see
whether it really is orpiment, which is easily combustible, or just some inert stone material. I hope to be able to extract some powdered elemental
arsenic from this.
|
|
|
Doped-Al2O3-fusion
Hazard to Self
Posts: 99
Registered: 11-4-2018
Member Is Offline
Mood: Maniacal
|
|
I've seen arsenic on eBay while browsing through sellers items. I'm always surprised that it can be obtained so easily.
https://www.ebay.com/itm/Arsenic-Metal-Crystalline-Element-S...
|
|
|
Boffis
International Hazard
Posts: 1867
Registered: 1-5-2011
Member Is Offline
Mood: No Mood
|
|
Native arsenic is surprisingly common. I worked on one silver project once in Central Asia that was next to a giant iron mine in which native arsenic
occurred in the altered volcanic rocks below the main magnetite seam in considerable quantities in nodules 2-4 inches in diameter (5-10cm) in calcite
veins with native silver, rare silver sulphides and zeolites.
I have also tried making things out of orpiment too. If you use sodium sulphide solution and sulphur you can make sodium tetrathioarsenate. As2S3 is
supposed to be soluble in NaOH solution alone, presumably you get a mixture of partial thioarsenites. Maybe you could oxidise this solution with H2O2
to sodium arsenate and sulphur or sulphate ions. Sodium hypochlorite dissolve metallic arsenic so maybe it will dissolve orpiment too being strongly
alkaline.
The arsenate and sulphate ions can be separated by precipitating with barium chloride and then liberating the arsenic acid with dilute sulphuric acid
and concentrating the filtrate.
|
|
|
clearly_not_atara
International Hazard
Posts: 2787
Registered: 3-11-2013
Member Is Online
Mood: Big
|
|
I think an easier way to separate arsenate and sulfate might be to use the differences in solubility of the magnesium salts -- sources tell me
magnesium arsenate is insoluble, whereas we're all familiar with the very high solubility of MgSO4.
IIRC sodium arsenIte is key to the highly unusual reaction of reducing a haloform to the corresponding dihalomethane. This is a very sought-after
reaction among some people.
[Edited on 19-7-2018 by clearly_not_atara]
|
|
|
DavidJR
National Hazard
Posts: 908
Registered: 1-1-2018
Location: Scotland
Member Is Offline
Mood: Tired
|
|
Rather you than I...
|
|
|
Boffis
International Hazard
Posts: 1867
Registered: 1-5-2011
Member Is Offline
Mood: No Mood
|
|
Quote: Originally posted by clearly_not_atara  |
IIRC sodium arsenIte is key to the highly unusual reaction of reducing a haloform to the corresponding dihalomethane. This is a very sought-after
reaction among some people.
|
Yes, as a mineralogist I use lots of diiodomethane because of its high refractive index, high density and its ability to dissolve covalent arsenic
compound giving refractive liquids with very high RIs (though somewhat toxic) but I suspect that you are thinking of other uses.
The idea of using magnesium sulphate is a good one as far as separating the sulphate and arsenate ions goes but then how do you isolate the free
arsenic acid?
I once tried fusing orpiment with sodium nitrate to give sodium sulphate and sodium arsenate but the mixture deflagrates just as it does with a
chlorate. I eventually found that it was best to fuse the orpiment with NaOH and then add the sodium nitrate in small amounts as prills. The problem
with this method was that it required a fairly large excess of NaOH to inhibit deflagration but it did work. I you are going to try this use a steel
pot as a crucible and a piece of iron rod or an 8" nail to stir it, the reaction is vigorous!
|
|
|
Doped-Al2O3-fusion
Hazard to Self
Posts: 99
Registered: 11-4-2018
Member Is Offline
Mood: Maniacal
|
|
I recently boiled down a quart of waste HCl containing god knows what from dissolving local rocks/minerals from rockhounding. I thought I could get
something to crystallize, but instead, all I got was this yellow solid that was incredibly hygroscopic. I thought it was more gel like than solid,
but it can be boiled/evaporated to dryness. Within minutes it is wet again. I couldn't figure out what to make of this substance so I decided to see
what aluminum would do. It reacted in solution forming a dark grey precipitate. This reactant product dissolves in water forming an almost white
cloud, which I assume is microscopic bubbles from a possible reaction taking place. It also slightly reacts with ethanol turning a lighter grey
color, but after 10 minutes, I'm not observing anything else. I'm concerned this substance is possibly arsenic or a compound of arsenic from
remembering a bit of my research.
Due to knowing more now about the local geology and mineralogical composition, I have a reasonable concern of arsenic sulfides being a waste product
from dissolving the igneous rocks. I would like to determine if this substance is as much of a hazard as I'm treating it. I'm open to suggestions of
additional tests I can perform that won't output dangerous gasses or create other additional nasty things to deal with. I'd also like to reduce this
stuff into the most safe form (ideally solid) before adding it into my hazardous waste collection bin.
*Edit
Maybe I'm getting my compounds confused. I'm trying to find information pertaining to the observations I made on the sample of mystery substance I
have.
[Edited on 26-7-2018 by Doped-Al2O3-fusion]
|
|
|
Herr Haber
International Hazard
Posts: 1236
Registered: 29-1-2016
Member Is Offline
Mood: No Mood
|
|
If you're looking for Arsenic a visit to "Place des Gaz" near Verdun should fulfill your needs.
Billions of As or Sb hardened lead shrapnell and gases such as Lewisite left the site with as much as 17% by weight Arsenic.
Or at least, that's what people claim.
|
|
|
clearly_not_atara
International Hazard
Posts: 2787
Registered: 3-11-2013
Member Is Online
Mood: Big
|
|
| Quote: | | The idea of using magnesium sulphate is a good one as far as separating the sulphate and arsenate ions goes but then how do you isolate the free
arsenic acid? |
Oxalic acid would be my first guess: it is about five times as acidic as arsenic acid and magnesium oxalate is highly insoluble. The only concern is
the possible reduction of arsenic acid by oxalic acid.
|
|
|
Boffis
International Hazard
Posts: 1867
Registered: 1-5-2011
Member Is Offline
Mood: No Mood
|
|
clearly_not_atara you have given me an interesting idea!
To me As3+ compounds, specifically As2O3 or an alkali arsenite are the most interesting and useful compounds because they are the starting material
for the preparation of 2-aminophenyl arsonic acid and related compounds which are themselves used to prepare numerous reagents for the detection of
metals (eg Thoron, Arsenazo I and III etc). The problem with the preparation is that the Bart's synthesis section requires sodium arsenite.
As3+ is volatile in hydrochloric acid and this was historically the method of separation and analysis of arsenic in minerals and ores. Arsenates and
As5+ are not volatile so the strong hydrochloric acid solution was reduced with sulphur dioxide. I have tried this and I can tell you that it may work
for milligram amounts but for tens of grams its a bugger of a process even using sodium metabisulphite to generate the SO2 in situ. However, oxalic
acid sounds like a much better idea if it works. If oxalic acid is capable of reducing arsenate in strongly acid solutions you could simply distil the
magnesium arsenate with >6M HCl and oxalic acid. The HCl distillate could them be simply diluted and partially neutralized to precipitate the
sparingly soluble arsenous oxide .... in theory  .
Unless anyone has a better idea.
|
|
|
![[*]](images/xpblue/default_icon.gif){kind=icon}
