Cadmium - Proper disposal

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snoman701

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Oct 8, 2016
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Can anyone help here.

Many silver products are alloyed with cadmium for a variety of reasons. For a simple nitric acid digestion, once you drop the base metals with iron, you've got hazardous waste.

I think I've read the forum forward and backwards on any post that has "cadmium" in it.

While you can create cadmium hydroxide by coagulating with a lime slurry, this isn't the easiest process for a small volume...and frankly, jury is still out as to whether it is acceptable.

On edit, base metal hydroxides are all hazardous waste.

Is there any way of treating this copper/cadmium/etc sludge that will make it legal to dispose of in an easy manor?

If not, what is the proper method of disposal?
 
goldsilverpro said:
Cadmium hydroxide and the hydroxides of nickel, copper, etc., are considered hazardous wastes.
Thank you, that's what I thought.

Regardless, I am still looking for a method of disposal that is legal...even if that makes it necessary to do it through proper channels.

To my knowledge, this has not been covered on the forum, and seeing as I know there are people that are refining silver from contacts, there are people that are producing hazardous waste, so is this an elephant that should at least be talked about?

So, this is handled in one of a couple of ways.

Treating the cadmium so that it is no longer hazardous...OR...disposing of it in a responsible ethical manor.

If I simply call up "Hazardous waste r us" and say "I need to dispose of 50 lbs of copper/cadmium powder". What kind of hornest nest am I kicking?
 
The reason the metals you have in your waste are considered hazardous is because they are some of the 8 metals defined by the EPA as RCRA metals under the Resource Conservation Recovery Act. The way these metals are tested is by a test called the TCLP, which means Toxic Characteristic Leaching Procedure.

There are many other reasons a waste can be considered hazardous but for the general wastes resulting from waste treatment sludges generated from acid refining the RCRA 8 metals are what applies.

The way these metals are tested is the sludge, solids or chunks of material you need tested are pulverized and exposed to a leach which is supposed to simulate the long term effect acid rain will have on these metals if they are in an unprotected landfill. A buffered acetic acid leach is used to extract the metals for analysis and the exposure time to the leach is 18 hours.

The metals, or the RCRA 8 are; Arsenic, Barium, Cadmium, Chromium, Lead, Mercury, Selenium and Silver.

So any reduction of these metals from the salt form they are in as hydroxides to a metallic form put them in a form that is more likely to remain insoluble in the TCLP leach. But it is not guaranteed based on things like particle size and shape and the chemistry of the leach. So what larger shops do is chelate the metals into a form that will not leach. There are many chemical compounds used in the precipitation process to chelate these metals.

What is normally done is the waste you have treated with your process is sent to a lab for TCLP testing and if it passes the limits it is deemed non hazardous. Disposing of a non-hazardous waste is much less costly than disposing of a hazardous waste obviously.

The EPA limits for each of the RCRA8 metals are;
Arsenic 5ppm
Barium 100 ppm
Cadmium 1ppm
Chromium 5ppm
Lead 5ppm
Mercury 0.2ppm
Selenium 5ppm
Silver 5ppm

This applies to solid wastes, liquid wastes may contain other metals in solution which are also governed by Local, federal and state regulations. This covers metals like copper zinc and many others.

It gets rather complicated for a lot of reasons but mostly because government is involved!
 
4metals said:
The metals, or the RCRA 8 are; Arsenic, Barium, Cadmium, Chromium, Lead, Mercury, Selenium and Silver.

I understand why the rest of these are on here, except for silver.

The only possibilities I could think of is that silver kills bacteria, or fulminating silver.
 
Silver in solution will sterilize any bacteria so it is not so good for natural ecosystems systems as it inhibits bacterial growth. It is not toxic to humans. Seems a weak reason to make the RCRA 8 list!
 
4metals said:
Silver in solution will sterilize any bacteria so it is not so good for natural ecosystems systems as it inhibits bacterial growth. It is not toxic to humans. Seems a weak reason to make the RCRA 8 list!

I was thinking about it more in the long run (cycle of life). If it's not so good for natural ecosystems, eventually bugs, plants, animals, people.

Mainly the certain types for the breakdown of lignins, growth of algae etc.
 
Silver in the ecosystem kills the things that fish eat, which kills the fish, etc. Just because it doesn't kill humans directly doesn't mean it's ok, we are part of the great circle of life.
 
Silver is also toxic to the biological filtering in waste treatment plants.
http://www.iwapublishing.com/books/9781843393993/impact-silver-nanoparticles-wastewater-treatment
One of the most sensitive organisms is algae. 7.6 ug (micro gram) of silver salt per liter water kills half of the algae according to a study. That means 7.6 g of dissolved silver is enough to poison 1000 cubic meters of water.
Silver chloride is soluble enough to be poisonous to algae.

Crustaceans is even more sensitive, with just 0.85 ug / liter for 50% lethal dose.
http://www.who.int/water_sanitation_health/dwq/chemicals/Silver_water_disinfection_toxicity_2014V2.pdf
That is the main reason that silver is classified as "very toxic to aquatic organisms" in the EU, and I believe that is the reason it is in the EPA RCRA8 group.

Göran
 
A couple years ago (maybe even 3 years ago) I got to a point I was creating enough waste I decided to send it out for disposal rather then treat it my self for disposal - one of my (local) chem suppliers also handles chemical waste products

When talking to the Chem supplier about them handling my waste I learned a couple things

One was the cost of handling based on the pH --- if the pH is to high or to low the cost is significantly higher

High or low pH waste cost about $1,200 per 55 gallon drum to ship due to EPA hazmat regulation

If the pH is adjusted to a neutral range (pH between 6 - 8 ) the cost to ship drops to about $150 per 55 gallon drum

Also - labeling makes a difference - & because of how long ago it was I don't remember the exact details/explanation (I was more interested in cost) so hopefully 4metals, Lou, or GSP will correct &/or better detail the following

I was told - because my business is metal recycling/recovery DO NOT label the metal containing solutions as WASTE - they are not considered waste "until" you label it as waste --- rather - it is a chemical metal solution "product" (or by product) so label it as the "product" it is

Examples; - say you used zinc to cement PGMs from AR - don't label it zinc "waste" or zinc chloride "waste" --- simply label it zinc chloride (or ZnCl)

Solder dissolved in HCl - don't label it tin chloride "waste" (or solder waste) --- label it tin chloride (or SnCl)

Because its solder which is generally an alloy of metals it should actually be labeled - tin chloride & other metals NOS (Not Otherwise Specified)

In other words if alloys have been dissolve & often no real way to know all the metals in the alloy the labeling should list the "primary" metal as well as indicate other metals present - just not known (NOS)

Example; - brass/bronze is primarily copper with a "wide" variety of other metals used for the alloys making it impossible to really know what all other metals are in solution so - waste from pins to recover foils should be labeled - copper nitrate & other metals NOS - or copper chloride & other metals NOS - depending on method used to dissolve the brass/bronze

If you adjust the pH to the neutral range which of course forms the hydroxides or carbonates of metals (depending on if you use a hydroxide or carbonate to adjust the pH) then you label it as a hydroxide or carbonate of the metal(s)

If its a completely unknown "soap" of metals (in solution) dumped together from many different processes - then it should simply be labeled as - acidic NOS metals (if you don't adjust the pH) or if you adjust the pH then labeled as - NOS metal hydroxides or NOS metal carbonates (depending on which you used to adjust the pH)

This is (as I understand it) not just important for shipping & handling of waste - it is also important (even MORE important) for storage

(again - if I understand right) when you label something as "waste" --- rather then identify it as a product (or by product) it changes the EPA/hazmat rules/laws that apply to the shipping/handling/storage &/or permitting for what you have

Example (as I understand it) if the EPA/fire department/DNR (or other authority) comes snooping around & sees a bunch of jugs/buckets labeled "waste" it won't go well for you because the regulations for "waste" are more stringent then the regulation for a product (or by product) from which ether you intend to recover from - or intend to send out for recovery

So - at least what I was told - is DO NOT label metal containing solutions as WASTE --- label them as a product according to there chemical composition intended for recovery of the metals in them

Kurt
 
i personally think that dropping the cadmium waste with sodium thiosulfate or even dithionite is the way to go. since waste disposal is charged by volume, the CdS is extremely insoluble in water the Kps is 8.0 x 10-27 which is even less soluble than elemental cadmium. the rest of the solution is for all intensive purposes, safe to put into the drain assuming that there's no other metals present. the CdS can be filtered off, bagged, and sent to a waste facility cheaply and safely
 
One was the cost of handling based on the pH --- if the pH is to high or to low the cost is significantly higher

This goes back to the different classifications the EPA has for waste. They call them characteristic wastes and the types of characteristic wastes are Ignitability, Corrosivity, Reactivity, and Toxicity. The waste which has a pH less than or equal to 2 or greater than or equal to 12.5 are both considered corrosive. And these are described as D002 type wastes.

Wastes are complicated and whe variations subtle for different industries. AND you, THE GENERATOR are responsible to label the waste correctly. This involves testing. As I mentioned earlier with the TCLP testing and others. The US has a phrase describing its waste handling methods, it's called Cradle to grave. That means for a manifested waste from any business, the waste is picked up and you have a manifest to state what the waste is. You can put down all of the proper codes, define the toxic metals you know to exist above limits and call the rest NOS as Kurt has suggested. And a waste hauler usually will accept your descriptions. And that drum will be traceable back to you from beyond the grave. So you better have labeled it correctly.

But here's the rub. A few years down the line the material you defined as non hazardous waste with all of the right codes but no analytical report to back it up will come back to your business if for example the drum corrodes away and spills the contents. That drum is always traceable to you if it was removed legally on a manifest.

I deal with lots of refiners, they all precipitate the metals out of solution using liquid caustic to form metal hydroxides and most add a compound called CPX which is a proprietary product sold by a company in Florida called ETUS. The sludges are de-watered and annually sampled by TCLP testing and removed as non hazardous waste if they pass the TCLP criterion. Dosing properly with CPX is effective in enough chelation to pass TCLP testing.

Believe it or not, cementation with copper for PM's followed by iron will drop all of the metals in a typical refining process, and a hydroxide chelated for good measure will produce an iron hydroxide which will Pass TCLP testing limits for the RCRA 8 metals from an aqua regia refining operation. A lot of refiners melt this stuff into bars and it is sold as scrap, non hazardous, no manifests, just metal bars. And the iron comes out at a low pH as a gelatinous solid which can be dried as it is just iron and not a hazard.

Just because you are targeting cadmium, as in this thread, do not assume the other metals in the waste stream will not bite you as far as the environmental regs go. You cannot solve the issue for one target metal without affecting everything else in the solution.
 
So what your saying is, don't over think it. And just stick with the 2 step treatment?

Copper, then to iron,then to NaOH. Then separate and dry the oxides/hydroxides and dispose of the salt water.

Thats fantastic news... This thread was really starting to make me go "oh god what have I gotten myself into"...
 
4metals said:
I deal with lots of refiners, they all precipitate the metals out of solution using liquid caustic to form metal hydroxides and most add a compound called CPX which is a proprietary product sold by a company in Florida called ETUS. The sludges are de-watered and annually sampled by TCLP testing and removed as non hazardous waste if they pass the TCLP criterion. Dosing properly with CPX is effective in enough chelation to pass TCLP testing.

Precipitate the PM's, or the copper following cementation?

4metals said:
Believe it or not, cementation with copper for PM's followed by iron will drop all of the metals in a typical refining process, and a hydroxide chelated for good measure will produce an iron hydroxide which will Pass TCLP testing limits for the RCRA 8 metals from an aqua regia refining operation.

So drop the copper, treat the iron nitrate with sodium hydroxide to precipitate iron hydroxide. The whole mass of precipitate is then treated with the CPX??


4metals said:
A lot of refiners melt this stuff into bars and it is sold as scrap, non hazardous, no manifests, just metal bars. And the iron comes out at a low pH as a gelatinous solid which can be dried as it is just iron and not a hazard.
Can't say I understand this at all. They melt the copper/iron/cadmium/etc mix together?
 
The copper would cement everything below it in the reactivity series.

Next step (after decanting from the pm solids) the solution would have iron drop everything except aluminum, zinc, magnesium, calcium, sodium, potassium.

After decanting from the solids, the solution then has the ph increased for the metal hydroxides to precipitate out of solution, to be decanted again.

Then the ph would be adjusted to neutral and it would be salt water
 
Topher_osAUrus said:
The copper would cement everything below it in the reactivity series.

Next step (after decanting from the pm solids) the solution would have iron drop everything except aluminum, zinc, magnesium, calcium, sodium, potassium.

After decanting from the solids, the solution then has the ph increased for the metal hydroxides to precipitate out of solution, to be decanted again.

Then the ph would be adjusted to neutral and it would be salt water

I get all of this, it's the "now what do I do with my copper/cadmium/tin/lead/etc mixture".

Legally, it has to be tested to ensure it passes TCLP limits. If it passes TCLP, then it's not hazardous waste, and simply waste.

But he also said that a lot of refiners just melt it all.
Bringing that mixture up to a temperature that is hot enough to melt copper is going to fume off cadmium, which doesn't seem like something that one really wants to do...am I wrong in my understanding?

That was one of my original considerations, is actually dropping the copper with lead, then the lead/cadmium with iron. Lead/cadmium forms a eutectic alloy that melts pretty low.

I have a healthy respect for cadmium. And I'm interested in the appropriate legal channels. But that's not to say that there aren't responsible methods of disposal that may not be entirely legal. Working in a residential neighborhood, I can't really register as a hazardous waste producer...or at least, I don't care to. And I think most hobbiests are in the same boat.
 
The biggest problem with metal "waste" is when it's in a soluble form. That's when it can easily contaminant a water supply, (and us).

If you have dropped it out of solution and back to a solid form your legal options are greatly expanded.

As another poster suggested I would not call it waste, but a product or by-product for recovery. Then see if you can find a metals refiner that would take this recovery product from you either to refine or dispose of for you.
 
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