# Roasting and Incinerating



## Macleight (Jan 7, 2015)

Hello,

I have read many posts referring to 'roasting' and 'incinerating' and I am curious as to what the difference is and what exactly they mean. I haven't really found the answers using the search bar. If anyone could point me in the right direction, I would appreciate it.

Basically, as I understand it, 'roasting' is heating PMs after they have been separated from the majority of the base metals. The goal is to further oxidize base metals to make them more soluble, or more susceptible to acid treatment. Heating is not done to the melting point of the PM's involved, rather just a gentle heat treatment, whether it be to buttons, flakes, or powders.

Incinerating, on the other hand, is done at the beginning of recovery, mostly to eliminate carbon, but any other halogens that decide to liberate are welcome to leave as well. Incineration can also be used at any time in any recovery process to 'undo' mistakes and essentially return to square one. This may melt many things, be they base metals or PMs.

The biggest issue with both incinerating and roasting is that any heating of recovered metals comes with the risk of volatilizing them and losing them to either gas, sticking to the incineration vessel or becoming trapped in an alloy with other metals.

Do I have it?

Second, where shall I look to read up the actual ways these two things are accomplished?

Thank you!


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## butcher (Jan 7, 2015)

Macleight,

I may be wrong, but to me there is not much difference between roasting and incineration.

The both heat the crushed materials red hot, and expose them to air or oxygen to form oxides of metals many of which will oxidize easier at these high temperatures, they both will burn off the anion salts as volatile gases (examples like carbonates, chlorides, sulfates, nitrates ...), they both will burn off organic materials.

Roasting is a term you will normally see more often when discussing ore, and incineration when burning other materials.

With ore sometimes they use the term roast, when they are actually talking about what I would call a fusion, like a roast with a salt like chlorides to make the gold dissolve easier in a later chloride leach. Other times they use the term roast, to describe more of an incineration to oxidize base metals and burn of the unwanted material's...

I am not that great with words, and sometimes I may use these words kind of interchangeably. which may not be correct, I do not know.

Maybe someone better with words can give us a better definitions of these.

we roast the pig, we incinerate the trash :lol: 
They both see the fire and burn of the unwanted material and put them both in a state we desire more.


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## g_axelsson (Jan 7, 2015)

I've only heard the term roasting together with ores while incinerating usually applies to scrap or other materials with carbon containing materials or gold containing material to drive off acids.

Roasting ores is done to turn sulfides, arsenides, tellurides... into oxides while driving off the problematic elements as a gas(As, S, Te, ...) It also liberates gold from the mineral grains it is embedded in so it will be possible to leach with various solutions. This was usually an initial step in ore processing because then the oxides could be reduced with carbon to give the base metals.

In refining, incineration is a similar process but in this case we usually want to reduce the amount of material and remove carbon containing material as that is a problem in the refining of precious metals. Carbon does absorb gold chloride and various organic residues can mess things up if we try to process it without incineration.
Incineration is basically burning the material with enough heat and oxygen to remove any carbon in the material. The temperature needed to remove the carbon also removes any chlorides and nitrates in the material and that is also beneficial for the refining as it makes it possible to switch acid without dissolving gold.

... but this is of course only my view on the topic and I wrote it before seeing Butcher's response. It looks like we more or less agrees on the meaning of the words. 8) 

Here are the wikipedia articles on roasting and incineration.

We also have calcining or calcination when we heat carbonatic ores to thermal break down without adding any air. More on wikipedia here.

Göran

Edit : spelling


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## Macleight (Jan 7, 2015)

Thanks!


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## Macleight (Jan 8, 2015)

The pictures of the old roast yards are pretty cool!


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## Macleight (Jan 8, 2015)

At my work we have a few TGA's. Almost all TGA is based on heating samples in a nitrogen atmosphere and recording the mass loss as compounds evaporate without burning. Does this still fall under the definition of 'calcining' or 'calcination?" The first part of the wiki entry says 'thermal treatment in the absence of oxygen.' It brings up ores, but then says 'other solid materials.'

Formally, the question is, "Is any heating in the absence of oxygen calcination?"


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## g_axelsson (Jan 8, 2015)

Macleight said:


> At my work we have a few TGA's. Almost all TGA is based on heating samples in a nitrogen atmosphere and recording the mass loss as compounds evaporate without burning. Does this still fall under the definition of 'calcining' or 'calcination?" The first part of the wiki entry says 'thermal treatment in the absence of oxygen.' It brings up ores, but then says 'other solid materials.'
> 
> Formally, the question is, "Is any heating in the absence of oxygen calcination?"


I would say no. You can heat an object without any reaction and that wouldn't be calcination. The term calcining is mainly used in chemistry and ore processing and I'm not an expert in either area so it might be wrong what I'm writing.
Following the wikipedia definition " is a thermal treatment process in absence of air or oxygen applied to ores and other solid materials to bring about a thermal decomposition, phase transition, or removal of a volatile fraction." but one of the articles references to IUPAC has the definition "Heating to high temperatures in air or oxygen." which in mining would be roasting. Apparently the term could be used in a little different ways depending on which area it is used in.
Calcining is an old term that meant "Reducing to ashes or it's earth (Calx)" and was used for processes where strong heat decomposed materials, for example lime stone into calcium oxide. This was in a time before modern chemistry and when people thought that everything was made up of earth, water, air and fire.

We also have the term pyrolyzing for heating organic matter until breakdown. Sometimes used before incineration to minimize loss of fine particles that could otherwise go up as dust in the chimney. For a while people were using pyrolyzing when speaking about incineration on the forum. I took it as a personal quest to correct any improper usage and today it is hardly seen used in the wrong context.

When you speak of TGA I assume you are talking about Thermogravimetric analysis.
I might have been using one for a lab back in school, but I have no working knowledge of the system but I understand the principle behind the instrument. It can do so much more than only heating. For example it can be used it to study gas-solid reactions and oxidation / reduction of metals.

Personally I use the term calcining for treating industrial ores with high heat or for reducing PGM salts into their metals, roasting when breaking down sulfide ores and incinerate and pyrolyze for non ore materials.

Göran


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## rickbb (Jan 8, 2015)

It was my understanding that roasting and incineration are done at different temperatures, at least as it applies to recovering PM's from electronic scrap. 

Roasting being at lower temperatures, (red hot), to remove organics and oxidize the materials. 

Incineration done at higher, (yellow/white hot, but not high enough to melt the metals), to burn any plastics as you would find in computer chips to ash so as to make them easier to break up and release the PM's to be able to leach them.


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## mls26cwru (Jan 8, 2015)

The terms you mention are used so interchangably, that most people would not say there is a difference. But the method in which you heat something will give you different results.

Combustion is the heating of a material with the presance of oxygen unually involving a reaction with fuel of some sort.

pyrolysis is the heating of material in the absensce of oxygen.

the classic example of the differences is burning wood. burn it with oxygen and you get a pile of ash when you are done. burn it without, and you get charcoal.

M


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## goldsilverpro (Jan 8, 2015)

The about 8'x8'x8' gas incinerator we used to burn film enzyme/silver sludge in stacked steel trays ran about 900F-1000F, if memory serves. We had a big afterburner and the system was tested and approved. Red-hot is about 1200F - cigarette tip temp. I've burned both circuit boards and film sludge and, believe me, the smoke off of film sludge is just as nasty or nastier than the smoke off boards. The board material burning might be more self-sustaining, although I think I remember that they contain flame retardants such arsenic (older) or antimony.

Another example of when I used 900F-1000F was in the incineration of gold-bearing resin. Talk about nasty smoke!

Looking at online definitions, I would say that the term "roasting" should be used when the purpose is to oxidize ore by exposing a lot of surface to the air. "Incineration" is usually used when oxidizing carbonaceous material to ash by exposing it to air above the ignition point. It means to burn completely.


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## g_axelsson (Jan 8, 2015)

I don't agree that the terms are used without any difference. I can't remember ever seen in a mining text that the ore were incinerated.
In the same way I've never seen anyone saying that the floor boards of the jewellery shop were roasted to get the gold.

It can be quite an overlap between the two terms but they applies to two different areas as I wrote above.

Göran

Edit : Just wanted to clarify that my response was to mls26cwru. I never saw that GSP managed to get a post in between.


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## Platdigger (Jan 8, 2015)

I like GSP's definitions.
Only thing I would add is when roasting the purpose may not be just to oxidize the ore although this is happening, it may be to also drive off volatiles, as in the case of sulfide ores, sulfur.
mls26cwru got it right that when heating in the absence of oxygen this is pyrolysis.


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## Macleight (Jan 9, 2015)

g_axelsson said:


> We also have the term pyrolyzing for heating organic matter until breakdown. Sometimes used before incineration to minimize loss of fine particles that could otherwise go up as dust in the chimney. For a while people were using pyrolyzing when speaking about incineration on the forum. I took it as a personal quest to correct any improper usage and today it is hardly seen used in the wrong context.



I think I understand this difference. The best example would be with a polymer. Pyrolysis of a polymer results in oil, incineration of a polymer results in smoke. Usually toxic smoke.



g_axelsson said:


> When you speak of TGA I assume you are talking about Thermogravimetric analysis.



Yes.



g_axelsson said:


> Personally I use the term calcining for treating industrial ores with high heat or for reducing PGM salts into their metals.



Is this the same thing? I understand calcining = treating industrial ores (sort of. I've never actually seen a smelting plant). Reducing PGMs is both the same (heating a group of things with one group of things) but also not (heating some metals that have been separated from other metals but that also may contain PGMs)?


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## solar_plasma (Jan 10, 2015)

Sorry,but to me it sounds, as if one would say welding, soldering and cooking is the same, because one always applies heat. Just as Göran already pointed out. There is a reason to call one process roasting, the other pyrolyzing, incineration, calcining, smelting, melting, distilling, sublimating, reduction, oxidation, even if all of them can include the application of heat.

Even I know, that I only know some few aspects and application of those and much less, than any professional metallurg already has forgotten. I can't see the benefit in discussing terms that can be read in books and wikis with only a few clicks to understand the difference. On the other side it is my impression that you can read metallurgical books for years and still find new aspects and applications.

Sorry for mistakes in spelling, I have to find out, why my spell check add-on has stopped working.


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## g_axelsson (Jan 10, 2015)

Macleight said:


> g_axelsson said:
> 
> 
> > Personally I use the term calcining for treating industrial ores with high heat or for reducing PGM salts into their metals.
> ...


Calcining is not smelting.

Calcining of industrial minerals includes :
* Heating lime stone until breakdown, carbon dioxide goes off as gas, calcium oxide remains.
* Heating clays to drive off water locked in the crystal structure of the clay molecules. Water goes off as gas, anhydrous clay remains.
Calcining of PGM:s
* When refining platinum and other PGM:s we end up with a pure salt of the metal. By heating it will break down and the non-metal part goes off as gas while the pure metal remains.
* Search the forum for more examples

Smelting is to extract metals from metallic ores by high temperature chemical reactions:
* Mix iron oxide ore with carbon and heat, the carbon reacts with the oxygen from the oxide, leaving iron in the melt.
* Mix copper oxide with carbon and heat, the carbon reacts with the oxygen from the oxide, leaving raw copper in the melt.

I don' think discussing terms that can be looked up on wikipedia is wrong. When we have reached a common understanding of what the terms means then we can raise the discussion to a new level as we are standing on a common ground. As an example are several older threads on this forum where people used incineration and pyrolyzing interchangeable. There were some confusion in those threads as people tried to follow procedure but arrived on different results. Just as spelling is important in chemistry, to use the correct terms are also important.



solar_plasma said:


> Sorry,but to me it sounds, as if one would say welding, soldering and cooking is the same, because one always applies heat. Just as Göran already pointed out. There is a reason to call one process roasting, the other pyrolyzing, incineration, calcining, smelting, melting, distilling, sublimating, reduction, oxidation, even if all of them can include the application of heat.


I like that example! 8) 

Göran


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## Geo (Jan 10, 2015)

The name of the process is relative to the material you are working with. You wouldn't incinerate ore and you wouldn't roast electronics.


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## Macleight (Jan 10, 2015)

All these responses make great sense! Thanks!


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## saadat68 (Jan 19, 2019)

Hi
I try to find a exact definition for incineration process in my language 
(Incinerate definition is - to cause to burn to ashes)

We Incinerate chips or other materials to produce ashes. This is an incineration process and here I have a synonym for that. But when we Incinerate powders to convert chlorides and nitrates to oxides, I can not use incineration word in my language. It means incinerate powders to produce ashes!!! 

So I decide use incineration, When I want to convert materials to ashes and use roasting or calcination, When I want to convert just chlorides and nitrates to oxides 
And I think calcination is better choice because sounds like Roasting is for sulfide materials.
What do you think? Is incineration process, a type of calcination?


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## g_axelsson (Jan 20, 2019)

That's an interesting question and the answer is more or less depending on which business you are working in, according to my research in this topic.

- The mining industry is talking about roasting when concerning ores and calcining when you have non-metallic minerals as burning limestone to make cement.

- A chemist would call it calcining when doing it in the lab. For a chemist the term calcining includes what a miner would call roasting. IUPAC have a definition of calcining but no definition for roasting, so roasting is not a term used in pure chemistry (any longer). Older texts might use roasting while talking about calcining.

- A refiner talks about incineration, mostly for burning trash and get rid of carbon residues. Lazily we also use that term for what we do when switching acids, in my opinion it is closer to calcining when we heat something to a dull red to break down nitrates and chlorides to remove them from a batch of material. When a refiner is talking calcining then it's often about breaking down PGM salts into metal and volatile substances, sometimes also called ignition if my memory doesn't fail me.

http://goldrefiningwiki.com/mediawiki/index.php/Incineration
http://goldrefiningwiki.com/mediawiki/index.php/Calcining

Göran


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