Pyrometallurgy: Roasting, Smelting, Refining & Electrowinning

Pyrometallurgy: Roasting, Smelting, Refining & Electrowinning 2017-03-23T09:55:18+00:00
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Fine Carbon Coagulant – Molten Dore Temperature (15 replies)

Raje Singh
1 year ago
Raje Singh 1 year ago

What is a good coagulant for carbon fines? What is the best way to measure the temperature of a molten Dore bar in a furnace? Good software for determining angularity/roundness of carbon?

Currently, we have a de-watering screen "for the stripped carbon" after the elution column which separates the coarse and fine carbon. The fine carbon is transported to carbon fines tank (We have another sizing screen after the regeneration circuit which also separates coarse/fine carbon). However, the carbon fines are not settling in the tank with our current method and are overflowing into tailings. So what is a good coagulant that can help settle the carbon fines?

We currently know the time the Dore bar is ready to be poured by visual inspection. I am trying to look for a way to control and measure the temperature of the molten metal in the furnace to be accurate. I've looked into thermocouples; however, I believe the thermocouple will fracture if is removed from the crucible while still hot (Will not handle fast temperature reduction). In addition, slag penetration will also fracture the thermocouple. I was looking into a way where the thermocouple can be inserted between the lid and the furnace, so we don't have to take it out when we open the lid and pour the charge (The thermocouple along with the cable can also be protected by a sheet, so the thermocouple does not fracture and the cable does not melt), but I am not sure about this method.

So what are some of the best practices to actually measure and control the temperature of the molten metal in the furnace?

I am doing carbon sieve analysis and I want to determine angularity, sphericity, and roundness of the carbon I am using by taking an image and uploading it to software. I came across ImageJ, Fiji, and JMicrovision software but I have not used them before. Is anyone familiar with good software? 

Dizzy Flores
1 year ago
Dizzy Flores 1 year ago

A hand held disappearing filament thermometer can be used, but after a while you'll be able to recognise the temperature without an aid. The main thing is to leave the gold until the slag reactions are complete, and all bubbling in the melt is completed.

Using a green face mask also makes it much easier to differentiate the gold from the slag. If your current practice is to use only clear shields then I'd really suggest getting a green one.

John Koenig
1 year ago
John Koenig 1 year ago

In many plants those carbon fines are pumped through a small plate and frame filter press. The fines are then collected and burnt. If you did want to settle an anionic floc (lab tests recommended) would probably do the trick.

Raje Singh
1 year ago
Raje Singh 1 year ago

Thank you for your input.
Yes; currently we recognize when the gold is ready to be poured by visual inspection using a green face mask.

What we want to accomplish is to measure the temperature of just the molten metal at the bottom of the crucible, so we want to be able to insert some kind of equipment in the crucible to measure the temperature below the slag (Slag has different temperature than the molten metal at the bottom); I believe a hand held disappearing filament thermometer will be able to only measure the temperature of the furnace and not the molten metal at the bottom of the crucible.

I am familiar with the filter press and the carbon ashing, but I am trying to find some chemical to settle the fine carbon without using filter press "Unavailable" (I'll be doing lab tests too). We currently use aluminum salt but it is not efficient enough.

I am going to search for an efficient anionic floc like you suggested. Thank you. (If you have the name of a specific chemical, that would be great)

OberstGruppen
1 year ago
OberstGruppen 1 year ago

Diatomaceous earth (DE) filtration is extremely effective at collecting even the smallest particles of the carbon fines. The solution post filtration will sparkle.

Amar
1 year ago
Amar 1 year ago

He's on the right track for your first query try a high MW anionic polymer such as Ciba's Magnafloc 155 or Ashland Chemicals DrewFloc DF2490;

For your 2nd query, investigate Vulcan’s site for >T melt thermocouples http://is.gd/OfQEm4 Am curious about your 3rd query attrition tests (w/silica sand) determine the degree of fines loss from virgin C prior to introduction into the downstream circuit; why are you attempting to determine the shape characteristics of the C assuming that the primary purpose is for CIC/CIL or CIP adsorption? Are you wet or dry screening virgin C?

Victor Bergman
1 year ago
Victor Bergman 1 year ago

Try Ferric sulphate as coagulant combine with flocculants at right dosage will provide good settling of your carbon fines.

Raje Singh
1 year ago
Raje Singh 1 year ago

Magnafloc seems like a very good flocculant. http://is.gd/TNtau0

And I believe Vulcan have what I need. I am going to call them soon to see if they have a thermocouple for my application (Measuring the temperature of the molten metal below the slag) without getting fractured if it was removed suddenly from the furnace (some thermocouples cannot handle the shock of temperature reduction)

We are actually doing attrition tests using a specialized test plant that simulates the movement in the CIP tanks, with about 40% fluidization. I am wet screening the virgin C, then put the C in the test plant with water, and then at each interval I am wet screening the C again to determine the fines loss at each sieve size.

I want to determine the shape characteristic for research purposes, to see the effect of angularity and roundness on attrition.

OberstGruppen
1 year ago
OberstGruppen 1 year ago

Perhaps the better question is "what is wrong with your carbon and/or agitation system to have so much carbon fines in the first place"? One of the plants I was hired to restore to profitability had a similar problem. Discovering the causes and solving the interrelated problems resulted in an increase of more than 20% in gold recovery.

Raje Singh
1 year ago
Raje Singh 1 year ago

I believe you're right. Ferric sulfate seems like a good coagulant. I'll be doing some test work with it and combine it with different dosage of flocculants and measure the turbidity of each.

OberstGruppen
1 year ago
OberstGruppen 1 year ago

Don't be surprised to see Prussian blue generated when you add ferric or ferrous salts to cyanide solutions. This is a common method of destroying waste cyanide.

Ace Levy
1 year ago
Ace Levy 1 year ago

We do not actually have much gold losses "carbon fines losses", but we're trying to capture as much carbon fines as we can since the fines probably have high activity. Producing carbon fines in the circuit is inevitable because of the attrition that happens between the carbon in the CIP tanks and during the transfer as well.

By the way, we did some test work on Diatomaceous earth (DE) filtration; it works alright but I am trying to find a solution for the fines without needing to install a pressure filtration unit. And yes you're right about the ferric sulfate.

OberstGruppen
1 year ago
OberstGruppen 1 year ago

That is good, but surprising; to hear you are not suffering from carbon fines losses. Due to the extremely large surface area of carbon fines, they are tenacious absorbers of precious values and must be kept to an absolute minimum. They also increase pulp viscosity and as a consequence, decrease agitation efficiency.

Kumar Choudhry
1 year ago
Kumar Choudhry 1 year ago

We had the same problem with our fines in the carbon fine tank; it was overflowing into our tailings sump pump. So determine the right dosages you can also use lime and the fines will settle at the bottom.

Raje Singh
1 year ago
Raje Singh 1 year ago

Yes, you're absolutely right. Carbon fines have high activity and this is why we're trying to capture as much as possible, more than what we're capturing now. Currently we have many screens in the carbon regeneration circuit that separate the coarse and fine carbon. The fine carbon goes into carbon fines tank where aluminum salt is added to the process to act as a coagulant, but it is not efficient enough; some but not much carbon fines are overflowing into tailings.

I will do some test on lime in the lab. Water chemistry plays an important role on the effect of any coagulant/flocculant on carbon fines. So what works for your process, might not work for us. But I will definitely try it.

Dizzy Flores
1 year ago
Dizzy Flores 1 year ago

Suggest you try removing water faster such as a plate and frame press or vacuum rather than putting too much cost into flocculants and other devices. OK you will need to do some testing to find the right cloth, but just a water drain through a sock filter may be adequate, if you have sufficient head.

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