Pyrometallurgy: Roasting, Smelting, Refining & Electrowinning

Pyrometallurgy: Roasting, Smelting, Refining & Electrowinning 2017-04-21T02:33:06+00:00
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Remove Lead from Bullion Dore Bar (14 replies)

Subhash-Kumar-Roy
1 year ago

We produce gold and silver bar with Merrill Crowe process. The bar has some lead but we remove this metal with oxy-blower in the refinery. I want to learn, have a different process or idea?

Marshal Meru
1 year ago
Marshal Meru 1 year ago

The Pb can be oxidized and removed in the slag. There will be additional loss of Ag. But the question I have is - Are you adding lead nitrate in the zinc cone? What is the dissolved oxygen in the solution after de-aerating? The Pb in the bullion is because you are adding too much in the solution.

Subhash-Kumar-Roy
1 year ago

We are oxidized in refinery (potassium nitrate), but lead is too much in concentrate. We are not using lead nitrate in zinc cone. D.O is approx. 1-2 ppm in pregnant solution.

Lead, dissolved in leach tanks with cyanide solution and precipitation by metallic zinc in press filter! Do you know another advice?

Marshal Meru
1 year ago
Marshal Meru 1 year ago

The DO concentration is too high. It must be less than 0.5 ppm. My guess is your Zn: (Ag+Au) consumption is above 2. Pb is not very soluble in high pH cyanide solution. But check the quality of the Zn dust you are using.

What is the Pb content of the bullion?

Subhash-Kumar-Roy
1 year ago

We checked the zinc quality but there is no problem (%99 metallic zinc.) Lead is little dissolved in cyanide solution it is true but lead is too much in ore (approx. %20). Bullion lead ratio always changes (%5-%25).

Marshal Meru
1 year ago
Marshal Meru 1 year ago

Interesting the ore contains 20% lead. Why not recover a lead concentrate by flotation and sell this concentrate?

The Kupol silver mine owned by Kinross uses kg/t of lead nitrate in the leaching to improve silver recovery yet has no problem with lead in the bullion. This is first for me. What is the concentration of lead in solution? What is the process used to dissolve the metal? Only cyanide or chloride leach followed by cyanidation?

Subhash-Kumar-Roy
1 year ago

Yesterday I measured again lead in pregnant solution apex. 170 ppm, barren solution is 5 ppm so lead is precipitation in press filter. We think about, install flotation pilot system for concentrated in refinery. Because lead grade is too much and economics!

We are using sodium cyanide in leach tanks for gold and silver.

Marshal Meru
1 year ago
Marshal Meru 1 year ago

First I have heard of this issue. Pb is not soluble at hi pH. The Darwin project in California retreated flotation tailing containing Pb carbonate. They did not have this problem of Pb in the bullion.

The Pb can be oxidized with potassium nitrate and placed in the slag. You will need to assay the precipitate first to calculate the amount of nitre required for the oxidation. The slag should be slightly basic to increase the amount of Pb in the slag. Another possibility is a pre-aeration of the pulp before cyanide addition to precipitate the Pb.

What are the Pb minerals in the ore? You mentioned the grade of Pb in the ore was 20%. AM I correct in this statement?

Subhash-Kumar-Roy
1 year ago

Lead compounds formed are slightly soluble in alkaline cyanide solutions so our ore is soluble in leach tanks. I will consider your recommendations but we are using barren solution all plant so it is going to grinding area and leaching start at mill therefore I do not do pre aeration. Maybe I should calculate again the amount of nitrate in flux but it is very harmful for SIC crucibles.

Marshal Meru
1 year ago
Marshal Meru 1 year ago

You are correct on the effect of nitre on graphite. You have an interesting issue. What is the gold to silver ratio in the ore and solution? What volume of solution are you processing in the M-C? The pre-treatment of the solution using the SART process will precipitate both the Pb and Ag. The filter cake would be sold to a Pb smelter. The gold will pass to the M-C.

What are you using for clarification filters? What is the pH and cyanide concentration in the pregnant solution?

Subhash-Kumar-Roy
1 year ago

Now, solution ratio are, Au: 2 ppm Ag: 70 ppm. We are using perlite for clarifications filters.

Tarun Karakoti
1 year ago
Tarun Karakoti 1 year ago

In oxy blowing or pyro refining will have limitation only electro winning is the solution to get .9999 grades

Hauptsturm
1 year ago
Hauptsturm 1 year ago

An interesting discussion you have created. Lead is usually controlled in cyanide leach by application of a high pH but this in turn requires high cyanide levels. The metallurgist conundrum another optimum!

Using a low grade zinc powder will introduce metallic lead as it is the major contaminant in zinc powder, check your zinc is lead free!

Subhash-Kumar-Roy
1 year ago

We are checking metallic zinc in our laboratory and there is no any problem. And, we have technical spec for all reagents. If the supplies do not apply this spec it is going to penalty. So it should be a carefully to sell.

Hauptsturm
1 year ago
Hauptsturm 1 year ago

Lead is in PLS is unusual as Pb(CN)2 is insoluble, nevertheless you’re not the first in my limited experience.

Again the metallurgist has several options; one is to removal prior to the MC Zinc cementation circuit. If it is colloidal lead, which is possible from a high lead deposit, then you should review the pre MC filtration. If colloidal particles are in the PLS then the investigation should focus on the pre MC filtration technology selection. The filter selection should logically be favouring the high adsorption capability of a media bed filter in preference to a membrane filter unless the project can afford the huge capital of an automated ultra or Nano filtration membrane. The type of media will also be critical, textiles which provide an inert surface in the alkaline pH of PLS would be favoured over sand material which takes on a negative surface potential at that pH. Not to mention that textile media filters are much cheaper than sand filters with their significantly smaller footprint.

If the plant has good pre filtration, thus the lead is truly in dissolved form in the PLS then perhaps a coagulant can be added to precipitate the lead with capture at the pre MC filter.

An alternative is to run with high free cyanide to form the soluble tetracyanoplumbate complex. Now there is a big word! It will then pass through the filter as it is highly soluble, whereas Lead (II) Cyanide is insoluble. Difficulty may then be encountered with high cyanide leaching more lead from the ore or higher cyanide requiring higher hydroxide for safety which in-turns causes lead hydroxide precipitation.

Maybe for an ore body of 20% Lead, there is scope to review the leaching of the lead and precipitation recovery of a value lead chemical product. 2% lead could be profitable if the project has sufficient scale. Turn a problem into a profit, sounds good.

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