Further things which may be of interest to members

mahalas · Mar 2, 2016

Deano
Thanks for the answer. I know that fire assay gives me the total amount of gold, but with table combination it gave me also gold distribution. Because of that I collect slime for separate leaching ( close to 30 % of total gold ).

The poorest part are middlings , mostly quartz 1 - 1.5 ppm Au. Tabling is fine but is rather a slow process, especially on
M - 7. Next week I am going to get a small continuous ball mill. Plan to use it like tromel to separate slime, regrind the rest and -following your advice - leach everything .

Looks like carbon striping would require additional investment in equipment. I think I should stick to zincing.
What about pretreatment in a leaching tank ? Something like aeration 24 hours or addition of soluble salt of lead ?

Cheers Adam

Deano · Mar 3, 2016

Fire assay gives you gold distribution but it does not give you leach available gold distribution.

You can only get this with aqua regia / cyanide leaches.

If you have a ball mill and are planning to leach the total feed you only want to mill the tailings to the size which size testing says will get you the best cyanide recovery.

It really is nice to know what size you should be milling to before you start milling.

Doing pre-sizing etc in the mill circuit may seem a good idea but you get no advantage over just milling the unsized feed in total.

The final mill discharge is placed straight into a settling dam or series of dams. When the dam is full and the free water has been removed from the surface the material is ready to be machine mixed with a backhoe or excavator before being placed into the leaching vat.

Because the vat leach will have several cycles of wetting and drying there is occurring a lot of surface oxidation reactions on the surface of the ore grains.

In most cases this means that pretreatment is either not required or is an expensive waste of time for little gain.

Deano

mahalas · Mar 3, 2016

Deano
I am sorry but I mixed something up. ( English is not my first language ) If I am correct vat leaching for you means something like percolation closer to heap leaching. I try to focus on tank leaching with stirrer . It gives me more possibilities to control the process.

My first attempt with percolation ( 30 kg conc in the bucket ) showed me 33 ppm total gold left in tailing after leaching.
I assume that was because conc was to coarse. Now I am in the process of doing second try with finer batch.

My goal is to recover 90% and up of total gold, not only what is available for leaching. I am not sure if it is possible with my tailings, but at least I am going to try.

I am afraid that very fine grinding will clog percolation circuit that is why I prefer the tank with stirrer.
During leaching my ORP shows around - 50 mV , is it OK ? Does it make sense to measure ORP during leaching with cyanide?

Cheers Adam

Deano · Mar 4, 2016

If you run the vat as detailed in my earlier post you will not have any clogging of the tailings in the vat, this method I consider important enough to be available to all users.

The advantages of this method are recovery of all leachable gold both in the sulfides and in the quartz fraction and the simplicity of the circuit and operation.

Leaching of sulfide cons in a tank will not give you the recovery level that you are hoping for, it will always give lower recoveries compared to vat leaching.

You are also missing out on the values in the non sulfide fraction.

Running the sulfide cons in a tank will give you less control over the process than running a vat.

In a vat the entire ore is leached so the average grade of material in the vat is lower and the process requirements are correspondingly lower.

Tank leaching of sulfide cons requires the use of a leach promotor as well as the usual cyanide and lime if you are to get really good recoveries.

The leach promotor will give you problems in the zincing stage.

I have no idea how you expect to get the non-leachable gold, a leach circuit will only recover leachable gold.

During cyanide leaching you are really only interested in pH, cyanide level and dissolved oxygen level(DO).

Those are the things you need to monitor throughout the leach cycle

Deano

mahalas · Mar 6, 2016

Hi Deano.
I had to digest it. The more I think about it, the more I am convinced that you are right. Does not make sense inventing the wheel. Will do a few more tests to check what size gives me the best response for cyanide, and I will leach everything in vat.

Especially that on the mine site there is a 10 000 liter plastic tank I can use to build the vat for leaching.

Oryginally I had idea to mill the tailings as fine as possible and do the leaching in tank with stirrer. Additionally in pre treatment stage I planned to do aeration with ozone in hope to oxidize sulfides and liberate all gold for leaching .

You mentioned about leach promotor. How is it used and how does it work?

And thanks again for sharing your knowledge . It is priceless.

Cheers Adam

Deano · Mar 6, 2016

Leach promotor is a powder formulation designed to speed up cyanide leaching and break down the components of the ore to allow cyanide more access to the gold.

Think blends of peroxides and chelates.

In Australia the most used brand is Leachwell, others are available both here and overseas.

These promotors are expensive and do not give you any better gold recovery than a vat leach will give you.

Note that a vat leach will run for months whereas a tank agitated leach with a promotor will be days at the most.

Like all things in mining the use of a vat leach is a compromise between time and cost/recovery.

The vat will take longer but will give the highest recovery at the lowest cost.

This gives you a problem if you want to use your plastic tank as a vat.

It will hold roughly 20 tons of material only and will then be tied up leaching this 20 tons for several months.

This is why only concentrate vats are small, vats for run of ore material are much larger to allow economies of scale.

My advice is for you to add up all of the tailings you have access to so you have a total in tons.

Halve this and you will have an approximate vat size in cubic metres to handle all of your material in one go.

This vat is built as a two or more cell vat so that the drying and rewetting cycles can be practiced.

Please realise that your tailings will be only part of the leachable material which can be leached in the vat, there will be large quantities of waste rock which will not have a high enough grade to have been viable to process when the mine was being first worked but which will be a large resource for your vat leaching.

In many mines the waste piles are a greater resource than the tailings heaps.

In vat leaching you are going to be making money at 0.5 grams per ton leachable gold, this will be your cyanide leach assay value you are looking for.

Most of these waste dumps are best treated by running only through a jaw crusher before being placed in the vat, the cost of finer milling is not recovered in the leach cycle.

Deano

Deano · Apr 4, 2016

When using distillation processes there is always the possibility of sucking the distillate back up the tube and into the heating bowl. This generally does not end well.

I have always used what is called a soft plumb section between the end of the condenser and the container of distillate.

The soft plumb section can be made of just a piece of rolled cloth tied to the end of the condenser such that the inside of the cloth roll acts as a pipe for the distillate.

The end of the rolled cloth dips into the distillate in the receiving container so that the distillate can wick its way up the cloth and form a fully wetted tube of cloth from the end of the condenser to the distillate.

If something unexpected happens during the processing then the distillate cannot be sucked back up the cloth tube as this tube collapses in on itself.

If distilling aggressive liquids the cloth can be replaced with very finely woven soft polypropylene or ethylene cloth or even high density thin carbon felt.

Deano

Deano · Apr 15, 2016

Many people who chase alluvial gold are frustrated by the gold being in cracks in the bedrock.

Most of these people have not the permits or expertise to use explosives to break up the bedrock and thus gain access to this trapped gold.

There are non-explosive alternatives available to break up the bedrock which usually do not require either permits or expertise.

Systems such as Cardox and Nonex whilst not being classified as explosives do require some expertise to be used successfully.

The expansive mortar systems are different in that the operation requires a hole to be drilled and a container of grout to be mixed and placed in the hole.

It can all be done with a battery operated hammer drill and stirrer.

There are many brands of these systems available such as Expando, Novatech and Dexpan, Google "chemical rock breaking" for web sites.

These systems really do work silently and safely, the only noise is the hole being drilled.

Deano

kurtak · Apr 15, 2016

Doesn't sound anywhere near as much fun as Kinestick or Kinepac though :lol: (both of which I have worked with)

I have heard tell that the old timers would drive (dry) wooden wedges into the bedrock cracks & they would split the crack open by hydraulics as the wood expands from soaking up the water

Kurt

Deano · Jul 5, 2016

When recovering gold from filter papers there are two main options.

The first and most used is to digest the filters up in aqua regia and thus get the gold as gold chloride in solution.

Commercial plants will usually substitute cyanide for aqua regia.

The second is to ash the filter papers and to then digest the ashed residue.

Some gold is always lost in this ashing no matter how careful the operator is and what ashing system is used.

A scrubbing system is not really viable for the small scale operator.

A simple method of stopping these losses is to ash the filter papers in porcelain crucibles where a covering layer of activated carbon is placed over the filter papers.

The carbon layer thickness must be at least two particles thick, preferably three particles thick.

Only half fill the crucibles with papers before covering with the carbon.

The crucibles are placed in an electric muffle and furnaced overnight at 650C.

After cooling the ash can be digested in the solvent of your choice for gold recovery.

Any gold which was volatilised from the papers is immediately adsorbed on the activated carbon and is retained there until the gold chloro complexes are broken by temperature.

This occurs before the carbon is ashed so there is only particulate gold on the carbon during the ashing process.

Deano

Deano · Jul 21, 2016

I am presently processing metallic pieces resulting from large scale smelting of a high lead/silver accessory mineral type gold ore.

The pieces range in size from 5 to 500 grams each in weight and are generally 5 to 10mm thick, they appear like flat gray stones.

Metal levels are approximately 40% silver, 50% lead and 10% gold.

I have tried all possible combinations of commonish type solvents but have not been able to prevent the formation of passivation layers with one simple exception.

Not wishing to spend all of my time carrying out separate leaches in sequence in order to separate the metals I have opted for a 10% NaOH solution with 2% NaCN added.

This leach will slowly dissolve in total all of the metals, agitation is by an overhead stirrer with a plastic stirrer.

The pregnant solution is continuously pumped through a carbon column using a peristaltic pump, the return liquor is plunged into the leach bucket to maintain dissolved oxygen levels.

When the gold level in the return liquor is near the same as that in the leach solution the carbon is saturated with metals.

The carbon is then changed for new carbon and the loaded carbon is ashed overnight in porcelain dishes in an electric furnace.

The ash from the carbon is then digested in aqua regia and allowed to cool to precipitate out the lead and silver chlorides.

The lead chloride in the photo is white, it appears yellow from the gold solution, note that the silver chloride is the first to precipitate.

After filtration and rinsing the lead chloride is separated from the silver chloride by hot water rinsing.

Deano

Deano · Aug 9, 2016

When the gold industry changed from Zinc recovery of the gold to CIP, there were several reasons for the change.

CIP is cheaper and simpler to run as a process than zincing.

Theft of loaded carbon is less attractive than theft of zinced gold.

More importantly the recovery of gold by CIP is usually greater for most ores than zincing.

The reason for this is tied up with re-adsorption and solution tenors.

Gold complexes in a leach solution will both adsorb onto suitable materials in the ore and displace onto other suitable materials.

The degree and rate of these occurrences are mainly controlled by the solution tenor of the gold complexes.

The greater the gold tenor in the solution, the faster and more complete are the adsorption and displacement reactions.

Maximum gold losses occur when the gold tenor is high.

When zincing for gold recovery the gold from an ore must all be solubilised before the filtration stage.

This gives two options.

1 Maintain as high a pulp density as possible to minimise filtration and zincing costs, this results in a high gold tenor in the leach liquor.

2 Lower the pulp density to give a lower gold tenor in the leach liquor but have an increase in filtration and zincing costs.

Option 1 will ensure that maximum losses of gold from adsorption and displacement will occur, this is balanced by the cheaper operating cost.

Option 2 will ensure minimum losses of gold from adsorption and displacement but will have higher operating costs.

With CIP there is a continuous removal of gold complexes from the leach solution so that the solution tenor remains low compared with a zincing solution tenor.

This minimises the adsorption and displacement losses.

A similar technique can be applied to the leaching of gold from scrap material.

This involves the running of a continuous bleed stream of leach liquor through a gold adsorbent column or electrowin cell such that the gold tenor of the leach liquor is maintained at a low level.

If gold is being leached from scrap which has surfaces of copper or zinc to name just two common metals then there will always be competition between the leach solubilising the gold and the other metals displacing the gold from solution.

By keeping the gold tenor low the displacement reactions are minimised and the maximum gold recovery is attained.

Deano

Deano · Aug 16, 2016

Images which may be of interest are porcelain dishes containing loaded carbon which has been ashed in an electric furnace at 650C.

The left hand dish was sourced from carbon fully loaded from a 50% lead, 40% silver, 10% gold leach solution under high pH 13, high(1%) cyanide conditions.

The right hand dish was sourced from carbon fully loaded from a 70% gold, 20% copper, 10% silver leach solution under standard pH 11, 0.1% NaCN conditions. The red colour is from the copper which loaded on the outer carbon surface at a faster rate than did the gold.

This is a view of the carbon from the left hand dish before ashing, the blue/white material is lead reduced on the carbon.

The carbon from the right hand dish appeared to have no deposit on it before ashing.

Deano

anachronism · Aug 25, 2016

To add to Dean's already excellent ashing pictures here's some I did yesterday. The raw product was type 43 plated connectors and the ash contained mostly gold with traces of copper and nickel. Ashing really is the way to go for recovery from leach solutions over dropping with zinc IMHO.

patnor1011 · Aug 25, 2016

Do you have picture how it look like after ashing?

anachronism · Aug 25, 2016

That is after ashing Pat.

nickvc · Aug 25, 2016

Looking good have to tell us the yield.

Deano · Aug 28, 2016

Following the write up of how a vat leach is set up these photos are a mix from two sites which together show the various stages.
It appears that I can only place and comment on 5 photos at a time so I will have to do several posts to fit them all in.
Note that the plastic liners used here are the old 0.1mm thick ones, now days you need to run 2mm thick liners which need heat welding.

Initial cuts for vat

Forming up walls, lengthwise slope from right to left, crosswise slope from left corner to pump sump immediately behind photographer.

Forming up walls

Start of liner placing, pump sump in position, crossfall from right side to left side, sump at lowest point.

Unrolling and placing liner, drum type sump in position, agricultural drain lines ready for fitting.

Deano · Aug 28, 2016

Two vats side by side, nearest one filled with ore prior to leach solution addition, second vat in process of being lined.

Left hand vat in leach cycle, right hand vat being constructed. In the right hand vat a holding layer of screened creek gravel is being placed over a white filter fabric sock covered agricultural drain pipe.