Fine grinding .

The old timers using a stamper , always had the crushing pass through a 100 mesh . Aperture size 0.147 m.m. or 0.006 inches .
this is the way you could recover most of the gold . Some of us like to crush up rocks, using a impact mill for example . This will crush to 2 m.m. or less . After screening you have some oversize that still has gold in . What are you going to do with that ?

This is my idea and only an idea .First step buy and old cement mixer . Next get an old compressor tank or maybe an old LPG gas bottle , like off a caravan . Cut the top off and fit it onto the cement mixer . It is no good using the cement mixer by itself , the steel is too thin . Compressor tanks and gas bottles have round bottoms . You need some s/steel balls and they can be got on E-bay . Get a.few different sizes . Put the balls in and say 5 kg. of over size plus water . Let it run for 30 mins and then screen again . The good thing about a cement mixer is that you can tip it out .

What do you think of this idea ?

I like the idea for the simple reason it's outside the square so to speak :Y: Be careful cutting any gas bottle it can be a disaster waiting to happen tick tick BOOM :bomb: if you don't know what you are doing get someone who knows or do your research. If you have never cut a gas bottle before but you are going to research the cutting of a gas bottle have your research results checked out by someone who knows what their doing to test your research before going ahead with it.

As for the steel balls I'd use mild steel so you can use a magnet to pick up any fines in the processed cons. I'm sure it will test you and your thought processes will change but I'm looking forward to hearing of your results :beer:

I take it your idea is to use the cut gas cylinder and balls as a ball mill placed in the cement mixture to roll the gas cylinder and process the pay dirt. If I've understood it properly I'm pretty sure you'll have to alter the mixer bowl to suit the gas cylinder so it doesn't spew out the balls and cons.

Let me start by saying this is advice only and you should refer to a professional who has a SWMS and equipment and premises for the task.

I have processed literally 1000s of gas bottles, domestic, BBQ and car gas tanks at work and at home

The safeset way to do it is like this imho.

Open gas bottle in well ventilated area, its not against the law to do this as some people will suggest. Best on a warm breezy day and have the bottle completely isolated on concrete or bare earth and somewhere noone will come into the area for a few hours.

This will release all the gas and stop it from creeping along near ground level which it will do if its too cold and still.

Once a couple of hours has passed walk up to it, if you still can smell gas within 1 metre of it, leave it longer.

Once the gas has dispelled check there isnt liquid still in it. If there is place the bottle horizontal with the outlet away from you and using good thick gloves. I assure you it will cold burn you and its not pretty. Do this gently tipping on to its side maintaining contact with the ground at up times. Roll the tank so the liquid can come out the outlet on a 45 degree angle.

Repeat waiting times until no gas can be smelt from 1 metre away.

Take hose and fill tank with water. Release all water onto ground.

If theres still a gas smell fill again and stand upright with nozzle open.

Release all water.

99.9% of the time twice will be enough. Then you can use a shifter and/or drill to remove taps, gauges, lines etc.

To cut.

Get tub that fits tank.

Fill tank and tub untill submerged with water.

Use grinder (9 inch) to cut side facing up.

Now when I was processing them at the business we cut them dry but only after 3 days of immersion and a day of drying . All the ones I did at home I cut submerged. Later we went to brass spiking for safety.

If in doubt find someone who does this regularly.

They are pretty safe to handle and will take way more punishment than common sense would say, but 1 spark in that vapour and it will go bang before you know whats happened.

Some dodgy aircon refillers and backyarders have been known to re-gas an ac in cars with it (lpg) one of the blokes I meet while scrapping put a grinder through the line. Lucky to be here still. Youd pick him in a lineup without any trouble poor bugger.

For what its worth Id go with the compressor tank. Might cost a few dollars but saves the hassle.

Thanks for all that info on cutting . I would not be cutting it with any sign of liquid in . Thinking of taking the valve out and steaming it out . I would prefer a compressor tank as it is longer . I did see one dumped on a tip in Q'land a few years ago . It is 2,000 kms away from me at the moment .
Yes the mixer would have to be modded to take the compressor tank , brackets and weld ? I think most mixers run at say 5 degrees up . It would be so easy to clean out after 1/2 hour running .

I did work in a metallurgic lab for many years , as a fitter . Mild steel balls would wear away but of course it depends how much they are used. In the lab we had small ball mills , the balls were very hard ferro manganese and nickle ? They had to be got from USA and cost a lot of money . I would go with stainless steel balls as they are easy and cheap to get . Was also thinking of adding some Bocce balls , they are about 70 m.m dia .

When the mets. were doing flotation tests , the ore would be finely ground in a stainless steel rod mill . The drum and rods were s/steel . I think the charge was 1 kg . I have a sketch and sizes of these mills , if any body wants a copy . They were turned on rubber rollers but I do not know the rpm .

A mixer by itself works alright for this if its not an ebay cheapie to be honest. Take the lifters out.Bocce balls go pretty well too, just haunt the op shops for them.

not now i guess but they're probably pretty cheap at kmart or similar.

about 1/3 quartz, 1/3 balls, 1/3 water by weight. more small balls is more efficient than a few large balls if you can source them easily.

Roughly how long does a mixer last ? The steel drum is not very thick . That's why I was thinking of putting a thicker drum in .

S/steel balls can be got on E-bay , many sizes , not expensive .

Couldn't tell you to be honest, I've put about half a ton of 1/2 inch minus through mine so far and other than stripping paint it looks okay.
I had considered upgrading the drum but figured i might as well get my moneys worth out of this one first. I have heard of people lining the drum so as to have a replaceable wear surface too.
You'll find the gold gets harder to recover if you run it too long, starts to roll up into tiny little ball bearings.

Definitely worth sourcing a compressor tank over an old gas bottle, as OldGT said a gas bottle needs to be thoroughly purged.
You need to essentially push out and replace 100% of the contents with an inert compound, water and co2/exhaust are old favourites.

Not technically difficult, but you want to be bloody sure, and steaming won't do the job.

I remember getting a metal petrol tank repaired . It was done by a radiator repairer , he boiled it up in a tank of caustic soda before working on it . It was off a Landrover .

My plan it to smash the rocks up with an impact mill to less than 2 m.m. Remove gold at that stage , screen at 100 mesh and then grind the oversize in the mixer . I want to get it all passing 100 mesh to recover most of the gold .

Bocce balls are available on E-bay from a guy in Q'land .

Worth considering passing the oversize back through the impact mill? This is the one you're building yeah? looks reasonably large.
I use the concrete mixer because my impact mill is one of those little angle grinder ones, takes bloody forever to do a bucket or two. the mixer takes a while too, but you load a bucket of stone and some balls, turn it on and come back later.

Petrol tanks are similar, the caustic acid is to remove varnish deposits, and the boiling process should flush it too. you'd have to force the steam through and ensure no air pockets of vapourised gas remain.

Yes, I have thought of passing the oversize back through the impact mill . It would be quick and easy but would it reduce the material by much ? Been working on the mill to day , trying to do a little bit every day .

Like you , I think I would use the concrete mixer until it wore out ! The compressor tank is the way to go .

Also got a Knelson 3 inch concentrater half built that I started many years ago . Will finish the mill first and then have a look at the Knelson . Never finished the Knelson because there was one at work that I could use any time ! Had the keys to the factory and could go there any time .

Two passes does alright with the little angle grinder mill I've got at least, be worth a shot for small runs I'd say.
The concentrator sounds interesting.

If the concrete bowl wears out , it maybe could be replaced by a 50 lt. stainless steel keg ? They can be picked up in Sydney for less than $100 . Cut the top off with a grinder and work out a way to hold it in place .