# Heap Leaching



## rusty (Oct 2, 2010)

Quit often we get a new comer to the forum who claims to have found an old tailings pile, the expense to process such a project more than the average man has at his disposal. 

Once it was determined the values were viable to heap leach from the tailings piles, a large area of land was graded giving it a gradual slope, then a large rubberized mat was placed down before the tailings were trucked in from their current locations then placed onto the mat in layers. This alone had taken two years to complete.

There were for equipment, an excavator loader, 10 dump trucks and a cat at the tailings pile to level out the layers. My old Mac was on-site but after I had sold it and reaped no benifits. For inside equipment there would have been plumbing, pumps and furnace, labors and technical crew.

From the mat the leach trickled into a settling pond then into the reclamation unit housed inside a large building, I believe they passed the cyanide leach through steel wool to reclaim the values - gold and silver.

If your hoping to reclaim an old tailings pile you had better have deep pockets.

http://minfile.gov.bc.ca/Summary.aspx?minfilno=092HSE244

The Mascot Tailings prospect is located on Lots 1795 (3186s) and 1796, along the east and west banks of Hedley Creek, 1.35 to 2.1 kilometers northeast of the creek's confluence with the Similkameen River, just northeast of the town of Hedley.

This deposit consists of two old tailings dumps derived from the Mascot gold mine (092HSE036), which was operated by Hedley Mascot Gold Mines Ltd. between 1936 and 1949. The larger dump, on Lot 1795, is 290 meters long and up to 240 meters wide, while the second dump, across the creek, on Lot 1796 to the north, is 320 meters long and up to 130 meters wide. Total reserves are estimated at 621,000 tonnes grading 1.75 grams per tonne gold (Canadian Mines Handbook 1989-90, page 430).

The south dump has a gross mineral inventory of 335,000 tonnes, with 176,000 tonnes grading 1.20 grams per tonne gold. The north dump has reserves of 186,000 tonnes grading 1.35 grams per tonne gold (B.H. MacLean, 1991, page 2).

Sumac Ventures Inc. drilled 47 auger and percussion holes totaling 340 meters in 1988. The company proposed to recover gold by heap leaching the tailings. The two tailings dumps were drilled in 1990 and 1991 by Candorado Mines Ltd., operator of the Hedley Tailings deposit (092HSE144), 1.5 kilometers to the south. The company plans to selectively mine the outer perimeter of the south dump and all of the north dump.

In 1995, production from the tailings totaled 93 kilograms of gold and 10 kilograms of silver from 42640 tonnes processed.


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## 4metals (Oct 3, 2010)

That averages 2.18 grams per ton, higher than the assay!
Plus gold was in the $200-300 range back then.


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## Richard36 (Jan 22, 2011)

A project like that may not be feasible, but we can always dream.

I have often thought of building a recirculating leach pad out of an old fiberglass satellite dish that I own, a plastic water tank from a travel trailer that I scraped out as a fluid tank for the leach solution, pvc pipe, a plastic water pump out of an old washing machine to circulate the leach, with a 12 VDC electric motor out of an old scooter to spin the pump, and a 110 Ac to 12 VDC, 40 amp output power supply to power the motor.

Maybe even mount all that on one of the travel trailer frames 
I have from the two I tore down.

Sounds good in theory, 
but I haven't put it together and tested it yet.

I've often imagined that this would be what I'd build if I found some small 
"High Grade" pocket that I wanted to try my hand at processing by leaching 
after I recovered the "High Grade Cons" by tabeling, sluicing, or floatation.

Sincerely, Rick. "The Rock Man".


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## rusty (Jan 23, 2011)

Richard36 said:


> A project like that may not be feasible, but we can always dream.
> 
> I have often thought of building a recirculating leach pad out of an old fiberglass satellite dish that I own, a plastic water tank from a travel trailer that I scraped out as a fluid tank for the leach solution, pvc pipe, a plastic water pump out of an old washing machine to circulate the leach, with a 12 VDC electric motor out of an old scooter to spin the pump, and a 110 Ac to 12 VDC, 40 amp output power supply to power the motor.
> 
> ...



Rick sounds like a great plan and an easy economical build. Have you considered eliminating the battery and inverter, using a small windmill to run that washing machine pump, since your not building head this would be perfect.

Using the wind.

There is a lot of energy in the wind. Power is the cube of speed, so a 40kmh wind has 8 times the power of a 20kmh wind. As an example a perfectly efficient windmill may produce 200 watts of power in a 20kmh breeze, 800 watts in a 40kmh wind, and 6400 watts in a 80kmh storm gust.

But what sort of windmills are we talking about. First up a few simple rules about windmills. Windmills behave in a way very similar to your average car engine. They have a power and torque curve, with different speeds for maximum power or torque. For electrical power generation ideally you need to operate your windmill in its peak power output.

1. More blades = less speed, less power but more torque, perfect for pumping water.

2. Less blades = more speed.

3. Larger propeller diameter = less speed but more power.

Two other factors to consider are turbulence and wind-shadow. Turbulence can be caused by the disrupted wind from one blade to the next, or anything up-wind of the windmill and will have a big effect on efficiency. Wind shadow is the effect the windmill mast has on the propeller as each blade passes the mast. This shadow causes a sudden pressure change behind the propeller blade and results in vibration. 

As a rule 3 blades is the best compromise between power, torque and speed. A 2 blade propeller will run faster, but there are dramatic vibration problems with 2 blade windmills during wind direction changes and therefore not recommended.

Size is important. A 2 meter turbine would struggle to make 500 watts in a gust, and will average 10 to 100 watts in most locations. A 4 to 5 meter turbine can generate power over 3000 watts (3kw) during strong winds, and more importantly, will average 100 to 800 watts in a typical location.

The old farm style of windmills ( Southern Cross, Comet ) used for water pumping have lots of blades, giving them a lot of torque, however many blades means low RPM, and they are not suited to power generation. It is possible to use a gear box to speed up the output, but this creates its own problems and is best avoided.

Windmill blades can be made from just about anything. Wood, steel, fibreglass, carbon fibre, etc. I've even seen a windmill using 8 wheelbarrows! Wood is the most common material for the DIY handyman, its cheap, easily formed, strong and flexible, remember trees are very good at bending in the wind without breaking

The profile of a well designed windmill blade resembles a aircraft wind, giving lift on the trailing edge. The blade has a angle of attack to the wind to give its best lift, and this lift drives the blade forward. There also needs to be a slight twist along the length of the blade, the blade tip is travelling much faster than the part of the blade closest to the centre of the propeller, so the blade needs to be tilted to give the same angle of attack.

You also need to consider tip speed, or TSR (Tip Speed Ratio). The tips of the windmill blade travel much faster than the wind speed, so a TSR of 7 means the tips travel at 7 times the wind speed. A typical 2 meter diameter turbine at 500rpm could have a tip speed of over 200kmh, and any airborne dust or unfortunate insects will be very abrasive at this speed. For windmill blades made from a soft material, such as timber, a layer of wear resistant aluminium tape or fibreglass is usually applied to the leading edge.

Credits: http://www.thebackshed.com/windmill/articles/GettingStarted.asp

Regards
Gill


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## Richard36 (Jan 23, 2011)

Hello rusty,

A windmill isn't a bad option.

I figure I could get the same amount of power and usage with a solar panel,
4 series 27 truck batteries, and a voltage regulator out of a car to keep my battery bank from over charging. 

If I needed 120 VAC or 240 VAC, I could hook up a 12 VDC to 120 VAC inverter to produce the 120 VAC, and for the 220 VAC, I could hook up the output of the inverter to a control box for a water well pump to convert the 120 VAC to 240 VAC. I could then split the lines on this to produce a single line of 120 AC output, and use the other line to another control box to produce a single line of 240 AC output. 

Just another angle to achieve the same result.

Sincerely, Rick. "The Rock Man".


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## rusty (Jan 23, 2011)

Richard36 said:


> Hello rusty,
> 
> A windmill isn't a bad option.
> 
> ...



Me bad, I thought you were pulling leach from a storage tank, and that you were looking towards building an economical mobile leach unit keeping costs down by using junk yard and salvaged parts from around your yard.

A windmill would work 24/7 at no cost to you with little maintenance, no expensive solar panels or heavy lead acid storage battery's or inverter for someone to steal in your absence.

For a small leaching set up that you discussed in your first thread you would not need many gallons per minute circulation, so why the fancy set up using battery's and solar panels - go with the windmill on a folding tower attached to your trailer.

How large in diameter is that old dish, if it's over 8 feet your going to have to tilt it on your trailer to move it, on public highways and roads over width loads exceeding 8'6" would require a pilot car - during daylight hours only.

Your idea of using an automotive voltage regulator wont work for solar panels, here's a DIY build regulator for solar panels with schematic.

When the panel isn't generating, the entire circuit is off and there is absolutely no current drain from the battery. When the sun gets up and panel starts producing at least 10 Volt, the LED lights and the two small transistors switch on. This powers the regulator circuit. As long as the battery voltage stays below 14V, the operational amplifier (which is a very low power device) will keep the MOSFET off, so nothing special will happen and the panel current will go through the Schottky diode to the battery.

When the battery reaches the trigger voltage, which is nominally 14.0V, U1 switches on the MOSFET. This shorts out the solar panel (a condition that is perfectly safe), the battery no longer gets charging current, the LED goes off, the two small transistors go off, and C2 powers the regulator circuit while slowly discharging. After roughly 3 seconds, C2 has discharged enough to overcome the hysteresis of U1, which switches the MOSFET off again. Now the circuit will again charge the battery, until it again reaches the trigger voltage. In this way, the regulator works in cycles, with each OFF period being 3 seconds, and each ON period lasting for as long as necessary for the battery to reach 14.0V. The pulse length will vary according to the current demand of the battery and any load connected to it.

The minimal ON time is given by the time C2 takes to charge up with the current limited by Q3 to roughly 40mA. This time is quite short, so this regulator can work down to very short pulses.

Construction
Building this circuit is very simple. All components are widely available, and most can be easily replaced by other types if necessary. I would not advice to replace the TLC271 nor the LM385-2.5 by different ones, unless you know very well what you are doing. Both of them are low power devices, and their power consumption directly defines the OFF time of the regulator. If you use replacements that have a different power consumption, you will need to change the value of C2, adjust the biasing of Q3, and maybe even then you might run into unexpected trouble.

The MOSFET can easily be replaced by any type you like, as long as its RDSON is low enough so that its dissipation will remain acceptable at the maximum current delivered by your panel. For D2, basically any diode is acceptable as long as it can safely handle the total current produced by your panel. A Schottky diode like the one shown is an advantage because it will produce only half as much voltage drop as a standard silicon diode, and thus generate only half as much heat. But a standard diode is perfectly suitable if properly sized and mounted. With the components shown, the regulator comfortably handles a 4 Ampere panel. For larger panels, only the MOSFET and diode need to be replaced by larger ones. The rest of the circuit remains the same. No heat sink is required for the power level shown. The indicated MOSFET can handle a much larger panel if fitted with a modest heat sink.

R8 in this circuit is 92k, which is a nonstandard value. I suggest that you use an 82k resistor in series with a 10k one, which is simpler than trying to find a special resistor. R8, R10 and R6 define the cutoff voltage, so it's nice if they are reasonably accurate. I used 5% resistors, which usually are a lot better than the rated 5%, but if you want to be on the safe side, use 1% resistors here or pick the more precise 5% ones after measuring several with a digital meter. You could also include a trimpot in this circuit, so that you can adjust the voltage, but I would not suggest this if your application calls for high reliability in a corrosive environment, like mine did. Trimpots just do fail in these conditions.






Regards
G :idea:


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## Richard36 (Jan 23, 2011)

All points made.
I was just having some fun being the gear-head that I am.
Ever heard of over engineering something? lol!

Sincerely, Rick. "The Rock Man".


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## rusty (Jan 23, 2011)

Richard36 said:


> Ever heard of over engineering something? lol!
> 
> Sincerely, Rick. "The Rock Man".



Guilty every time, when I look at some of the commercially designed products often shake my head wondering why the parents spent all that money sending junior though university to become an engineer.

The engineer sitting at his CAD computer needs to take into consideration the life span of said equipment, price per pound of material needed to manufacture said goods, while I look at what's available from my scrap pile usually ending up with over kill.

Regards
Gill


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