Prepared by

John Guo (P. Geo, Ph D)

Eco-Goldex.com

Tel: +1 438-825-5288

Email: john@eco-goldex.com

July 27, 2016 (Version 3)

Instructions of Using Eco-Goldex

O/C Series Reagent

in Gold Ore Leaching and

Gold Recovery Procedures

Declarations and Notes • Though Eco-Goldex is a low toxic chemical reagent invented for

effective gold extraction of various materials (gold ores, E-

waste, sulfide concentrates…), it does contain certain level of

toxic and can cause harms to human body and health problem if

it is not properly handled.

• All precautions and safety protections in an operation site should

be followed and respected!

• Reagent should be stored at place where children can’t reach;

solution made of reagent should not intake and

leaching/stripping operation should be conducted at open

space.

• This instruction is prepared for gold stripping dummies who

don’t have much background of gold leaching and procedures.

• If you already have a lab with cyanidation test facility or gold

mine operation, have your lab technician treats eco-goldex

reagent the same way as cyanide as eco-goldex reagent has the

same operation conditions and procedures as cyanide except

eco-goldex is low-toxic and eco-friendly.

Equipment, agents will be used in the leaching Test:

• Two (2) leaching tanks(beaker, rolling bottle…), size of the tank depends on leaching test scale;

• Eco-goldex reagent; • Lime (CaO) or tablet Sodium hydroxide (NaOH) • Precise pH test strip or pH test pen; • Agitating device;

Most common agitating leaching test equipment in lab

Gold Leaching Processes

Gold in ores/electronic pins is dissolved by eco-goldex solution.

Gold (through chemical reactions) get into the solution

Separate the leaching solution and the residual solids. Keep the leaching solution, this solution is also called Pregnant solution as it contains gold (in ions format)

Au (Solid) 0

Au (solution) 3+

Precipitate Au from the pregnant solution, two common methods

Activated Carbon method

Zinc dust method

Au (solution) 3+ Au (Solid)

0

water

Prepare proper volume of water

in a tank

Alkaline water

Add lime (CaO) or NaOH to adjust water pH value around

11. stirring solution

Step 1: prepare the alkaline solution

1 2

Note: Add CaO/NaOH a little bit at a time and test pH value frequently , make Ph value close to 11 and not over 12!

For most common gold ores (oxidized ore, mixed gold ores (oxide + sulfide), eco-goldex reagent concentration is about 0.5-1‰ (which means add 0.5-1 kg reagent in 1 ton ores). Sulfide and complex ores need more reagent (2-3 times more).

Watch this video about how to prepare the leaching solution

Alkaline leaching solution

Use the equation below to calculate the quantity of

eco-goldex add to the tank; and stir the solution

slurry concentration is about 30%

Add ores (grind to -200 mesh) to the leaching tank

3

4

Step 2: prepare the alkaline leaching solution and start the leaching process

Cw =𝐶 .𝑊𝑤

1000−𝐶

C: reagent concentration in solution, unit: ‰; Ww: water weight, unit: grams Cw: reagent weigh, unit: grams

Example: in a tank with 15kg water, to make a 0.5‰ leaching solution, 0.5 ∗15000

1000−0.5=7.5 grams eco-goldex will be used

How to decide eco-goldex concentration in leaching solution?

Reagent quantity added (g/t)

0.5 0.8 1 1.5 2 2.5 3

Au leaching rate (%) 92.25 94.45 95.66 96.78 96.8 96.9 97

Practically, proper eco-goldex concentration in leaching solution is defined through lab tests (test on different concentrations and find out proper eco-goldex with best gold recovery . Like the example below., 1.5‰ is the optimum concentration for leaching

For SSM (Small Scale Miners) or artisanal miners, these have no access to lab test. A rule of thumb to decide leaching concentration is recommended as follow: • Oxidized gold ores with average gold grade ~2 g/t, eco-goldex concentration: 0.8 ‰(

add 0.8 kg reagent in 1 ton ores); • Sulfide gold ores (2-3 g/t): eco-goldex concentration: 2-4 ‰; • Complex gold ores (As, Sb, Zn…):eco-goldex concentration: 3-6 ‰; • High grade gold concertation (Au>40g/t): eco-goldex concentration: 8-12 ‰ (add 8-12

kg reagent in 1 ton concentrate) For mine with qualified lab facility, series metallurgical tests will define the proper reagent consumption rate in leaching.

Leaching slurry concentration: for tank (CIL, CIP) leaching, solid : solution = 30-40 : 100

4 gallon alkaline leaching solution

Start stir the slurry in the tank using a stirring equipment,. Stirring is set to such a speed that materials slowly but constantly moving in tank, no materials settle down to the bottom

Notes: both pH and eco-goldex reagent concentration in leaching solution should be monitored during leaching process and new reagent should be added as instructed in the next page.

5

Step 3: Leaching Process

Leaching time（h） 0 2 4 6 9 12 21 27 30 36 45 48

PH (1) 11.0 11.0 11.0 10.7 11.2 11.1 10.3 11.1 11.1 10.8 10.7 10.9

Added Lime ratio (2)

(kg/t) 3 0.6* 1* 1* 1*

Reagent cons (1) (3) （‰）

5 4.7 4.8 4.6 4.7 4.5 4.8 4.9 4.9 4.9 4.95 4.95

Reagent added (1) (4) (g)

75 4.5 3 6 4.5 7.5 3 1.5 1.5 1.5 0.75 end

The table below is a typical agent supplement scenario in a complete leaching cycle. It can be used as a reference in your case when and how much agents (lime, eco-goldex) to add into the agitating tank)

1) Real time measurement value at specified time period; 2) This is a general ratio of lime to be added into the solution. In practice, periodical monitoring of

pH value test is important, adding proper amount of lime to maintain pH value around 11. 3) Assume 5 ‰ is the optimized eco-goldex concentration in the leaching system, periodical

measurement of eco-goldex concentration in the leaching solution is crucial to maintain 5 ‰ eco-goldex in the course of leaching by adding reagent;

4) Formula of calculating eco-goldex added = (initial concentrate – current concentrate) * solution volume. i.e. at hour 4, eco-goldex is 4.8 ‰, so added eco = (5-4.8)* 15 = 4.5 grams

5) use this link http://eco-friendly-gold-leaching.com/index.php?topic=10.0 how to detect reagent concentration in solution.

Initial status

* The quantity of lime added depends on pH value test results,

Step 4: End of leaching process

1. After 48 hours, stop agitation and let solid settle down

3. Properly dispose residual solid after pregnant solution is transferred to storage tank and restart a new tank leaching if necessary.

Pregnant solution

2. Using a pump to transfer the leaching (pregnant) solution to a storage tank for gold adsorption

Attention to these who don’t have access to assay lab

• Your leaching test materials are usually in small quantity (n lbs ~ nx10kg). You need to expect how much gold you can recovery in theoretical condition( assume 100% recovery);

• Your gold quantity is usually small (~ grams) in the solution unless you cumulate your leaching solution or process large amount of materials;

• You might not be able to SEE your gold if you don’t pay attention or in worse case, your gold might be lost in the processes from leaching to adsorption.

• Two methods to tell you have gold or not in the solution: – Qualitative : using Stannous chlorite coloring method;

– Quantitative: send your leaching solution to a qualified lab to assay gold concentration in the solution .

This color indicates there is gold in the solution. But it can’t tell how much gold (gold grade) in the solution.

Before Stannous chlorite solution added

After Stannous chlorite solution added

A simple Stannous Chlorite Color reaction method can be effective to tell whether there is gold in the leaching solution .

(note, this method works well only when Au concentration is high enough in the solution; if Au concentration is low,

color reaction may be not obvious.)

Step 5: Gold recovery from pregnant solution

Pregnant solution Activated carbon in Pregnant solution to

adsorb gold

Diluted solution (recycled for gold

leaching)

Add coco nut shell activated carbon

Activated Carbon Method (a specially treated Coco nut shell activated Carbon for gold adsorption is required. BBQ carbon DOESN’T work!! We provide Activated Carbon if

you don’t know where to buy)

Two common methods: • Activated Carbon adsorption • Zinc powder/strips precipitation

How to Use Activated Carbon to Adsorb Au out of the pregnant solution

• Use specially treated coco nut shell activated carbon (AC) for gold adsorption;

• the portion of AC added to the pregnant solution is about 4 g / L;

• Adsorption time is about 4 hours;

• Gentle stirring of solution help adsorption process;

• Carefully remove the loaded activated carbon out of the solution and let it dry under sunlight;

• Recycle the leaching solution if necessary;

• Carefully burn the dried activate carbon in a crucible.

• You will see the ash shall turn into brownish color if a lot of gold is stripped out.

• There are two ways to continue after this:

– Continue to burn/melt the ash using high temperature propane torch;

– Using Aqua Regia to dissolve activated carbon ashes to purify gold as shown in next page.

Gold recovery from pregnant solution

Aqua regia

Gold ash to be purified in Aqua Regia

using SMB to precipitate of gold from aqua regia

SMB

Sponge gold

Activated carbon with gold loaded will be burned

How to use zinc powder/stripes to precipitate gold out of the pregnant solution

• Separate pregnant solution and residual materials by filtering; storing pregnant solution in a container;

• With constant stirring (for zinc powder), adding zinc powder into pregnant solution (use the ratio of 1 g Au : 2-4 g zinc powder);

• The gold will drop out and appear as a brownish powder. • To insure all the gold drop out, add a slight excess of zinc, which is of

a gray color. Add the zinc in increments, allow it to work for a couple of minutes, and observe the color. When the observed powder is of a uniform gray color, all the gold should be out.

• Allow the powder to settle overnight, Either siphon or dip off most of the solution without disturbing the settled solids.

• For zinc strips precipitation, just sock curl zinc strips into the pregnant solution, let the chemical reaction does its work for 6-10 hours.

• Filter (coffee filter paper can do the job) the solids and retian all the solids from the filter paper and put them into a plastic bucket. Keep the filter paper(s) for future incineration.

Step 1: Drop gold out of the pregnant solution

Continued:

• Add proper amount of water to the solids and stir a bit to break up the solids and create a slurry;

• UNDER A FUME HOOD!, add a small amount of concentrated HNO3 or H2SO4 acid. You should see an immediate reaction. When the reaction subsides, give it a stir and add a little more acid. Repeat until an addition of acid produces no reaction; this step is to remove base metallic elements such as Cu, Fe… that might be dissolved during stripping process. And extra Zn strips remain. Base metal sulfides(i.e. CuSO4, FeSO4, ZnSO4) are soluble in water, while Au can’t be dissolved by H2SO4 or HNO3. these base metals (junks) will be separated from Au through filtration.

• Filter the acid solution and transfer the solids to a beaker, cover with water, and heat to a little below boiling. Add some acid and heat for about 15 minutes to make sure all soluble base metal sulfites are dissolved.

• Filter the solids and rinse several times with hot water. Remove the solids from the paper and slowly dry.

• At this point, you should have 99+% gold powder(usually dark color!). To purify it further, you can use the standard aqua regia method.

Step 2: purify gold with acid washing

We recommend a portable Intermediate Frequency (IF) melting furnace for gold /Ag refinery for SSM gold miners

Au/ Ag smelting crucible

Au/Ag crucible in work

Au/Ag crucible in work

Process capacity: 1-200 kg per run, 20-30 minutes (hot start)

Residual (tailing) Materials and Solution Treatment

• Eco-goldex reagent concentration in residual solution is very low and is very low-toxic, the solution may still be alkaline, you may use lemon acid or Muriatic acid (HCl) to neutralize it before discharge into drain system.

• Please follow your local government policy/regulation how to treat the residual materials.