Prepared by

John Guo (P. Geo, Ph D)

Eco-Goldex.com

Tel: +1 438-825-5288

Email: john@eco-goldex.com

Oct. 20, 2016

Instructions of Using Eco-Goldex E

Series Reagent in E-Waste Gold

Stripping 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 at operation site should be exercised and

respected!

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

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

because eco-goldex reagent has the same operation conditions and procedures

as cyanide except eco-goldex is low-toxic and eco-friendly.

Chemicals and Tools Needed in Gold

Stripping Operation • Chemicals:

– Eco-Goldex E series (from eco-goldex, for gold stripping)

– Zinc strips (from eco-goldex, for gold precipitation)

– Gold Precipitation agent package (A,B,C) (or Ammonia solution)

(from your local supplier, catalyst work together with Zinc strips for

gold precipitation in pregnant solution)

– Sulfuric acid *( from your local supplier, for gold purification)

– Borax ( from your local supplier, for gold purification during refinery )

• Equipment/tools – Filter (filter paper) (we provide a special filtering paper for large scale filtering

purpose)

– stripping tanks/Pail /container(4-5)

– Heating stove

– Glass beaker, evaporating dish

– Crucible

– Torch/Muffle furnace

* HCI, H2SO4, HNO4 are all capable for gold purification purpose in this stage. But we consider H2SO4 is better

HCI is cheaper but not as strong as H2SO4, gold purified by HCI won’t reach 99%; HNO3 is strong but more expensive than H2SO4, it can make 99.8% gold as H2SO4. H2SO4 is good enough to purify impurities such as Zn, Cu, Fe, Ni… from gold to make 99.8% gold.

It is your decision which acid you will use in this stage.

Major Gold Stripping/Recovery Steps

Dissolving gold (stripping) from by eco-goldex E Series solution.

Separate stripping solution and the residual solid materials. The solution is also called Pregnant solution as it contains

gold (in anions format)

Au (Solid) 0

Au (solution) 3+

Precipitate Au from pregnant solution through Zinc strips (powder)

Purification

Au (solution) 3+ Au (Solid)

0

Stripping

Precipitation

Sponge gold Refinery

Filtering

Eco-goldex E Series Reagent Concentration in Solution

Many users ask this question, there is no direct answer for this

because it depends on how fast you want your gold stripping goes. If

you want to have very fast stripping, you need to have high E series

concentration, if time is not an issue, you can do stripping slowly, then

you can have lower E concentration in solution.

We give the following general guidelines:

• E series reagent weight ratio with water of 1-4 :100 (i.e. Add 1-4 kg

E reagent into 100 liter water) will give a moderate stripping speed.

• A role of thumb, If stripping is too slow, it means you need add more

E series into the solution.

• Hot water stripping solution (i.e. 40-60oC) will significantly increase

gold stripping speed.

• It is NOT recommended to recycle the stripping solution since

the effective components are ran out in the solution at the end

of the process; in addition, once gold precipitation agents

added into the pregnant solution, solution chemical property is

changed and the solution can’t be sent back to stripping

solution.

• It has been confirmed that Activated Carbon is NOT a good

candidate to recover gold from Eco-goldex E series product

derived pregnant solution.

• E co-goldex E series stripping solution is alkaline, it is safe

using steel tank.

Agitating is always a

plus for stripping as this

will increase solution

dynamics and

accordingly chemical

reactions in the solution

water

Prepare proper volume of water

in a tank

Alkaline water

Add E series reagent based on the ratio proposed above into water, agitating

water make sure reagent dissolved well. stirring solution if necessary

Step 1: prepare gold stripping solution

1 2

Note: though you don’t need to adjust pH value in the stripping solution, but make sure never add acid into the solution!

For most common gold bearing E-waste (CPU, RAM, Pins, electronic circuit boards…) , eco-goldex reagent concentration is about 1-4% (which means add 1-4 kg E series reagent in 100 liter water) for moderate stripping speed.

Watch video about how to prepare the leaching solution on youtube

• Warm to Hot water temperature: 40-

60oC is perfect.

• Room temperature works well if you

don’t want to pursue fast stripping

speed.

Stripping solution can be prepared in

advance to ensure complete dissolving

of the reagent (i.e. 2 -3 hours before

stripping)

4 gallon alkaline leaching solution

Once stripping solution is prepared with proper quantity. Make sure

E-waste materials are completely submerged into the solution.

Stirring if necessary and check the surface color visually to see

whether stripping is done. When E series concentration is high, the

stripping is going very fast, 10-30 seconds depending on the

thickness of the coating.

Notes: by visually checking the surface of the electronic parts to decide the stripping time and make decision should more E reagent be added into the solution to speed up stripping process.

5

Step 2: Stripping

stripping usually goes very fast

when stripping starts then slow

down as effective components

consumed quickly.

Step 3: Filtering 1. upon satisfaction of the stripping result, stop agitation and filter the solid and pregnant solutions.

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

Pregnant solution

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

Depends on your situation, the filtering process can be as simple as just pouring out pregnant solution into a solution storage and dismiss the residual solid waste to another storage bins as shown in next page.

• Once stripping is done, filtering the pregnant solution from the residual waste

materials. Retain the pregnant solutions. This filtering is to separate waste solid from

pre solution, these solids are metals that may contain Cu, Pb, Ni, Fe…, it should be

removed from preg solution as much as you can.

• You need only to filter the preg solution, As long as it contains no solid materials,

preg solution may looks dirty, that is fine.

• Make sure rinse the residual solids with water before dismiss.

How to know you have gold in your preg solution

• Your stripping test materials are usually in small quantity (n lbs

~ nx10kg). You need to expect how much gold you may recover

in theoretical condition( assume 100% recovery);

• Your gold quantity is usually small (~ grams) in the solution

unless you cumulate your stripping solution in one batch

process or process large amount of materials;

• Two methods to tell you have gold or not in the pregnant

solution:

– Qualitative : using Stannous chlorite coloring method;

– Quantitative: send your pregant solution to a qualified lab to assay

gold concentration in the solution .

This color indicates there is gold 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.)

In E-waste gold stripping, visual checking can tell

whether gold is dissolved or not.

Before stripping

Original chip

After stripping completed

Chip is partially stripped

Step 4: Precipitation

The following chemicals and materials are needed to precipitate

gold from pregnant solution:

• Zinc strips (some people like to use zinc powder, it is the

same function, but zinc strips will avoid you solution filtering

process after the zinc precipitation is done) .

• Ammonia solution (NH3.H2O), or

• Gold precipitation package A,B,C.

Notes: 1. Using Ammonia solution or the gold precipitation package A, B,C depends on their

availability at your local suppliers. 2. These two chemicals (package) service the same purpose of helping precipitation of

gold onto zinc strips. Without them, gold won’t precipitate with zinc strips. 3. Quantity of ammonia solution added in pregnant solution is 20-40% in volume; 4. Quantity of package A,B,C refers to next page. 5. Quantity of Zinc strips is about 10 times of gold to be precipitated from preg solution

About the gold precipitation package

The package is composed of three chemicals A, B, C: A: citric acid; CAS No: 77-92-9; B: Ammonium fluoride, CAS No: 12125-01-8; C: Magnesium sulfate, CAS No: 7487-88-9 the mixing ratio of the three chemicals is: A:B:C = 2.5:1.5:1

• 1 liter of pregnant solution needs 20 grams A, 12 grams B and 8 grams of C.

• Add proportional gold precipitation agent A,B,C into the pregnant solution

based on the volume of the pregnant solution to be precipitated.

• Ammonia solution has better gold precipitation than the package A,B,C.

• We provide the package here as an option since Ammonia solution is not always available in some countries. The three chemicals A,B,C are all solids, this make their transportation are more acceptable in some countries as well.

Gold precipitation from pregnant solution

Pregnant solution (measure volume and estimate Gold contents in it to determine the package quantity or the volume of Ammonia solution and zinc strips will be added)

Add Zinc strips in the pregnant solution.

i.e. if 4 grams in pregnant solution, add 40 grams of zinc

strips.

Add gold precipitation agent package (A,B,C)

Or Add 25-40% ammonium solution (NH3.H2O)

• A,B,C is proportionally mixed according to the ratio of 2.5 A: 1.5B: 1C.

• 1 liter of pregnant solution need 20grams A, 12 grams B and 8 grams of C.

• Add gold precipitation agent A,B,C into the pregnant solution.

Gold Precipitation Agents

The package is composed of three chemicals A, B, C: A: citric acid; CAS No: 77-92-9; B: Ammonium fluoride, CAS No: 12125-01-8; C: Magnesium sulfate, CAS No: 7487-88-9

Agent 1: Chemical package

Just add industrial grade ammonium solution into the pregnant solution. The proportion is about 25-40% of the volume of the pregnant solution. The criterial is that when ammonium solution percentage is right, the zinc strips added in the pregnant solution should change color quickly, if no obvious color change, it indicates too much E series concentration still in the pregnant solution, then continue add ammonia solution.

Gold Precipitation agents

Agent 2: Ammonium solution (NH3.H2O/ NH4OH)

!! Agent 1 and agent 2 can be alternatively used. It depends on their availability from your local market. !! Remember Ammonia is restricted for shipment by air, it will be better buy locally.

Zinc Strips Precipitation • Add zinc strips into the catalyst agent (ammonia /package A,B,C)

regulated pregnant solutions;

• The amount of zinc strips is as follows:

weight (zinc strips) = 10 times Au to be Precipitated from pregnant

solution.

i.e.

if 6 grams of Au expected from preg

solution, then add 60 grams of zinc

strips into Preg solution.

• The precipitation time should be

About 2-3 hours depends on the

quantity of pregnant solution.

It is recommended to test Au contents

in diluted preg solution before disposal.

• Second time precipitation of the diluted

Preg solution is recommended to maximize

gold recovery

Normal Zinc Precipitation process

2-3 hours precipitation to ensure complete Au-Zn exchange. If you put Zinc strips in the pregnant solution too long, Zinc strips will be broken into small pieces as the solution is too alkalinic. If that does happen, don’t worry, as gold is still at the bottom. Filter the solution to get your gold.

After 3 hours

This photo shows the reason why we recommend to use zinc

strips not zinc powder (if zinc powder is used, another filtration is

required. With zinc strips, you just need to pickup them easily)

Diluted preg solution

Au Loaded zinc strips

Add new zinc strips into the diluted preg solution will help improve gold recovery (second precipitation)

• Use clean water to rinse the Au loaded zinc strips;

• Recover the rinse solution into the diluted preg solution to have the second time precipitation to avoid loss of gold.

• The rinsed and Au-loaded zinc strips are ready for purifying.

Step 5: Purification • Put Au loaded zinc strips into a plastic pail, and then add

proper amount of clean water;

• Slowly add sulfuric acid into the pail and slowly stirring the

zinc strips.

• the zinc strips will be dissolved in the diluted sulfuric acid

solution;

• The purpose of this step is to remove the extra zinc metals and

other soluble metals.

Pre-added water will act as a diluting solution to prevent strong reaction between Zinc and sulfuric acid

Always gloves!

Slowly add high concentration of sulfuric acid (H2SO4) into the pail to dissolve loaded zinc strips

Gentle stirring the solution still all Zinc strips are dissolved and become small tiny particles

Add sufficient clean water to dilute sulfuric acid to prepare filtering. Strong sulfuric acid will damage the filer paper if not diluted properly

!! Strong and dangerous gas released, do this in open space or in well

ventilated space !! If it is possible, you may add minor

HNO3 to remove other impurities here before adding water,

Filtration of the primary gold dust

These tiny black dusts are primary gold with impurity

Make sure dry this dark sludge as much as you can to remove water from it. As extra water in sludge may cause the next purification solution spill over under heated condition.

Second time purification

Carefully pouring high concentration of H2SO4 into a 2L glass beaker, amount of H2SO4 depends on the filtered primary gold dust, enough to submerge all solid materials

Slowly put the filtered primary powder including the filtration paper into the beaker with H2SO4 solution. You should see the filter paper will be dissolved quickly.

H2SO4 only

Make sure not much water in the sludge, it will cause spill when heated

98% H2SO4

This shows what it looks like after the filtration paper is dissolved with the dark tiny primary gold dust in the strong H2SO4 solution

• Sitting the beaker onto a stove to

cook the sulfuric acid to remove

other metals (Cu, Fe, Ni…).

• Slowly rise stove temperature to

prevent possible beaker burst.

• Use an evaporating dish cover the

beaker

An evaporating dish cover the beaker will depress smog!!

Double safety container! In case the beaker is broken, the gold will be in this container.

stove

• Cook the H2SO4 solution till the solution color changes to brownish red from dark.

• This process is critical to ensure high purity of your gold!

• The longer time you cook, the more impurity metals (Cu, Ni, Fe…) will be removed by H2SO4, and the higher purity of your gold.

• Through this cook process, your gold should have at least 99.8% purity!

smog

Note the solution color changed after ~30 minutes cooking

• After 30-40 minutes cooking, remove the beaker carefully to an open space to let the solution cool down.

• You should see a brownish color mud-like sediment sitting at the bottom of the beaker. this is the sponge gold!

• Note: this solution is very acid! You have to use special filter paper to filter the solution. Retain the brownish mud

Sponge gold

!! Make sure to rinse the sponge gold

several times and thoroughly with

water to remove residual acid !!

Transfer your sponge gold to filter

paper, and then to a crucible

Sponge gold in a crucible and

ready for refinery

borax

Don’t forget to add borax

to remove other

impurities

1.05 kg

In just 3 hours

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)

3 Residual Materials and Solution Treatment

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

• Eco-goldex E reagent itself has no significant

residual materials need to be treated.

• The residual diluted preg solution after precipitation

may contain Zn2+ ,Pb2+, Fe3+… in the solution. The

solution itself is alkalinic and should be neutralized

before disposal.

• The sulfuric acid wash solution is very acidic and

should be stored and handle properly;

• The acidic solution can be reused in zinc strip

dissolving stage.

• The solution contain a lot of metallic anions(Cu, Ni,

Fe…)

• The residual metal materials can be resold or treated

properly at designated dump site