Technology

Eco-Goldex Product and Its Proprietary
Precious Metal Recovery Technology

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Eco-Goldex Agent Work Mechanism

Eco-Goldex’s gold extraction agent series represent a group of chemical compounds that are capable of effectively extracting gold from gold ores or E-scrap materials. Eco-Goldex product series is not a simple chemical but a compound that is produced of several common chemicals mixed and fused in a high-temperature autoclave (650-760 oC).

Unlike gold leaching mechanism in sodium cyanide solution that CN- is the only powerful component that attacks (dissolves) gold and forms soluble Au(CN)− 2 ion, Eco-Goldex solution contains several components, though each individual component may not as strong as CN -, that involve gold dissolving process and form soluble Au complexions. The combined gold dissolving capacity of these individual components released from Eco-Goldex is equivalent or even stronger than that of Cyanide. Below are several possible chemical reactions that may involve in the Eco-Goldex gold extraction mechanism:

4Au + S2O82- + 4CS(NH2)2 → 4Au[CS(NH2)2]2+ + 2SO42-
4Au + 4CS(NH2)2 + 2H2O + O2 → 4Au[CS(NH2)2]2+ + 4OH-
Au + 4NH3 → Au(NH3)43+ + 3e
6Au + 4[Fe(CN)6]3- +O2+ 2H2O →6[Au(CN)4]3- + 4Fe3+ + 4OH- + 2e

Eco-Goldex Agent series

Eco-Goldex has finalized its two-product series to cover gold extraction from gold ore leaching (the O series) and E-scraps (the E series), respectively. A common feature of Eco-Goldex product series group is that they are simple systems and work in alkaline conditions. Below are the descriptions of the two product series and their features.

The O series are invented and produced with the goal of replacing cyanide in the rock ore process. This chemical agent can be used for lixiviation of the following type of:

  • Gold Ores
  • Silver Ores
  • PGM Ores
  • Oxide Copper Ores
  • Historic gold mine heap leach /tailing materials

 

Eco-Goldex O series share many similarities with cyanidation in precious metal recovery methods such as Carbon in Leach (CIL), Carbon in Pulp (CIP), Zinc cementation (Merrill-Crowe Method) for precious metal recovery in pregnant solution.

The E series are specially formulated for precious metals (Au, Ag, Pd, Pt, Rh…) stripping in E-Scrap materials. This chemical agent can be used for lixiviation of the following type of:

    • E-Scrap materials that contain plated precious metals such as RAM, CPU, PCB
    • Old Au/Ag plated jewelry
    • Old Car catalytic converter
    • Exposed internal gold such as crushed/ground IC Chips powder

 

Eco-Goldex provides two options for precious metal stripping in E-scrap materials:

  1. For discontinuous plated gold-bearing components such as RAM, CPU, PCB, Pins…, stripping method (washing E-scrap materials in E series stripping solution) is used;
  2. For large or continuous e-scrap materials such as silver plated plates, silver plated communication box base, jewelry chains, connectors, electrolysis method can be used for direct recovery of precious metals from these E-scraps.

Eco-Goldex O Series:

As an alternative of sodium cyanide chemical applied in gold/silver/PGM ore lixiviation, the O Series shares similar working conditions as cyanidation as shown below:

Working pH Condition

9-12, optimum at 11.5, Lime (CaO) or Sodium Hydroxide (NaOH) is used for pH control

Empirical Reagent Concentration in Leaching Solution

For most common gold ores, reagent concentration in solution is 0.5-1‰, Complex materials usually consume more reagent. optimum reagent concentrate should be defined through metallurgical tests.

Applicable method

Heap leach, CIL/CIP, VAT leaching.

Applicable ores types

Oxidized, Semi-Oxidized Au(Ag, PGM), non-refractory sulphide gold ores or gold ore concentrates

Eco-Goldex E Series:

The Eco-Goldex E series has much simpler working conditions:

Working pH Range

Free. Since the reagent itself is alkalinic in solution, and its gold stripping efficiency is so strong and quick, there is no need to control, monitor or adjust pH in E-waste stripping solution.

Empirical Reagent Concentration

for most electronic parts, Eco-Goldex E concentration in stripping solution is around: 4.5% - 5.5% (45-55 grams of E reagent in 1 litre of water). If quicker stripping speed is desired, higher reagent concentrates (i.e. 6.5-8%) can be used

Applicable Materials

Any material contains surface gold (electronic connectors, pins, RAM, CPU, PCB, Jewelry) or internal gold but exposed to stripping solution such as IC chips

Application Method

the Eco-Goldex E series solution can be used either for plated gold materials stripping (i.e. RAM, CPU, PCB, pins and connectors) or in direct gold or silver electrolysis such as silver-plated plates or communication board base, or jewelry chains etc

Stripping Effect Factors

Three factors affect gold stripping speed in E-waste processes: reagent concentrations in solution, solution temperature (idea temperature range: 40- 50 oC), and stripping dynamics (stirring)

Advantages
of Eco-Goldex Agent

Comparative metallurgical and eco-toxicological tests on Eco-Goldex product series vs Cyanide and Aqua regia on toxicity, work efficiency and operational costs reveal that Eco-goldex has several advantages over cyanide and aqua regia in gold extraction processes. These advantages can be summarized as following:

Both Eco-Goldex E and O product series are low-toxic. Eco-toxicology test results indicate that the toxicity of the Eco-Goldex series is only about 1-2% in that of cyanide.
ChemicalNaCNCuSO4.H20ZnCl2K3Fe(CN)6Eco-Goldex (O)Eco-Goldex (E)K4Fe(CN)6
Test SpecieRainbow TroutCOBIACOBIABASSRainbow Trout,
Daphnia Magna
Golden FishBASS
LC50(ug/l)276031316001000-4999650013900
Test SpecieRatRatRatRatRatRatRat
LD50 (mg/kg)1048232929705846805000

One of the biggest challenges most of the small-medium gold miners facing is that they can’t get a government permit to either purchase or use sodium cyanide due to its extreme toxicity and it is an internationally highly restricted chemical. Many small-scale gold project owners are accordingly can’t develop their gold projects due to lack of the essential but toxic chemical to process gold ores. With Eco-Goldex product agent, this barrier will be lifted.

With Eco-Goldex product, this barrier will no longer exist because Eco-Goldex product is classified as ordinary goods and can be transported via marine, air freight and ground. No purchase permit or usage permit is required. Eco-Goldex product series has been tested and certified as ordinary goods by the authorized national institute (CNAS).

Eco-Goldex E product series has a unique feature that it can selectively strip surface gold from plating electronic parts such as pins, connectors, RAM, CPU and PCB, while other metals like copper, nickel, aluminum are not or slightly attacked. This selective stripping feature makes the gold stripping process much easier, and it simplifies E-waste recycling processes into separate steps in which specific metals are separated and recovered.

In addition, the Eco-Goldex E series has exceptional fast gold stripping and gold/silver electrolysis efficiency that can strip surface gold in minutes.

before-stripping11after-stripping11
connectors-before-strippingconnectors-after-stripping
beforestrippingafterstripping
before-stripping22after-stripping22

In the electrolysis method, silver/gold plated parts can be instantly electrolyzed (gold/silver striped and precipitated on cathode plate directly) in the Eco-Goldex E series agent solution.

Eco-Goldex agent can strip not only Au, but also Ag, Pd and Pt (if any) from precious metal bearing materials. These precious metals can be easily recovered through one of our three precipitation methods. The table below shows compiled results of precious metal recovered through zinc cementation and chemical precipitation method of E series pregnant solution.

Precipitation MethodPreg Solution (liter)Precipitated gold ingot (grams)Ingot Composition (%)
AuPtPdAgInIr
Zinc Cementation2.210.0493.750.000.340.980.000.00
Chemical Precipitation2.210.0394.750.000.001.340.030.00
Zinc Cementation1.01.3987.591.211.192.400.040.15
Zinc Cementation1.46.3494.670.000.001.220.000.00

The O series has better leaching performance than cyanide in gold ore lixiviation. For most common gold ores, Eco-Goldex (O) can reach a 90% leaching rate in 48 hours (CIL/CIP) while Eco-Goldex reagent consumption rate is lower than cyanide.

The charts below show original industrial CIP test results on sulphide (pyrite, arsenopyrite) gold ores at a gold mine in Myanmar with the Eco-Goldex O product series. Test results indicate that the Eco-Goldex O product series has better leaching performance in gold ore leaching kinetics (short leaching time), less reagent consumption rate (click the images to view their large size charts).

Eco-Goldex Onsite Leaching Test results

Leaching time (Hrs)Au in tailing (ppm)Leaching rate (%)
01.40
41.1518
81.0525
120.7844
160.7149
200.5859
240.5164
280.4965
320.47566
360.4667
400.4469
440.4270
480.3575
Gold ore Leaching rate curve
(Leaching time vs leaching rate)
Click on the graph to enlarge

Parameters:

  • Raw ore head grade: 1.4 ppm (Au)
  • Eco-Goldex concentration: 0.80 kg/ton
  • Slurry density: 37%
Leaching time (Hrs)Au in tailing (ppm)Leaching rate (%)Notes
000raw ore
190.6788
290.6788
390.5290
480.4891
Gold ore Leaching rate curve
(Leaching time vs leaching rate)

Parameters:

  • Raw ore head grade 5.45 ppm (Au)
  • Eco-Goldex concentration: 2.03kg/ton
  • Slurry density: 37%
leaching time (Hrs)Au in tailing (ppm)Leaching rate
000
73.651
172.6763
212.5465
252.171
301.6777
411.5279
451.481
481.1684
Gold ore Leaching rate curve
(Leaching time vs leaching rate)

Parameters:

  • Raw ore head grade: 7.29 ppm (Au)
  • Eco-Goldex concentration: 0.80 kg/ton
  • Slurry density: 37%

Performance Comparison

Waste Management Cost
Eco-Goldex
NaCN
Reagent Consumption
Eco-Goldex
NaCN
Process Flowcheet
Eco-Goldex
NaCN
Overall Operational Cost
Eco-Goldex
NaCN
Leaching Kinetic
Eco-Goldex
NaCN
Toxicity Level
Eco-Goldex
NaCN
Product Stability
Eco-Goldex
NaCN
Product Adaptability
Eco-Goldex
NaCN
Permitting Difficulty
Eco-Goldex
NaCN
Logistics Cost
Eco-Goldex
NaCN
Equipe Requirement
Eco-Goldex
NaCN
Au Recovery Rate
Eco-Goldex
NaCN

Eco-Goldex Products & Systems

Eco-Goldex has commercialized its chemical agents O, E series for precious metal bearing materials leaching and their relevant equipment system and technology for Au/Ag/PGM recovery, respectively.

Eco-Goldex Chemical Agent Product

Eco-Goldex has commercialized its chemical agents O, E series for precious metal bearing materials leaching and their relevant equipment system and technology for Au/Ag/PGM recovery, respectively.

The O series is invented and produced with the goal of replacing cyanide in the rock ore process. This chemical agent can be used for lixiviation of the following type of:

  • Gold Ores
  • Silver Ores
  • PGM Ores
  • Oxide Copper Ores
  • Historic gold mine heap leach /tailing materials

 

Eco-Goldex O series share many similarities with cyanidation in precious metal recovery methods such as Carbon in Leach (CIL), Carbon in Pulp (CIP), Zinc cementation (Merrill-Crowe Method) for precious metal recovery in pregnant solution;

The E series is specially formulated for precious metals (Au, Ag, Pd, Pt, Rh…) stripping in E-Scrap materials. This chemical agent can be used for lixiviation of the following type of:

    • E-Scrap materials that contain plated precious metals such as RAM, CPU, PCB…
    • Old Au/Ag plated jewelry
    • Old Car catalytic converter
    • Exposed internal gold such as crushed/ground IC Chips powder

 

Eco-Goldex provides two options for precious metal stripping in E-scrap materials:

  1. For discontinuous plated gold-bearing components such as RAM, CPU, PCB, Pins…, stripping method (washing E-scrap materials in E series stripping solution) is used;
  2. For large or continuous e-scrap materials such as silver plated plates, silver plated communication box base, jewelry chains, connectors… , electrolysis method can be used for direct recovery of precious metals from these E-scraps.
The table below lists precious metal recovery methods that can be effectively used in Eco-Goldex pregnant solutions.
Precious metal recovery methodO Series Preg-solutionE Series Preg-solution Notes
Carbon in Leach / Carbon in Pulp
V
Resin in Leach
V
V
(1)
Zinc cementation(Merrill-Crowe method)
V
Modified Zinc cementation method
V
(2)
Electrowinning + Active Carbon Adsorption
V
Chemical precipitation
V
(3)
Electrolysis
V
(4)

Legend

(1) – Resin used in Eco-goldex E series pregnant solution can only be processed with Incineration method, elute does not work well. activated carbon can’t be directly used for gold adsorption in E series preg solution

(2) – The modified zinc strips/powder method is dedicated to gold precipitation from Eco-Goldex E reagent-derived pregnant solution.

(3) – The chemical precipitation method is specially formulated for gold precipitation from the E series pregnant solution process.

(4) – The electrolysis method fits only to these continuous plated (Au/Ag) E-Scrap materials.

Among the five methods developed for precious metal recovery in E series preg-solution, each one of them is effective and can be used separately with a satisfying recovery rate. Clients can select their preferred method based on their experiences, their situations and resource availability.

Preferenced methods that we recommend users select:

Modified Zinc cementation

For small-medium scale E-waste recycling operators and gold stripping hobbyists.

Electrowinning + AC Adsorption

for regular and large-scale E-Scrap materials recycling operators. The advantage of this combination is that only one chemical (The E series) is used in the whole process from gold stripping to precipitation. The prerequisite condition of this method is that operator must have reliable e-scrap material source supply to ensure continuous operation and hence higher upfront investment.

Chemical precipitation

For occasional gold stripping hobbyists. Features of this method are that the whole process is quick, preg solution temperature needs to be elevated to a certain range before effective gold precipitation initiates

Eco-Goldex O product series has been successfully used in gold mines with various scales from artisanal to large-scale operators including countries in China, Vietnam, Myanmar, the Philippines, Canada, Mexico, USA, Brazil, Tanzania, Russia and Burkina Faso.

Eco-Goldex E product series, so far, is the only type of this kind with outstanding fast gold stripping performance globally accepted and appreciated by its users from more than 50 countries worldwide in the E-waste material recycling business.

Eco-Goldex Proprietary Gold Stripping/Recovery Equipment

Eco-Goldex provides a relevant equipment system for precious metal recovery of the Eco-Goldex O and E series.

The precious metal recovery system of the O series shares the same system as the cyanidation process.

Eco-Goldex provides conventional Activated Carbon adsorption and Merrill-Crowe (Zinc cementation) methods that can be used in CIL/CIP/ heap leach flowsheet.

Eco-Goldex has developed its proprietary technology and equipment for precious metal recovery in the E series preg-solution. Its two-stage precipitation methods of the modified zinc cementation, chemical precipitation and the electrowinning + AC adsorption method may ensure a higher than 98% precious metal recovery rate from preg-solution. More importantly, the waste solution from the electrowinning + AC adsorption process can be recycled in the next stage stripping process.

Flowsheets and equipment layouts

Eco-Goldex has developed its own technology and flowsheet for complete precious metal extraction in E-scraps from stripping to recovery. 

Below are two commercialized gold stripping and recovery flowsheets and equipment layouts developed by Eco-Goldex:

Electrowinning + AC / Resin Adsorption Method

Click on the images below to enlarge

Stripping / Precipitation Flowsheet

STRIPPING / PRECIPITATION SYSTEM LAYOUT​

Final Waste Solution Treatment

No matter which method is used, the final waste solution of the E series process is nutralized when the precious metal recovery process is done.

The waste solution can be discharged according to local authority regulation.

Due to the feature of metal ions in E series preg-solution, precious metals recovery from loaded Resin beads are through incineration, resin elute method won’t apply to this process. For this reason, the Resin adsorption circuit is restricted to a small portion (about 5-15% in gold precipitation) in the whole precious metal precipitation process.

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