The Growing Importance of Precious Metal Recovery

Gold and silver are essential materials in electronics, industrial manufacturing and advanced technologies. With increasing attention to resource efficiency and recycling, the recovery of valuable metals from ores, industrial residues and electronic waste has become an important field of technological development.

Traditionally, cyanide-based processes have played a dominant role in gold extraction. However, environmental concerns and increasingly demanding operational requirements have encouraged research into alternative chemical processes.

One of the substances attracting scientific interest is Thiourea (CH₄N₂S), also known as Thiocarbamide.

What Makes Thiourea Interesting?

Thiourea is an organosulfur compound with the chemical formula SC(NH₂)₂ and CAS number 62-56-6.

An important characteristic of thiourea is its ability to form soluble complexes with precious metals, particularly gold and silver.

In acidic solutions, and in the presence of a suitable oxidising agent, thiourea can facilitate the dissolution of metallic gold.

This property makes thiourea an interesting reagent for hydrometallurgical research and selected precious metal recovery processes.

How Does Thiourea-Based Gold Recovery Work?

The underlying principle is based on complex formation. In an acidic environment, gold can be oxidised and subsequently stabilised in solution through interaction with thiourea molecules.

A simplified chemical reaction is:

Au + 2 SC(NH₂)₂ + Fe³⁺ → [Au(SC(NH₂)₂)₂]⁺ + Fe²⁺

In this reaction, ferric ions act as the oxidising agent, while thiourea forms a soluble gold complex.

Research has demonstrated that thiourea-based systems can achieve rapid gold dissolution under appropriately controlled conditions. However, reagent stability, chemical consumption and process economics remain important technical challenges.

Applications in Modern Metal Recovery

Thiourea has attracted interest in several areas of metallurgical research and development.

Gold and Silver Extraction

Thiourea-based leaching has been investigated as an alternative approach for recovering precious metals from certain ores and concentrates.

Electronic Waste Recycling

Printed circuit boards and other electronic components may contain recoverable quantities of gold and silver. Thiourea is being studied for its potential role in recovering these metals from processed electronic waste.

Industrial Residues

Selected metallurgical residues and secondary raw materials may offer opportunities for specialised hydrometallurgical recovery technologies.

Electrochemical Recovery

Research has also investigated the recovery of dissolved precious metals from thiourea solutions through electrochemical methods, including electrodeposition.

Opportunities and Technical Challenges

Thiourea offers several characteristics of interest to researchers and process developers:

• Formation of soluble precious metal complexes.
• Potentially rapid gold dissolution under controlled acidic conditions.
• Possible applications in the recycling of secondary raw materials.
• Compatibility with selected hydrometallurgical and electrochemical recovery concepts.

Nevertheless, thiourea is not a straightforward replacement for cyanide.

Oxidative degradation, reagent consumption, process control and economic feasibility can limit its industrial application. Thiourea also has its own hazardous properties and requires appropriate handling and environmental controls.

Further research is therefore essential to improve process efficiency and evaluate its suitability for specific industrial applications.

Thiourea and the Circular Economy

The recovery of valuable metals from industrial residues and electronic waste can contribute to more efficient resource utilisation.

Thiourea-based processes represent one of several technologies being investigated for future recycling and recovery applications.

Developments in hydrometallurgy, process optimisation and reagent management may create new opportunities for thiourea in specialised metal recovery systems.

Thiourea Supply from Gentrochema B.V.

Gentrochema B.V., based in the Netherlands, supplies Thiourea (CAS 62-56-6) to industrial customers throughout Europe.

With experience in chemical distribution, international sourcing and European regulatory requirements, Gentrochema supports customers seeking a reliable supply of Thiourea for industrial and technical applications.

Thiourea is available in 25 kg bags, supported by Gentrochema’s European logistics network.

Gentrochema holds a REACH registration for Thiourea.

Contact Gentrochema

Are you looking for a reliable European supplier of Thiourea for industrial applications, metal processing or research and development?

Contact Gentrochema B.V. for product information, availability and a commercial quotation.

Gentrochema B.V. – Your European Thiourea Supplier

Website: www.gentrochema.nl
Email: info@gentrochema.nl

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Ferrocyanide-based electrolytes are enabling the next generation of safe, scalable energy storage.

The global transition from fossil fuels to electrification is accelerating rapidly, driven by the need for sustainable and low-carbon energy systems. This shift requires reliable and scalable solutions for storing electricity generated from renewable sources such as wind and solar power.

Among the promising technologies supporting this transition are iron-based redox flow batteries, which are increasingly regarded as a key future solution for safe and cost-effective long-duration energy storage.

Several ferrocyanide compounds supplied by Gentrochema are being used in research and development of these systems, including sodium ferrocyanide decahydrate, potassium ferrocyanide trihydrate and potassium ferricyanide, which can function as electrochemically active species in aqueous electrolyte solutions.

Iron-Based Redox Flow Batteries

Redox flow batteries store electrical energy in liquid electrolytes containing dissolved redox couples. During operation, the electrolytes are circulated through an electrochemical cell where reversible oxidation and reduction reactions occur.

These systems are increasingly seen as a key technology in the transition toward electrification and renewable energy systems.

Iron-based flow battery systems are attracting increasing interest due to several advantages:

• Water-based and inherently non-flammable electrolytes
• Use of abundant and relatively low-cost materials
• Independent scaling of power and energy capacity
• Potential for long operational lifetimes

These characteristics make iron-flow batteries particularly suitable for grid-scale energy storage, renewable energy integration and stationary storage systems, positioning them as an important technology in the future energy landscape.

Ferrocyanide Redox Couples

In several battery concepts, the ferrocyanide / ferricyanide redox couple is used as an electrochemically reversible system within the electrolyte.

Gentrochema supplies the following compounds that are being investigated or applied in such systems:

• Sodium Ferrocyanide Decahydrate – Na₄[Fe(CN)₆]·10H₂O
• Potassium Ferrocyanide Trihydrate – K₄[Fe(CN)₆]·3H₂O
• Potassium Ferricyanide – K₃[Fe(CN)₆]

These well-known coordination compounds exhibit stable and reversible redox behaviour in aqueous environments, making them suitable candidates for electrochemical energy storage applications.

Figure 1. Simplified illustration of a ferrocyanide / ferricyanide redox system in an iron-flow battery.

Safety and Handling

Although the term “cyanide” may raise concerns, ferrocyanide and ferricyanide compounds are well-known for their high chemical stability. In these coordination complexes, the cyanide groups are strongly bound to iron, preventing the release of free cyanide under normal conditions.

As a result, these products are widely used in industrial applications such as water treatment, food additives and electrochemical systems, where they are handled safely.

Only under strongly acidic conditions can decomposition occur, potentially leading to the formation of hydrogen cyanide. Under the neutral and controlled conditions typically used in aqueous battery systems, these compounds remain stable and are considered suitable for use.

REACH Registration

Gentrochema holds REACH registrations for sodium ferrocyanide, potassium ferrocyanide and potassium ferricyanide under the European chemicals regulation (EC) No. 1907/2006.

For these substances, Gentrochema also acts as Lead Registrant within the respective Substance Information Exchange Forums (SIEFs). This role reflects the company’s long-standing expertise with ferrocyanide compounds and its active involvement in regulatory compliance and data management for these substances.

Gentrochema is one of the few European suppliers holding full REACH registrations for these ferrocyanide compounds, providing customers with a reliable and compliant supply within the European market.

Supporting Innovative Electrochemical Applications

Gentrochema has long experience in supplying ferrocyanide compounds for industrial and chemical applications. In addition to traditional markets such as water treatment, pigments and chemical synthesis, these materials are increasingly being explored in advanced electrochemical technologies, including redox flow batteries.

The development of iron-based energy storage systems illustrates how established chemical compounds can contribute to new sustainable energy solutions.

Contact

For more information about sodium ferrocyanide decahydrate, potassium ferrocyanide trihydrate or potassium ferricyanide and their potential applications in electrochemical systems, please contact Gentrochema.

Email: info@gentrochema.nl
Website: www.gentrochema.nl

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As from 21st September 2024 our (REACH) Authorizations for Sodium Dichromates and Potassium Dichromates will expire!

We will NOT extend these authorizations and from this date, our EUROPEAN based customers cannot use these 2 products, under these applications, anymore:

POTASSIUM DICHROMATE

REACH/20/2/0; Formulation of mixtures for surface treatment of metals (such as aluminium, steel, zinc, magnesium, titanium, alloys), composites and sealings of anodic films intended exclusively for use REACH/20/2/1

REACH/20/2/1;Surface treatment of metals (such as aluminium, steel, zinc, magnesium, titanium, alloys), composites and sealings of anodic films for the aerospace sector in surface treatment processes in which any of the key functionalities, listed in the Annex, is required

SODIUM DICHROMATE

REACH/20/4/0: Formulation of mixtures for surface treatment of metals (such as aluminium, steel, zinc, magnesium, titanium, alloys), composites, sealings of anodic films and for use for electrolytic passivation of tin plated steel for the packaging industry intended exclusively for uses REACH/20/4/1 and REACH/20/4/2

REACH/20/4/1: Surface treatment of metals (such as aluminium, steel, zinc, magnesium, titanium, alloys), composites and sealings of anodic films for the aerospace industry in surface treatment processes in which any of the key functionalities listed in the Annex is required (see end of this MSDS)

REACH/20/4/2: Electrolytic passivation of tin-plated steel for the packaging industry. (ALREADY EXPIRED 14th April 2024)

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It will be necessary to re-apply to extend the review period (after 2024) and to ensure the on-going use of the chromates (amongst others : Potassium and Sodium dichromate) while work progresses to find suitable alternatives.

More information can be found here : www.adcr-consortium.eu

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This substance now become an ENVIRONMENTALLY HAZARDOUS SUBSTANCE, ADR/IMO/IATA 9, UN 3077. 

You can download MSDS here

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