Nowadays at the forefront of every activity of every precious metal refinery is its sustainability.
Investors use environmental, social and governance (ESG) criteria to screen investments. ESG credentials are also used by companies to benchmark their practices, and by various stakeholders to understand a company’s overall impact and sustainability. The adoption and implementation of ESG practices are increasingly seen as a critical factor in long-term financial performance and corporate responsibility. For these reasons, manufacturers of production plants and technology suppliers are committed to developing solutions applicable to the refineries’ processes that have a positive impact on areas impacted by ESG concerns.
The manufacturers’ approach and its contribution are to provide innovative technologies to enable refineries to achieve sustainability goals and go beyond current practices.
This article explores some of the innovative technologies under development that focus on the more efficient use of space and energy within refineries.
Among the various plant manufacturing companies involved in the development of these topics, the IKOI SpA company, for example, has called this approach the SUS.GOLD program – a name derived from the phrase ‘sustainability in the refining of gold and precious metals’ – which is based on three pillars:
- Less energy and space
- Low impact refinery
- The comfortable refinery
Efficiency and sustainability: essential considerations for a refinery
Precious metal refineries are complex organisations where materials are constantly transformed in shape, composition and size using a wide variety of chemical, electrochemical, metallurgical and pyrometallurgical processes. In these operations, efficiency and sustainability are essential.
The SUS.GOLD program aims to optimise the use of space, volume and energy in precious metals refineries. One way to improve both is to apply processes that can improve material handling by reducing bulk volume, increasing the capacity of existing equipment and reducing energy consumption.
Mechanical processes such as shredding, chipping, compacting, pressing and briquetting are already available on the market today, all specifically designed to treat pure, alloyed and doré precious metals, as well as production plants for bank bars and ingots in closed systems. All these new technologies can be implemented in different parts of the refinery to improve overall handling, dosing, material processing and even to propose alternative value-added products.
Silver electrolysis
Most production steps in refineries produce a specific output in a particular shape, volume and size as a direct result of the process itself. As a non-limiting example, the process of electrolysis of silver produces pure metallic silver in the form of crystalline ‘sand’, often called crystals or dendrites.
This pure silver ‘sand’ presents practical challenges in terms of drying, loading, unloading and storage. It is quite easy to understand these challenges simply by considering that the bulk density of pure silver ‘sand’ in dendritic form is between 1.8 and 2.8 kg/dm³, while the bulk density of silver in solid metallic form is 10.49 kg/dm³. This ‘sand’ product occupies a volume of around five times greater that of the solid metal.
One can imagine all the consequences related to factory processes, such as when a crucible or a mould is loaded with this ‘sand’ – the volume of the crucible or mould must be five times larger than the space occupied by the metal once molten.
Using a variety of mechanical processes, it is possible to make optimisations to create a more efficient use of space, volume and energy in many refinery production phases.
Here follows an overview of some of the new technologies and new processes – some of which have already been developed and others currently under development – aimed at achieving efficiency of space, volume and energy.
Bar chipping/biting machines
Bar chipping/biting machines (illustrated above) are machines specifically designed to treat pure, alloyed and doré precious metals, that reduce solid bars into chips or shavings. Uses and benefits include:
- Reduces the market standard 1,000oz bar or 15kg solid ingots of pure silver into flakes/shavings, making them easier to handle and improving the melting speed while reducing energy consumption. This allows the shavings to pass through a subsequent densification and crumpling process to produce grains without the traditional foundry steps, reducing energy consumption and fumes, while reducing typical foundry risks for operators.
- Reduces solid doré ingots into flakes/shavings, facilitating their direct dissolution, reducing the consumption of energy and chemical products. This allows for the creation of new forms of anodes for electrolysis, with the aim of increasing the dissolution speed and reducing the consumption of energy and chemicals.
Density booster machines
These machines compact the silver ‘sand’ from electrolysis and transforms it into coarse mechanical sand – and crumple the flakes or shavings, transforming them into mechanical grains – boosting its density and reducing the occupied volume. They too are machines specifically designed to process pure, alloyed and gold precious metals.
Uses and benefits include:
- Doubles the density of the pure silver ‘sand’ from electrolysis, halving the volumes utilised in following processes. This means halving the dimensions of the crucibles, ingot moulds, transport and transfer systems, halving the energy and space required.
- Transforms the chips or shavings produced with the chipping machines into mechanical grains with the same bulk density of the traditional casting grains but without using the traditional foundry and casting steps. This reduces the energy required, as well as fume consumption and typical foundry risks for
operators.
High surface anodes
Uses for the shavings, flakes and chips obtained using the above-outlined technologies are currently being explored, as they could lead to the development of new types and shapes of anodes which could perform better than traditional anodes obtained by casting. New types of anodes could be used instead of traditional anodes, for example in the electrolytic chemical dissolution phase such as the Wohlwill or other known methods.
New designs or types of electrolytic dissolution could even be developed.
Uses and benefits include:
- The elimination of the requirement for foundry processes to produce anodes.
- An increase in dissolution speed, reduction in energy, and chemical product consumption.
Closed flameless chamber bar casting plants (illustrated below)
Following the halving of the volume occupied by the traditional ‘sand’ produced by the electrolysis of silver, the systems to produce bank bars have also become less bulky and safer, adopting closed chambers without the use of flames.
These types of plants are “foundries in a box” – that is, they are plants that constitute a complete foundry enclosed in a closed system. These make automatic the processes of loading the raw material, weighing, melting, solidification, cooling, and even the unloading of the bars – and internally, within the system –
without emissions of fumes and heat, and are totally safe for operators.
Uses and benefits include:
- Reduction of the overall dimensions of the system.
- Elimination of open flames and heat released by traditional foundry processes.
- Elimination of typical foundry risks for operators.
- Reduction of energy consumption.
- Elimination of fume production.
- Creation of a safe process.
- Cancellation of ‘head and tail’ production losses typical of long tunnel furnaces.
Closed flameless chamber bar casting plants.
