Why Buyers Shift from Powdering to Flake Machines in Precious Metal Refining?
Why Buyers Shift from Powdering to Flake Machines in Precious Metal Refining?
Why Buyers Shift from Powdering to Flake Machines in Precious Metal Refining? The buyer’s switch from using gold and silver powder to using gold and silver flakes for aqua refinery is indeed a process optimization worthy of attention. This change is mainly based on the following significant advantages:
1、 Melting and forming stage: Flake process significantly reduces losses
A:Water atomization powder making
(1) The inherent losses of water atomization powder making process:
- Oxidation loss is inevitable: When molten metal is crushed into tiny droplets by high-pressure water flow, huge surface area is exposed to air/water.
- Precious metals (especially silver, palladium, etc.) are very easy to oxidize at high temperatures, forming a metal oxide film that wraps on the surface of the particles.
- Consequences: This part of the oxides will have a reduced or no reaction when the aqueous regia is dissolved later, becoming a “package loss”, requiring additional steps (such as reduction) to be processed and cannot be 100% recycled.
(2) “Putting” loss (specifically water atomization):
Extremely fine particles (<10μm) are swept by high-pressure water vapor or airflow, making it difficult to completely collect, enter the water circulation system or emptied.
The atomizing chamber walls, pipelines, and dust removal equipment will absorb a large amount of ultrafine powder.
(3) Volatile loss (high temperature metals such as gold):
When the molten metal stream is impacted by high-pressure water, locally violent cooling produces steam, which may entrain metal vapor to escape (especially when the vacuum atomization is incomplete).
B. Centrifugal technology flake making
1.How to reduce losses in centrifugal film making process:
(1) Extremely short exposure time & controllable atmosphere:
The molten metal flows out through the fine holes at the bottom of the crucible and immediately falls on the high-speed rotating copper disk.
The entire process is carried out in a protected or sealed/semi-sealed environment of inert gases (such as nitrogen, argon).
Advantages: The time for metals to be exposed to oxidized environments is very short (milliseconds), and the surface oxide layer is extremely thin (usually only nanometers), which is negligible.
(2) No “collective” problem:
It is molded into a solid sheet (ten to hundreds of microns thick), with a large size and high density, and falls directly into the collection container.
There is no airflow/water flow crushing process, which completely avoids the loss of fine powder being taken away by the medium.
(3) Volatility controllable:
The melt flow is small and fast solidified, with extremely small volatility. The inert atmosphere further suppresses volatility.
2. Improve dissolution rate and efficiency：
Powder problem: Although the total surface area of ultrafine powder is large, it is easy to float on the liquid surface or clump when it is actually poured into aqua regia, forming a “crusting” phenomenon. This hinders the full contact between the acid and the inside of the powder, but reduces the effective reaction area, and the dissolution rate becomes slower and uneven. In addition, the powder made by water atomization is wet, and it takes a long time to dry before entering the next process.
Flake advantage: Flakes (especially thin flakes) are easier to sink and remain separated after being put into aqua regia, allowing the acid to continuously and evenly contact the metal surface. Although the total surface area may be slightly smaller than that of ultrafine powder of the same weight, the effective contact area is higher, the dissolution process is smoother, faster and more thorough, and the overall efficiency is improved. In addition, metal sheets made using centrifugal technology do not need to be dried and can be directly put into the next process.
3. Reduce precious metal losses：
(1) Reason 1: Powder problem: Fine powder is very easy to generate dust during operation (such as weighing, transferring, feeding). Gold and silver are extremely valuable, and even a small dust loss will accumulate to a huge cost. The gases (NO, NO₂, Cl₂) produced when aqua regia is dissolved are also more likely to carry fine particles and splash or form aerosols.
Flake advantage: Flakes are physically larger and heavier, and almost no dust is generated. During the feeding and dissolution process, the risk of loss due to gas entrainment is also greatly reduced, which significantly improves the recovery rate of precious metals.
(2) Reason 2: Metal powders are generally made by water atomization, and metal sheets are generally made by centrifugal technology. After smelting, casting and weighing, the production loss of sheets is relatively small. After production, precious metal sheets are also easier to collect.
4. Improve operational safety and environmental friendliness：
Powder problem: Gold and silver powders, especially ultrafine powders, have a high risk of explosion (when reaching a certain concentration and encountering a fire source). At the same time, operators inhaling heavy metal dust is extremely harmful to their health. Dust can also easily pollute the working environment.
Flake advantage: Flakes eliminate the risk of dust explosion, greatly reduce the risk of operators inhaling heavy metals, improve the working environment, and are more in line with modern safety production and environmental protection requirements.
5.Simplify the operation process:
Powder problem: Handling powder requires more precise weighing equipment (easy to adsorb and float), more careful transfer operations, more attention to preventing agglomeration and splashing during dissolution, and subsequent reactor cleaning may also be more troublesome (residual powder).
Flake advantages: Flakes are easier to weigh, grab and feed. The feeding process is simpler and faster. The dissolution process is more controllable and the risk of splashing is reduced. The residue in the container after the reaction is usually less and easier to handle.
6.Improve the controllability of the dissolution process:
Powder problem: When the powder is added to aqua regia, the reaction may be too violent and concentrated, generating a large amount of heat and gas, resulting in splashing and even increased risk of loss of control. Violent local reactions may also produce unnecessary side reactions.
Flake advantages: Flakes can be added in batches and in an orderly manner, and the reaction rate is relatively smoother and easier to control. Heat release and gas generation are more uniform, reducing operational risks and also conducive to obtaining a purer solution.
7.It is conducive to subsequent solid-liquid separation:
Powder problem: If the dissolution is incomplete, the remaining extremely fine powder or some fine precipitates produced by the reaction (such as AgCl under certain conditions) will bring difficulties to the subsequent solid-liquid separation steps such as filtration, and it is easy to penetrate or block the filter material.
Flake advantage: Flakes usually dissolve more thoroughly. Even if there is a small amount of undissolved residue (such as some insoluble alloy components or encapsulated impurities), its particle size is relatively large, which is easier to filter and separate, and obtain a clearer precious metal solution.
8.It may reduce the consumption of aqua regia:
Although the amount of aqua regia required for one kilogram of gold and silver is fixed in theory, more efficient and thorough dissolution (avoiding incomplete local reaction caused by powder agglomeration) and reducing splashing losses may mean that less aqua regia is required to achieve the same dissolution effect in actual operation, or less waste.
In summary, the main driving forces for customers to switch from powder to flake are:
Economic benefits: Reducing precious metal losses (dust, splashing) is the core, directly improving recovery and profits. Improving dissolution efficiency also means increased production capacity.
Safety and environmental protection: Eliminating dust explosions and health risks, complying with increasingly stringent regulatory requirements, and reducing accident costs.
Easy to operate: Simplify the process, improve production efficiency, and reduce operational difficulty and labor intensity.
Process optimization: Obtain a more controllable and thorough dissolution process and a more easily handled solution.
If you are interested in CDOCAST Metal Flake Making Machine, you can click the link to learn more details: https://youtube.com/shorts/P_AglRgfw-4?si=GCUKI8V78NsUOze5
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