So what is Aluminium Dross Recycling? Have you ever wondered what happened to the by-products that we get from the extraction of valuable minerals? One of the best recyclable minerals you can find in our surroundings is Aluminium. Generally, the process of extracting Aluminium from its oxide, by the Hall-Héroult process, is known as the aluminum smelting process. So this smelting process gives us a very important by-product, which is Aluminium Dross.
So let’s have a detailed look at Aluminium Dross and recycling methodologies that can prove beneficial to boost the circular economy and sustainable development. If you need the help of an expert to help with dross recycling and other recycling methodologies, you can connect with our waste management consultants.
How do we get Aluminium Dross?
As we know, aluminum dross is a mass of solid impurities. These impurities float on molten metal. It usually appears on the melting of low melting point metals or alloys. It can also be obtained by oxidation of the metal. Aluminum dross can be mechanically recycled to separate the residual Aluminium metal from the Aluminium oxide.
Aluminum dross ranges from 1-2% of the Aluminium manufactured and comprises 30-70% Aluminium by weight. You will be amazed to know that 1 tonne of Aluminium metal production generates 10 to 20 kg of dross. Currently, in India, there is very limited processing of dross in an organized manner. The world produces approximately 65 million tonnes of Aluminium per annum, which results in approximately 1 million tonnes of aluminum dross being produced every year. Furthermore, out of which ~100k is produced in India. Hence, the environmental impact of this waste is a global problem that needs to be addressed on priority.
For aluminum dross processing, we need to know its mechanism in detail. Firstly, it is formed as a by-product during the extraction of aluminum. Secondly, aluminum dross can be wet and dry.
Waste aluminum dross consists of metallic and nonmetallic substances, like alumina, nitride, carbide, salt metal oxide, etc. In this process, aluminum dross is produced. It is an oxide film structure over metallic aluminum. At the point when the liquid aluminum interacts with atmospheric oxygen. This oxide item is called aluminum dross. It is physically expelled away from the liquid aluminum. It is a blend of metallic aluminum entangled in alumina and salt transitions utilized in smelter plants. The range of basic and auxiliary dross delivered per tonne of liquid metal is approximately 1.5% to 2.5%. Also, per year the range is up to 8% to 15%.
So now let’s talk about Types of Aluminium Dross!
Types of Aluminium Dross
There are two kinds of dross.
- Non-salt is known as white dross.
- Salt-containing is known as black dross.
White dross contains a high percentage of an aluminum substance such as Al, Al2O3. Also, it is delivered from essential and optional aluminum flux. White dross consists of a large amount of metallic aluminum substance. It’s up to 15 to 75%. It consists of fine powder separated from the liquid aluminum. But in the case of black dross, it consists of a low amount of metal substance. Also, it is created at the time of secondary aluminum refining processes. Black dross involves a mix of aluminum oxides and slag. Although, with recoverable aluminum content in the scope of 12–18%. And greater salt substance, for instance, higher than 40%, stood out from white dross.
Now, you know that waste aluminum dross consists of metal and non-metal. It is developed when molten aluminum reacts with atmospheric gases and its outer surface. White dross is produced during the elementary aluminum fabrication process. It is marginally unsafe and is all valence in the optional steel industry or ancillary Aluminium formation. The aluminum dross having a low amount of metal composition, which is somewhere in the range of 5–20 wt% of the whole weight of trash is known as secondary dross. The coarse grain or secondary dross mainly contains high amounts of salt and gas expansion compared to the compact or primary dross. The coarse grain dross has a bulk density in between the range of 0.79 to 1.11 g/cm3. So if the quantity of metallic compound increases, then the bulk density of dross decreases because the specific gravity of aluminum material is lower than its oxide form.
|White Dross||Black Dross|
|White dross consists of a large amount of metallic aluminium substance. It’s upto 15 to 75%.||But in the case of black dross, it consists of a low amount of metal substance.|
|White dross contains a high percentage of an aluminium substance such as Al, Al2O3 . White dross is formed during refining of primary Al.||It is formed during the secondary aluminium refining processes; formed when secondary recycled aluminium is refined, where a relatively large amount of chloride salt flux is used.|
|It consists of fine powder separated from the liquid aluminium. It is marginally unsafe and has less salt content.||Although, with recoverable aluminium content in the scope of 12–18%. And has greater salt substance, for instance, higher than 40% stood out from white dross.|
Aluminium Dross Recycling
Recycling the best way to save natural resources for future generations
As discussed earlier, aluminum dross is a byproduct of the aluminum smelting process. It can be mechanically recycled to separate the residual aluminum metal from the aluminum oxide. In fact, hot dross processing is a system whereby the majority of metal is recovered without chemically reducing the aluminum oxides. In this process, the dross is first crushed. Then it is separated into aluminum metal-rich particles and aluminum oxide-rich particles. This separation is usually based on density. Further, the metal-rich particles are then melted in a furnace to remove the remaining oxide particles.
So until now, you are aware of the fact that aluminum dross is an industrial waste from the aluminum refining industry. However, you will be surprised to know that aluminum dross is classified as a toxic substance. Yes! Because the disposal of dross as waste is a tough job for aluminum manufacturing industries. Dumping waste is hazardous to plants, organisms, and, lastly, the environment due to its negative impact on the environment and especially on groundwater. So the best option to sort out this problem would be aluminum dross recycling. So the very next question you arise with is how you should start with aluminum dross recycling.
Firstly, I would like you to know that a variety of products can be made from the residual aluminum dross after it is recycled into aluminum oxide. Secondly, I would like you to be clear that aluminum dross recycling is a completely different process than aluminum recycling. Aluminum recycling is where pure aluminum metal products previously used are remelted into aluminum ingots and then reused for new aluminum products. At the same time, aluminum dross recycling is a byproduct of the smelting process. It’s in the creation of aluminum from bauxite, which can be mechanically recycled. The process follows by separating the residual aluminum metal from the aluminum oxide.
To maintain a balance between development and the natural environment, recycling metal values is an essential part of the ecosystem. Now let’s take a closer look at aluminum dross recycling. Aluminium Dross Recycling is proven to be one of the beneficial methodologies. Waste aluminum dross recycling can find their ways in the following aspects given below. To learn about efficient recycling methods, connect with the best recycling consultants here.
Production of η-alumina from waste aluminium dross
- By melting at various facilities, dross is generated. It is remelted with salts to recover residual metal value. No doubt how precious these procedures are for the valuable recovery of metal.
- The remaining dross residue contains aluminum oxide, alloying elements, and salts like Sodium chloride (NaCl) and Potassium chloride (KCl).
- This residue dross while stockpiling creates pollution of the adjoining area as salts leach out to the water stream and also emit harmful gases.
- At present day domestic aluminum dross is used for developing a suitable process flow to obtain η-alumina. Currently, it is a highly valued product.
- Initially, H2SO4 leaching was carried out for both unwashed and washed dross.
- With unwashed dross, the leaching efficiency achieved was approximately 71%.
- But, washing of dross followed by leaching raised the recovery to approximately 84%.
- Washing dross is important to have maximum alumina recovery. Also further used to recover salt for recycling.
- The liquor obtained in the treatment of the dross with acid is then processed to get aluminum hydroxide of amorphous nature.
- It is done by hydrolyzing aluminum sulfate with aqueous ammonia.
- Aluminum hydroxide then proceeded to calculations which resulted in the formation of η-alumina at 900 °C.
Dross Recycling: Pyrometallurgy and Hydrometallurgy
Pyrometallurgy and Hydrometallurgical processes are best practices for the recovery of alumina from waste aluminum dross.
- Because of the advantages of low raw material requirements and little waste liquid production, pyrometallurgical technology is suitable for recycling in large-scale industrial applications.
- The presence of leachable salts like NaCl and KCl in aluminum dross aggravates the environmental crisis.
- Whereas the metallic aluminum entrapped in the matrix of alumina can be used as raw material for metal extraction.
- Pyrometallurgical methods, like rotary salt furnaces and salt-free technologies, are industrially applied for the recovery of aluminum.
- Many hydrometallurgical technologies have been patented that consume aluminum dross to produce aluminum alum and other industrially applicable products.
- Newer applications of aluminum dross include its direct utilization in the production of zeolites, ion exchangers, refractories, composites, cement and concrete products, and the generation of gases like hydrogen, ammonia, and methane.
Potash Alum From Dross Recycling
- Until now, we know that there are means of recycling dross through pyrometallurgical and hydrometallurgical routes.
- Still, a very large amount of aluminum dross is left in a landfill.
- This emphasizes the recycling of aluminum dross by the production of potash alum.
- Powdered aluminum dross is produced by reacting with potassium hydroxide.
- It is then followed by various means methodologies by filtration and slow addition of sulphuric acid. Then it is coupled with constant stirring of the solution, heating it, and cooling it in the cold water bath to produce potash alum.
- The crystals of potash alum are obtained in the solution after a few hours.
- Analysis of the product potash alum, parent liquor, and residual liquor shows that nearly 89.2% of aluminum present in the parent liquor is successfully transferred into the product potash alum crystals.
- Potash alum has many applications in wastewater treatment, pharmaceutical industries, cosmetic industries, leather tanning units, and many more.
- So, obtaining potash alum from aluminum dross recycling is a very positive solution to tackle landfill waste.
Commercial applications of aluminium dross:
- Aluminum dross can be used as filler in concrete with higher flexural and compressive strength compared to pure cement.
- As a source of calcined alumina for refractory applications.
- To produce sintered calcium aluminates used as a protective cover for liquid metals.
- As substitute green silica sand in mold material for aluminum alloy castings.
- It can be used in steel plants as desulfurization, and deoxidizer agent in refining furnace
Benefits Aluminium Dross Recycling
- Reduces landfills :
Landfills are a global issue affecting humanity. All sorts of trash are dumped, which causes serious environmental and health issues. Recycling can reduce the number of landfills considerably. Since most of the aluminum is being recycled, for dross, the amount of aluminum in landfills has also reduced. If you need assistance with landfill waste, connect with our landfill waste experts.
- Conserve natural resources:
Aluminium is a naturally occurring metal that is extracted from the earth’s surface. Since it is recycled, the mining for this metal can be reduced considerably. This prevents depletion of the resource. As a result, the extraction pressure on mother earth decreases.
- Recycled infinite time:
One of the most striking properties of aluminum is that it can be recycled many times without losing its quality. It can be recycled because aluminum is light in weight. The quality can also be maintained, which means that the value of aluminum will be maintained throughout.
- Saves energy :
Very less energy is used in recycling aluminum when compared to extracting new ones. This considerably reduces greenhouse gas emissions which is beneficial to the environment as a whole. Ultimately it will also decrease carbon footprint. Thus promoting a sustainable future for us. As it reduces energy usage in aluminum production.
- Reduce fluoride emissions:
As aluminum dross recycling helps to reduce metal content in waste which further helps to reduce fluoride emissions in aluminum production.
- Created job opportunities:
Since recycling is a lengthy process, a lot of job opportunities are created, right from picking up valuable minerals to transportation. A lot of people depend on the recycling industry for their daily livelihood.
Aluminium Dross Recycling Unit
A successful Business Story From India
We know very well how recycling encourages not only sustainable living but also provides wonderful business ideas. One of the successful business models that encourage aluminum dross recycling is- Runaya, a metals startup founded by brothers Annanya and Naivedya Agarwal. The startup offers the commencement of its aluminum dross processing and refining unit in Jharsuguda in Odisha. It ensures 100% utilization of waste through pioneering technology. Runaya’s new facility in Odisha is currently the best practice in the industry, and one can easily process 50% of waste.
They provide end-to-end green and sustainable solutions for the recovery of aluminum from dross. Also provides processing residual waste to manufacture steel slag conditioners. The steel slag conditioner briquettes have found wide acceptance in steel refining. It helps the steel industry by reducing costs and improving productivity. Thus contributing to the manufacture of more sustainable and greener steel. According to Runaya, the aluminum dross processing and refining plant in Odisha, with a capacity to process 30,000 tonnes of aluminum dross per annum. It comprehensively addresses one of the biggest challenges faced by the aluminum industry. Further on, that relates to handling, evacuation, processing, and disposal of hazardous dross in an environmentally friendly manner; besides this, Runaya has implemented an innovative and sustainable model to eliminate waste and recover metal through a patented cutting-edge technology to process the mining waste and maximize metal recovery. Runaya’s innovative technology makes aluminum dross recycling an easy process.
Aluminium Dross and Environmental Concern
Start recycling, Stop wasting!
An enormous extraction of aluminum dross delivered is landfilled. This is an inappropriate method of managing such an unsafe waste item. Management of aluminum dross is a matter of concern for all aluminum smelter units. The purpose of the current scenario is to represent another technique for reusing aluminum dross. There are majorly three byproducts generated from waste aluminum flux furnaces. These are liquid aluminum, flue gases, and waste dross. The flue gases essentially contain CO2, SO2, and H2F. It has been observed that physical and chemical processing during the aluminum dross fabrication process may contribute almost 50% of the total metal loss of approximately 1% in a primary aluminum smelter. After the refining of aluminum, a large amount of waste is generated. The aluminum industry delivers roughly around 3 million tonnes of waste dross to the environment as pollution. This harmful waste not only harms the environment but is also dangerous to individuals, plants, and even groundwater ecosystems. Hence, recycling aluminum dross is a necessity at the current time. It not only contributes to the circular economy but also saves natural resources.