So what is Aluminium Dross Recycling ? Have you ever wondered what happened to by-products that we get from 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 aluminium smelting process. So this smelting process gives us a very important by-product that is Aluminium Dross.

So let’s have a detailed look about Aluminium Dross and recycling methodologies that can prove beneficial to boost the circular economy and sustainable development. If you need help of an exert with dross recycling, you can connect with our waste management consultants.

How do we get Aluminium Dross?

How do we get aluminium dross

As we know, aluminium dross is a mass of solid impurities. These impurities are floating on a molten metal. It appears usually on the melting of low melting point metals or alloys. It can also be obtained by oxidation of the metal. Aluminium dross can be mechanically recycled to separate the residual Aluminium metal from the Aluminium oxide.

Aluminium 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 organised manner. The world produces  approximately 65 million tonnes of aluminium per annum. Which results in approximately 1 million tonnes of aluminium 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.

Mechanism

For aluminium dross processing we need to know  it’s mechanism in detail. Firstly, it is formed as a by-product during the extraction of aluminium. Secondly, aluminium dross can be wet and dry.

Waste aluminium dross consists of metallic and non metallic substances. Like alumina, nitride, carbide and salt metal oxide, etc. In this process, aluminium dross is produced. It is an oxide film structure over the metallic aluminium. At the point when the liquid aluminium interacts with atmospheric oxygen. This oxide item, called aluminium dross. It is physically expelled away from the liquid aluminium. It is a blend of metallic aluminium entangled in alumina and salt transitions utilised in smelter plants. The range of basic and auxiliary dross delivered per tonne of liquid metal is approximately 1.5% to 2.5%. Also, for per year the range is upto 8% to 15%.

So now let’s talk about Types of Aluminium Dross!

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Types of Aluminium Dross 

Difference between white and black aluminium dross
Difference between white and black aluminium dross

There are two kinds of dross.

  1. Non-salt containing known as white dross.
  2. Salt-containing known as black dross. 

White dross contains a high percentage of an aluminium substance such as Al, Al2O3 .   Also it is delivered from essential and optional aluminium flux. White dross consists of a large amount of metallic aluminium substance. It’s upto 15 to 75%. It consists of fine  powder separated from the liquid aluminium.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 aluminium refining processes. Black dross involves a mix of aluminium oxides and slag. Although, with recoverable aluminium 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 aluminium dross consists of metal and non-metal. It is developed when molten aluminium reacts with atmospheric gases and its outer surface. White dross is produced during the elementary aluminium fabrication process. It is marginally unsafe and is all valence in the optional steel industry or ancillary Aluminium formation. The aluminium dross having a low amount of metal composition, which is somewhere in the range of 5–20 wt% of the whole weight of dross is known as secondary dross. The coarse grain or secondary dross mainly contain 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 aluminium material is lower than its oxide form. 

White DrossBlack 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

Aluminium Dross Processing Method
Aluminium Dross Processing Method

Recycling the best way to save natural resources for future generations

As discussed earlier, aluminium dross is a byproduct of the aluminium smelting process. It can be mechanically recycled to separate the residual aluminium metal from the aluminium oxide. Infact, hot dross processing is a system whereby the majority of metal is recovered without chemically reducing the aluminium oxides. In this process, the dross is first crushed. Then it is separated into aluminium metal rich particles and aluminium 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 about the fact that aluminium dross is an industrial waste from the aluminium refining industry. Although you will be surprised to know that, aluminium dross is classified as toxic substances. Yes! Because, the disposal of dross as a waste is a tough job for aluminium manufacturer 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 aluminium dross recycling. So the very next question you arise with is how you should start with aluminium dross recycling?

Firstly, I would like you to know that a variety of products can be made from the residual aluminium dross after it is recycled into aluminium oxide. Secondly, I would like you to be clear that aluminium dross recycling is a completely different process than aluminium recycling. Aluminium recycling is where pure aluminium metal products or previously used are remelted into aluminium ingots and then reused to new aluminium products. Whereas aluminium dross recycling is a byproduct of the smelting process. It’s in the creation of aluminium from bauxite, which can be mechanically recycled. Process follows by separating the residual aluminium metal from the aluminium oxide.

To maintain a balance between development and natural environment, recycling of metal values is an essential part of the ecosystem. Now let’s take a closer look towards aluminium dross recycling.Aluminium Dross Recycling is proven to be one of the beneficial methodologies.Waste aluminium dross recycling can find their ways in following aspects given below.

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Production of η-alumina from waste aluminium dross

Formation Of N Alumina
Formation Of N Alumina
  • 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 aluminium 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 water stream and also emit harmful gases. 
  • At present day domestic aluminium 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 use to recover salt for recycling.
  • The liquor obtained in treatment of the dross with acid is then processed to get aluminium hydroxide of amorphous nature.
  • It is done by hydrolyzing aluminium sulphate with aqueous ammonia.
  • Aluminium hydroxide then proceeded to calcinations which resulted in the formation of η-alumina at 900 °C.

Dross Recycling: Pyrometallurgy and Hydrometallurgy

Pyrometallurgy and Hydrometallurgical process are best practises for the recovery of alumina from waste aluminium 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 aluminium dross aggravates the environmental crisis.
  • Whereas the metallic aluminium 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 recovery of aluminium.
  • Many hydrometallurgical technologies have been patented that consume aluminium dross to produce aluminium alum and other industrially applicable products.
  • Newer applications of aluminium dross include its direct utilisation in the production of zeolites, ion exchangers, refractories, composites, cement and concrete products and generation of gases like hydrogen, ammonia, 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 aluminium dross is left in landfill. 
  • This emphasises recycling of aluminium dross by the production of potash alum. 
  • Powdered aluminium dross is produced by reacting with potassium hydroxide.
  • It is then followed by various means of methodologies by filtration, slow addition of sulphuric acid. Then it is coupled with constant stirring of the solution, heating the solution 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 the residual liquor shows that nearly 89.2% of aluminium 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 aluminium dross recycling is a very positive solution to tackle landfill waste.

Commercial applications of aluminium dross:

Commercial applications of aluminium dross recycling
Commercial applications of aluminium dross recycling
  • Aluminium 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 mould material for aluminium alloy castings.
  • Can be used in steel plant as desulfurization, deoxidizer agent in refining furnace

Benefits Aluminium Dross Recycling

Benefits of aluminium dross recycling
Benefits of aluminium dross recycling
  • Reduces landfills :

Landfills are a global issue affecting mankind. All sorts of trash are dumped which causes serious environmental and health issues. Recycling can reduce the amount of landfills considerably. Since most of the aluminium is being recycled, for dross, the amount of aluminium in landfills has also reduced.

  • Conserve natural resources: 

Aluminium is a naturally occurring metal that is extracted from the earth’s surface. Since its being 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 aluminium is that it can be recycled many times without losing its quality. It can be recycled because aluminium is  light in weight. The quality can also be maintained which means that the value of aluminium will be maintained throughout.

  • Saves energy :

Very less energy is used in recycling aluminium when compared to extracting new ones. This considerably reduces the greenhouse gas emission 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 aluminium production.

  • Reduce fluoride emissions:

As aluminium dross recycling helps to reduce metal content in waste which further helps to reduce fluoride emissions in aluminium 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.

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Aluminium Dross Recycling Unit

A successful Business Story From India

We know very well how recycling not only encourages sustainable living but also provides wonderful business ideas. One of successful business models that encourage aluminium dross recycling is- Runaya, a metals startup founded by brothers Annanya and Naivedya Agarwal. The start-up offers the commencement of its aluminium dross processing and refining unit in Jharsuguda in Odisha. It ensures 100% utilisation of waste, through pioneering technology. Runaya’s new facility at 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 aluminium 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 in reducing costs and improving productivity. Thus contributing to the manufacture of more sustainable and greener steel. According to Runaya, the aluminium dross processing and refining plant in Odisha, with a capacity to process 30,000 tonnes of aluminium dross per annum. It comprehensively addresses one of the biggest challenges faced by the aluminium 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 maximise metal recovery. Runaya innovative technology makes aluminium dross recycling an easy process.

Aluminium Dross and Environmental Concern

Start recycling, Stop wasting!


An enormous extraction of aluminium dross delivered is landfilled. This is an inappropriate method of managing such an unsafe waste item. Management of aluminium dross is a matter of concern for all the aluminium smelter units. The purpose of the current scenario is to represent another technique for reusing aluminium dross. There are majorly three byproducts generated from waste aluminium flux furnaces. These are liquid aluminium, flues gases and waste dross. The flues gases essentially contain CO2, SO2 and H2F. It has been observed that physical and chemical processing during aluminium dross fabrication process may contribute almost 50% of the total metal loss of approximately 1% in a primary aluminium smelter. After the refining of aluminium, a large amount of waste is generated. The aluminium industry delivers roughly around 3 million tonnes of waste dross to the environment as pollution. This harmful waste not only harms the environment but it is also dangerous to individuals, plants, and even groundwater ecosystems. Hence, recycling aluminium dross is a necessity for current time. It not only contributes to the circular economy but also saves natural resources.

Prajakta bhujbal
Author

Prajakta Bhujbal is an enthusiastic BSc Environmental Science student. She is a passionate reader and willing to share her thoughts with you. Today, at a peak of climate change, she strongly believes that it's the responsibility of each and every one to show an honest gratitude towards our mother earth.Her blogs aim to teach people about how our environment can become more beautiful with innovative designs of ideas and technology.

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