BCONTVentures wrote:Thanks for the link HARJAY, very interesting. Here is some great information on PyroGenesis' DROSRITE System: PYROGENESIS' DROSRITE(TM) SYSTEM: Maximizing Aluminum Recovery Salt-Free https://www.youtube.com/watch?v=72dPyULE3wc Sustainable & Profitable Aluminum Dross Practices https://www.linkedin.com/pulse/sustainable-profitable-aluminum-dross-practices-david-d-aoust/ Dross is a waste stream generated by aluminum smelters, caused by oxygen coming into contact and reacting with molten aluminum to form a ‘scum’ or ‘oxide phase’ on the top of the metal pool. The oxides act like a sponge, floating on the surface and soaking up metallic aluminum beneath it. This presents an expensive problem when skimming the oxides out of a furnace because unavoidably a significant amount of valuable aluminum will be lost with it. Smelters typically lose anywhere from 2%-10% of their total annual melt production in the form of oxides, and the oxides can be composed of as much as 80% metallic aluminum, so the financial impact of this aluminum loss cannot be overlooked.
Dross is usually categorized as either white dross or black dross. White dross is generated from primary smelters and downstream ingot smelting operations. White dross tends to be very rich in aluminum, with aluminum content percentages ranging from 40-80%. Black dross conversely is produced by secondary smelters during their scrap re-melting processes, and as a result the dross typically contains a higher concentration of oxides, salts and various other impurities, and a lower metallic aluminum content which typically ranges from 5-25%
According to a recent report titled "Aluminum Dross Processing: A Global Review" by AlCircle, worldwide production of dross was an estimated 3 million tonnes in 2017. Despite the profitable economies in recycling dross, an estimated 1.6 million tonnes of that material went directly into a landfill. The remaining 1.4 million tonnes was recycled & resulted in approximately 460,000 tonnes of aluminum being returned back upstream into the value chain, yielding a global average recovery rate of only 33%.
Global dross production is projected to grow at 4-5% per annum, keeping pace with increasing global aluminum production, so unfortunately this waste stream will not be disappearing any time soon. So how does the aluminum industry plan to reduce the impact of dross on the bottom line and reduce the environmental impact of dross and dross processing? The industry has set three key objectives below.
Objectives:
How are we doing today? Let's take a look at our current dross practices and how they stack up against our objectives.
There are three ways to manage your dross. 1. You can simply sell the material at a percentage of the price of LME (London Metal Exchange) aluminum prices. This practice is typically used by smaller downstream smelting operations who produce 100-500 tonnes per year of dross. Largely this is because it is a hands-off practice and requires almost no effort on the smelters part. However, this practice is usually the worst from a financial perspective, as you will always be selling the material at a fraction of its actual metallic aluminum content value.
Option 2 is off-site thermal processing, by far the most common industry practice across the aluminum smelting industry. Off-site is defined as processing dross far enough away from the dross generation source to require the dross to be completely cooled before processing. Off-site processing is often times handled by a third-party contractor or toller, whereby smelters will ship their dross to the toller who will then recover as much aluminum as they can, and return the recovered material in the form of solid aluminum back to the smelters casting facilities.
Options 1 and 2 share the same pros and cons. On the upside, they are both hands-off practices which will slightly reduce the financial impact of dross while requiring very little effort on the smelters or more specifically the cast-houses part. The downsides are both environmental and economic. The requirement for transporting dross has inherent supply chain and environmental problems. Transporting dross is expensive and extremely challenging, there will always be the risk of spillage, emissions being released, or even spontaneous combustion during transport. The biggest financial downside is in the cooling of the dross. When dross is skimmed from a furnace, it is aggressively thermiting. The metallic aluminum that is attached or entrapped within the oxides is rapidly reacting with the atmosphere, converting into unrecoverable oxides. Hot dross can lose as much as 1% of the metallic aluminum contained per minute due to this thermiting reaction. In order to minimize the aluminum loss at the cooling stage, smelters will typically employ a rapid cooling process or technology such as a dross press. Unfortunately, no dross cooling technology is perfectly efficient, and a large portion of recoverable aluminum will always be lost.
Option 3, on-site processing (defined as processing close enough to the dross generation source to enable hot dross processing) would appear to be the solution to all of these problems. On-site processing eliminates the requirement to transport dross, eliminating the environmental concerns associated. On-site processing enables the dross to be processed while it is still hot, eliminating the requirement for an additional dross rapid cooling step and reducing the amount of metallic aluminum that will be lost to thermiting. Processing hot dross also comes with the added advantage of retaining and reusing the thermal energy in the dross for the recovery process.
Why haven't smelters adopted on-site processing?
Unfortunately due to the limitations of the conventional technologies being used today for dross recovery, on-site processing is simply not practical. The most commonly used technology is called the Rotary Salt Furnace (RSF). In the RSF process, cold dross is charged with a salt flux in the furnace. The furnace is heated with either an oxy-fuel burner or fossil fuel burner, usually being either natural gas, propane or fuel oil. The furnace rotates, to separate the aluminum from the oxides and salts. Oxygen is always present during the separation stage, hence why fluxing salts must be added in the furnace. Fluxing salts help protect the metallic aluminum from oxidation during the separation stage, and also to facilitate the separation of the metal from the oxide phase. As much as 30% salt is added to the dross in RSF.
After rotation, the recovered metal is ready to be tapped. The aluminum is removed from the furnace, cast into ingots and left to cool. Unfortunately the fluxing salts do an imperfect job of protecting recoverable aluminum from oxidation/thermiting during the recovery stage, and as much as 10-20% of the metallic aluminum is lost to thermiting, and another 5-15% will be lost by merging deeply inside the oxides which have now become saturated in salts and are now considered salt-cake or salt-slag residues. For these reasons, RSF can at best recover 85% of the aluminum contained within dross. After the molten metal has been tapped, the toxic by-product residues called salt-cake remain. Salt-cake is a mixture of oxide, metallic aluminum, salts and nitrides. This by-product is considered hazardous in many jurisdictions and presents very serious environmental challenges in its management: toxic leachates can be released, and because landfills are not inert, the cake can be reactive. The resulting reactions can be highly exothermic, heat generating, slowing down or stopping the desirable anaerobic microbial activity and even igniting surrounding solid waste materials. These reactions can also release toxic and flammable gases. For these reasons, managing this waste stream is extremely expensive and challenging, ruining the business case for a smelter or cast-house that otherwise would operate this technology on-site.
How can we process dross on-site?
DROSRITE™:
Due to a breakthrough innovation by a Canadian thermal green-tech engineering and metallurgical company PyroGenesis Canada Inc, there is a new, salt-free dross recovery technology called DROSRITE™ enabling smelters to operate their dross recovery on-site, streamlining the dross supply chain, eliminating all environmental concerns, and resulting in significantly improved aluminum recovery rates at a lower operating cost.
In the DROSRITE™ process, hot dross can be charged directly into the furnace. DROSRITE™ automatically injects a controlled amount of argon gas, quenching the thermiting reaction and preventing any further loss of aluminum to oxidation. The furnace tilts and rotates, separating the metallic aluminum from the oxides. After the separation period is complete, the recovered metal is tapped and can be returned directly back into the smelters holding furnaces in a molten condition, or left to cool down as ingots. Because the argon does an exceptional job of protecting the metallic aluminum from oxidation, DROSRITE™ recovers 98% of the aluminum that was contained within the dross. Next, a partial amount of the remaining oxide/residue material is discharged from the furnace, and some residue material is left inside the furnace. This residue material still contains about 2% metallic aluminum, for which there is no economical method to recover. So instead of land-filling this aluminum, as is done in the RSF process, DROSRITE™ now injects a controlled amount of oxygen to react with it (controlled thermiting reaction) therefore generating the heat required for melting the next processing batch.
Thus, under normal operating conditions, DROSRITE™ does not require any external heat source (no burner required) or salt fluxes, making the process energy requirements very low and the carbon footprint significantly lower than competing technologies. Furthermore, the residue being salt free, it can be fed directly back to the electrolytic cells of an aluminum smelter (pure alumina) or in the case of alloyed dross, reused as a flux in the steel making industry. 100% of the residues remaining from the DROSRITE™ process are recyclable.
How does DROSRITE™ stack up against the industries dross objectives?
1. DROSRITE™ recovers 98% of the aluminum contained within dross, and the remaining 2% aluminum is used as a source of fuel to power the process, meaning zero metal is wasted.
2. DROSRITE™ uses argon gas to prevent thermiting during the process, instead of fluxing salts. As a result, DROSRITE™ does not produce any toxic salt-cake or salt-slag residues.
3. DROSRITE™ wastes zero metal, and because the residues are salt-free, they can be 100% recycled either being fed directly back into the smelters operations as pure alumina, or being used as a flux for the steel making industry. All dross and dross residues produced through the DROSRITE™ process have commercial applications and avoid going to a land-fill.
The financial impact of these efficiencies is obvious. Increasing aluminum recovery rates alone yields millions of dollars per year in annual savings, exceeding $1,000,000 per 1500-5000 tonnes of dross processed.
How will you take advantage of DROSRITE™?
PyroGenesis Canada Inc. offers clients the option of on-site tolling services, whereby they will build, install and operate a DROSRITE™ plant inside the aluminum smelters facility to recycle the dross for a fixed fee per metric tonne, also charging a bonus based upon increased metal recovery rates. These outsourced environmental services allows aluminum smelters to take advantage of the massive operational and environmental benefits in having an on-site dross facility, without having to invest any capital. More importantly, this allows aluminum smelters to focus on their core business, which is smelting and casting high quality semi-finished aluminum goods to compete with steel and plastics.
In conclusion, DROSRITE™ is the worlds first highly profitable and environmentally friendly method of extracting aluminum from dross. DROSRITE™ solves all three of the key dross related issues currently facing the aluminum industry by completely eliminating the use of fluxing salts,thereby avoiding the production of toxic-salt cake residues, and recovering 98% of aluminum contained within dross, utilizing the remaining 2% aluminum as a source of fuel in place of a burner. The result is a technology that minimizes the impact of dross on the bottom line, and eliminates all environmental issues associated with the waste stream.