aluminium dross - a case study-final
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aluminum wasteTRANSCRIPT
ALUMINIUM DROSS PROCESSING-A CASE STUDY
By:Waheed Ahmed General Manager Cast Aluminium Industries
WHAT IS ALUMINIUM DROSS
Aluminium dross is the mixture of metallic aluminium and non metal part mostly Aluminium oxide.
Dross is formed on the surface of molten Aluminum or its alloys by oxidation.
Dross is a valuable by product of any Aluminium Smelter or Aluminium Foundry.
Dross is recycled to recover the valuable Aluminium Metal world wide.
Typical dross generation from a primary operation can be from 0.8% to 1.3% of Aluminium output.
From the secondary smelters it can reach up to 10%.
TYPES OF ALUMINIUM DROSS
Broadly there are two types of drosses White Dross (Primary Dross) Black Dross (Secondary Dross)
The drosses are heterogeneous in nature because of so many steps involved at generator’s site. The recoverable metal content varies from 10% to 70%.
EFFECT OF SMELTER’S PRACTICE ON DROSS QUALITY Following key steps are involved
Drossing Temperature. Fluxing Practice before drossing. Skimming Practice. Cooling of dross as soon as possible.
WAYS TO COOL THE DROSS. Air Cooling. Rotary Dross Cooler. AROS Argon Cooler. Dross Press (Most Widely used Practice)
ALUMINIUM DROSS PROCESSING TYPES
On site Processing
Off Site Processing
ONSITE PROCESSING In this process the dross is skimmed from the molten
metal and is transferred directly to the Hot Dross Processing Machine or furnace. The equipment uses the hot dross thermitting reaction of Aluminium Metal and the Al metal is separated from the oxides by means of specific gravity and the agitation.
The metal is either cast into the ingots or the liquid metal is fed directly to the smelters furnaces.
Following are the challenges associated with this process, Relatively low metal recovery as some metal is used as
fuel. Unstable process encourages Al Metal thermiting. Specialized Equipment requires more maintaince.
OFF SITE PROCESSING The off site processing of Al dross is the most
commonly done practice in the world. In this practice the processor removes the dross from the smelters premises and takes it to the processing facility. The dross from the smelter is taken on the following 2 basis.
The processor buys the dross The processor takes the dross on tolling basis
i.e. the metal goes back to the smelter.
There are a number of challenges associated with the off site processing of the Aluminium dross specially when on tolling basis like, Transportation of dross from Smelter in safe and
environment friendly manner. The storage of dross at the processing facility in
an environment friendly manner. The processing of dross with the BAT to maximize
the metal recovery. The safe and sound disposal / usage of salt slag /
NMP with no liability towards the smelter. The effective & efficient processes of
communication.
CHALLENGES IN OFF SITE PROCESSING
STEPS IN OFF SITE PROCESSINGSegregation Process
Pressed Skull Breaking Process
Tapping Process
Enrichment of aluminium
dross.
Smelting Process in Tilting Rotary Furnace.(TRF)
Chemical Analysis
Met
al &
Dro
ss M
ass B
alan
ce to
Clie
nt.
Aluminium Dross Physical Quality Check
Client
NMP<1mm
Loose Dross
DROSS STORAGE & ENRICHMENT The dross is off loaded in covered shed /
designated bunker. The quality inspection team keep record of
each delivery by visually inspecting the quality of dross.
Any observation of foreign items and un melted alloying metals is immediately reported back to the generator.
The breaking of dross pressed lumps is done by the JCB Jack Hammer.
The loose material is passed through a enrichment process where by NMP is taken out the process.
PROCESSING OF DROSSThere are many methods and technologies available for the processing of dross. The key criteria of selection should take into account the local environmental laws, smelter’s vision and industrial infrastructure of the country.
TYPES OF OFFSITE PROCESSING The major types of off site processing are as
follows. The Salt Process. Most stable process,
Maximizes the waste thus requires more energy and down stream handling of salt slag requires bigger plant.
The Low Salt process. Stable process, does not contribute much in increasing the waste but still requires down stream recycling of salt slag
The No Salt process. Unstable process, Can be made stable and requires less work down stream to recycle salt free waste.
SALT PROCESS The Salt Process uses between 20-30% of
fluxes that is the combination of sodium and potassium chlorides with a small portion of cryolite.
The challenges associated are, The washing of salts. The inertization of oxides. The reuse of oxides in other allied industries.
LOW SALT PROCESSThe Low Salt process uses between 8-14 %
of fluxes having the same composition as of the salt process.
The challenges associated are the same as that of the salt process. The washing of salts. The inertization of oxides. The reuse of oxides in other allied industries.
SALT LESS PROCESS The Salt Less process uses no additional
fluxes at all. The challenges associated are,
To achieve the maximum recoveries equivalent to the more established salt processes.
The control of thermitting reaction during the melting of the dross is of utmost importance and requires experience & special technology / tools.
Manageable environmental challenges. No washing is required and relatively easy use
of oxides in other industrial sectors.
SALT SLAG / NMP HANDLING , STORAGE & DISPOSAL Salt slag handling, storage and disposal
should be in accordance with the local authorities rules & regulations. It should be kept in mind that the smelter should not get any complaint for the salt slag or NMP. A no liability must be provided to the smelter.
REPORTING MECHANISM Mass balance of the complete incoming material
with traceability. Chemical Analysis : The analysis of each heat to be
marked on the sows as per smelter’s requirement along with the heat number for tracebility.
All the steps involved in the dross processing must be reported to the smelter on weekly, fortnightly and monthly basis.
The visits between the smelters & the processor keeps the relationship close and the technological collaboration not only improves the benefits of both the organizations to the maximum but also helps to develop a trust between the organizations.
DISPATCH OF METAL TO SMELTER Metal is weighed and the specific heat
numbers are marked along with the weighs on the metal and is sent to the smelter in an safe and environment friendly manner.
Before the dispatch of metal to the smelter the metal is checked for the quality assurance so that there is no complain in the final product from the smelter and is safe for the use of smelter as well.
CONCLUSION Dross is not a waste but a valuable by
product of the smelter. Dross Handling at smelter is of utmost
importance. Reporting mechanism and complete
traceability of the dross by the processor is key a factor for smelter’s peace of mind.
Vision of the smelter / authorities is the vital factor in achieving the “Zero Waste Status”.
Down Stream handling of the waste is very important in selecting the dross processing process.
Thank You