ALUMINIUM DROSS PROCESSING - A Case Study

1. ALUMINIUM DROSS PROCESSING-A Case Study By: Waheed Ahmed General Manager Cast Aluminium Industries

2. 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%.

3. 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%.

4. 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)

5. Aluminium dross processing types • On site Processing • Off Site Processing

6. 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.

7. 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.

8. Challenges in off site processing • 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.

9. Steps in off site processing Segregation Process Aluminium Dross Physical Quality Check Pressed Skull Breaking Process Loose Dross Client Enrichment of aluminium dross. NMP <1mm Smelting Process in Tilting Rotary Furnace.(TRF) Metal & Dross Mass Balance to Client. Tapping Process Chemical Analysis

10. 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.

11. Processing of dross There 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.

12. 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.

13. 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.

14. Low salt process • The 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.

15. 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 drossis 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.

16. 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.

17. 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.

18. 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.

19. 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.

20. Thank You