Minor Metals & Mineral Conservation an Overview: Part Five
By Dr Pradeep K. Maitra
dipalyconsultants@hotmail.com, Smriti Nagar Bhilai, India

요약:

The recycling of minor metals and minerals is an important factor of the overall conservation strategy and can be separated into two developing areas. Recycling of end of life wastes has a number of key pre-treatment steps which are followed by scrap dealers including collection, sorting, labeling and recovery.
Recycling of mixed metal scraps presents some other obstacles and it is therefore necessary to follow some clear guidelines to ensure the processing of such materials is handled correctly and efficiently.

For conservation of MMs various processes are being developed by several agencies, with two important recycling processes briefly discussed below;

a) Recycling of EoL-EEE wastes:

For economical and systematic recovery of metals from e-wastes certain pre-treatment steps are to be taken by the scrap dealers, as given under;

i) Collection & Dismantling - After collection of EoL-EEE scraps, the first step involves disassembling of equipment into various parts.

ii) Sorting - The separation of wastes into different categories such as (metal frames, power supplies, circuit boards, PCBs, structural metallic parts made up of Fe, Al, Cu, electronic components, diodes, resistors, electrodes, electric components like valves, screens, cables & cable tapes, transformers, switches, batteries, heat sinks glass parts etc.). The traditional methods of component recovery from PCB may be replaced by liquid N2, treatment resulting in the formation of numerous micro cracks & enabling liberation of Cu circuit network from embedded plastic of PCBs.

iii) Labeling – After sorting & identification of individual parts & components all items are labeled and the stock inventory is taken for value assessment and the labeled components are shipped to the appropriate, competent & established recyclers.

iv) Recovery- The EoL commodities containing valuable metals, of which Ni, Cu, Cr, Se, Pd, Sn, Au, Ag, Cd, Pb, Co, PGM etc. and their compounds are all examples. Such complex aggregate of metals pose a technical challenge in identification, separation and their efficient recoveries, since potential metal losses would occur if inefficient recovery processes are employed. To solve these problems, the recycling technology & effluent treatment process were developed and transferred to the registered recyclers. Consequently for efficient recovery of MMs from EEE, the identified scraps are required to be received (as per National & International regulations) by the recyclers equipped with adequate licence, working facilities and knowledge of waste recycling for recovery of metals.

b) Recycling of Mixed Metal Scraps - The mixed old scraps containing valuable MMs are sorted by the scrap traders & earmarked as per ISRI (Institute of Scrap Recycling Industries) nomenclatures and specifications. (the uncontaminated new scraps are usually recycled by primary producers but often appear in the market). The various MMs are recovered from the mixed scraps which serve as a major source of industrial applications. Common nonferrous metal or alloy scraps contain, Cu, Al, Zn, Mg, Sn, Ni, Pb and may rarely contain precious metals such as Au, Ag, and Pt and distinct metals such as Co, Hg, Ti, W, As, Be, Bi, Ce, Cd, Nb, In, Ga, Ge, Li, Se, Ta, Te, V, and Zr are frequently found.

The initial sorting of scrap is done, based on physical appearances & magnetic devices into metallic/non-metallic, ferrous & non-ferrous metals and then into groups like mild steel, cast iron, alloys-steel, Al & Al-alloys, Cu & Cu-alloys, Cu-Ni, Brass, Gun metal, Zn & Zn-dross, Zn- alloys Pb & Pb-alloys etc then into sub-groups like sheet, plates, wires, rods, etc. Usually scrap consists of metal items of almost every type in bulk quantities like HMS (The heavy melting scrap)1 & 2, used rails, shredded MS-scrap, and cast iron.

Subsequently the precise identifications are made, based on their source of supplies and primary producers trademarks such as; Special Metal Corporation (Inconel, Incoloy, Nimonic, Udimet, Monel and Nilo), General Electric (alloys-GE-718), Rene-41 (trade name of GE-high temperature Ni base alloy containing Cr-15, Co-12, Mo-10, Ti-3, % each) recovered from Gas turbine, aircraft and land/marine equipment etc. Monel (trade name of special metal corpn. 400, 401, 404, K-500, R-405 etc. as per ASTM/ALSI, B-127, 164, 865) & Inconel (600, 617, 625, 718, X-750 ) contain Ni, Cr, Mo, Nb etc. Stellite-(Delero-stellite Co), wear resistant alloys with Co Ni and Fe. Haynes (Haynes International Inc), Alloy-25, 75, 230, 242,,718,,C263, HR-12O, R41, X-750 etc) & Hastelloy (B-2,3, C-4,22, 276, 2000, G-30, N, W, X etc) are recovered from aerospace, metalworking, automotive wastes. Waspaloy (United Technologies Corps), contains Ni-58, Cr -19, Co-13, Mo-4, Ti-3, Al-1.4 each %.

Ni-hard white cast irons scraps which are low-Cr alloys contain 3 to 5% Ni and 1 to 4% Cr. Mixed scraps are handled by the traders at their scrap yards where identification, sorting, and often downstream melting & casting are executed. The MMs recycling from mixed scrap requires their separation on site by shearing, chopping, stripping, baling & up grading the scrap into a marketable package. The following steps are involved in recycling;

Sorting- The different types of metals are sorted from the mixed scrap through chemical analyses of metals and by using other physical methods. The various metals are identified and shorted by the recyclers at the scrap yard itself. Currently the metal & alloys are identified by in-situ chemical analysis with hand held X-ray spectrometer. The quick analyses exhibit the compositions of different types of metals & alloys representing tool steel, high speed steel, low or high alloy steel, heat or corrosion resistant alloys, magnet alloys, heating elements, electrodes, alloy-cast iron, alloy-steel, super alloys etc.

Baling- Hydraulic scrap baling presses are capable of compressing various metal structural, metallic chips into cuboid bales. The density of these bales is high, so that they are convenient to store, transport & melt. Balers are used to reduce material handling costs and for recycling waste generated by manufacturing processes. It can process tons of metal chips at both manufacturing plants & scrap yards.

Shearing- Used to cut metal pieces into manageable sizes with the help of a hydraulically operated chopping machine capable of exerting high extremely high cutting pressures.

Magnetic separation- includes permanent magnetic separators, liquid line magnetic separators, eddy current separators, high intensity drum separators, high tension electrostatic drum separator, high intensity roll separators, and many more.

Media Separation- Shredders and rotating magnetic drums used to separate non- ferrous & ferrous metals. Further separation is also achieved by employing high pressure air flow and by solid liquid separation techniques.

Melting- The melting furnace is used to melt down the scraps and the melt is poured into ingot casts. The ingots may be used by foundries or making semi-finished products. Cu- scrap is especially useful for small copper items like small pieces and wire cuttings into ingots. The identified scraps are labeled with codes and a photograph of each lot representing particular compositions which are then packed for delivery to the buyers.

Conclusion

The International Resource panel (UNEP-2010) report warned that the recycling rates of some rare metals used in applications such as mobile phones, battery packs for hybrid cars and fuel cells are so low that unless future EoL recycling rates are significantly stepped up, these critical metals will become unavailable for use in modern technology. India produces large quantities of metallurgical & electronic goods and simultaneously generates huge metal scraps and EoL EEE. The metal scraps containing ferrous & major non-ferrous alloying metals are recovered satisfactory, but not all the minor metals are recovered so effectively. Similarly electronic gadgets have reached to the remotest locations especially mobile phones, TV, CFL, Radio, watches, toys etc., but there is no such agency which could collect the EoL commodities from the end users, and hand it over to the appropriate recyclers. Such flaws in commodity marketing should be addressed. The onus lies on the both sellers & users to conserve the MMs & protect minerals from depletion and the environment from the harmful effects of spent toxic wastes. In addition metal and mineral conservation provides an excellent opportunity for researchers to develop economic and efficient methods of reclamation of valuables from the waste.

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