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Home Material Sciences Environmantally friendly and productive reclamation of scarce metals from superalloy scrap

Environmantally friendly and productive reclamation of scarce metals from superalloy scrap

Description

Current situation:

The Ni-base superalloys may contain additionally up to 19 elements that include Chromium, Cobalt, Hafnium, Niobium, Rhenium, Tantalum, Molybdenum, Tungsten, and Titanium. The majority of them are among scarce elements. The main feature of the scarcity is demonstration of the regular great surges in the metal market prices. The problem is currently so pressing that a special purpose workshop is taking place at R’07 World Congress that is the 8th event in the bi-annual correspondent Congress series. One of its topics is “How can recycling industry contribute to the prevention of metal scarcities …”.

Mostly hydrometallurgical methods are proposed for extraction of the valuable elements from Ni-base superalloys. They are based on decomposing of its fines with the acidic chloride aqueous solutions saturated with chlorine gas or with the ammoniacal leach solutions. The electrochemical methods should be also used for the operation of decomposing. The decomposing of fines is followed by the processing operations for extraction of the valuable elements including Re. It is undoubtedly typical scarce metal with fluctuant prices. The methods are efficient enough in many cases. However the requires sufficient efforts for neutralization of the spent solutions. At the same time a lot of the residues are generated at the neutralization operation. It is difficult and expansive to get rid of the residues by their following disposal, processing or recycling. The great disadvantage of the above methods is still slow rate of the decomposing operation although the several approaches for its facilitation arranging interaction of scrap with Zn were proposed.

Currently there are several technologies in operation for recycling the less complex Re-containing alloys. The general pyrometallurgical approach of processing Re-W and Re –Mo scrap is used at a plant of TOMA Group from Estonia. the technology is based on calcining of the scrap. The generated volatile Re2O7 is collected. Finally it is bounded by ammoniac for production of NH4ReO4. The brief information indicates that the Heraeus company processes Re-W(Mo) alloys by salt fusion and Pt/Re spent catalyst by alkaline pressure or sulfuric acid leach, The final Re powder is produced by hydrogen reduction. The correspondent multistage hydrometallurgical process of complex reclamation of the scarce metals including Re from superalloy scrap is rather slow and very expensive.

Proposition:

The current proposition is just devoted to developing of a novel approach in utilization of all scarce elements from the superalloy scrap that is not directly reused in the new alloy melts with or without preliminary refinement. The special emphasis will be paid for Re extraction.

The main idea of the proposed process of Re extraction from superalloy scrap is arranging the condition when the metallic Re goes into solute non-volatile state during its oxidation in a form of salts ReO4-anion without leaving the reaction zone. So the Re-containing material (Fig. 1) is processed by an oxidizer at the elevated temperatures. The binding component is introduced for transferring of Re in easily soluble non-volatile form. Drying of the product with following its calcining provides complete oxidation of the scrap. After that Re was separated from generated cake in a form of soluble salt by environmentally friendly water leaching. Next processing of the solution allows extracting Re in a form of corresponding commercial product (Re2S7, NH4ReO4, LiReO4, KReO4). The result of the preliminary trial is shown at the flowchart (Fig. 2). The rest valuable elements (Nickel, Niobium, Tantalum, Chromium, Molybdenum, Tungsten, Cobalt) are left in the oxidized form as residue. They should be reclaimed by the aluminothermic reduction process with liquid start. It has been proved by us on the titanium containing oxides that this approach provides high purity of the produced superalloys.

Innovative Aspect and Main Advantages

The technology anticipates application of the pyrometallurgical approach that is sufficiently faster than hydrometallurgical one. None hazardous waste is generated. At the same time the mostly complete oxidation of Re in the scraps at the elevated temperatures does not lead to formation of rhenium oxides in non-safety volatile form. As an accessory advantage the rate of Re reclamation is increased in terms of absence of non-desirable disorganized sublimation of Re2O7.

The extraction of Re and the other scarce metals from the superalloy scraps is environmentally sound ant cost efficient operation. It should be introduced into the recycling industry as a technology with increase productivity. The main advantage for the superalloy industry is significant increase of value of the generated scrap in terms of Re reclamation.

The Re-containing waste material
Fig. 1 The Re-containing waste material

Flowchart of the original process
Fig. 2 Flowchart of the original process

 

Contact Details

Dr. Eugene Zhidkov, Head of Department
Organization: Physico-Technological Institute of Metals and Alloys of NASU.
Address: 34/1 Vernadsky Avenue, 03680, Kiev-142, Ukraine.
Phone: +38044- 424-6057
Fax: +38044- 424-1210
E-mail: This e-mail address is being protected from spambots. You need JavaScript enabled to view it

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