Field of the Invention

[0001] This invention relates to a method of recovering high-value metals such as rhenium from superalloys, a process for making a polymer for use in a metals recovery method, and a polymer adapted for such use.

Background to the Invention

[0002] Superalloys are metallic materials with a basic composition of nickel and cobalt or nickel and iron which, combined with other metals, form a highly resistant material. Use of metals such as rhenium in superalloys confers extraordinary properties to these alloys, such as increased resistance to corrosion and mechanical strength.

[0003] Recycling of rhenium from superalloys is an emerging market, with very little recycling actually being carried out currently using scrap super alloy or other alloys, or usually discarded production material.

[0004] Concerns and fluctuations in the mined supply of Rhenium are the main driving force behind its recycling. This is due to the fact that mining for Rhenium per se is not economically viable; it is actually a by-product of Copper and Molybdenum mining. If the price of either of these metals falls to an uneco- nomic level, the mine is closed. The U.S. Geological Survey Mineral Commodity Summaries in January 2008 identified the World reserves of this metal to be around 10 million kilograms.

[0005] It is known that the current recycling methods employed are quite long (at 6 - 9 months). The properties that the alloy is designed to offer, i.e. high strength, toughness and extraordinary wear resistance, make it a very difficult substance to work with. The preparation of super alloys for Rhenium recycling involves processes that specifically grind these materials. The actual decomposition in turn is carried out by wet chemistry involving heat treatment in mineral acids. This is followed by solvent extraction combined with sulphide precipitation and electro-deposition. Current costs for the process are in the region of $3000 per kg Rhenium recovered, with yields of around 70%. To be commercially attractive, an innovation to recycle rhenium requires added value by reducing the time constraints, reducing costs, increasing yields or a combination of the previous ones.

[0006] The present invention includes the manufacturing process of a poly- meric material able to trap rhenium in order to obtain highly purified extracts of this metal in a short period of time.

Summary of the Invention

[0007] The invention provides a process for forming a porous polymer template material for use in selectively recovering a metal from a solution of the metal ions, comprising polymerising a monomer admixed with a compound of the metal to be recovered, and then treating the polymer to remove the metal compound therefrom.

[0008] Preferably, the template material is formed by cross-linking a monomer in the presence of a porogen and said metal compound. [0009] The invention also provides a method of selectively recovering a metal from a solution containing the metal ions, comprising contacting a polymer template material formed by a process according to the invention with the solution containing the metal ions, and recovering the metal from the polymer. The selectivity of the polymer for a specific metal enables an aqueous solution of mixed metal ions, in which the metal of interest may be a minor constituent, to be treated economically.

[0010] The invention further provides a polymeric material adapted to capture from a solution containing ions of plural metals a specific one of the metals.

Detailed Description of the Invention

[0011] The general manufacturing process of the polymer used in the recycling of solutions with an important rhenium content involves the creation of a carbon lattice using a monomer, a cross-linker, initiator and a porogen and the use of a rhenium compound to create a template that is imprinted into this synthetic carbon polymeric material. Following the key-lock principle the rhenium compound found in a concentrated solution of this metal will be trapped selectively and the rest of the solution will be eluted unaffected.

[0012] The general process of manufacturing involves the production of the template using a rhenium salt, namely ammonium perrhenate, with a rhenium concentration ranging between 10-250mg/ml_ to control the trapping capacity of the polymer. These amounts can be increased to obtain higher yields.

[0013] The polymer is manufactured using the following proportions: 5-9% template (such as a rhenium salt), 2-6% monomer (such as vinylpyridine), 42- 54% porogen (such as chloroform) and 35-45% of crosslinker (such as Eth- yleneglycoldimethacrylate). To finalise the reaction mixture, 90-150mg of initiator (such as 1 ,1 '-azobis(cyclohexanecarbonitrile)) is added to the container.

[0014] Once all the chemicals have been added to the reaction container the mixture is vortexed for a period of time not less than 2 minutes. After the complete mixture has been homogenised a flow of nitrogen is pumped into the solu- tion to eliminate all traces of oxygen that might be present for no less than 10 minutes. Once the solution has been purged with Nitrogen, the container is then sealed and then placed in an oven for not less than 48hours, at a temperature of 70°C to allow the solution to polymerise. As the pressure within the container is likely to increase, the material used for the container needs to be able to withstand high pressures.

[0015] After the polymerisation is completed the solid polymer is removed from the glass vial and crushed into smaller particles mechanically with aids of mortar and pestle or a ball mill until the particle size is homogenous and the material reaches a sand-type texture. [0016] Once the material has been produced is placed in a column or in a container as the template has to be removed to make it functional and ready to trap rhenium. The template is dislodged by adding to the column or to the container where the material is kept, a 8M solution of hydrochloric acid (pH=-0.8) and left for 20-30 min until all the template has been removed. The final condi- tioning consists of a washing process of the polymer until the pH of the eluents reach values close to 6-7. A new addition of a solution containing rhenium at pH close to neutrality will result in rhenium being trapped.

[0017] The material can be re-used without loss of the trapping properties or damage to its structure for at least 5 cycles (number tested) but it is believed the durability goes beyond this number of cycles.

[0018] Using X-ray Fluorescence (XRF) the molecular imprinted polymer (MIP) could be analysed to determine the percentage of rhenium present within the solid MIP when samples of rhenium solution were eluted through, determining how much rhenium has been trapped by the polymer. Also Fourier trans- form infrared spectroscopy (FTIR) was also used to determine whether or not rhenium is trapped in the MIP at a wavenumber of 900 cm-1 .

[0019] It has also been proven that the MIP traps rhenium in a selective way. A solution containing seven different metals present in a typical alloy is proven to retain only rhenium when processed and eluted through the MIP when ana- lysed using XRF.