Nano Tungsten Carbide Fibers Recovery from Tungsten Waste

Tungsten carbide (WC) is a black hexagonal crystal with metallic luster and similar hardness to diamond. Since Levy R B first pointed out that tungsten carbide has platinum-like (Pt) catalytic effect in 1973, researchers began to try to use tungsten carbide instead of noble metal catalysts in heterogeneous catalysis and electrocatalysis.

nano tungsten carbide fibers recovery from tungsten waste image

Some scholars have proposed a method to prepare micro-nano tungsten carbide fibers from tungsten scrap. The diameter of tungsten carbide fibers prepared by this method is nanometer and the specific surface area is large. The production cost is greatly reduced by using tungsten scrap as raw material, and the recycling of tungsten scrap is promoted as well as the better economic benefit.

(1)Tungsten waste is extracted from tungsten leaching residue. The main components were determined to be 2.8% WO3, 23.6% Fe, 14% Mn and 2.4% CaO. The tungsten leaching residue of 500g is roasted at 600 ℃ for 8h. The roasting material is crushed after cooling and sifted through 60 meshes. Subsequently, 20% ammonia water was used to leach the tungsten oxide at 78 ℃ for 8 hours. Ammonium Paratungstate Crystal was prepared by filtration, evaporation and concentration of filtrate, adjusting the pH value to 6, lowering the temperature to 10 ℃ and holding for 4 hours. The crystals of ammonium paratungstate were heated for 4 hours at 230 ℃. Then deionized water was added to leach the thermal dissociation products, and the liquid-solid ratio was 10:1. When boiling at 80 for 6 hours under stirring conditions, the pH value of the solution should always be kept at 3.0. After cooling and clarifying, transparent supernatant was obtained, insoluble slag was removed by filtration, and ammonium metatungstate aqueous solution was obtained. Ammonium metatungstate solid was obtained by concentrated crystallization, filtration and drying of ammonium metatungstate aqueous solution.

(2)8 mg PAN powder (molecular weight 23 000) was mixed with 10 ml N, N-methyl-methylamine (DMF, analytical pure) and sealed and stirred at room temperature in a magnetic stirrer until the solution was uniform and transparent, so that the polymer was fully dissolved in organic solvents. The prepared polyacrylonitrile solution was poured into a plastic syringe with a metal needle with an inner diameter of 0.45 nm. The nano-PAN fibers were spun at 15 kV voltage and received by an aluminium sheet collector. The diameter of micro-nano PAN fibers ranges from 100 to 460 nm.

(3) The PAN fibers were heated to 220 ℃ for 30 minutes to complete the pre-oxidation process.

(4)Ammonium metatungstate aqueous solution was prepared by dissolving 345 mg ammonium metatungstate solid (85% WO3) in 10 mL water. In step (3), the pre-oxidized micro-nano PAN fibers were immersed in the aqueous solution of ammonium metatungstate until all the samples were wetted by the aqueous solution of ammonium metatungstate to prepare the primary composite fibers of ammonium metatungstate/micro-nano PAN fibers, and then dried naturally for 24 hours.

(5)Ammonium metatungstate/micro-nano polyacrylonitrile fibers were carbonized in a reduction furnace filled with H2 and C2H2 gas. The carbonization temperature was raised to 750 ℃ at a heating rate of 5 ℃/min and kept for 2 hours to prepare micro-nano tungsten carbide fibers.

The prepared tungsten carbide fibers have a diameter of nanometer and a large specific surface area, which is similar to platinum in catalyzing hydrogen and oxygen, and can catalyze hydrogenation, alkane Hydrogenolysis and reforming of syngas. At the same time, micro-nano tungsten carbide fibers have high electrochemical activity and good catalytic effect in low temperature acidic medium, acid resistance, high temperature resistance and CO poisoning resistance, and exhibit excellent catalytic oxidation performance for hydrogen, water and methanol oxidation. Therefore, micro-nano tungsten carbide fibers are expected to be used in heterogeneous catalysis and electrocatalysis instead of noble metal catalysts.

 

 

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