X-ray absorption
fine structure (XAFS)

Development of High-Efficiency Recycling
Technology for Tungsten

Research method

Chemical state analysis of tungsten during ion exchange in collection system

Role of SPring-8

Achievements

BackgroundResults*Tungsten is a rare metal with the chemical symbol W and the highest melting point of all metals. Tungsten production is small, and its extraction
is locally distributed in China. Tungsten carbide is used as the principal component of carbide tools because of its high hardness.
**Ion exchange method: A sample is placed in a column filled with an ion exchange resin, and the target substance is adsorbed onto the resin.
Then, a buffer solution used for elution is introduced into the column to separate the adsorbed substance from the resin and obtain the target
substance.

Demand for tungsten is increasing, whereas its
natural abundance is small. To help ensure astable supply of tungsten, techniques for
efficiently collecting and recycling tungsten fromused carbide tools and tips are necessary.
Among the various methods for collecting
tungsten, a method using an ion exchange
column, which can be performed in a small-scalesystem compared with conventional methods, isexpected to reduce the environmental load oftungsten recycling. To achieve efficient ion
exchange, tungsten should be fully adsorbed onto
an ion exchange resin and be completely eluted.
In practice, however, tungsten crystals precipitate,clogging the column, and preventing thecomplete elution of tungsten. This has remained along-standing problem.

X-ray absorption fine structure (XAFS)
measurement using SPring-8 synchrotron
radiation can reveal the electronic state andchemical structure of substances in a sample.
Three tungsten ion species, WO42-, HW6O215-, andH2W12O406-, were introduced separately into the ion
exchange column, where they were adsorbed
onto the ion exchange resin and eluted. XAFS
measurement revealed that some of the adsorbed
H2W12O406- ions, which contain the most tungsten
atoms of the three species, still remained in theresin. Detailed analysis clarified that the ions werepartly decomposed into the other two ion species
and these three ion species remained in the resin
at a certain proportion.
From the above result, optimal conditions forthe adsorption and elution of tungsten weredetermined, thus improving the collection
efficiency of tungsten.

Used carbide tools and tips containing tungsten

XAFS measurement at SPring-8

Development of a method of collecting tungsten* using an ion exchange
method**Analysis of the change in the chemical state of tungsten during ion exchange
Optimization of adsorption and elution conditions to enable the highly efficientcollection of tungsten throughout the entire process (95%) and to reduce energy
consumption by 40%
R&D facility: Sumitomo Electric Industries, Ltd.
† This research was supported by Japan Oil, Gas and Metals National Corporation (JOGMEC).

XAFS measurement results for adsorbed ions remaining inresin during ion exchange of H2W12O406-

The long thin tube is the ion exchange column.
Synchrotron radiation is irradiated onto the orange film.

Used carbide tips

Tools for urban development Used drills and endmills

White circles represent measured values. The spectra of three tungsten ionspecies (WO42-, orange; HW6O215-, blue; H2W12O406-, green) are used as referencesin the analysis. When the percentages of WO42-, HW6O215-, and H2W12O406- are 32,13, and 55%, respectively, the spectrum of the adsorbed ions remaining in theresin fits the white circles. From this result, the percentages of the remaining
ion species in the resin were obtained.

Wear-resistant tools
Adsorbed ions remaining in resin

Used carbide tools are dissolved in molten salt to obtain a Na2WO4 solution. The solution is introduced into an ion exchange resin to collecttungsten ions in the (NH4)2WO4 solution, which is then heated and condensed so that it crystallizes as ammonium paratungstate (APT). APT isoxidized by roasting to obtain WO3, which is then reduced to tungsten. The obtained tungsten is reacted with carbon to form the reusable tungsten
carbide (WC).
Research and development
Used carbide
tools

Direct dissolution
using molten salt

Residue

Na2WO4solution

Direct exchange byion exchange, etc.

(NH4)2WO4
solution

Crystallization

Ammonium
paratungstate(APT)RoastingReduction
Reactionwith carbon

Tungstencarbide (WC)

Absorption intensity (arb. unit)

Recycling process of tungsten

WO42-: 32%
HW6O215-: 13%
H2W12O406-: 55%

Rare metals such as cobalt (Co) and tantalum (Ta)12050

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Reference samples

12100
X-ray energy (eV)12150

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