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Newsletter "SEI NEWS" 2011

Home > Company Information > SEI WORLD > Back number > Vol.403

[Newsletter "SEI NEWS" Vol.403]

Cemented Carbide Recycling System

Tungsten and other rare metals, used for producing cemented carbide tools, are valuable resources. The Sumitomo Electric Group has established a cemented carbide recycling system, under which, used indexable inserts and other cemented carbide products are collected, molten, processed and recovered as high-quality tools.

Cemented Carbide Recycling System

Background of Recycling System Development

タングステンの推定埋蔵量

Japan depends on imports for most of its cemented carbide indexable insert materials, such as tungsten, cobalt and other rare metals. Tungsten in particular is produced in a limited number of countries, like rare earth metals. Once the supply of tungsten is restricted for some reason, we will be confronted with great difficulty in obtaining this metal.

The current recycling rate for tungsten in Japan is only 25%. This means that Japan is behind overseas countries in rare metal recycling. For example, the USA recycles 50% of its tungsten, while European countries recycle 40%.

In these situations, the Sumitomo Electric Group has established a rare metal recycling system to ensure a stable supply of rare metals and effective utilization of scarce resources. This system employs two types of metal recycling techniques, zinc treatment and wet-chemical treatment, to process all cemented carbide indexable inserts that the Sumitomo Electric Group sells in Japan.

 
Zinc treatment

zinc treatment

In zinc treatment, used cemented carbide indexable inserts (scrapped cemented carbide) are mixed with zinc ingots in a tray and the mixture is heated in a furnace. The liquefied zinc then permeates the scrapped carbide, ultimately transforming it into a sponge-like material, which is then pulverized and recovered as a rare metal powder. This process is environmentally friendly because it is low in energy consumption and uses no chemicals. The Sumitomo Electric Group has been using zinc treatment since the 1980s.

zinc treatment

* Zn: zinc     Co: cobalt     WC: tungsten carbide

Item Recovered as rare metal powder having the same composition as the original rare metal
Techniques

Zinc treatment process

•High-temperature treatment
•Cold-stream process
•Direct crushing technique

Features

Advantages

•Low energy requirement
•Reduced CO2emissions
•No chemicals used
•Small-scale systems

■Disadvantages

•Requires prescreening of scrapped cemented carbide
•Difficult to control purity

 
Wet-chemical treatment

Although zinc treatment as detailed above can recover scrapped cemented carbide as a rare metal powder having the same composition as the original metal, it requires prescreening of scrapped carbide and lacks versatility. In contrast, wet-chemical treatment, currently under development as a national project in Japan, regenerates used cemented carbide products to rare metals having nearly the same quality as those refined from original ores. This process commenced operation this spring on a trial basis.
In wet-chemical treatment, scrapped carbide products are immersed in nitrate of soda and placed in a furnace for melting by chemical reaction. The molten carbide is then passed through an ion-exchange process for recovery as tungsten oxide.

Wet-chemical treatment

 
Item Collection after chemical separation according to component
Techniques

Dissolution by molten salt ? Wet-chemical treatment

•Oxidation ? Wet-chemical treatment
•Alkali dissolution

Features

Advantages

•Same quality as obtained by ore refining
•Wide range of applications (particle size etc.)

Disadvantages

•High energy consumption
•Chemical substance discharge
•Requires large-scale facilities (large facility installation cost).

Recyclable products

Used indexable inserts

 

Earth auger bits

Used drills and end mills

 

Wear-resistant tools

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