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TUNGSTEN - How to Get It?

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by - 11/30/2015 2276 Views

Recovering Tunsten

 How To Recover Tungsten Carbide From Tungsten Carbide Scrap?

We are going to discuss particularly about recovering tungsten carbide from its scrap by a method called, “selective electrolysis” in which a chelating agent is added to the electrolyte for blending with tungsten ions produced during electrolysis to prevent passivation of tungsten carbide.

Due to its high quality hardness, cemented tungsten carbide has been extensively used in the manufacture of cutting tools, drill, dies, and abrasion-resistant mechanical components. As a matter of fact, tungsten is not available in abundance; process for its recovery is of a great concern in many countries. Statistics reveal that recovered tungsten carbide comprises about 20% to 30% of the total supply, lowering the raw material cost by about 15% to 50%.

Till date two methods have been used to recover tungsten carbide from its scrap. Firstly, getting tungsten carbide scrap to react with a physical or chemical method to form an intermediate, such as oxide, and then reducing the oxide to pure tungsten for Eg high potential electrolysis. Secondly, the dissolution of a cementing agent to get a fine powder of tungsten carbide which can be directly used. Such methods include the molten zinc method, the cold stream flow method and low potential electrolysis.

The most frequently applied methods are the molten zinc method and the cold stream flow method. According to the molten zinc method, the tungsten carbide scrap is heated to 900° C. with the introduction of argon gas, and is then vacuum distilled. The energy consumption is therefore great, about 4000 to 6000 kWh is required for one ton of tungsten carbide. The cold stream flow method includes heating cemented carbide scrap to a high temperature, injecting a high speed cold air flow to the scrap to break and separate the scrap, and then recovering tungsten carbide. This method also inevitably requires a lot of energy.

Recovering tungsten carbide from cemented carbides by electrolysis has been used since 1950. Such problems as complicated procedures and severe pollution encountered initially have been overcome recently with new developments in electrochemical technology. The electrolysis method has the following advantages: it saves energy, there is no pollution, the recovered product has high purity, and the investment for the equipment is low. For example, according to the high potential direct electrolysis method, tungsten carbide scrap, which serves as an anode, is electrolytically oxidized into anode slime of tungstic acid, and the cobalt cementing agent therein is thus dissolved in electrolyte to form cobalt ions. The anode slime of tungstic acid is then recovered by extraction or is reduced to tungsten metal. The cobalt can be recovered by electrolysis or by precipitation with the addition of oxalic acid. One disadvantage of this method is that the process for the recovery of tungsten carbide from anode slime of tungstic acid is complicated and therefore is not economical.

According to Nutzel and Kuhl, in selective electrolysis, the applied potential and energy consumption are low, the process and equipment for recovery are simple, and tungsten carbide can be directly recovered. According to Ghandehari, if a solution containing phosphoric acid is used as electrolyte in selective electrolysis for recovering tungsten carbide, the electrolysis can be carried out at a lower potential, and the efficiency for separating tungsten carbide and cobalt can be much improved.

In conclusion,  the process includes the steps of: (a) dipping the cemented tungsten carbide scrap in an electrolyte having an anode and a cathode therein, the electrolyte being an acidic solution and including a chelating agent, and the cemented tungsten carbide scrap being connected to the anode; (b) fixing a constant potential between the anode and the cathode to electrochemically and selectively dissolve at least a portion of the cementing agent without significant dissolution of the tungsten carbide; and (c) collecting the tungsten carbide from the electrolyte.

Category : General

Tags : Tungsten Scrap, Recovering Tungsten, Tungsten Scrap Price, Tunsten Scrap Metal, Tungsten Carbide Scrap


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About Georgy Abraham

As the bright morning of 28th May dawned in the year 1972, in the fulfillment of time according to the plan & will of Almighty Godbrought me forth into this world and I was brought up & educated in Orissa. My parents provided me with the best of education in an English medium school with high standa .... more info

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