Chromium Removal From Waste Tungsten Alloy Recycle
With the shortage of tungsten ore resources, the utilization of tungsten resources becomes more and more urgent. Waste tungsten alloy is one of the main sources of tungsten recycle.
According to statistics, about 35% of the tungsten in Europe and America developed from waste tungsten alloy recycling. With the emphasis on tungsten resources in China, the recycle rate of tungsten resources in China has been increasing year by year, and it has reached 20%.
In the waste recycling process of tungsten alloy technology, recycle process of waste tungsten by sodium carbonate smelting process is relatively mature and widely applicable, much as it is used, but a lot of problems also appeared in the actual production, the most troublesome is chromium. During the leaching of waste tungsten alloy by sodium carbonate smelting process, a large amount of chromium impurity elements also enter into sodium tungstate solution, which can not meet the purity of tungsten products.
The chemical properties of chromium show that the precipitation of chromium from sodium tungstate solution requires the reduction of Cr6+ to Cr3+, this process can be done by acid and alkali, but in the current industrial atmosphere, the alkaline process has the mass base.
If you want to remove chromium, you have to do it once more, removing impurities is necessary. In general, sodium tungstate crystals need a series of procedures, such as dissolution neutralization purification, removal of sulfide, acid extraction, extraction stripping, APT crystallization, etc.. Some experts believe that the removal of chromium during the curing stage is a wise choice, this is mainly the curing process can be carried out with the removal of chromium and molybdenum removal, this is less than the two stages of reduction, hydrolysis and filtration in the dissolution stage of crude sodium tungstate;
In the process of removing chromium by vulcanizing stage, sodium sulfide 4 times of theoretical quantity is added into the present process of molybdenum removal by sulfuration, besides, the chromium removal was controlled when the reaction pH value was 8-9, by selecting suitable temperature and aging time, better chromium removal effect can be achieved, moreover, it is necessary to add a filtration process on the basis of the original production process to accomplish the task. More importantly, in the curing stage, the APT obtained from chromium treatment can basically achieve the purity of APT - 0. From the recycling standard of waste alloys, this should be a very good result.
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