A Strategy for the Perfect Removal of Chromium from Waste Tungsten by Nitrate Melting

With the rapid development of economy, the demand for tungsten metal materials is increasing. Almost all the metal elements constituting cemented carbide materials are rare elements. It is increasingly urgent to make comprehensive use of various tungsten resources. Over the years, the industry has done a lot of work on the comprehensive utilization and regeneration of tungsten resources. At present, the recovery and utilization of waste tungsten accounts for 20% of China's tungsten consumption. The regeneration and utilization of tungsten resources plays an important role in the national economy.

Recycling and reuse of waste cemented carbide mainly includes mechanical crushing method, direct electrolysis method, zinc melting method, cold flow method and leaching method. However, these methods have many shortcomings, such as immature technology and poor adaptability to industrial production. For example, at present, the technology of recovering waste tungsten by nitrite smelting method is relatively mature, and its adaptability is extensive, and different metal elements can be used. In the process of smelting and leaching, the chromium element is leached into sodium tungstate solution in the form of hexavalent chromium, which causes the chromium element in sodium tungstate solution to exceed the standard and can not meet the production of high purity tungsten products.

In order to effectively remove chromium impurity elements from sodium tungstate leached by nitrite smelting, some scholars have adopted the following methods to deal with them:

Waste tungsten was leached from sodium tungstate solution by nitrite smelting. The concentration of WO₃ was 150 g/L, the concentration of alkali was 20 g/L, and the concentration of chromium was 800 mg/L. Sodium tungstate solution was poured into the reactor with volume of 10 m³, heated to 80 ℃, then added 30 kg NaHS, heated and stirred to control the reaction temperature to 80 ℃, controlled the pH to 9.5 during the reaction, stirred for 4 hours, and the chromium was filtered by plate-frame press filter. High purity sodium tungstate solution was obtained from slag. The WO₃ concentration of sodium tungstate solution after removing chromium was 152 g/L, alkali concentration was 16.2 g/L and chromium concentration was 0.

The main principle of the process is that the waste tungsten containing high content of chromium is leached into the leaching solution by nitrite smelting and leaching. By adjusting the pH and temperature of the solution and adding special precipitator, the chromium in the solution can be precipitated. The chromium removal rate is over 99% and the tungsten loss is less than 0.1%, which can meet the requirements of high-quality tungsten products. Moreover, it has the advantages of simple operation, large capacity, simple process flow, low investment cost, high chromium removal rate, low environmental pollution, and is suitable for industrial production.

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