Recovery of Various Valuable Metals From Tungsten Slag

Tungsten slag is produced in tungsten smelting process, that is, tungsten ore and waste tungsten carbide raw materials are decomposed by wet method in high temperature or aqueous solution to obtain primary tungsten products (sodium tungstate, ammonium paratungstate) and solid waste slag (i.e. tungsten slag).

At present, the recovery of valuable metals from tungsten slag mainly adopts mineral processing, high-pressure alkali leaching, soda roasting, hydrochloric acid leaching and so on. Although the output of tungsten is improved to a certain extent, there are still limitations of single varieties of valuable metals recovery and high energy consumption. Because tungsten slag is also rich in valuable metals such as Co, Ni, Cu, Ag, Ta and Nb, single recovery has not made full use of resources and benefits.

In view of this, some scholars have developed a scheme for recovering valuable metals such as artificial scheelite, cobalt chloride, sponge silver, sponge copper, nickel carbonate and low-grade tantalum-niobium ore from multi-metal tungsten slag. The process includes:

(1)Tungsten slag is grinded by wet ball mill to produce fine pulp. The fineness of fine pulp is - 100 mesh.

(2)The alkaline pulp of 1N~3N is prepared by adding liquid alkali into the fine pulp prepared by step (1). The pulp is stirred and heated to 80 ℃ by steam, then ozone is introduced. The reaction temperature is kept at 80 C and the reaction time is 1 hour to 2 hours.

(3) The slurry after ozone alkali leaching reaction was separated from solid and liquid. The filtrate was adjusted to pH value by hydrochloric acid or sulphuric acid to 8-9. After silica removal, artificial scheelite was recovered by precipitation with calcium chloride.

Using ozone alkali leaching technology, only O₂ and H₂0 are produced in the process, which will not have adverse effects on the environment. The process is easy to realize, environmentally friendly and the purity of the artificial scheelite obtained is high.

(4)Mixing the filtrate residue obtained in step_with water, the slurry with solid-liquid ratio of 1:3 is prepared. The slurry is heated to 70 ℃ by steam and added with hydrochloric acid. The final acidity pH value is controlled to 0.5-1.0, and the reaction time is 1-2 hours. During the process of hydrochloric acid leaching, most metal oxides react with hydrochloric acid into the solution, while silver oxide forms silver chloride in the leaching residue.

(5)The slurry after hydrochloric acid leaching reaction is separated from solid and liquid. After washing and filtering, the filter residue is added with water, beating, adding hydrochloric acid, controlling the terminal acidity pH value to 0.5-1.0, heating up with steam more than 85 ℃, adding chloride salt to complex silver-solubilizing agent, adding water to form slurry with solid-liquid ratio of 1:3. After 1-2 hours of reaction, solid-liquid separation is carried out; the filter residue is tantalum ore of low grade. Silver sponge was recovered by replacement of liquid iron powder.

(6)After the leaching reaction of hydrochloric acid, the slurry is separated by solid-liquid method. First, iron is removed by oxidation, then calcium and magnesium are removed by fluoride, and then the extracting liquid is prepared. First, the extracting liquid is extracted by P204, and the impurities of copper, manganese and zinc are removed by deep purification. Then, the solution rich in copper, manganese and zinc is extracted by loading organic phase, and the sponge copper is recovered by replacement of iron powder. Then, nickel and cobalt are separated by P507 extraction. Nickel carbonate was recovered from P507 raffinate by precipitation with sodium carbonate, cobalt chloride solution was recovered by backextraction with hydrochloric acid from loaded organic phase, and cobalt chloride solution was evaporated and crystallized. After centrifugal separation, electronic cobalt chloride was recovered.

The above technical scheme can oxidize the metals in tungsten slag into oxides, leach tungsten, and separate and recover other valuable metals. The by-products are only O₂ and H₂0, which will not have adverse effects on the environment. The process is easy to realize and environmentally friendly. The obtained scheelite has high purity and can efficiently separate tungsten, cobalt, copper, nickel, silver, tantalum and niobium. High recovery rate, good comprehensive recovery effect, low energy consumption, environment friendly, simple and easy to operate, suitable for industrial production.

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