Low-grade tungsten mineral raw material chemical beneficiation process

Some low-grade tungsten concentrates produced by tungsten-selective plants do not meet the quality standards. The grade of WO ₃ is 5-30%, and other impurities are also relatively high. Mainly for low-grade ore of tungsten fine mud, tungsten, tin ore, tungsten-iron sand and other refractory containing tungsten intermediate products. Such products are chemically beneficiated to produce tungsten in the form of sodium tungstate or white tungsten , ammonium paratungstate, tungstic acid or tungsten trioxide, and other useful components are recovered from the leach residue.

Low-grade tungsten mineral raw material chemical beneficiation principle process, the process can be divided into material preparation.

First, material preparation

In order to ensure the quality of the chemical concentrate, the impurity content in the raw material should be lower than a certain value, such as arsenic not more than 0.3-0.5%, sulfur not more than 1.3-1.5%, when the content of impurities is high, it should be reduced to a certain amount when the material is prepared. Value; in order to improve the decomposition efficiency of minerals, the requirements for the fineness of materials depend on the decomposition method of the subsequent operations and the characteristics of the raw materials. For example, the soda sintering method needs to be ground to below 100-150 mesh; the direct leaching needs to be ground to below 200-300 mesh.

Second, the sintering - leaching of materials

Industrial production uses soda sintering-water immersion method, soda solution pressing method, caustic soda solution leaching method and acid decomposition method. Its purpose is to decompose tungsten minerals to form water-soluble tungstates. The choice of decomposition method depends mainly on the characteristics of the tungsten mineral raw materials and the specific conditions and conditions of the manufacturer. Method can be divided into

(1) Soda sintering - water immersion method. It is suitable for processing low-grade black tungsten raw materials containing a small amount of quartz , such as tungsten fine mud, tungsten-containing iron sand, tungsten-tin ore, etc., and can also process low-grade white tungsten raw materials containing a small amount of quartz, which makes the water-insoluble black when sintered. Tungsten ore and scheelite react with soda to form water-soluble sodium tungstate. The water-soaked agglomerate converts tungsten into solution, and solid-liquid separation removes insoluble impurities. The sintering temperature of the black tungsten ore raw material is 700-850 degrees, and the white tungsten raw material is about 860 degrees.

(2) Caustic soda solution leaching method. The milled mineral raw material is leached under pressure with a 35-40% strength caustic soda solution and heated to 110-120 degrees, and the tungsten is transferred into the leachate in the form of soluble sodium tungstate. There are two treatment methods for leaching: one is to directly dilute to a density of 1.3 g / cm 3 and then sent to purification; the second is to dilute it to a density of 1.45 g / cm 3 to precipitate sodium tungstate crystals, the crystallization liquid returns In the leaching operation, the aqueous solution of the crystal is sent for purification. Compared with the soda sintering-water immersion method, this method has simple process, low investment, and can process tungsten mineral materials such as tungsten fine mud and tungsten-tin ore with higher silicon content.

The reaction of leaching scheelite by caustic soda solution under normal pressure is a reversible reaction. Generally, a mixed solution of caustic soda and sodium silicate should be used as a leaching agent to obtain a satisfactory leaching result. However, when the scheelite raw material contains a considerable amount of silicon oxide, a single caustic soda can be used.

(3) Acid decomposition method. The acid decomposition method can be used to treat two raw materials of scheelite and wolframite, and use 32-38% concentrated hydrochloric acid or nitric acid as a leaching agent to directly decompose the tungsten mineral at a temperature of about 100 degrees to form a tungstic acid precipitate. In order to increase the leaching rate of tungsten, the material must be ground to -300 mesh. When the acid is decomposed, a considerable part of the impurities enter the solution and are separated from the tungstic acid by solid-liquid separation. The residue is separated and that the tungstic acid, alkali fusion of the tungsten used was an alkali metal tungstate solution into shape to obtain a more pure solution of ammonium tungstate or sodium tungstate. The acid decomposition tungsten has a high leaching rate, but the reagent consumption is large.

(4) Soda solution pressing method. This method can be used to treat white tungsten and black tungsten mineral raw materials. The leaching process is carried out in a press cooker, and the raw material is ground to -300 mesh, and the tungsten leaching rate is related to the amount of soda, the leaching pressure, and the leaching temperature.

The advantage of this method is that a good applicability, not suitable for processing low-grade scheelite (5-15%), further adapted to process sulfide concentrates containing tungsten, such as tungsten ore bismuth, bismuth, molybdenum and tungsten ore. When the high sulfur tungsten is leached, the cassiterite, stibnite and stibnite remain in the residue, and all the copper , some silicon oxide, fluorine, phosphorus , arsenic and other impurities in the oxide are transferred into the immersion liquid together with the tungsten. The immersion liquid is sent to the purification treatment.

Third, the purification of leachate

The sodium tungstate solution obtained by the above various methods for decomposing the low-grade tungsten mineral raw material contains impurities such as silicon, phosphorus, arsenic, and copper to various degrees, and sometimes contains impurities such as sulfur and fluorine. In order to ensure the quality of the chemical concentrate, the leachate must be purified to remove impurities. The following methods are commonly used at present.

(1) Removal of silicon, phosphorus, and arsenic with ammonium magnesium salt . When the weight ratio of SiO ₂ /WO _{3 in the} immersion liquid is more than 0.1%, silicon should be removed. Silicon is present in the solution in the presence of sodium silicate, and when the alkalinity of the solution is lowered, the hydrolysis is precipitated as silicic acid. Therefore, adding 1:3 dilute hydrochloric acid to the immersion liquid to lower the pH to 13, then adding ammonium chloride to lower the pH to 8-9, sodium silicate can be completely hydrolyzed to form SiO2 precipitate, and then clarified and filtered. After washing, the silicon oxide in the liquid can be reduced to 0.25 g/l.

In the form of phosphorus and arsenic, respectively, HPO ₄ ^2- and HAsO ₄ ^2- present in addition to the silicone liquid, and thereto is added at room temperature a density of 1.16-1.18 g / cc solution of magnesium oxide, magnesium, phosphorus and arsenic respectively form ammonium phosphate The morphology of Mg(NH ₄ )PO ₄ and ammonium magnesium arsenate Mg(NH ₄ )AsO ₄ precipitated.

(2) Removal of silicon, phosphorus and arsenic by magnesium salt method. This method firstly dilutes the pH value of the immersion liquid to less than 11 with dilute hydrochloric acid (1:3). After partial hydrolysis of sodium silicate, the phosphorus in the immersion liquid is in the form of HPO ₄ ^2- and arsenic in the form of HAsO ₄ ^2- . . When a density of 1.6-1.18 g/cm 3 of magnesium chloride solution is added until the alkalinity of the immersion liquid is 0.2-0.3 g/L NaOH, precipitates of MgSiO ₃ , Mg ₃ (PO ₄ ) ₂ and Mg ₃ (AsO ₄ ) ₂ are precipitated. Therefore, the addition of magnesium chloride removes silicon, phosphorus, and arsenic.

The main point of this method is to neutralize the immersion liquid to pH 11 with hydrochloric acid, and then add magnesium chloride solution, otherwise magnesium hydroxide precipitation will occur. When the content of the fluorite in the raw material is large, magnesium chloride may be added to precipitate the F- in the immersion liquid as MgF ₂ .

The ammonium magnesium salt method and the magnesium salt method can only remove high-priced arsenic. If low-cost arsenic is present, the low-priced arsenic must be oxidized to high-priced arsenic with an oxidizing agent such as hydrogen peroxide or sodium hypochlorite, and then magnesium oxide can be added to achieve the purpose of removing arsenic.

The magnesium salt method has higher efficiency than the ammonium magnesium salt method, has a large processing capacity, and has a short production cycle, and the slag contains low tungsten (about 4-5% WO ₃ ), but the amount of slag is large. The amount of ammonium magnesium salt slag is small, but the slag contains high tungsten (about 15-20% WO ₃ ), so the best purification method should be determined through experiments according to the characteristics of the raw materials.

(3) Alkaline removal of molybdenum. Molybdenum exists in the form of sodium molybdate in the immersion liquid. In the filtrate after removing silicon, phosphorus and arsenic, sodium sulfide solution is first added to convert molybdenum into thiomolybdate, and arsenic remaining in the solution is also converted into thioarsenic. The acid salt was then neutralized with hydrochloric acid until pH=8.5, at which time molybdenum and arsenic did not precipitate. Further, a calcium chloride solution is added, and tungsten is precipitated as calcium tungstate, and molybdenum and arsenic remain in the form of the corresponding thioacid salt, and the molybdenum and arsenic are removed by filtration. In addition to the molybdenum rate of 70-90%, the amount of sodium sulfide added is 8-8.5 times the total amount of molybdenum and arsenic, and the temperature is 80 degrees.

When the amount of molybdenum contained in the immersion liquid is less than 0.25 g/L, it is not necessary to separately remove the molybdenum process, and the method for improving the acidity of decomposing and synthesizing scheelite achieves separation of tungsten and molybdenum, high acidity, high temperature and good molybdenum removal effect. There are other methods other than molybdenum, which are not described here.

All of the above are chemical precipitation methods to remove impurities such as silicon, phosphorus, arsenic, and molybdenum in the immersion liquid, and other methods such as ion exchange.

4. Preparation of tungsten chemical concentrate

In the industry, synthetic white tungsten or ammonium paratungstate is generally precipitated from the purification liquid, and then tungstic acid or tungsten oxide is produced. The process is as follows.

(1) Synthesis of white tungsten. Precipitation and synthesis of white tungsten generally use calcium chloride as a precipitant (sometimes with calcium hydroxide or calcium sulfate) to precipitate calcium tungstate. The reaction formula is:

Na ₂ WO ₄ +CaCl=CaWO ₄ +2NaCl

Calcium chloride also produces calcium salt precipitates for impurities such as silicon, phosphorus, arsenic, molybdenum and the like, and thus has no purification effect, and only purifies sulfur. The quality and precipitation rate of synthetic white tungsten are mainly related to the tungsten content of the cleaning liquid, the alkalinity, the type of precipitant and the amount of addition. The tungsten content affects the fineness of the synthetic white tungsten and the filtration and washing performance.

Regarding the comparison of precipitants: calcium chloride can obtain high-grade synthetic white tungsten: (WO3 reaches 70-76%), the precipitant has little pollution to the product, and the disadvantage is that calcium chloride is easily deliquescent, and transportation packaging is difficult. Lime is cheap, but the obtained synthetic white tungsten has a low grade, generally only 60-68% WO ₃ , difficult to filter and wash, high tungsten content in mother liquor, and high titan content of WO ₃ obtained from calcium sulfate, but the product is highly polluted (sodium sulfate, Calcium sulfate), and the reaction time is long. Therefore, calcium chloride is preferred.

When synthetic white tungsten is used as the final product, it is filtered and dried, and then packaged; if tungstic acid or tungsten oxide is used as the final product, the synthetic white tungsten is filtered and washed and sent to prepare tungstic acid.

(2) Preparation of tungstic acid. Industrially, hydrochloric acid or nitric acid is often used to decompose and synthesize white tungsten to prepare tungstic acid. A commonly used synthetic white tungsten hydrochloric acid decomposition method, the reaction formula is:

CaWO ₄ +2HCl=H ₂ WO ₄ +CaCl ₂

The impurities of silicon, phosphorus and arsenic in the synthesis of white tungsten have a great influence on the preparation of tungstic acid, which makes the size of tungstic acid fine and gelatinous, which is difficult to precipitate and filter. At the same time, it also forms heteropoly acid with tungsten to increase the tungsten content in the mother liquor. .

The main influencing factors for the preparation of tungstic acid are: (1) Temperature: high temperature is conducive to the preparation of coarse-grained tungstic acid. The decomposition of impurities is complete, but the acid loss is large, the working environment is poor, and the initial temperature is usually 70-80 degrees. After the addition, boil for another 10-15 minutes; (2) hydrochloric acid concentration: high concentration is favorable for coarsening of tungstic acid particle size, complete decomposition of impurities, 30% hydrochloric acid concentration is generally used in production; (3) residual acidity: low acidity at the end of decomposition The tungstic acid has a small particle size and a low purity, and generally has a residual acidity of 70-80 g/l. In addition, the addition of an appropriate amount of nitrate (nitrate) during acid decomposition is beneficial to accelerate the decomposition process and oxidation of impurities. And it is beneficial to increase the total recovery of tungsten.

The filtered tungstic acid should be washed. The quality of tungstic acid meets the standard before it can be shipped or sent to produce tungsten oxide. Otherwise, it should be cleaned. The ammonia method is commonly used for the purification of tungstic acid, that is, the tungstic acid solution is dissolved in ammonia water to be converted into an ammonium tungstate solution, and most of the impurities such as silicon, iron, manganese remain in the precipitate.

(3) Preparation of ammonium paratungstate. The ammonium paratungstate is prepared from the ammonium tungstate solution by concentrated crystallization, and the tungstic acid is first dissolved in the ammonia water, and the tungsten is separated from some impurities, and the reaction formula is:

_{H 2 WO 4 + 2NaOH = (} NH 4) 2WO 4 + 2H 2 O

Certain impurities such as iron, manganese, and calcium chlorides simultaneously form hydroxide precipitates and tungsten separation. The solution was filtered through sedimentation and the filtrate was an ammonium tungstate solution.

The tungsten leaching solution is treated with a strong alkaline or weakly basic anion exchange resin, and the tungsten-loaded resin is rinsed with an ammonium chloride solution, and the resulting eluent is used to prepare ammonium paratungstate; in addition, an ammonium tungstate solution can also be obtained by solvent extraction. Sodium tungstate as a stock solution, tertiary amine or quaternary amine coal oil as the organic phase, the tungsten extraction conditions at PH = 2-4, and 2-4% of the ammonia stripping available ammonium tungstate solution.

The preparation of ammonium paratungstate from the ammonium tungstate solution can also be carried out by a neutralization method. When the ammonium tungstate solution is neutralized to pH=7-7.4 by using 10-20% hydrochloric acid, the form of tungsten in the form of needle-like ammonium paratungstate is precipitated, and the crystallization rate is up to 85-90%, but the neutralization method can not recover ammonia and consume hydrochloric acid, and has been replaced by the evaporation method.

When the ammonium tungstate solution is concentrated, a part of ammonia can be evaporated. After cooling (greater than 50 degrees), the plate-like ammonium paratungstate crystal is crystallized: ie:

12(NH ₄ ) ₂ WO ₄ = 5(NH ₄ ) ₂ O ₁₂ WO ₃ 5H ₂ O+14NH ₃ +2H ₂ O

Since the solubility of ammonium paratungstate is smaller than that of ammonium paramolybdate, in order to prevent the product from being contaminated by molybdenum, the tungsten and molybdenum can be separated by a stepwise crystallization method. For example, if 60% of the liquid is evaporated, the crystallization rate of tungsten is 55%, and the crystallization rate of molybdenum is only 12%, so the ammonium arsenate which is initially crystallized contains little molybdenum. The late stage ammonium tungstate precipitated with higher molybdenum.

The ammonia gas volatilized during evaporation is recovered by the washing tower, and the obtained ammonia water is returned for use; the mother liquid rich in impurities is recovered for tungsten.

(4) Preparation of tungsten trioxide. Industrial tungsten oxide powder can be obtained by calcining dry pure tungstic acid or ammonium paratungstate. The reaction formula is:

H ₂ WO ₄ =WO ₃ +H ₂ O

5(NH ₄ ) ₂ O ₁₂ WO ₃ nH ₂ O=12WO ₃ +10NH ₃ + (5 ⁺ n)H ₂ O (calcined)

When the calcination temperature is 500 degrees, the tungstic acid can be completely dehydrated, and the temperature above 250 degrees can completely decompose the ammonium paratungstate. The tungsten trioxide used for the production of tungsten and tungsten carbide should have a certain purity, but also meet certain particle size requirements. The particle size of tungsten trioxide is closely related to the particle size and calcination temperature of tungstic acid such as ammonium paratungstate.

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