Rough alkaline slag recovery 碲

Tellurium, bismuth basic alkaline slag refining crude output, the ingredients are listed in the following table, which contains Te6 ~ 30%, was recovered starting material for tellurium.

First, the process

The process of producing plutonium is shown in Figure 1.

Figure 1 碲 production process flow chart

Second, the main technical conditions

(1) Ball grinding and leaching. The slag is charged into a wet ball mill to 100 to 120 mesh, the liquid-solid ratio is 1:1, and each batch is ball milled for 4 hours. Then, the ball mill liquid is pumped to the leaching tank, diluted with water to three times the original volume, and heated to 80 ~. Clarified at 95 ° C for 6 hours. The supernatant component is (g/L): Te30~32, Se2~3, Bi<0.1, Pb0.01~0.03, Fe<0.1, As0.1~0.3, Sb0.1~0.2, Ca<0.1,Zn <0.1, free NaOH 30 to 32.

(2) Purification. Purification in order to remove heavy metal impurities and SiO 2. Adding Na 2 S to make heavy metal impurities into sulfide precipitates, the amount of Na 2 S added per liter of solution is generally 1.5 to 2.5 grams, and the reaction is:

Na 2 PbO 2 +Na 2 S+2H 2 O=PbS↓+4NaOH

Adding an appropriate amount of CnCl 2 causes SiO 2 to form a calcium silicate precipitate, and the reaction is:

Na 2 SiO 8 +CaCl 2 =CaSiO 8 ↓+2NaCl

The control solution contains NaOH in an amount of 25 to 35 g/L, and the liquid temperature is above 85 ° C. When the filter paper is brownish gray, it is the end point.

(3) Neutralization. The purpose of neutralization is to convert sodium citrate to TeO 2 , and at the same time, to remove selenium , warm to 60-80 ° C, and neutralize to pH 4.5-6 with dilute sulfuric acid (acid: water = 1:4). TeO 2 precipitates and the reaction is:

Na 2 TeO 3 +H 2 SO 4 =TeO 2 +Na 2 SO 4 +H 2 O

After blast stirring, filtration, and washing of TeO 2 with boiling water, the chemical composition is (%): Te70-75, Se<0.1, Cu<0.1, Pb0.5-1.5, SiO 2 4-5, Bi0.2- 0.4, Sb0.2 to 0.3.

(4) Calcination. The purpose of calcination is to further deselenize. The calcination temperature is 300 to 450 ° C, and the temperature is 1 to 3 hours. When TeO 2 is yellowish white, it is a good product.

(5) Liquid production. TeO 2 can be dissolved in NaOH solution and the reaction is:

TeO 2 +2NaOH = Na 2 TeO 3 + H 2 O

0.55 to 0.65 kg of NaOH per kg of TeO 2 was added, the liquid-solid ratio was 5:1, the liquid temperature was 90 ° C, the solution density was more than 1.36 g/cm 3 , and it was used after standing for two days.

(6) Electrowinning. The electrolyte is a purified sodium sulfite solution. Its chemical composition is (g / liter): Te 180 ~ 220, NaOH 80 ~ 100, Se < 0.3, Pb < 0.003, Cu < 0.003. Electrode current at room temperature, current density 40~60A/ m2 ; same pole pitch 50~110mm; tank voltage 1.5~2.8V; electrolyte solution added with new liquid, so that solution contains 碲 more than 100g/L; anode using iron plate, a cathode plate made of stainless steel; electrolysis period of 5 to 12 days.

After passing through the direct current, the crucible is deposited on the stainless steel cathode plate, and the anode releases oxygen.

(7) Casting. After the tank is removed, the cathode is tapped with a wooden hammer, and the precipitated crucible is crushed and dropped into a stainless steel bucket for cooking. A small amount of oxalic acid can be added first, and after cooking for 36 hours, it is then washed with distilled water for 48 hours. The washed precipitate tellurium drying, the crucible casting, the mold temperature is 480 ~ 600 ℃ borax may be added a small amount of slag, the ingot surface of the air-blast cooling.

Third, the main equipment

(1) Ball mill. Φ600 × 1000 mm, speed 45 rpm.

(2) Leaching tanks, neutralizing tanks, and purifying tanks. One each, using a jacketed enamel reaction kettle (φ1000 × 1500 mm), mechanically stirred.

(3) Vacuum pump. Two sets of SZ-2.

(4) Electrolytic tank. Six, steel plated rubber, 790 × 600 × 640 mm.

(5) Silicon rectifiers. One GZH3-40, 100 amps, 50 volts.

Fourth, product use

碲Used in the semiconductor industry for thermoelectric power generation and temperature difference refrigeration; as a metallurgical additive to improve the performance of steel and copper , lead and its alloys; also used in organic chemical synthesis as a catalyst for the glass and ceramic industry as a dye.

V. Product quality

No. 1 fine chemical composition (%): Te≥99.99, Cu≤0.001, Pb≤0.002, Al≤0.001, Bi≤0.001, As≤0.0005, Fe≤0.001, Na≤0.003, Si≤0.001, S≤0.001 , Se ≤ 0.002, and Mg ≤ 0.001.

Sixth, other methods of recycling 碲

(1) Reduction method. In the reduction method, TeO 2 powder is blended into flour as a reducing agent, and is reduced and smelted in a crucible. After the white vapor is volatilized, borax slag is added. The produced bismuth ingot contains 99% bismuth and can be used as a metallurgical additive and a glassware dye.

(2) Soluble anodic electrolysis. The anode plate is made of coarse bismuth containing 99%, the cathode is made of stainless steel, sodium citrate electrolyte is used, NaOH 80-100 g/L, Te 90-100 g/L, room temperature, current density 50-100 An / m 2 , the tank voltage is 1.5 ~ 2 volts. Can produce No. 1 fine.

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