Since zirconium, hafnium and titanium metallurgy metallurgy have many similarities, this section focuses on the processing material containing radioactive elements.
Due to the different origins and mineral structures, the content of radioactive elements such as Th and U in zircon sand and the orientation and distribution in the metallurgical process of zirconium and hafnium are different. The foreign and Shandong Rongcheng zircon sands contain relatively low Th and U, so There is no need for special radioactive treatment in the production of zirconium. For example, when the zircon sand itself exceeds the standard of Th and U, the intermediate materials, waste water, waste residue and waste gas should be intensified from the carbonization process. According to the test results, protective measures should be taken according to the national radioactive requirements. See Table 1 for requirements. When using a P204-N235 extraction combined process to treat a mine zircon sand, it has a good effect on Th, U protection and three waste treatment. In the example, the raw material zircon sand contains U 0.06%~0.10%, Th 0.08～0.10%, and the wastewater in alkali decomposition adopts countercurrent water washing method. The amount of wastewater is only 1/3 of that of clean water washing, 1t ZrSiO 4 per treatment, 8t of wastewater The left and right, which contain 8% to 10% of Na 2 O and 3% to 5% of SiO 2 , are raw materials for the production of foaming alkali. The wastewater and waste residue have been comprehensively utilized, and the products produced have been identified to meet the requirements of industrial raw materials. The radioactive specific strength of the alkali and its waste residue is 3 × 10 -9 Ci / L and (2 ~ 4) × 10 -9 Ci / kg.
Table 1 "Three wastes" specifications produced in the production of zirconium and hafnium
Project | Request (not greater than) |
Radioactive intensity in carbonized waste residue | 1×10 -7 Ci/kg |
Radioactivity in a chlorinated residue | 1×10 -7 Ci/kg |
Zircon and graphite powder dust concentration during mixing | SiO 2 10% 2mg/m 3 |
Dust concentration during chlorination | SiO 2 10% 10mg/m 3 |
Dust concentration when zirconium carbide is broken | SiO 2 10% 10mg/m 3 |
Radiation intensity of radioactive mixture in washing water in wastewater | 5×10 -11 Ci/L |
Radiation intensity of α- radioactive mixture in cooling water of carbonization furnace | 5×10 -11 Ci/L |
Radiation intensity of α- radioactive mixture in a chlorination furnace tail gas leaching water | 5×10 -11 Ci/L |
Radiation intensity of α- radioactive mixture in the discharge port of sewage pumping tank | 5×10 -11 Ci/L |
Total discharge waste water | 500mg/L |
Total discharge wastewater pH | 6 to 9 |
In the process of extracting acid leaching, Th and U are transferred into the leachate, which contains U 100-200 mg/L and Th50-60 mg/L, and is recovered in the process:
(1) U enters the organic phase together with Zr in the N 235 system, and uses selective back extraction to separate U and Zr completely. In the production, Zr is back-extracted with a mixture of 2.5 mol/L NH 4 Cl and 2.5 mol/L HCl. The ZrO 2 obtained by selective stripping has a radioactive specific strength α of (4-5)×10 -8 Ci/ Kg, containing U<0.0055%, and the ZrO 2 produced by the original TBP extraction process, because the step of stripping U is not used, the specific gravity intensity α is (2～5) 10 -6 Ci/kg, and the U content is 0.035%. .
(2) After stripping Zr, the organic phase is further extracted with 10% NH 4 HCO 3 and 2 mol/L NH 4 OH, and the stripping solution is hydrolyzed to add U slag, which can be further processed to obtain (NH 4 ). 2 U 2 O 7 hydrolysis mother liquor, containing 2 ~ 3NCl - , in order to control the "three wastes", can be adjusted again, and used as a stripping Zr solution.
(3) Th is added to the P204 system along with Hf, Th remains in the aqueous phase, its content is 10~12mg/L, [H + ]=3~3.5mol/L, and it is concentrated by graphite tube heat exchanger. (1.5mol/L H 2 SO 4 is concentrated to 9mol/L), and its radioactive specific strength is about (1~3)×10 -5 Ci/L, which can be used for commercial sale or return to the front acid leaching process. After the acid is concentrated, it is partially precipitated in the slag after precipitation, and can be stored because it is extremely small in quantity. In the waste acid, Th can be recovered by primary amine extraction. The test shows that the recovery rate can reach 99%, but after the recovery, the radioactive specific gravity of the waste acid is unchanged, so it is not used in production.
(4) Waste ammonia water, measured, the specific gravity of the radioactivity is (1 ~ 2) × 10 -11 Ci / L, can be used as fertilizer or abandoned after neutralization.
(5) After further treatment, TiO 2 can be used as an industrial raw material for producing enamel, and its radioactive specific strength is (3 to 5) × 10 -8 Ci/kg.
(6) The total discharge water wastewater has been determined, and its radioactive specific strength is 2.4×10 -11 to 7.7×10 -12 Ci/L, which meets the discharge requirements.
When adopting the P204-N235 combined process, it is necessary to establish the necessary auxiliary workshop for the treatment of waste water slag. For each 1t of sponge zirconium produced, the bubble base 600t can be comprehensively utilized.
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