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CN-122010062-A - Rectification purification method for removing trace metal impurities in selenium dioxide

CN122010062ACN 122010062 ACN122010062 ACN 122010062ACN-122010062-A

Abstract

The invention relates to the technical field of high-purity inorganic compound preparation, and discloses a rectification purification method for removing trace metal impurities in selenium dioxide, which comprises the steps of dissolving crude selenium dioxide in an aqueous solvent to form a selenic acid aqueous solution, adding a chemical reducing agent to regulate the valence state of impurities, and adding an iron nitrate auxiliary agent and a hydrolyzable alkaline precursor substance; the method comprises the steps of heating to hydrolyze precursor substances to generate alkali in situ, carrying out thermal dehydration on the purified selenic acid aqueous solution obtained after separation by separation precipitation, crystallizing to separate selenium dioxide, and carrying out thermal decomposition and removal of residual nitrate anions by heating.

Inventors

  • YANG YU
  • LI ZHONGHUA
  • ZHANG YOUJUN
  • ZHANG HAILONG

Assignees

  • 泸溪蓝天高科有限责任公司

Dates

Publication Date
20260512
Application Date
20260407

Claims (10)

  1. 1. A rectification purification method for removing trace metal impurities in selenium dioxide, which is characterized by comprising the following steps: Step a, dissolving crude selenium dioxide containing trace metal impurities in an aqueous solvent to form a selenious acid aqueous solution; Step b, adding a chemical reducing agent into the selenic acid aqueous solution to reduce the arsenic impurities with high oxidation state in the trace metal impurities to a preset low oxidation state; Step c, adding ferric nitrate as a sacrificial ferric salt auxiliary agent into the selenic acid aqueous solution, and adding a hydrolyzable alkaline precursor substance; Step d, heating the selenic acid aqueous solution to hydrolyze the hydrolyzable alkaline precursor substance to generate alkali in situ, so that the pH value of the selenic acid aqueous solution is raised to a preset range, and ferric cations of ferric nitrate are hydrolyzed to form ferric hydroxide precipitates and preset arsenic impurities in a low oxidation state to form coprecipitated floccules; Step e, separating coprecipitated floccules from the selenic acid aqueous solution to obtain a purified selenic acid aqueous solution carrying nitrate anions derived from ferric nitrate; and f, carrying out thermal dehydration treatment on the purified selenic acid aqueous solution, evaporating the aqueous solvent by heating in a preset temperature interval, separating out high-purity selenium dioxide crystals, and thermally decomposing nitrate anions and escaping in a gaseous product form.
  2. 2. The method according to claim 1, wherein the method further comprises a precipitation and aging step of maintaining the selenious acid aqueous solution containing coprecipitated floccules at an aging temperature for an aging time after the step d and before the step e, wherein the precipitation and aging step comprises running a stirrer at a constant rotation speed, stirring the selenious acid aqueous solution, driving the stirrer by a motor, monitoring the torque of the motor in real time, and dynamically determining an end point of the aging time based on a time change rate of the torque, wherein the end point is determined as that the time change rate of the torque is continuously lower than a preset torque change threshold value within a preset time period.
  3. 3. The method of claim 1, wherein the chemical reducing agent in step b is oxalic acid.
  4. 4. A method of rectifying and purifying selenium dioxide to remove trace metal impurities according to claim 1, wherein the hydrolyzable basic precursor material in step c is urea.
  5. 5. The method of rectifying and purifying selenium dioxide according to claim 1, wherein the step d of heating the aqueous selenite solution is performed in a closed container under a predetermined back pressure greater than atmospheric pressure to dissolve carbon dioxide generated by hydrolysis of the hydrolyzable alkaline precursor into the aqueous selenite solution.
  6. 6. The method for purifying selenium dioxide by distillation to remove trace metal impurities according to claim 2, wherein the aging temperature is 40 To 70 。
  7. 7. The method for purifying selenium dioxide by distillation according to claim 1, wherein the predetermined temperature range in step f is 105 To 130 to 。
  8. 8. The method for purifying selenium dioxide by rectification as recited in claim 1, wherein the thermal dehydration treatment of step f further comprises monitoring the purified aqueous selenite solution at the current time in real time Turbidity of (2) At the previous time Turbidity of (2) Calculating turbidity change rate And the heating power of the thermal dehydration treatment is controlled in a closed loop manner ; According to Calculation and control follow the following rules if Then If (1) Then Wherein, the method comprises the steps of, In order to preset the threshold value of the rate of change, For a preset reduced heating power, Is the preset basic heating power.
  9. 9. The method of claim 1, wherein the predetermined range in step d is pH 3.0 to 4.0.
  10. 10. The method of claim 1, wherein the chemical reducing agent in step b is sodium sulfite.

Description

Rectification purification method for removing trace metal impurities in selenium dioxide Technical Field The invention relates to a rectification purification method for removing trace metal impurities in selenium dioxide, belonging to the technical field of high-purity inorganic compound preparation. Background In the current production of electronic grade selenium dioxide (SeO 2), the industry consensus is that a wet process has higher potential in removing trace impurities compared with the traditional dry sublimation, the wet process generally comprises the core steps of dissolution, chemical purification, impurity removal, pyrolysis regeneration crystallization and the like, in the chemical purification process, in order to remove trace key impurities such as arsenic and iron in selenious acid (H 2SeO3) solution formed by dissolving a crude selenium dioxide raw material in water, a sacrificial auxiliary agent such as ferric salt is adopted for targeted coprecipitation, which is considered to be an effective technical path in the chemical principle, the ferric salt is hydrolyzed into hydroxide floccules depending on regulating and controlling the pH value (pH) of the solution, and the high-efficiency adsorption and encapsulation capacities of the floccules on specific impurities are utilized to carry out the removal by precipitation together. However, when the chemical principle is applied to industrialized mass production, a plurality of restriction factors of engineering and physical layers are displayed, the mismatch between chemical reaction and physical operation in a process chain is difficult to realize cooperatively with the engineering operability, on one hand, the conventional alkaline regulation and pH operation in an industrial reaction kettle usually generates a transient local strong alkaline environment at an alkaline liquid dripping point, the pH heterogeneity leads to the transient precipitation and formation of compact particles due to local over-concentration before the sacrificial ferric salt is fully contacted and mixed with trace impurities in a solution main body, so that the chemical efficiency of adsorbing the impurities is reduced in industrial practice, on the other hand, even if chemical adsorption occurs, the formed hydroxide precipitation product is usually a colloid with high viscosity and high specific resistance, the colloid can quickly block pores of the colloid when contacting an industrial filter medium, so that the filtration flux tends to be zero, the whole process flow is interrupted due to separation difficulty, and the conventional improvement thought such as optimized stirring or adding a flocculating agent in the prior art cannot eliminate local concentration mutation under the limitation, and the novel impurity is introduced into a system aiming at producing high-purity products. In order to avoid the bottleneck that physical forms of precipitation are difficult to control in wet process, the technical scheme is changed to a purification path adopting coupling of Pressure Swing Adsorption (PSA) and rectification, for example, chinese patent application publication No. CN112624050B discloses a FTrPSA separation and purification method of deep defluorination and drying of HC1 gas containing low concentration HF, in an attempt to realize purification of HC1 gas through complex coupling of multiple unit operations such as medium-temperature pressure swing adsorption (FTrPSA), membrane separation and HC1 rectification, etc., however, the path connects processes of different physical principles such as adsorption, filtration and rectification in series, and relies on complex circulation loops, so that the whole process flow is extremely sensitive to fluctuation of working conditions, dynamic balance of desorption gas such as pressure swing adsorption and feeding of a rectification column is difficult to match and maintain between unit operations, partial batch product purity cannot reach standards, instantaneous mass nucleation is easy to be initiated in a pyrolysis crystallization step, and crystals are wrapped to form volatile impurities when fast precipitation is performed. Disclosure of Invention In order to solve the problems in the background technology, the technical scheme of the invention is as follows, a rectification purification method for removing trace metal impurities in selenium dioxide, comprising the following steps: Step a, dissolving crude selenium dioxide containing trace metal impurities in an aqueous solvent to form a selenious acid aqueous solution; Step b, adding a chemical reducing agent into the selenic acid aqueous solution to reduce the arsenic impurities with high oxidation state in the trace metal impurities to a preset low oxidation state; Step c, adding ferric nitrate as a sacrificial ferric salt auxiliary agent into the selenic acid aqueous solution, and adding a hydrolyzable alkaline precursor substance; Step d, heating the seleni