Resource treatment method for waste residues in process of preparing metal hafnium through calcium thermal reduction

Abstract

The invention provides a resource treatment method for waste residues in the process of preparing metal hafnium through calcium thermal reduction, which specifically comprises the following steps: (1) preparing metal hafnium through calcium thermal reduction, and generating calcium thermal products and waste heat in the process of preparing metal hafnium through calcium thermal reduction; (2) carrying out acid leaching on a calcium thermal product in the metal hafnium preparation process by adopting the recycled acid liquor; (3) performing solid-liquid separation through a centrifugal machine after acid leaching to obtain a hafnium powder and calcium salt mixed solution; (4) pre-concentrating the calcium salt mixed stock solution in a stock solution tank, and then feeding the pre-concentrated calcium salt mixed stock solution into an evaporative crystallization salt separation system for mixed salt separation; and (5) the hafnium powder and mixed acid generated in the hafnium oxide production process react in the acid leaching tank, and a hafnium product is obtained. Separation and purification of the divalent calcium salt are achieved, no waste liquid is generated, condensate water reaches the direct discharge standard, the purity of the obtained product reaches the national or industrial standard, the obtained calcium salt can be reasonably utilized, and comprehensive utilization of energy and resources is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of wastewater treatment, and particularly relates to a method for resource disposal of waste residue in the process of preparing hafnium metal by calciothermic reduction. Background Art

[0002] A lot of waste heat and waste salts are generated in the traditional preparation of metals by calciothermic method, resulting in high production costs, high energy consumption and environmental impact. The current industrial waste salt treatment methods mainly include: 1. Recycling through appropriate methods; 2. Advanced oxidation technology; 3. Landfill treatment. Among them, landfill treatment is the most common method. However, due to the requirements of environmental protection policies, the treatment cost of many waste salts is very high, which not only causes serious environmental impact but also results in waste of resources. If the mixed salts are separated, it will not only reduce the environmental pressure, but also reuse the waste and increase the enterprise income.

[0003] China has rich recoverable waste heat resources, which are widely present in industrial production in various industries. Among them, the utilization technology of high-grade waste heat (≥300°C) has been gradually mature, but the recovery and utilization of low-grade waste heat (60°C - 300°C) are relatively few. Low-temperature evaporation is a method relative to high-temperature evaporation and boiling evaporation in the atmospheric pressure range. Using this method to treat high-salt wastewater can not only avoid entrainment or chemical reactions of pollutants other than water in high-salt wastewater during evaporation, but also avoid the requirement for high-grade heat sources, and realize the recovery and utilization of low-grade waste heat resources.

[0004] Patent CN104649495A discloses a refining process for chemical industrial waste salt, which uses adsorption to remove organic substances, and obtains sodium chloride by the methods of evaporation crystallization, high-temperature calcination, dissolution filtration, and evaporation crystallization. Patent CN105523676A discloses a method for separating high-salt wastewater zero-discharge evaporation crystallization salts by quality, which is to pass the high-concentration salt concentrate through an evaporation crystallization device, a freezing crystallization device and a salt evaporation crystallization device once, and separate the salts in the order of sodium sulfate, sodium chloride or sodium chloride, sodium sulfate by quality.

[0005] Patent CN108622969A discloses a method and equipment for spray evaporation and brine separation and full recovery of high-salt wastewater driven by low-quality waste heat, which is used for high-salt wastewater treatment, including a high-salt wastewater circulation part, a circulating gas circulation part, an absorption refrigeration circulation part, an evaporation chamber, a condensation chamber, a crystalline salt recovery part and a PLC control part. According to the spray evaporation of high-salt wastewater and absorption refrigeration forced condensation to recover clean water, brine separation is realized. The present invention uses low-quality waste heat as the energy source for high-salt wastewater treatment, couples spray evaporation and absorption refrigeration technologies, and realizes the comprehensive utilization of energy and resources. Using this method, the water-salt separation effect is good, the low-quality waste heat is fully utilized, the energy consumption is low, and the treatment cost is reduced to the greatest extent; the recovered liquid water quality reaches the distillation standard, and the recovered solid substances can be recycled, realizing zero discharge; scaling and high-temperature corrosion are avoided.

[0006] Therefore, applying the heat generated during the production of hafnium oxide to the treatment of high-salt wastewater while achieving the separation of mixed salts with the same valence state is a beneficial exploration that not only saves energy but also efficiently treats high-salt wastewater. Summary of the Invention

[0007] In view of a series of related problems in the prior art, such as the waste residue generated during the preparation of metallic hafnium by the calciothermic method and the ineffective utilization and resource disposal of a lot of low-grade waste heat during the process. This application proposes a method for resource disposal of the waste residue during the calciothermic reduction for preparing metallic hafnium. The acid solution generated during the production of hafnium oxide or the acid solution recovered in step (5) is used to acid-leach the calciothermic product during the preparation of metallic hafnium, so as to improve the leaching efficiency and effectively separate divalent calcium salts such as calcium chloride and calcium nitrate, realizing the effective resource utilization of the waste residue and waste acid solution; the waste heat generated by the calciothermic process is used as the heat source for the evaporation crystallization and salt separation system and the acid-leaching process, realizing the secondary effective utilization of energy.

[0008] A method for resource disposal of the waste residue during the calciothermic reduction for preparing metallic hafnium, the specific steps are as follows:

[0009] (1) Carry out calciothermic reduction to prepare metallic hafnium, and waste heat is generated during the process;

[0010] (2) Use the recovered acid solution to acid-leach the calciothermic product during the preparation of metallic hafnium;

[0011] (3) After acid-leaching, carry out solid-liquid separation by a centrifuge to obtain a mixed solution of hafnium powder and calcium salts;

[0012] (4) Pre-concentrate the original calcium salt mixed solution in the original solution tank and then enter the evaporation crystallization and salt separation system for separating mixed salts;

[0013] (5) React the hafnium powder with the mixed acid generated during the production of hafnium oxide in an acid-leaching tank to obtain hafnium products;

[0014] Process flow of calciothermic reduction for preparing metallic hafnium: a. Mixing, mixing hafnium oxide, calcium granules and calcium chloride in a certain proportion and then placing them in a calciothermic reaction crucible; b. Placing the crucible into an electric heating furnace; c. Evacuating, heating to the reaction temperature, keeping warm until the reaction ends and then cooling down. The temperature during this heating process is above 950 degrees, and waste heat will be generated during this process. d. After cooling to room temperature, take out the furnace under the protection of an inert atmosphere to obtain a calciothermic product, and the calciothermic product consists of metallic hafnium and waste residue (mainly calcium oxide).

[0015] The calcium thermal product is neutralized and leached with the acid solution recovered in the above step (5) or the waste mixed acid generated during the separation of zirconium and hafnium to prepare hafnium oxide. The calcium salt enters the solution to obtain the calcium thermal product, metallic hafnium. To further improve the quality of the hafnium product, it is further soaked with the waste mixed acid generated during the separation of zirconium and hafnium to prepare hafnium oxide, stirred to remove impurities, and then washed with water to obtain the calcium thermal product, metallic hafnium.

[0016] Process for preparing hafnium oxide: Using zirconium oxychloride as the raw material, nitric acid is added to prepare the mother liquor. The mother liquor is mixed with an organic solvent to separate zirconium and hafnium and enter the organic phase. The mother liquor after extraction and separation only contains chloride ions and nitrate ions, and this solution is used for acid leaching in step (5) or step (2).

[0017] In the above step (1), the waste heat can be divided into the primary waste heat, secondary waste heat, and tertiary waste heat of the calcium thermal process, which are respectively used for pre-concentration of the stock solution, evaporation crystallization and salt separation system, and acid leaching heating. The acid leaching temperature is controlled at 35 - 45 °C. The calcium thermal reduction temperature is 950 °C. During the reduction process, cooling generates waste heat of about 300 °C (generally humid hot air), and the furnace cover uses water cooling to generate hot water of about 60 °C. The waste heat of about 300 °C can be used for the evaporation system of calcium salt or the drying heat source. For example, the salt coming out of the centrifuge can be dried with hot air, and steam can be produced through heat pump technology for evaporation or recrystallization. The secondary steam of the evaporation system heats the stock solution in advance through heat exchange in the stock solution tank, making the stock solution entering the evaporation system higher than room temperature. The cooling hot water of the furnace cover can be directly connected in series to the coil of the acid leaching tank for heating.

[0018] Pre-concentration step of the stock solution tank: The stock solution is pre-concentrated by waste heat to improve the evaporation efficiency;

[0019] Evaporation crystallization and salt separation system step: The stock solution is pre-heated by waste heat in advance to save energy and improve the processing capacity;

[0020] Acid leaching step: Waste heat assists acid leaching to improve the leaching efficiency of the mixed acid. The leaching efficiency is improved, the processing capacity per unit time is increased, and the production cycle is shortened.

[0021] The recovered acid solution in step (2) is the waste mixed acid generated during the separation of zirconium and hafnium to prepare hafnium oxide or the acid solution recovered in step (5). Preferably, the recovered acid solution in step (2) is the acid solution recovered in step (5); The acid leaching time in step (2) is based on the complete leaching of the calcium salt to ensure the neutralization efficiency. The control method of the acid leaching temperature in step (5) is as follows: In the calcium thermal reaction, the furnace mouth uses jacket water circulation cooling, and the heated water is introduced into the acid leaching tank for heat exchange. By controlling the flow rate of the circulating water, the heating temperature is controlled.

[0022] The evaporation crystallization and salt separation system in the above step (4) includes an evaporation crystallization system and a recrystallization system.

[0023] The specific working process of the evaporation crystallization system is as follows: The original solution first enters the original solution tank, and the original solution is preheated by the calcium thermal waste heat. The heated liquid enters the evaporation crystallization system for evaporation concentration and crystallization. When the density of the concentrated liquid is between 1.6 and 1.65, calcium chloride starts to be produced and is pumped to the calcium chloride centrifuge by the discharge pump for solid-liquid separation. The separated calcium chloride mother liquor enters the mother liquor tank and then flows back to the evaporation crystallization system for continuous concentration and crystallization. When the online densitometer detects that the calcium nitrate concentration is about to reach the saturation density at the current temperature, the mother liquor in the mother liquor tank is cooled by heat exchange in the heat exchanger and then pumped into the thickening kettle. After evaporation and cooling for concentration, it enters the calcium nitrate centrifuge for solid-liquid separation. The centrifuged mother liquor is a saturated solution of calcium chloride and calcium nitrate, and this solution flows back to the evaporation crystallization system. The water content of the calcium chloride separated by the calcium chloride centrifuge is 5%, and dry salt with a purity of 96%-98% is obtained after drying; the water content of the calcium nitrate separated by the calcium nitrate centrifuge is about 5%, and it enters the recrystallization system for further purification.

[0024] The specific working process of the recrystallization system is as follows: Calcium nitrate is stirred and mixed with pure water or saturated calcium nitrate solution in the reaction kettle, heated to 90 °C, and then cooled. At this time, the calcium nitrate crystals are pumped to the calcium nitrate centrifuge by the discharge pump for solid-liquid separation, and calcium nitrate crystals with a purity of more than 98% are separated. The separated mother liquor enters the mother liquor tank and then flows back to the reaction kettle to continue dissolving calcium nitrate crystals. The concentration of calcium chloride at the current temperature is detected by the online densitometer / mass fraction meter. When the concentration reaches saturation, the mother liquor in the mother liquor tank enters the evaporation system.

[0025] In step (5) above, the acid leaching is heated to 35 - 45 °C to improve the efficiency of corrosion and impurity dissolution. If the temperature is too low, the speed increase is not obvious; if the temperature is too high, the acid volatilization will be serious, affecting the corrosion and dissolution process.

[0026] The acid solution after acid leaching in step (5) is recovered and used in step (2). The recovered acid solution in step (2) is mainly obtained from step (5), and can also be the waste mixed acid generated during the separation of zirconium and hafnium to prepare hafnium oxide.

[0027] The main components of the waste mixed acid solution in step (5) above are nitric acid and hydrochloric acid, and the hydrogen ion concentration in the waste mixed acid in step (5) is 5.5 - 6 mol / L. The hydrogen ion concentration in the recovered acid solution in step (2) is 4.5 - 5.8 mol / L.

[0028] In the acid leaching processes of step (2) and step (5) above, the liquid-solid ratio is (3 - 4):1. The acid leaching time in step (5) is 2 - 3 h, and the stirring speed is 60 - 65 revolutions per minute, alternating forward and reverse, and the direction is changed every 10 minutes.

[0029] This application has the following advantages compared with the prior art:

[0030] (1) This application realizes the separation and purification of divalent calcium salts, without generating waste liquid, the condensed water meets the direct discharge standard, and the purity of the obtained product reaches the national or industrial standard. High-purity calcium chloride can be obtained and used as a raw material for calcium thermal reduction, reducing the raw material cost; high-purity calcium nitrate salt can be obtained and sold as a by-product.

[0031] (2) The calcium thermal solid product of this application is acid-leached using the acid solution generated in the production of hafnium oxide. The acid used is the recycled acid solution, avoiding the discharge of waste acid, and the leaching efficiency of the mixed acid is higher.

[0032] (3) The raw liquid tank can pre-concentrate raw liquids with different concentrations, improving the evaporation efficiency.

[0033] (4) This process method is intermittent and matches the intermittent calcium thermal production. Description of the Drawings

[0034] Figure 1 It is a flow chart of the resource utilization and disposal method of the waste residue in the process of calcium thermal reduction to prepare hafnium metal in this application. Detailed Embodiments

[0035] Next, the technical solutions of the present invention will be clearly and completely described in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative work belong to the scope of protection of the present invention.

[0036] Example 1:

[0037] The calcium thermal product and the waste acid solution after acid leaching are adjusted to neutral in a neutralization tank, and solid-liquid separation is carried out by a centrifuge to obtain hafnium powder of the calcium thermal product and a mixed solution of calcium nitrate and calcium chloride. The raw liquid containing calcium salt enters the evaporation crystallization and salt separation system; the hafnium powder of the calcium thermal product enters the acid leaching system. The hafnium powder reacts with the mixed acid generated in the process of producing hafnium oxide in an acid leaching tank for 2 hours, and the heat during the calcium thermal process is used to heat the leaching process to 40 degrees to improve the acid leaching effect, and finally hafnium products are obtained; the acid solution after acid leaching of hafnium powder is used to neutralize calcium oxide in calcium thermal reduction.

[0038] The concentration of the calcium-containing stock solution is 25% (15% calcium chloride and 10% calcium nitrate). 100 kg of the stock solution is pumped into the evaporation crystallization system. In the form of a forced circulation evaporator, after passing through the preheater, it enters the forced circulation evaporator for evaporation and concentration until it becomes supersaturated. Then, it is output to a centrifuge through a discharge pump for solid-liquid separation to centrifugally separate out 11.3 kg of calcium chloride crystals with a higher purity and a water content of 5%. After drying, 10.74 kg of crystals are obtained, with a purity of approximately 98%. The mother liquor after centrifugation is cooled and crystallized to 30 °C to precipitate calcium nitrate crystals containing calcium chloride impurities, with a purity of approximately 78.4%. The crystals are stirred and mixed with pure water in a reaction kettle, heated to 90 °C, and then cooled. At this time, the calcium nitrate is pumped to a centrifuge for solid-liquid separation to separate out calcium nitrate crystals with a purity of 99%. The mother liquor after separation enters the mother liquor tank and then returns to the reaction kettle to continue dissolving calcium nitrate crystals. When the calcium chloride concentration reaches saturation, the mother liquor enters the evaporation system of the forced circulation evaporator.

[0039] Comparative Example 1: During the acid leaching process (hafnium powder from the calcium thermal product enters the acid leaching system, and the hafnium powder reacts with the mixed acid generated during the production of hafnium oxide in the acid leaching tank), a separate nitric acid is used for the acid leaching operation, and the others are the same as in Example 1.

[0040] Comparative Example 2: During the acid leaching process (hafnium powder from the calcium thermal product enters the acid leaching system, and the hafnium powder reacts with the mixed acid generated during the production of hafnium oxide in the acid leaching tank), a separate hydrochloric acid is used for the acid leaching operation, and the others are the same as in Example 1.

[0041] Comparative Example 3: During the acid leaching process (hafnium powder from the calcium thermal product enters the acid leaching system, and the hafnium powder reacts with the mixed acid generated during the production of hafnium oxide in the acid leaching tank), the temperature is controlled at room temperature, and the others are the same as in Example 1.

[0042] The impurity detection was carried out on the hafnium products finally obtained in the above examples and comparative examples. The specific detection standards refer to the non-ferrous metal industry standard YS / T 1467-2021. The results are shown in Table 1 below:

[0043] Table 1

[0044] Ca Fe Na Al Si Example 1 0.013％ 0.0082％ 0.0037％ 0.0052％ 0.0016％ Comparative Example 1 0.098％ 0.026％ 0.012％ 0.0078％ 0.0048％ Comparative Example 2 0.095％ 0.027％ 0.013％ 0.0075％ 0.0044％ Comparative Example 3 0.076％ 0.015％ 0.0089％ 0.0067％ 0.0032％

[0045] It can be seen from the results in Table 1 above that in the method for resource utilization of waste residue in the preparation of hafnium metal by calcium thermal reduction in this application, the waste heat generated in the calcium thermal process is realized as an overall resource, and the rational utilization of waste heat achieves the effective application of resources; the purity of the finally obtained hafnium product is the best; and the waste acid generated during the process is also reasonably utilized. The calcium thermal product is acid leached to realize the separation and purification of divalent calcium salts, and the salt-containing substances are classified and recycled for resource utilization, achieving zero emissions and realizing the comprehensive utilization of energy and resources.

[0046] Although embodiments of the present invention have been shown and described, those of ordinary skill in the art will appreciate that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for recycling waste residues in the process of preparing metallic hafnium by calcium thermal reduction, characterized in that: The specific steps are as follows: (1) Preparation of metallic hafnium by calcium thermal reduction, during which calcium thermal products and waste heat are generated; (2) acid leaching the calcium thermal product in the process of preparing metal hafnium with acid solution; (3) after acid leaching, solid-liquid separation is performed by a centrifuge to obtain a mixed solution of hafnium powder and calcium salt; (4) pre-concentrating the calcium salt mixed stock solution in step (3) in a stock solution tank and then entering an evaporation crystallization salt separation system to separate the mixed salt; (5) reacting the hafnium powder in step (3) with the waste mixed acid in an acid leaching tank to obtain a hafnium product; The waste mixed acid in step (5) is the waste acid generated in the process of separating zirconium and hafnium to prepare hafnium oxide; The waste mixed acid in step (5) can be directly used in step (2) after being recovered; The acid solution used in step (2) is the waste mixed acid recovered in step (5) or generated in the process of separating zirconium and hafnium to prepare hafnium oxide.

2. The method for recycling waste residues in the process of preparing metallic hafnium by calcium thermal reduction according to claim 1, characterized in that: The waste heat in step (1) can be used for pre-concentration of raw solution, evaporation crystallization salt separation system and acid leaching heating respectively.

3. The method for recycling waste residues in the process of preparing metallic hafnium by calcium thermal reduction according to claim 2, characterized in that: The acid leaching temperature is controlled at 35-45°C.

4. The method for recycling waste residues in the process of preparing metallic hafnium by calcium thermal reduction according to claim 1, characterized in that: The evaporation crystallization salt separation system in step (4) includes an evaporation crystallization system and a recrystallization system.

5. The method for recycling waste slag in the process of preparing metallic hafnium by calcium thermal reduction according to claim 4, characterized in that: The specific process of the evaporation crystallization system is as follows: the stock liquid first enters the stock liquid tank, and the stock liquid is preheated by the residual heat of calcium heat. The heated liquid enters the evaporation crystallization system for evaporation concentration and crystallization. When the density of the concentrated liquid is 1.6-1.65, calcium chloride begins to be discharged, and is pumped to the calcium chloride centrifuge for solid-liquid separation through a discharge pump. The separated calcium chloride mother liquor enters the mother liquor tank, and then flows back to the evaporation crystallization system to continue to concentrate and crystallize. When the calcium nitrate concentration at the current temperature is about to reach the saturated density detected by the online density meter, the mother liquor in the mother liquor tank is cooled by the heat exchanger and then pumped into the thickening kettle. After evaporation, cooling and concentration, it enters the calcium nitrate centrifuge for solid-liquid separation; the centrifuged mother liquor is a saturated calcium chloride and calcium nitrate solution, which flows back to the evaporation crystallization system; the calcium chloride separated by the calcium chloride centrifuge has a water content of 5%, and dry salt is obtained after drying, with a purity of 96%-98%; the calcium nitrate separated by the calcium nitrate centrifuge has a water content of about 5%, and enters the recrystallization system for further purification.

6. The method for recycling waste slag in the process of preparing metallic hafnium by calcium thermal reduction according to claim 4, characterized in that: The specific process of the recrystallization system is as follows: calcium nitrate and pure water or a saturated calcium nitrate solution are stirred and mixed in a reactor, heated to 90°C, and then cooled. At this time, the calcium nitrate crystals are pumped to a calcium nitrate centrifuge through a discharge pump for solid-liquid separation, and calcium nitrate crystals with a purity of more than 98% are separated. The separated mother liquor enters a mother liquor tank and then flows back to the reactor to continue to dissolve the calcium nitrate crystals. The concentration of calcium chloride at the current temperature is detected by an online density meter / mass fraction meter. When the concentration reaches saturation, the mother liquor in the mother liquor tank enters an evaporation system for evaporation and concentration.

7. The method for recycling waste residues in the process of preparing metallic hafnium by calcium thermal reduction according to claim 1, characterized in that: The main components of the waste mixed acid solution in step (5) are nitric acid and hydrochloric acid, wherein the hydrogen ion concentration is 5.5-6 mol / L.

8. The method for recycling waste residues in the process of preparing metallic hafnium by calcium thermal reduction according to claim 1, characterized in that: The hydrogen ion concentration in the acid solution recovered in step (2) is 4.5-5.8 mol / L.

9. The method for recycling waste residues in the process of preparing metallic hafnium by calcium thermal reduction according to claim 1, characterized in that: The liquid-to-solid ratio during the acid leaching process of step (2) and step (5) is (3-4):

1.

10. The method for recycling waste residues in the process of preparing metallic hafnium by calcium thermal reduction according to claim 1, characterized in that: The acid leaching time in step (5) is 2-3 hours, and the stirring speed is 60-65 rpm.

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