A process for precipitating uranium products from alkaline uranium solution by reduction method

Abstract

The present invention relates to the field of uranium resource development, and in particular to a process for precipitating uranium products from alkaline uranium solutions by reduction. The method is as follows: the alkaline uranium solution is heated and the pH is adjusted to 8-12; a carrier is added to obtain a pretreated liquid; the pretreated liquid is subjected to N-stage precipitation; the precipitation steps are specifically as follows: the pretreated liquid is heated and stirred, thiourea dioxide is added to react, the pH of the solution is maintained above 7, and precipitation is completed; in the N-stage precipitation process, other reducing agents are added for enhanced reduction to complete the N-stage precipitation; the other reducing agents are sodium sulfite or hydrazine hydrate; a flocculant is added to the precipitated liquid for solid-liquid separation and aging, and part of the concentrated slurry obtained is returned to step one to configure the raw material slurry, and part enters the next step; the concentrated slurry is filtered and dried to obtain a uranium product. The present invention realizes efficient reduction precipitation of uranium in alkaline solution and reduces reagent consumption.

Description

Technical Field

[0001] The invention relates to the field of uranium resource development, and in particular to a process for precipitating uranium products from an alkaline uranium solution by a reduction method. Background Art

[0002] For alkaline uranium ores, carbonates are generally used as leaching agents, and the resulting uranium-containing leachate usually contains a certain amount of organic matter such as humic acid. In order to obtain uranium products, alkali precipitation is directly added. Due to the complexation of carbonates and humic acid on uranium, uranium precipitation usually needs to be carried out at a higher pH value, the alkali consumption is high, and the uranium precipitation is incomplete. If uranium is first enriched by ion exchange or solvent extraction, and a leaching solution or stripping solution with a high uranium concentration is obtained before precipitation to prepare uranium products, due to the influence of humic acid, it is easy to cause resin poisoning or emulsification of the extraction process, affecting the normal operation of the process, and the concentration of organic matter such as humic acid may also be increased. In the uranium precipitation process, there are still problems such as high precipitation endpoint pH and incomplete uranium precipitation. In addition, the alkaline uranium solution can be acidified to remove CO2 first, and then alkali precipitation can be added. However, the reagent consumption is high, and some organic matter such as humic acid still remains in the solution, which still has a great impact on the uranium precipitation efficiency.

[0003] In view of this alkaline uranium solution containing organic matter such as humic acid, some people have studied the zinc powder reduction precipitation method to treat it. The results show that for alkaline eluent containing a considerable concentration of humic acid, the zinc powder reduction method has the advantages of high uranium recovery rate. However, the zinc powder reduction precipitation method has the advantages of high precipitation cost due to the high price of zinc powder on the one hand, and the precipitation product generated by this method has very fine particles and is in a colloidal state, which is difficult to filter. In addition, zinc powder generates basic zinc carbonate in the reaction, which cannot be separated from the uranium product precipitation product. The above problems make it difficult to further promote and apply this method in industry.

[0004] Therefore, it is of great significance to develop a more economical and efficient precipitation method to precipitate uranium from alkaline uranium solution, improve the precipitation efficiency of uranium, and reduce reagent consumption. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a process for precipitating uranium products from alkaline uranium solution by reduction method, so as to realize efficient reduction precipitation of uranium in alkaline solution and reduce reagent consumption.

[0006] The present invention provides a process for precipitating a uranium product from an alkaline uranium solution by a reduction method, comprising the following steps:

[0007] Step 1: heating the alkaline uranium solution and adjusting the pH to 8-12; adding a carrier to obtain a pretreated feed solution;

[0008] Step 2: performing N-stage precipitation on the pretreated feed liquid;

[0009] The precipitation step is specifically as follows: the pretreated feed liquid is heated and stirred, thiourea dioxide is added to react, the pH of the solution is maintained above 7, and precipitation is completed;

[0010] During the Nth stage precipitation process, other reducing agents are added to strengthen the reduction to complete the Nth stage precipitation; the other reducing agents are sodium sulfite or hydrazine hydrate;

[0011] N is an integer from 2 to 5;

[0012] Step 3: Add flocculant to the precipitated liquid for solid-liquid separation and aging, and return part of the concentrated slurry to step 1 to prepare the raw material slurry, and part of it to the next step;

[0013] Step 4: The dense slurry is filtered and dried to obtain a uranium product.

[0014] Preferably, in step 1, the temperature is heated to 50-90°C.

[0015] Preferably, the carrier is one or more of plant gum and pulp, and the added amount is 0.02-1.0% of alkaline uranium solution or the like.

[0016] Preferably, in step 1, the concentrated slurry obtained in step 3 is added to the heated alkaline uranium solution.

[0017] The added amount of the concentrated slurry is within 5% of the mass of the alkaline uranium solution.

[0018] Preferably, in the step 2, in the multi-stage precipitation and multi-layer, the temperature of the latter stage of precipitation is higher than the temperature of the former stage of precipitation.

[0019] Preferably, in the step 2, during the first stage precipitation, the reaction temperature is 65-85° C., and the reaction time is 10-30 minutes;

[0020] During the last stage of precipitation, the reaction temperature is 80-90°C.

[0021] Preferably, in the step 2, the total amount of thiourea dioxide used is 1.0 to 1.5 times the stoichiometric amount, and the amount of other reducing agents used is within 5% of the total amount of thiourea dioxide used.

[0022] Preferably, in the step 2, during the first stage precipitation, the amount of thiourea dioxide used is 0.8 to 1.1 times the stoichiometric amount.

[0023] Preferably, in step three, the flocculant is plant gum, and the amount of the flocculant is 0.02% to 0.5% of the mass of the feed liquid.

[0024] Preferably, in steps one and two, sodium hydroxide is used to adjust the pH.

[0025] Compared with the prior art, the reduction method of the present invention is a process method for precipitating uranium products from alkaline uranium solutions. For alkaline carbonate uranium solutions containing organic matter such as humic acid, composite reducing agents such as thiourea dioxide are used for multi-stage reduction precipitation process treatment. By controlling the temperature, time, reducing agent dosage and composition of the reduction precipitation process, efficient reduction precipitation of uranium in the solution can be achieved. The uranium concentration of the precipitation mother solution can be reduced to below 20 mg / L, and the uranium precipitation rate is above 99%, which avoids the problems of uranium being difficult to precipitate completely and high consumption of chemical reagents in the current conventional precipitation method; and the quality of the obtained uranium product is relatively high, and the uranium content in the product is above 80%. This method not only has high uranium precipitation efficiency and good quality of the uranium product obtained by precipitation, but also has simple process, low reagent consumption, strong operability, and good industrial application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 A flow chart showing the process for precipitating uranium products from alkaline uranium solution by reduction. DETAILED DESCRIPTION

[0027] In order to further understand the present invention, the embodiments of the present invention are described below in conjunction with examples, but it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, rather than limiting the present invention.

[0028] The alkaline uranium solution used in the present invention includes alkaline uranium ore leaching solution, alkaline uranium leaching solution of seawater uranium extraction adsorption material, alkaline leaching solution of ion exchange resin uranium extraction, etc. Its main components are uranium, carbonate (bicarbonate), sulfate, chloride, humic acid and other organic substances, etc. Among them, ρ(U)=0.1-20g / L, humic acid and other organic substances 0.5-5g / L.

[0029] The embodiment of the present invention discloses a process for precipitating a uranium product from an alkaline uranium solution by reduction, such as Figure 1 As shown, the following steps are included:

[0030] Step 1: heating the alkaline uranium solution and adjusting the pH to 8-12; adding a carrier to obtain a pretreated feed solution;

[0031] Step 2: performing N-stage precipitation on the pretreated feed liquid;

[0032] The precipitation step is specifically as follows: the pretreated feed liquid is heated and stirred, thiourea dioxide is added to react, the pH of the solution is maintained above 7, and precipitation is completed;

[0033] During the Nth stage precipitation process, other reducing agents are added to strengthen the reduction to complete the Nth stage precipitation; the other reducing agents are sodium sulfite or hydrazine hydrate;

[0034] N is an integer from 2 to 5;

[0035] Step 3: Add flocculant to the precipitated liquid for solid-liquid separation and aging, and return part of the concentrated slurry to step 1 to prepare the raw material slurry, and part of it to the next step;

[0036] Step 4: The dense slurry is filtered and dried to obtain a uranium product.

[0037] The present invention aims at the problems that the uranium product preparation process is difficult to completely precipitate uranium, the reagent consumption is high, and the precipitation process is complicated due to the presence of organic matter such as humic acid in a certain concentration in the current alkaline uranium solution. The invention adopts a thiourea dioxide reducing agent or a composite reducing agent composed of thiourea dioxide and other reducing agents to reduce the hexavalent uranium in the solution to a tetravalent uranium, and utilizes the extremely low solubility of the hydroxide generated by the hydrolysis of the tetravalent uranium to achieve efficient precipitation of uranium.

[0038] The reduction precipitation reaction formula of uranium by thiourea dioxide is:

[0039] CH4N2O2S+UO2 2+ +4OH-=(NH2)2CO+U(OH)4(or UO2·2H2O)+SO3 2-

[0040] Further, by adopting composite reducing agents and other enhanced reduction means, controlling the temperature and alkalinity of the precipitation process, and adopting graded precipitation to improve the reduction and precipitation efficiency of uranium, the amount of reducing agent used is reduced; at the same time, by adding plant gums such as sesbania gum and guar gum or other carriers, the seeding effect and flocculation effect of fine particles and the carrier effect on uranium precipitates are utilized to improve the precipitation efficiency and improve the particle characteristics of the precipitate, which is convenient for further solid-liquid separation. Through the above technical means, the economical and efficient precipitation of uranium in alkaline uranium solution is finally achieved, and a uranium precipitate product with good filtration performance and high quality is obtained.

[0041] The process for precipitating a uranium product from an alkaline uranium solution by the reduction method of the present invention is described in detail below in steps.

[0042] Step 1: Pretreatment of alkaline uranium solution. Specifically:

[0043] The alkaline uranium solution is heated to 50-90°C, and a certain amount of sodium hydroxide can be appropriately added according to the pH value of the alkaline uranium solution to maintain a certain alkalinity, and the pH is adjusted to 8-12; a carrier is added to obtain a pretreated feed solution;

[0044] The carrier is one or more of plant gum and pulp, and the addition amount is 0.02-1.0% of alkaline uranium solution or the like. The plant gum can be sesbania gum or guar gum.

[0045] The concentrated slurry obtained in step 3 is also added to the heated alkaline uranium solution to provide crystal seeds for the next step of reduction precipitation;

[0046] The added amount of the concentrated slurry is within 5% of the mass of the alkaline uranium solution.

[0047] Step 2: Multi-stage reduction precipitation.

[0048] Performing N-stage precipitation on the pretreated feed liquid;

[0049] The precipitation step is as follows: the pretreated feed liquid is heated and stirred, thiourea dioxide is added to react, the pH of the solution is maintained above 7, and precipitation is completed;

[0050] During the Nth stage precipitation process, other reducing agents are added to strengthen the reduction to complete the Nth stage precipitation; the other reducing agents are sodium sulfite or hydrazine hydrate;

[0051] N is an integer from 2 to 5.

[0052] Specifically:

[0053] The feed liquid from step 1 is taken into the first-stage stirred reactor, which controls the reaction process temperature at 60-80°C, the reaction residence time is 10-30min, and a certain amount of thiourea dioxide is added according to the uranium concentration in the feed liquid, and the amount is added according to 0.8-1.1 times the stoichiometric amount. If necessary, a certain amount of sodium hydroxide is added to maintain the solution pH above 7. The feed liquid from the first-stage reactor enters the second-stage reactor, the temperature of which is usually slightly higher than that of the first reactor, at 65-85°C, and the reaction residence time is 10-30min. If necessary, the reactor can be appropriately supplemented with part of the thiourea dioxide reducing agent and sodium hydroxide solution to maintain the pH value of the solution in the reactor above 7. By analogy, the feed liquid from the second kettle enters the third kettle, ..., until it enters the last kettle, which has the highest reaction temperature, usually 80-90°C. In order to reduce the uranium concentration of the precipitation mother liquor and improve the reduction precipitation efficiency of uranium, in addition to further adding a certain amount of thiourea dioxide, this kettle may also add a small amount of sodium bisulfite, hydrazine hydrate and other reducing agents for enhanced reduction according to the composition characteristics of the feed liquid, and at the same time add a certain amount of sodium hydroxide to make the pH of the feed liquid above 7. Usually, the reaction order is 2-5, the total reaction residence time is 1-3h, and the reaction temperature is 60-90°C.

[0054] The total amount of thiourea dioxide used is 1.0 to 1.5 times the stoichiometric amount, and the amount of other reducing agents used is within 5% of the total amount of thiourea dioxide used.

[0055] Step 3: Solid-liquid separation of precipitated slurry. Flocculants are added to the precipitated liquid for solid-liquid separation and aging. Part of the concentrated slurry is returned to step 1 to prepare the raw material slurry, and part enters the next step.

[0056] Specifically:

[0057] In step 2, the liquid after the reaction enters the thickener for solid-liquid separation and aging. In order to increase the sedimentation rate and the particle size of the precipitate, 0.02% to 0.5% of plant gum is added as a flocculant. At the same time, the uranium precipitate is aged in this process, and its physical properties such as particle density and size are improved. The supernatant obtained by the thickening overflows and is discharged. Part of the thick slurry returns to step 1 to prepare the raw material slurry, and part enters the next step of filtration to prepare the uranium product.

[0058] Step 4: Preparation of uranium products. Take part of the concentrated slurry obtained by the thickening treatment in step 3, filter and dry it to obtain the uranium product.

[0059] In order to further understand the present invention, the process for precipitating a uranium product from an alkaline uranium solution by a reduction method provided by the present invention is described in detail below in conjunction with examples, and the protection scope of the present invention is not limited by the following examples.

[0060] Example 1

[0061] The main components of an alkaline uranium ore leachate are uranium and carbonate, as well as a certain concentration of organic matter such as humic acid. The specific concentrations are: ρ(U)=1.4g / L, ρ(Na2CO3)=13.5g / L, ρ(NaHCO3)=7.6g / L, ρ(TOC)=0.96g / L.

[0062] First, the above leaching solution is heated to 60°C, and then 1.0% of the returned uranium precipitate is added and enters a two-stage stirring kettle for reduction precipitation reaction. The reaction temperature of the first kettle is 70°C, and the reaction temperature of the second kettle is 80°C. The residence time of the feed liquid in each kettle is 30 minutes, and the total residence time is 1 hour. A total of 1.3 times of thiourea dioxide (calculated based on the reduction reaction of uranium and thiourea dioxide) is added to the two kettles, of which 1.1 times of thiourea dioxide is added to the first kettle, and 0.2 times of thiourea dioxide is added to the second kettle.

[0063] After two-stage stirring reduction reaction, the slurry enters the thickener, where 0.2% guar gum is added as a flocculant. After sedimentation, part of the underflow is returned to the ingredients as a seed crystal, and part enters the plate and frame filter for filtration. The obtained product is further dried to obtain the uranium product.

[0064] After reduction precipitation, the uranium content of the mother liquor of the alkaline uranium ore leachate is reduced to below 10 mg / L, the uranium precipitation rate is 99.3%, and the uranium content of the obtained uranium product is 83.7%.

[0065] Example 2

[0066] The alkaline desorption solution of a certain seawater uranium extraction material is mainly composed of uranium, carbonate, chloride and a certain concentration of organic matter. The specific concentrations are: ρ(U)=9.3g / L, ρ(NaCl)=53.2g / L, ρ(NaHCO3)=8.6g / L, ρ(TOC)=2.9g / L.

[0067] Firstly, the above leaching solution is heated to 70°C, then 2.0% of the returned uranium precipitate is added, and at the same time, 0.05% of sesbania gum and 0.1% of pulp are added, and then the leaching solution enters a four-stage stirring kettle for reduction precipitation reaction.

[0068] The reaction temperatures of the first to fourth kettles are 75, 80, 85, and 90°C, respectively. The residence time of the feed liquid in each kettle is 20 minutes, and the total residence time is 80 minutes. A total of 1.5 times the chemical amount of thiourea dioxide is added, and 1.1, 0.1, 0.1, and 0.2 times of thiourea dioxide are added to the first to fourth kettles, respectively. At the same time, sodium hydroxide solution is appropriately added to each kettle according to the pH change to maintain the pH of the feed liquid reaction process above 7. In addition, a small amount of sodium bisulfite is added to the fourth kettle, and its amount is 10% to 20% of the amount of thiourea dioxide in the fourth kettle according to the reaction process.

[0069] After multi-stage stirring reduction reaction, the slurry enters the thickener, where 0.3% sesbania gum is added as a flocculant. After sedimentation, part of the underflow is returned to the ingredients as a seed crystal, and part enters the plate and frame filter for filtration. The obtained product is further dried to obtain the uranium product.

[0070] After reduction precipitation, the uranium content of the mother liquor of the alkaline uranium ore leachate is reduced to below 18 mg / L, the uranium precipitation rate is 99.8%, and the uranium content of the obtained uranium product is 81.2%.

[0071] Example 3

[0072] The alkaline eluent of a certain ion exchange resin is mainly composed of uranium, carbonate, chloride and a certain concentration of organic matter, the specific concentrations are: ρ(U)=17.6g / L, ρ(NaCl)=45.3g / L, ρ(NaHCO3)=5.2g / L, ρ(TOC)=0.74g / L.

[0073] First, the above leaching solution is heated to 60°C, and then 2.0% of the returned uranium precipitate is added, and at the same time, 0.08% of sesbania gum and 0.15% of pulp are added, and then enter the three-stage stirring kettle for reduction precipitation reaction. The reaction temperatures of the first to third kettles are 70, 75, and 80°C, respectively, and the retention time of the feed liquid in each kettle is 30 minutes, and the total retention time is 1.5 hours. A total of 1.2 times the chemical amount of thiourea dioxide is added, and 0.9, 0.15, and 0.15 times of thiourea dioxide are added to the first to third kettles, respectively.

[0074] After multi-stage stirring reduction reaction, the slurry enters the thickener, where 0.2% sesbania gum is added as a flocculant. After sedimentation, part of the underflow is returned to the ingredients as a seed crystal, and part enters the plate and frame filter for filtration. The obtained product is further dried to obtain the uranium product.

[0075] After reduction and precipitation, the uranium content of the mother liquor of the alkaline uranium ore leaching solution is reduced to below 15 mg / L, the uranium precipitation rate is 99.9%, and the uranium content of the obtained uranium product is 82.4%.

[0076] The above embodiments are only used to help understand the method and core idea of ​​the present invention. It should be noted that, for those skilled in the art, several improvements and modifications can be made to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the scope of protection of the claims of the present invention.

[0077] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A process for precipitating a uranium product from an alkaline uranium solution by reduction, characterized in that: The following steps are involved: Step 1: heating the alkaline uranium solution and adjusting the pH to 8-12; adding a carrier to obtain a pretreated liquid; the carrier is a plant gum, and the addition amount is 0.02-1.0% of the alkaline uranium solution; Step 2: performing N-stage precipitation on the pretreated feed liquid; The precipitation step is specifically as follows: the pretreated feed liquid is heated and stirred, thiourea dioxide is added to react, the pH of the solution is maintained above 7, and precipitation is completed; During the Nth stage precipitation process, other reducing agents are added to strengthen the reduction to complete the Nth stage precipitation; the other reducing agents are sodium sulfite or hydrazine hydrate; N is an integer from 2 to 5; The total amount of thiourea dioxide used is 1.0 to 1.5 times the stoichiometric amount, and the amount of other reducing agents used is within 5% of the total amount of thiourea dioxide used; during the first stage precipitation, the amount of thiourea dioxide used is 0.8 to 1.1 times the stoichiometric amount; Step 3: Add flocculant to the precipitated liquid for solid-liquid separation and aging, and return part of the concentrated slurry to step 1 to prepare the raw material slurry, and part of it to the next step; Step 4: The concentrated slurry is filtered and dried to obtain a uranium product.

2. The process for precipitating a uranium product from an alkaline uranium solution by reduction according to claim 1, characterized in that: In the step 1, heating is performed to 50-90°C.

3. The process for precipitating a uranium product from an alkaline uranium solution by reduction according to claim 1, characterized in that: In the step 1, the concentrated slurry obtained in step 3 is added to the heated alkaline uranium solution. The added amount of the concentrated slurry is within 5% of the mass of the alkaline uranium solution.

4. The process for precipitating a uranium product from an alkaline uranium solution by reduction according to claim 1, characterized in that: In the step 2, in the multi-stage precipitation and multi-layer, the temperature of the latter stage of precipitation is higher than the temperature of the previous stage of precipitation.

5. The process for precipitating a uranium product from an alkaline uranium solution by reduction according to claim 4, characterized in that: In the step 2, during the first stage precipitation, the reaction temperature is 65-85°C and the reaction time is 10-30 minutes; During the last stage of precipitation, the reaction temperature is 80-90°C.

6. The process for precipitating a uranium product from an alkaline uranium solution by reduction according to claim 1, characterized in that: In the step three, the flocculant is plant gum, and the amount of the flocculant is 0.02% to 0.5% of the mass of the feed liquid.

7. The process for precipitating a uranium product from an alkaline uranium solution by reduction according to claim 1, characterized in that: In the steps 1 and 2, sodium hydroxide is used to adjust the pH.

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