A method for preparing thorium sulfate by using monazite oversaturated slag

Abstract

The application provides a method for preparing thorium sulfate by using monazite optimal dissolution residue, and relates to the technical field of hydrometallurgy. The monazite optimal dissolution residue is subjected to leaching, and the leaching rates of uranium, thorium and rare earth are high, so that leaching ore slurry is obtained. The leaching ore slurry is mixed with a polyacrylamide solution, and solid-liquid separation is carried out, so that a primary liquid is obtained. The primary liquid is subjected to first solvent extraction, iron is removed at the same time of recovering uranium, and a thorium-containing raffinate is obtained. The thorium-containing raffinate is subjected to second solvent extraction, thorium and rare earth are efficiently separated, and thorium-loaded organic phase and a rare earth-containing raffinate are obtained. The thorium-loaded organic phase is subjected to crystallization back extraction, and thorium sulfate is obtained. The method provided by the application is simple in operation, good in separation effect of uranium, thorium and rare earth, high in product purity, continuous in operation, and suitable for industrial application. The results of examples show that the purity of the thorium sulfate prepared by the application is greater than or equal to 98wt%.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of hydrometallurgy, and particularly relates to a method for preparing thorium sulfate by using monazite optimal dissolution slag. BACKGROUND

[0002] The optimal dissolution slag is the tailing produced after the monazite rare earth is optimally dissolved, and more than 99% of thorium, uranium and about 10% of rare earth in the rare earth extraction process enter into the optimal dissolution slag, wherein the thorium grade can reach 14-24%. The monazite concentrate processing enterprises mainly adopt the centralized stacking mode to dispose the optimal dissolution slag, and the optimal dissolution slag is not treated, which not only causes the waste of resources, but also has great safety and environmental protection hidden dangers.

[0003] The prior art patent with publication number CN100471962C discloses a method for separating and enriching uranium and thorium mixture and rare earth from superior slag. The method uses nitric acid system ultrasonic leaching-extraction separation. The leaching and extraction separation are carried out simultaneously. The product obtained by extraction is thorium and uranium rare earth nitrate enrichment, which needs further separation and purification. The patent with publication number CN104775026A discloses a method for extracting high-purity uranium, thorium and mixed rare earth from superior slag. The method uses hydrochloric acid leaching. After the supernatant is clarified by siphon, methyl phosphoric acid dimethyl heptane is used to extract uranium, and then methyl phosphoric acid dimethyl heptane is used to extract thorium. Thorium nitrate product is obtained by nitric acid washing-water back extraction-vacuum concentration-cooling crystallization-filtration drying. The low concentration of hydrochloric acid leads to low leaching rate of uranium, thorium and rare earth. At the same time, the low acidity leads to small separation coefficient of thorium and rare earth, resulting in low purity of thorium product. The patent with publication number CN114164351A discloses a method for preparing thorium nitrate from monazite superior slag. The method uses nitric acid leaching. After filtration, tributyl phosphate is used to extract uranium, and then tributyl phosphate is used to extract thorium. The thorium-loaded organic phase is back-extracted by nitric acid heating. The back-extracted solution is concentrated and then subjected to uranium extraction operation. The raffinate is concentrated and crystallized. Thorium nitrate is obtained by solid-liquid separation. Since tributyl phosphate has extraction effect on uranium and thorium, the method needs to perform secondary extraction to remove uranium after concentrating the thorium back-extracted solution. The selectivity of the extraction process is poor. Rare earth, iron, chlorine, silicon, zirconium, titanium, uranium and other substances cannot be well separated and removed, resulting in many impurity types, high impurity content and low product purity of thorium nitrate. The patent with publication number CN110184464A discloses a thorium extraction separation method. The method uses hydrochloric acid to leach rare earth waste residue, adds sulfate electrolyte after adjusting the pH value, and uses primary amine N1923 to extract thorium. The method is mainly used in low-acidity and low-thorium-concentration sulfate solution. The method is not suitable for high-acidity and high-chloride-ion system under the current industrial hydrochloric acid leaching conditions. The method has great technical limitations and is not conducive to industrial application. The patent with publication number CN114277265A discloses a method for preparing thorium oxide from monazite superior slag. The method uses magnetic gravity separation and pressure filtration for pretreatment of superior slag. The method uses hydrochloric acid dissolution, ammonium bicarbonate precipitation and pressure filtration for the filter cake after pretreatment. The method uses hydrochloric acid redissolution, sodium carbonate precipitation and pressure filtration to obtain neutral filtrate. The method uses hydrochloric acid to adjust the pH value and filter to obtain thorium carbonate uranium precipitate. The method uses trioctyldecyl tertiary amine, tributyl phosphate, secondary octanol and sulfonated kerosene for extraction after the neutral filtrate is filtered. The method uses oxalic acid solution to obtain thorium oxalate precipitate. The method continues to dry and roast to obtain thorium oxide powder. The method has complex and tedious treatment process, large reagent consumption for acid and alkali adjustment, and high equipment requirement, which is not conducive to industrial application.

[0004] Therefore, there is an urgent need to provide a method for preparing high-purity thorium product from monazite superior slag to solve the problems existing in the prior art. SUMMARY

[0005] The application aims to provide a method for preparing thorium sulfate by using monazite optimal leaching residue, and the method can solve the problems of narrow application range, complex processing technology, poor element separation effect, high impurity content, low thorium product purity and poor industrial application of the prior art.

[0006] In order to achieve the above-mentioned application purposes, the application provides the following technical scheme:

[0007] The application provides a method for preparing thorium sulfate by using monazite optimal leaching residue, and the method comprises the following steps:

[0008] The monazite optimal leaching residue is subjected to leaching to obtain leaching slurry;

[0009] The leaching slurry and a polyacrylamide solution are mixed, and solid-liquid separation is performed to obtain a primary liquid;

[0010] The primary liquid is subjected to first solvent extraction to obtain thorium-containing raffinate;

[0011] The thorium-containing raffinate is subjected to second solvent extraction to obtain thorium-loaded organic phase;

[0012] The thorium-loaded organic phase is subjected to crystallization back extraction to obtain thorium sulfate.

[0013] Preferably, the leaching agent used in the leaching comprises an aqueous hydrochloric acid solution; the temperature of the leaching is 25-90 DEG C; and the leaching time is 1-4 h.

[0014] The solid-liquid mass / volume ratio of the monazite optimal leaching residue to the leaching agent is 1 kg:2-5 L, based on the dry residue of the monazite optimal leaching residue.

[0015] Preferably, the chemical composition of the primary liquid comprises: the concentration of iron is 2-6 g / L, the concentration of uranium is 2.5-5 g / L, the concentration of thorium is 50-90 g / L, the concentration of rare earth oxides is 20-80 g / L, the concentration of H + The concentration of H2SO4 is 2.5-6 mol / L.

[0016] Preferably, the extraction system used in the first solvent extraction comprises a first extractant and a first diluent; the first extractant comprises tricaprylyl tertiary amine; and the first diluent comprises sulfonated kerosene.

[0017] The volume concentration of the first extractant in the extraction system is 10-40%.

[0018] Preferably, the first solvent extraction also obtains an iron and uranium-rich loaded organic phase.

[0019] The first solvent extraction further comprises: stripping the loaded organic phase rich in iron and uranium to obtain iron precipitation and qualified uranium liquid.

[0020] Preferably, the second solvent extraction employs an extraction system comprising a second extractant and a second diluent; the second extractant comprises 2-ethylhexyl phosphoric acid mono 2-ethylhexyl ester and tributyl phosphate; the second diluent comprises sulfonated kerosene.

[0021] The volume concentration of 2-ethylhexyl phosphoric acid mono 2-ethylhexyl ester in the extraction system is 10-30%, and the volume concentration of tributyl phosphate is 2-15%.

[0022] Preferably, the thorium content in the thorium loaded organic phase is 8-30 g / L.

[0023] Preferably, the second solvent extraction further obtains a rare earth-containing raffinate;

[0024] The rare earth-containing raffinate contains 20-80 g / L of rare earth oxides and 2.5-6 mol / L of H + .

[0025] Preferably, the stripping agent used in the crystallization stripping is a sulfuric acid solution.

[0026] Preferably, the purity of the thorium sulfate is ≥98 wt%.

[0027] The present application provides a method for preparing thorium sulfate using monazite optimal dissolution slag, which leaches monazite optimal dissolution slag, has high leaching rates of uranium, thorium and rare earths, and obtains leached ore slurry; mixes the leached ore slurry with a polyacrylamide solution, performs solid-liquid separation, and obtains a raw liquid; performs first solvent extraction on the raw liquid, removes iron while recovering uranium, and obtains a thorium-containing raffinate; performs second solvent extraction on the thorium-containing raffinate, efficiently separates thorium and rare earths, and obtains a thorium loaded organic phase; performs crystallization stripping on the thorium loaded organic phase, and obtains thorium sulfate. The method provided by the present application is simple in operation, has good separation effects on uranium, thorium and rare earths, has high product purity, is continuous in operation, and is suitable for industrial application. The results of examples show that the purity of the thorium sulfate prepared by the present application is ≥98%.

[0028] As preferred, the present application uses high-concentration hydrochloric acid leaching, has high leaching rates of uranium, thorium and rare earths, adopts uranium-iron co-extraction, removes iron by precipitation stripping, has a coherent process, has good selectivity for uranium and iron, has good separation effects on thorium and rare earths, and reduces the impurity content of the product. The present application uses centrifugal extraction process to extract thorium and crystallization stripping technology to produce thorium sulfate product, has advanced process technology, has good selectivity for thorium, and has high thorium sulfate product purity. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 A process flow chart for preparing thorium sulfate by using monazite optimal dissolution slag according to the present application. DETAILED DESCRIPTION

[0030] The present application provides a method for preparing thorium sulfate by using monazite optimal dissolution slag, comprising the following steps:

[0031] The monazite optimal dissolution slag is subjected to leaching to obtain leaching ore slurry;

[0032] The leaching ore slurry and polyacrylamide solution are mixed, and solid-liquid separation is performed to obtain a raw leaching solution;

[0033] The raw leaching solution is subjected to first solvent extraction to obtain a thorium-containing raffinate;

[0034] The thorium-containing raffinate is subjected to second solvent extraction to obtain thorium-loaded organic phase;

[0035] The thorium-loaded organic phase is subjected to crystallization back extraction to obtain thorium sulfate.

[0036] The monazite optimal dissolution slag is subjected to leaching to obtain leaching ore slurry. In the present application, the monazite optimal dissolution slag has a wet basis water content of preferably 30-45wt%, more preferably 35.7-40.1wt%. In the present application, the chemical composition of the monazite optimal dissolution slag preferably comprises: Fe 1-4wt%, U 0.5-2wt%, Th 15-25wt%, rare earth oxides (REO) 15-30wt%, Cl - 7-15wt%, Zr 5-10wt%, Ti 0.5-2wt%, Si 3-6wt%, Al 0.5-2.5wt%; more preferably comprises: Fe 1.73-1.98wt%, U 0.97-1.11wt%, Th 18.32-20.63wt%, REO 22.42-25.23wt%, Cl - 7.93-9.11wt%, Zr 6.24-8.37wt%, Ti 1.02-1.71wt%, Si 3.77-4.68wt%, Al 1.37-1.86wt%.

[0037] In the present application, the leaching agent used in the leaching preferably comprises aqueous hydrochloric acid. In the present application, the aqueous hydrochloric acid is preferably prepared from concentrated hydrochloric acid and water. In the present application, the concentration of the aqueous hydrochloric acid is preferably 6-10mol / L, more preferably 7-9mol / L.

[0038] In the present application, the temperature of the leaching is preferably 25-90°C, more preferably 70-80°C; the time of the leaching is preferably 1-4h, more preferably 2-3h. In the present application, the leaching is preferably carried out under normal pressure. In the present application, the leaching is preferably carried out under stirring; the stirring rate is preferably 250-500rpm. In the present application, the leaching is preferably carried out in a water bath.

[0039] In the present application, the solid-liquid mass volume ratio of the monazite superior leaching residue to the leaching agent is preferably 1kg:2-5L, more preferably 1kg:3-4L, based on the dry residue of the monazite superior leaching residue.

[0040] After obtaining the leaching slurry, the present application mixes the leaching slurry and a polyacrylamide solution, carries out solid-liquid separation, and obtains a raw leaching solution. In the present application, the mass of the polyacrylamide solution is preferably 10-200g / t of the mass of the dry residue of the monazite superior leaching residue, more preferably 40-70g / t. In the present application, the mass concentration of the polyacrylamide solution is preferably 0.05-0.2%, more preferably 0.1-0.15%.

[0041] In the present application, the solid-liquid separation is preferably carried out by using a plate-and-frame filter press or a vacuum filtration device.

[0042] In the present application, the leaching solution obtained by the solid-liquid separation is a hydrochloric acid system dissolution solution containing iron, uranium, thorium, and rare earth elements, i.e. a raw leaching solution.

[0043] In the present application, the chemical composition of the raw leaching solution preferably includes: the concentration of iron is 2-6g / L, the concentration of uranium is 2.5-5g / L, the concentration of thorium is 50-90g / L, the concentration of rare earth oxides is 20-80g / L, the concentration of H + ; more preferably includes: the concentration of iron is 5.07-5.74g / L, the concentration of uranium is 3.21-3.65g / L, the concentration of thorium is 59.60-66.22g / L, the concentration of rare earth oxides is 63.67-74.85g / L, the concentration of H + is 2.83-3.52mol / L.

[0044] In the present application, after the leaching and the solid-liquid separation, the uranium leaching rate (based on the residue) is preferably 97-99.9%, more preferably 98.30-99.21%; the thorium leaching rate (based on the residue) is preferably 96-98%, more preferably 96.21-97.60%; the rare earth oxide leaching rate (based on the residue) is preferably 80-90%, more preferably 83.00-89.03%.

[0045] After obtaining the raffinate, the raffinate is subjected to first solvent extraction to obtain a thorium-containing raffinate.

[0046] In the present application, the extraction system used in the first solvent extraction preferably comprises a first extractant and a first diluent; the first extractant preferably comprises trioctyldecyl tertiary amine; and the first diluent preferably comprises sulfonated kerosene.

[0047] In the present application, the first solvent extraction is preferably multi-stage countercurrent extraction, and more preferably 3-5 stage countercurrent extraction.

[0048] In the present application, the thorium-containing raffinate preferably comprises thorium, rare earth and impurity elements.

[0049] In the present application, the first solvent extraction preferably also obtains an iron and uranium-rich loaded organic phase.

[0050] In the present application, after the first solvent extraction, the iron and uranium-rich loaded organic phase is preferably subjected to stripping to obtain an iron precipitate and a uranium qualified liquid.

[0051] In the present application, the first extractant is used to co-extract uranium and iron in a high hydrochloric acid system, and sodium carbonate is used to strip and recover uranium while removing iron.

[0052] After obtaining the thorium-containing raffinate, the thorium-containing raffinate is subjected to second solvent extraction to obtain a thorium-loaded organic phase. In the present application, the second solvent extraction is preferably carried out in a centrifugal extractor.

[0053] In the present application, the extraction system used in the second solvent extraction preferably comprises a second extractant and a second diluent; the second extractant preferably comprises 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester and tributyl phosphate; and the second diluent preferably comprises sulfonated kerosene. In the present application, the volume concentration of 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester in the extraction system is preferably 10-30%, more preferably 13-17%; and the volume concentration of tributyl phosphate is preferably 2-15%, more preferably 10-13%. The present application uses 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester and tributyl phosphate as extractants to extract thorium, and has a good separation effect on rare earths.

[0054] In the present application, the second solvent extraction is preferably multi-stage countercurrent centrifugal extraction, more preferably 3-5 stages of countercurrent centrifugal extraction.

[0055] In the present application, the thorium content in the thorium-loaded organic phase is 8-30 g / L, more preferably 12.8-15.1 g / L.

[0056] In the present application, the second solvent extraction preferably also obtains a rare earth-containing raffinate. In the present application, the rare earth-containing raffinate preferably contains 20-80 g / L of rare earth oxides and 2.5-6 mol / L of H + ; more preferably 63.60-74.33 g / L of rare earth oxides and 2.80-3.50 mol / L of H + . In the present application, the rare earth-containing raffinate is preferably returned to the rare earth preferential dissolution process for preparation of hydrochloric acid. The present application makes full use of the residual acid, improves the rare earth recovery rate, improves the economic benefit, and reduces the production cost.

[0057] After obtaining the thorium-loaded organic phase, the thorium-loaded organic phase is subjected to crystallization back extraction to obtain thorium sulfate. In the present application, the crystallization back extraction is preferably carried out in a crystallization back extraction device.

[0058] In the present application, the back extraction agent used in the crystallization back extraction is preferably a sulfuric acid solution. In the present application, the concentration of the sulfuric acid solution is preferably 1-5 mol / L, more preferably 3 mol / L. The present application uses sulfuric acid crystallization back extraction to produce thorium sulfate products, which have high purity.

[0059] In the present application, the crystallization back extraction is preferably multi-stage crystallization back extraction, more preferably 1-5 stages of crystallization back extraction, and specifically preferably 4 stages of crystallization back extraction.

[0060] Preferably, after the crystallization back-extraction, the obtained solid substance is dried to obtain thorium sulfate. In the present application, the temperature of the drying is preferably 400°C; the time of the drying is preferably 2h.

[0061] In the present application, the purity of the thorium sulfate is preferably ≥98wt%, more preferably 98.2-98.31wt%.

[0062] The present application uses a crystallization back-extraction process to produce thorium sulfate products, which can be continuously operated and is conducive to industrial large-scale production.

[0063] The technical solutions in the present application will be described clearly and completely below in combination with the embodiments in the present application. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0064] Embodiment 1

[0065] A monazite optimal leaching residue, the moisture content is 38.2wt%, and the main chemical components of the dry basis are shown in Table 1.

[0066] Table 1 Main chemical components of a monazite optimal leaching residue

[0067] Element name Fe U Th REO Cl - ]] Zr Ti Si Al Mass fraction / wt% 1.98 1.02 19.28 25.23 7.93 8.37 1.71 4.12 1.54

[0068] A 35% analytical pure concentrated hydrochloric acid is mixed with water to prepare a hydrochloric acid leaching agent with a concentration of 6mol / L. The solid-liquid mass volume ratio of the monazite optimal leaching residue (dry residue) and the hydrochloric acid leaching agent is 1kg:3L. The leaching is carried out in a constant temperature water bath at 90°C with stirring. The reaction time is 4h, and a leaching slurry is obtained.

[0069] The leaching slurry is mixed with a 0.1% polyacrylamide solution, and the amount of the polyacrylamide solution is 40g / t of monazite optimal leaching residue dry residue. A raw leaching solution is obtained by plate and frame pressure filtration. The concentration of iron in the raw leaching solution is 5.74g / L, the concentration of uranium is 3.34g / L, the concentration of thorium is 61.82g / L, the concentration of rare earth oxides is 74.85g / L, the concentration of H + The uranium leaching rate (calculated based on the residue) is 98.30%, the thorium leaching rate (calculated based on the residue) is 96.21%, and the rare earth oxide leaching rate (calculated based on the residue) is 89.03%.

[0070] The extraction solution was subjected to a 5-stage countercurrent extraction system using a 15% trioctyldecyl tertiary amine + 85% sulfonated kerosene (volume ratio) mixture and clarifier to obtain an iron- and uranium-rich supported organic phase and a thorium-containing raffinate. The uranium concentration in the iron- and uranium-rich supported organic phase was 4.97 g / L, and the iron concentration was 5.27 g / L. A 3-stage back-extraction process was performed on the iron- and uranium-rich supported organic phase using a 1 mol / L sodium carbonate solution as the back-extraction agent and a back-extraction device with solid-liquid separation to obtain an iron precipitate and a qualified uranium solution. The uranium concentration in the qualified uranium solution was 14.33 g / L. The pH of the qualified uranium solution was adjusted to 12 using solid sodium hydroxide, and the precipitate was filtered through a plate and frame filter press to obtain sodium diuranate. The sodium diuranate product contained 67.73 wt% uranium, 0.031 wt% iron, and 0.001 wt% thorium.

[0071] The thorium-containing raffinate was subjected to a 5-stage countercurrent centrifugal extraction using a 15% 2-ethylhexyl phosphate mono-2-ethylhexyl ester + 10% tributyl phosphate + 75% sulfonated kerosene extraction system to obtain a thorium-loaded organic phase and a rare earth-containing raffinate; the thorium concentration in the thorium-loaded organic phase was 12.8 g / L.

[0072] The thorium-supported organic phase was subjected to three-stage crystallization back-extraction using a crystallization back-extraction device with 3 mol / L sulfuric acid solution as the back-extraction agent. The crystallized product was then dried (at 400°C for 2 hours) to obtain thorium sulfate. The thorium sulfate product contained 98.2 wt% thorium sulfate, 0.0336 wt% iron, 0.0066 wt% magnesium, 0.43 wt% phosphorus, 0.21 wt% fluorine, and 0.096 wt% titanium.

[0073] The rare earth-containing raffinate H + The concentration is 2.80 mol / L, and the concentration of rare earth oxides is 74.33 g / L; the rare earth-containing raffinate is returned to the rare earth optimal dissolution process for hydrochloric acid reuse and rare earth recovery.

[0074] Example 2

[0075] A certain monazite slag has a wet basis moisture content of 35.7 wt%, and the main chemical components on a dry basis are shown in Table 2.

[0076] Table 2. Main chemical components of a certain monazite slag.

[0077] Element name Fe U Th REO Cl- Zr Ti Si Al Mass fraction / wt% 1.73 1.11 18.32 23.21 8.13 6.24 1.02 3.77 1.37

[0078] The monazite leaching agent with a concentration of 7 mol / L was prepared by mixing 35% analytical pure concentrated hydrochloric acid with water, the solid-liquid mass-volume ratio of monazite leaching agent and monazite optimum-soluble residue (dry residue) was 1 kg:3 L, and the leaching was carried out in a constant-temperature water bath at 70°C with stirring, and the reaction time was 4 h, to obtain a leaching slurry.

[0079] The leaching slurry was uniformly mixed with a polyacrylamide solution with a mass concentration of 0.1%, and the polyacrylamide solution was used in an amount of 50 g / t of monazite optimum-soluble residue dry residue, and then a raw leaching solution was obtained through plate and frame pressure filtration; the concentration of iron in the raw leaching solution was 5.07 g / L, the concentration of uranium was 3.65 g / L, the concentration of thorium was 59.60 g / L, the concentration of rare earth oxides was 64.21 g / L, and the concentration of H + The uranium leaching rate (calculated based on residue) was 98.70%, the thorium leaching rate (calculated based on residue) was 97.60%, and the rare earth oxide leaching rate (calculated based on residue) was 83.00%.

[0080] The raw leaching solution was subjected to 5-stage countercurrent extraction through a mixing clarifier using an extraction system of 20% trioctyldecyl tertiary amine + 80% sulfonated kerosene (volume ratio), to obtain a loaded organic phase rich in iron and uranium and a thorium-containing raffinate; the concentration of uranium in the loaded organic phase rich in iron and uranium was 5.13 g / L, and the concentration of iron was 6.33 g / L; the loaded organic phase rich in iron and uranium was subjected to 5-stage stripping using a stripping device with solid-liquid separation, using a 1.5 mol / L sodium carbonate solution as a stripping agent, to obtain an iron precipitate and a qualified uranium solution through phase separation; the concentration of uranium in the qualified uranium solution was 15.11 g / L. The qualified uranium solution was adjusted to pH=12 using solid sodium hydroxide, and a sodium diuranate product was obtained through plate and frame pressure filtration of the precipitate; the uranium content of the sodium diuranate product was 65.58 wt%, the iron content was 0.027 wt%, and the thorium content was 0.001 wt%.

[0081] The thorium-containing raffinate was subjected to 5-stage countercurrent centrifugal extraction through a centrifugal extractor using an extraction system of 13% 2-ethylhexyl phosphoric acid mono-2-ethylhexyl ester + 12% tributyl phosphate + 75% sulfonated kerosene (volume ratio), to obtain a thorium-loaded organic phase and a rare earth-containing raffinate; the concentration of thorium in the thorium-loaded organic phase was 13.5 g / L;

[0082] The thorium-loaded organic phase was subjected to 5-stage crystallization stripping using a crystallization stripping device using a 3 mol / L sulfuric acid solution as a stripping agent, and a thorium sulfate product was obtained through crystallization and drying (the drying temperature was 400°C, and the time was 2 h); the thorium sulfate content of the thorium sulfate product was 98.3 wt%, the iron content was 0.0288 wt%, the magnesium content was 0.0071 wt%, the phosphorus content was 0.376 wt%, the fluorine content was 0.187 wt%, and the titanium content was 0.083 wt%.

[0083] The H + The concentration of the rare earth-containing raffinate is 2.92 mol / L, and the concentration of rare earth oxides is 64.18 g / L; the rare earth-containing raffinate is returned to the rare earth preferential dissolution process for hydrochloric acid recycling and rare earth recovery.

[0084] Example 3

[0085] A certain monazite preferential dissolution residue, the moisture content is 40.1wt%, and the main chemical components of the dry base are shown in Table 3.

[0086] Table 3 Main chemical components of a certain monazite preferential dissolution residue

[0087]

[0088]

[0089] A 35% analytical pure concentrated hydrochloric acid is mixed with water to prepare a hydrochloric acid leaching agent with a concentration of 9 mol / L, the solid-liquid mass-volume ratio of the monazite preferential dissolution residue (dry residue) and the hydrochloric acid leaching agent is 1 kg:3 L, and the leaching is carried out in a constant temperature water bath at 80°C with stirring, and the reaction time is 3 h to obtain a leaching slurry.

[0090] The leaching slurry is uniformly mixed with a 0.1% polyacrylamide solution, and the amount of the polyacrylamide solution is 70 g / t of monazite preferential dissolution residue dry residue, and a raw leaching solution is obtained by plate and frame pressure filtration; the concentration of iron in the raw leaching solution is 5.46 g / L, the concentration of uranium is 3.21 g / L, the concentration of thorium is 66.22 g / L, the concentration of rare earth oxides is 63.67 g / L, and the concentration of H + The uranium leaching rate (calculated on the residue) is 99.21%, the thorium leaching rate (calculated on the residue) is 96.30%, and the rare earth oxide leaching rate (calculated on the residue) is 85.20%.

[0091] The raw leaching solution is extracted by a 17% trioctyldecylamine + 83% sulfonated kerosene (volume ratio) extraction system through a mixing clarifier, and 5-stage countercurrent extraction is carried out to obtain an iron and uranium-rich loaded organic phase and a thorium-containing raffinate; the concentration of uranium in the iron and uranium-rich loaded organic phase is 5.31 g / L, and the concentration of iron is 6.02 g / L; 5-stage stripping is carried out on the iron and uranium-rich loaded organic phase using a 3 mol / L sodium carbonate solution as a stripping agent and using a stripping device with solid-liquid separation, and iron precipitation and uranium qualified liquid are obtained by phase separation; the concentration of uranium in the uranium qualified liquid is 16.12 g / L. The uranium qualified liquid is adjusted to pH=12 using solid sodium hydroxide, and sodium diuranate product is obtained by plate and frame pressure filtration of the precipitation; the uranium content of the sodium diuranate product is 66.22wt%, the iron content is 0.028wt%, and the thorium content is 0.001wt%.

[0092] The thorium-containing raffinate is extracted by a 17% 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester + 13% tributyl phosphate + 70% sulfonated kerosene (volume ratio) extraction system in a 5-stage countercurrent centrifugal extractor to obtain a thorium-loaded organic phase and a rare earth-containing raffinate; the thorium concentration in the thorium-loaded organic phase is 15.1 g / L;

[0093] The thorium-loaded organic phase is subjected to 4-stage crystallization stripping using a crystallization stripping device using a 3 mol / L sulfuric acid solution as a stripping agent, and crystallization drying (drying temperature: 400°C, time: 2h) to obtain a thorium sulfate product; the thorium sulfate content in the thorium sulfate product is 98.31 wt%, the iron content is 0.0231 wt%, the magnesium content is 0.0042 wt%, the phosphorus content is 0.37 wt%, the fluorine content is 0.17 wt%, and the titanium content is 0.075 wt%.

[0094] The H + The concentration of the rare earth-containing raffinate is 3.50 mol / L, and the concentration of rare earth oxides is 63.60 g / L; the rare earth-containing raffinate is returned to the rare earth preferential dissolution process for hydrochloric acid recycling and rare earth recovery.

[0095] The above only describes the preferred embodiments of the present application, and it should be noted that those skilled in the art can make several improvements and refinements without departing from the principles of the present application, and these improvements and refinements should also be considered within the scope of protection of the present application.

Claims

1. A method for preparing thorium sulfate by using monazite optimum-solubility residue, comprising the following steps: leaching monazite optimum-solubility residue to obtain leaching slurry; mixing the leaching slurry with polyacrylamide solution, and performing solid-liquid separation to obtain raw leaching solution; performing first solvent extraction on the raw leaching solution to obtain thorium-containing raffinate; performing second solvent extraction on the thorium-containing raffinate to obtain thorium-loaded organic phase; performing crystallization back-extraction on the thorium-loaded organic phase to obtain thorium sulfate; wherein the leaching agent used in the leaching comprises aqueous hydrochloric acid solution, and the concentration of the aqueous hydrochloric acid solution is 7-9 mol / L; the extraction system used in the first solvent extraction comprises first extractant and first diluent; the first extractant is tricaprylylphosphonium; the first diluent is sulfonated kerosene; and the volume concentration of the first extractant in the extraction system is 10-40%; the extraction system used in the second solvent extraction comprises second extractant and second diluent; the second extractant is 2-ethylhexyl phosphoric acid mono-2-ethylhexyl ester and tributyl phosphate; the second diluent is sulfonated kerosene; the volume concentration of 2-ethylhexyl phosphoric acid mono-2-ethylhexyl ester in the extraction system is 10-30%, and the volume concentration of tributyl phosphate is 2-15%; the content of thorium in the thorium-loaded organic phase is 8-30 g / L; the back-extractant used in the crystallization back-extraction is sulfuric acid solution; and the concentration of the sulfuric acid solution is 1-5 mol / L. The temperature of the leaching is 25-90 ℃, and the leaching time is 1-4 h; the solid-liquid mass-volume ratio of the monazite optimum-solubility residue to leaching agent is 1 kg: 2-5 L, based on the dry residue of the monazite optimum-solubility residue; the first solvent extraction also obtains iron- and uranium-enriched loaded organic phase; the first solvent extraction further comprises back-extracting the iron- and uranium-enriched loaded organic phase to obtain iron precipitate and qualified uranium solution; the second solvent extraction also obtains rare earth-containing raffinate; and the purity of the thorium sulfate is ≥98 wt%. ​ ​ ​ ​ ​ ​ ​ ​ ​ 2. The method of claim 1, wherein, ​ ​ 3. The method of claim 1, wherein, The chemical composition of the leaching solution includes: the concentration of iron is 2-6 g / L, the concentration of uranium is 2.5-5 g / L, the concentration of thorium is 50-90 g / L, the concentration of rare earth oxides is 20-80 g / L, the concentration of H + 2.5-6 mol / L.

4. The method of claim 1, wherein, ​ ​ 5. The method of claim 1, wherein, ​ The rare earth-containing raffinate contains 20-80 g / L of rare earth oxide and 2.5-6 mol / L H + .

6. The method of claim 1, wherein, ​

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