A method for enhancing leaching of monazite optimum-soluble residue

Abstract

The application provides a method for strengthening leaching of monazite optimal-soluble residue and relates to the technical field of hydrometallurgy. The method uses two-stage leaching to strengthen leaching: in a first-stage pre-leaching procedure, the optimal-soluble residue is pre-leached by using residual acid of leaching solution generated in a second-stage strengthening leaching, so as to increase the valuable metal content of the leaching solution and reduce the residual acid concentration, thereby reducing the dissolution rate of other impurity elements and improving the filtration performance of the ore slurry; the utilization rate of the residual acid is improved, and the overall acid consumption is reduced; the first-stage pre-leaching does not need heating, and the reaction heat is used to naturally heat the ore slurry, so that the energy consumption is effectively reduced; the reaction condition is relatively mild, and the requirement for the equipment and the operating environment is low; aging or standing is not needed, the operation is continuous, and the process is smooth; in the second-stage strengthening leaching procedure, the first-stage pre-leaching residue is strengthened and leached by using high acid, so that the valuable metal leaching rate is effectively improved; after part of the elements are recovered from the optimal-soluble residue by pre-leaching, the dissolved matter is relatively reduced under the condition of high acid, the ore slurry concentration and viscosity are reduced, and the solid-liquid separation effect is good.

Description

Technical Field

[0001] This invention relates to the field of hydrometallurgical technology, and in particular to a method for enhanced leaching of monazite slag. Background Technology

[0002] Monazite is a rare earth mineral rich in valuable resources such as rare earth elements, uranium, and thorium. Industrially, a sodium hydroxide alkaline decomposition-preferential dissolution method is commonly used to extract and recover rare earth elements and phosphorus from monazite, while simultaneously generating a large amount of highly soluble residue. Approximately 10% of the rare earth elements and the vast majority of uranium and thorium from the monazite concentrate enter the highly soluble residue, with rare earth oxide grades of 7–15%, uranium grades of 0.4–1.0%, and thorium grades of 14–24%, exhibiting high resource recovery value.

[0003] Currently, the main method for treating monazite leaching residue is to use inorganic acids for complete dissolution, allowing valuable elements such as rare earth elements, uranium, and thorium, as well as impurities such as iron, titanium, and zirconium, to enter the leachate. After solid-liquid separation, each element is then separated and recovered. However, due to the complex composition and fine particle size of the leaching residue, the overall metal recovery rate after leaching is low, solid-liquid separation of the slurry is difficult, and the separation and recovery of valuable metals from the leachate is challenging. These problems severely restrict the industrialization and commercialization of the comprehensive recycling of valuable resources from leaching residue.

[0004] The invention patent with publication number CN112760485A discloses a method for leaching valuable resources from high-quality leaching residue. The method involves adding inorganic acid to the high-quality leaching residue and heating and stirring for leaching. The leachate is heated to 70-80°C, thiourea is added, and after boiling, the addition is stopped, and stirring and aging continue for 3-6 hours. The leachate temperature is then lowered to 50-70°C, a flocculant is added, and stirring continues until precipitation occurs in the solution. Stirring is then stopped, and the solution settles naturally. The filtrate is obtained by solid-liquid separation using a chamber filter press. However, this method requires two heating and cooling cycles of the leachate during the high-quality leaching residue treatment, resulting in high energy consumption. Furthermore, the leachate needs to be aged before adding flocculant and allowing it to settle naturally. The supernatant overflows, and the underflow slurry is separated by filter press, leading to long solid-liquid separation times and low processing efficiency. The invention patent with publication number CN111004920A discloses a method for smelting and separating uranium, thorium, and rare earth elements from monazite slag. The method involves leaching with hydrochloric acid at 80–95°C for 4–6 hours, followed by boiling the slurry at 100–109°C for 1–1.5 hours. After the solution cools to below 60°C, hydrogen peroxide is added for aging treatment for 8–12 hours. The supernatant after aging is separated by siphoning, and the slurry is separated by two-stage countercurrent thickening sedimentation and washing. It is then further separated by a single-stage chamber filter press. This method has high requirements for equipment and operating environment, long leaching and aging cycles, and low solid-liquid separation efficiency. The invention patent with publication number CN103014333A discloses a method for separating and recovering uranium, thorium, and rare earth elements from monazite slag. The method involves leaching with sulfuric acid under heating and stirring for 5-8 hours, followed by cooling and settling of the leached slurry for 4-8 hours. The supernatant is then siphoned, and the bottom slurry is washed using a plate and frame filter press to obtain filter residue. The siphon liquid, filter liquid, and wash water are combined to obtain the leachate. This method is time-consuming in the stirring leaching and cooling clarification processes. The leaching rates for uranium and thorium are around 80%, while the leaching rates for rare earth elements are 40-60%. The low leaching rates of valuable elements are not conducive to efficient resource recovery and industrial applications.

[0005] Therefore, there is an urgent need to provide a method for enhanced leaching of monazite slag to solve the above-mentioned problems in the existing technology. Summary of the Invention

[0006] The purpose of this invention is to provide a method for enhanced leaching of monazite slag, which can solve the technical problems in the existing monazite slag leaching process, such as long processing cycle, repeated adjustment of slurry temperature, difficulty in solid-liquid separation, discontinuous process, and low leaching rate of valuable elements. This method improves the processing efficiency of monazite slag, simplifies the production process, reduces costs, and enables rapid and efficient recovery of valuable elements.

[0007] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0008] This invention provides a method for enhanced leaching of monazite residue, comprising the following steps:

[0009] The monazite slag is pre-leached with hydrochloric acid, and the resulting leaching slurry is subjected to a first solid-liquid separation to obtain a first-stage leaching residue and a first-stage leaching solution; the concentration of the first hydrochloric acid is 6-9 mol / L; the first-stage pre-leaching is performed without heating;

[0010] The first-stage leaching residue is subjected to a second-stage enhanced leaching using a second hydrochloric acid, and the resulting leaching slurry is subjected to a second solid-liquid separation to obtain a second-stage leaching residue and a second-stage leaching solution; the concentration of the second hydrochloric acid is 6-9 mol / L; the temperature of the second-stage enhanced leaching is 60-90℃;

[0011] The second-stage leaching residue was washed with hydrochloric acid solution. The resulting wash water was mixed with the second-stage leaching solution as a leaching agent for the first-stage pre-leaching. This mixture was then used for the first-stage pre-leaching of the next batch of monazite dissolving residue. The resulting leaching slurry underwent a first solid-liquid separation to obtain a new first-stage leaching solution and first-stage leaching residue. The leaching agent contained H... + The concentration is 3–6 mol / L;

[0012] The newly obtained leaching residue is subjected to a second-stage enhanced leaching process, and the newly obtained leaching solution is used as the qualified leaching solution. This process is repeated.

[0013] Preferably, during the pre-leaching process, the volume ratio of the leaching agent to the mass ratio of the monazite solvent residue (based on dry residue) is 1.5–5 L: 1 kg.

[0014] Preferably, the pre-soaking time is 1 to 3 hours.

[0015] Preferably, during the two-stage enhanced leaching, the volume ratio of the second hydrochloric acid to the mass of the first-stage leaching residue is 1.5–5 L: 1 kg.

[0016] Preferably, the two-stage enhanced leaching time is 1 to 3 hours.

[0017] Preferably, both the first solid-liquid separation and the second solid-liquid separation are vacuum filtration.

[0018] Preferably, the first-stage leaching residue is not washed before proceeding directly to the second-stage enhanced leaching.

[0019] Preferably, both the first-stage pre-leaching and the second-stage enhanced leaching are carried out under stirring conditions.

[0020] Preferably, the rare earth oxide grade in the monazite slag is 7-15%, the uranium grade is 0.4-1.0%, and the thorium grade is 14-24%.

[0021] Preferably, the concentration of the hydrochloric acid solution is 3-10 g / L, the volume ratio of the hydrochloric acid solution to the mass ratio of the second-stage leaching residue is 1-2 L: 1 kg, and the washing is performed 2-3 times.

[0022] This invention employs a two-stage leaching process to enhance leaching: the first-stage pre-leaching process utilizes the residual acid from the second-stage enhanced leaching to pre-leach the high-quality leaching residue, increasing the valuable metal content of the leaching solution while reducing the residual acid concentration, thereby reducing the dissolution rate of other impurity elements and improving the filtration performance of the slurry; it also improves the utilization rate of residual acid and reduces overall acid consumption. The first-stage pre-leaching process requires no heating, utilizing the heat of reaction to naturally raise the temperature of the slurry, effectively reducing energy consumption; the reaction conditions are relatively mild, with low requirements for equipment and operating environment; no aging or settling is required, allowing for continuous operation and a smooth process; the second-stage enhanced leaching process uses high acid to enhance the leaching of the first-stage pre-leaching residue, effectively increasing the leaching rate of valuable metals; after pre-leaching to recover some elements, the high-quality leaching residue exhibits a relatively reduced amount of leached substances under high acid conditions, resulting in lower slurry concentration and viscosity, and better solid-liquid separation. The overall process of this invention is simple and continuous, with high processing efficiency, effectively reducing the consumption of reagents, energy, power, and equipment materials, making it suitable for industrial applications. Attached Figure Description

[0023] Figure 1 This is a flowchart of the method for enhanced leaching of monazite residue according to the present invention. Detailed Implementation

[0024] This invention provides a method for enhanced leaching of monazite residue, comprising the following steps:

[0025] The monazite slag is pre-leached with hydrochloric acid, and the resulting leaching slurry is subjected to a first solid-liquid separation to obtain a first-stage leaching residue and a first-stage leaching solution; the concentration of the first hydrochloric acid is 6-9 mol / L; the first-stage pre-leaching is performed without heating;

[0026] The first-stage leaching residue is subjected to a second-stage enhanced leaching using a second hydrochloric acid, and the resulting leaching slurry is subjected to a second solid-liquid separation to obtain a second-stage leaching residue and a second-stage leaching solution; the concentration of the second hydrochloric acid is 6-9 mol / L; the temperature of the second-stage enhanced leaching is 60-90℃;

[0027] The second-stage leaching residue was washed with hydrochloric acid solution. The resulting wash water was mixed with the second-stage leaching solution as a leaching agent for the first-stage pre-leaching. This mixture was then used for the first-stage pre-leaching of the next batch of monazite dissolving residue. The resulting leaching slurry underwent a first solid-liquid separation to obtain a new first-stage leaching solution and first-stage leaching residue. The leaching agent contained H... + The concentration is 3–6 mol / L;

[0028] The newly obtained leaching residue is subjected to a second-stage enhanced leaching process, and the newly obtained leaching solution is used as the qualified leaching solution. This process is repeated.

[0029] Unless otherwise specified, all raw materials used in this invention are commercially available products well known in the art.

[0030] This invention uses hydrochloric acid to perform a first-stage pre-leaching of monazite slag, and then performs a first-stage solid-liquid separation on the resulting leaching slurry to obtain a first-stage leaching residue and a first-stage leaching solution.

[0031] In this invention, the rare earth oxide grade in the monazite slag is preferably 7-15%, more preferably 8-14%, and even more preferably 9-13%; the uranium grade is preferably 0.4-1.0%, more preferably 0.5-0.9%, and even more preferably 0.6-0.8%; and the thorium grade is preferably 14-24%, more preferably 15-22%, and even more preferably 17-20%.

[0032] In this invention, the concentration of the first hydrochloric acid is 6-9 mol / L, preferably 7-8 mol / L; the volume ratio of the first hydrochloric acid to the mass ratio of the monazite solvent residue (based on dry residue) is preferably 1.5-5 L:1 kg, more preferably 2-4 L:1 kg. In this invention, the first-stage pre-leaching is preferably carried out under stirring conditions; the first-stage pre-leaching is not heated. The slurry reaction process is self-heating, which can raise the temperature of the reaction system to 20-60°C. In this invention, the first-stage pre-leaching time is preferably 1-3 h, more preferably 1.5-2.5 h. In this invention, the first solid-liquid separation is preferably vacuum filtration. In this invention, the H in the first-stage leachate... + The concentration is 3–6 mol / L.

[0033] After obtaining a first-stage leaching residue and a first-stage leaching solution, the present invention uses a second hydrochloric acid to perform a second-stage enhanced leaching on the first-stage leaching residue, and performs a second solid-liquid separation on the resulting leaching slurry to obtain a second-stage leaching residue and a second-stage leaching solution.

[0034] In this invention, the first-stage leaching residue is preferably subjected to a second-stage enhanced leaching without washing. In this invention, the concentration of the second hydrochloric acid is 6-9 mol / L, preferably 7-8 mol / L; the volume ratio of the second hydrochloric acid to the mass of the first-stage leaching residue is preferably 1.5-5 L:1 kg, more preferably 2-4 L:1 kg. In this invention, the second-stage enhanced leaching is preferably carried out under stirring conditions; the temperature of the second-stage enhanced leaching is 60-90°C, preferably 65-85°C, more preferably 70-80°C. In this invention, the time of the second-stage enhanced leaching is preferably 1-3 h, more preferably 1.5-2.5 h. In this invention, the second solid-liquid separation is preferably performed by vacuum filtration. In this invention, the H in the second-stage leachate... + The concentration is 5–7 mol / L.

[0035] After obtaining the second-stage leaching residue and the second-stage leaching solution, the present invention uses hydrochloric acid solution to wash the second-stage leaching residue, mixes the resulting wash water with the second-stage leaching solution as a leaching agent for the first-stage pre-leaching, performs the first-stage pre-leaching on the next batch of monazite slag, and performs the first solid-liquid separation on the resulting leaching slurry to obtain a new first-stage leaching solution and a first-stage leaching residue.

[0036] In this invention, the concentration of the hydrochloric acid solution is preferably 3-10 g / L, more preferably 4-8 g / L, and even more preferably 5-7 g / L; the volume ratio of the hydrochloric acid solution to the mass ratio of the second-stage leaching residue is preferably 1-2 L:1 kg, or a washing ratio of 1-2:1; the number of washing cycles is preferably 2-3. In this invention, the H in the leaching agent... + The concentration is 3-6 mol / L, preferably 4-5 mol / L. Except for the first pre-leaching stage, the leaching agent used in the remaining pre-leaching stages contains H... + The concentration was maintained at 3–6 mol / L. This invention eliminates the need to adjust the H+ content in the leachate. + Concentration, H after mixing wash water and second-stage leachate + The concentration is sufficient to meet the above requirements. The conditions for the pre-leaching process described above have already been discussed in this invention and will not be repeated here.

[0037] The present invention performs a two-stage enhanced leaching on the newly obtained leaching residue, and uses the newly obtained leaching solution as the qualified leaching solution, and repeats this process.

[0038] This invention utilizes a pre-leaching process in the first stage to pre-leach the high-quality leaching residue with residual acid generated from the second-stage enhanced leaching. This increases the valuable metal content of the leaching solution while reducing the residual acid concentration, thereby reducing the leaching rate of other impurity elements and improving the filtration performance of the slurry. It also improves the utilization rate of residual acid and reduces overall acid consumption. The first-stage pre-leaching process requires no heating; the heat of reaction naturally raises the temperature of the slurry, effectively reducing energy consumption. The reaction conditions are relatively mild, with low requirements for equipment and the operating environment. No aging or settling is required, allowing for continuous operation and a smooth process. The second-stage enhanced leaching process uses high acid to enhance the leaching of the first-stage pre-leaching residue, effectively increasing the leaching rate of valuable metals. After pre-leaching and recovery of some elements, the high-quality leaching residue exhibits a relatively reduced amount of leached material under high acid conditions, resulting in lower slurry concentration and viscosity, and better solid-liquid separation. The overall process of this invention is simple and continuous, with high processing efficiency, effectively reducing the consumption of reagents, energy, power, and equipment materials, making it suitable for industrial applications.

[0039] The following detailed description of the method for enhanced leaching of monazite slag provided by the present invention, in conjunction with embodiments, should not be construed as limiting the scope of protection of the present invention.

[0040] Example 1

[0041] like Figure 1As shown, a certain monazite leaching residue (U: 0.82%, Th: 16.23%, REO: 10.33%) was subjected to a two-stage leaching cycle at a dry residue mass-to-liquid-solid volume ratio of 2.5L:1kg.

[0042] Pre-leaching conditions: The leaching agent is the second-stage leachate, H + Concentration 5.6 mol / L, self-heating temperature during reaction 40–55℃, reaction time 1.5 h, leachate H + Concentration 2.2 mol / L.

[0043] Two-stage enhanced leaching: Leaching agent hydrochloric acid concentration 9 mol / L, reaction temperature 60℃, reaction time 1.5 h, leachate H... + Concentration 6.3 mol / L. 3 g / L hydrochloric acid was used as washing water, the washing ratio was 1:1, and the washing was performed twice.

[0044] Analysis, testing, and calculations showed that the leaching rates of uranium, thorium, and rare earth elements in the slag were 99.18%, 98.33%, and 91.25%, respectively.

[0045] Example 2

[0046] A certain monazite leaching residue (U: 0.76%, Th: 19.51%, REO: 12.66%) was subjected to a two-stage leaching cycle at a dry residue mass-to-liquid-solid volume ratio of 2L:1kg.

[0047] Pre-leaching conditions: The leaching agent is the second-stage leachate, H + Concentration 5 mol / L, self-heating temperature during reaction 40-50℃, reaction time 2 h, leachate H + Concentration 1.8 mol / L.

[0048] Two-stage enhanced leaching: Leaching agent hydrochloric acid concentration 7 mol / L, reaction temperature 70℃, reaction time 2 h, leachate H... + Concentration 5.8 mol / L. 5 g / L hydrochloric acid as wash water, washing ratio 2:1, 2 washing stages.

[0049] Analysis, testing, and calculations showed that the leaching rates of uranium, thorium, and rare earth elements in the slag were 99.26%, 98.15%, and 90.88%, respectively.

[0050] Example 3

[0051] A certain monazite leaching residue (U: 0.91%, Th: 20.17%, REO: 9.62%) was subjected to a two-stage leaching cycle at a dry residue mass-to-liquid-solid volume ratio of 3L:1kg.

[0052] Pre-leaching conditions: The leaching agent is the second-stage leachate, H +Concentration 4 mol / L, self-heating temperature during reaction 40–45℃, reaction time 1.5 h, leachate H + Concentration 1.6 mol / L.

[0053] Two-stage enhanced leaching: Leaching agent hydrochloric acid concentration 6 mol / L, reaction temperature 90℃, reaction time 2 h, leachate H... + Concentration 4.5 mol / L. 10 g / L hydrochloric acid as washing water, washing ratio 1:1, 2 washing stages.

[0054] Analysis, testing, and calculations showed that the leaching rates of uranium, thorium, and rare earth elements in the slag were 98.92%, 98.17%, and 91.12%, respectively.

[0055] As can be seen from the above embodiments, the present invention provides a method for enhanced leaching of monazite slag, which can solve the technical problems in the existing monazite slag leaching process, such as long processing cycle, repeated adjustment of slurry temperature, difficulty in solid-liquid separation, discontinuous process, and low leaching rate of valuable elements. It can improve the processing efficiency of monazite slag, simplify the production process, reduce costs, and quickly and efficiently recover valuable elements.

[0056] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for enhanced leaching of monazite slag, characterized in that, Includes the following steps: The monazite slag is pre-leached with hydrochloric acid, and the resulting leaching slurry is subjected to a first solid-liquid separation to obtain a first-stage leaching residue and a first-stage leaching solution. The concentration of the first hydrochloric acid is 6-9 mol / L. The first-stage pre-leaching is performed without heating. The first-stage pre-leaching time is 1-3 hours. The first-stage leaching residue is subjected to a second-stage enhanced leaching using a second hydrochloric acid, and the resulting leaching slurry is subjected to a second solid-liquid separation to obtain a second-stage leaching residue and a second-stage leaching solution; the concentration of the second hydrochloric acid is 6~9 mol / L; the temperature of the second-stage enhanced leaching is 60~90℃; and the time of the second-stage enhanced leaching is 1~3h. The second-stage leaching residue was washed with hydrochloric acid solution. The resulting wash water was mixed with the second-stage leaching solution as a leaching agent for the first-stage pre-leaching. This mixture was then used for the first-stage pre-leaching of the next batch of monazite dissolving residue. The resulting leaching slurry underwent a first solid-liquid separation to obtain a new first-stage leaching solution and first-stage leaching residue. The leaching agent contained H... + The concentration is 3~6 mol / L; when mixing the wash water with the second-stage leachate, it is not necessary to adjust the H in the leachate. + Concentration, H after mixing wash water and second-stage leachate + The concentration is sufficient to meet the above requirements; The newly obtained first-stage leaching residue is subjected to a second-stage enhanced leaching, and the newly obtained first-stage leaching solution is used as the qualified leaching solution. This process is repeated. Both the first and second solid-liquid separation processes involve vacuum filtration.

2. The method according to claim 1, characterized in that, During the pre-leaching process, the volume ratio of the leaching agent to the mass ratio of the monazite solvent residue (based on dry residue) is 1.5~5L:1kg.

3. The method according to claim 1, characterized in that, During the two-stage enhanced leaching, the volume ratio of the second hydrochloric acid to the mass of the first-stage leaching residue is 1.5~5L:1kg.

4. The method according to claim 1, characterized in that, The first-stage leaching residue is not washed before being directly subjected to the second-stage enhanced leaching.

5. The method according to claim 1, 2 or 4, characterized in that, Both the first-stage pre-leaching and the second-stage enhanced leaching are carried out under stirring conditions.

6. The method according to claim 1 or 2, characterized in that, The rare earth oxide grade in the monazite slag is 7-15%, the uranium grade is 0.4-1.0%, and the thorium grade is 14-24%.

7. The method according to claim 1, characterized in that, The concentration of the hydrochloric acid solution is 3~10g / L, the volume ratio of the hydrochloric acid solution to the mass ratio of the second-stage leaching residue is 1~2L:1kg, and the washing is performed 2~3 times.

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