A method for leaching valuable elements from silicate rare earth ore

Abstract

The application discloses a method for leaching valuable elements in silicate rare earth ore, and belongs to the technical field of rare earth metallurgy. The method adopts a process of "low-temperature sulfur acidification and intensified roasting - clinker hydro-metallurgy - leaching of ore slurry and flocculation - washing of filter cake" to realize efficient leaching of valuable elements in rare earth concentrate. The intensified low-temperature sulfur acidification roasting process avoids the problems of high energy consumption, serious equipment corrosion, low rare earth leaching rate and complex waste gas treatment (SO2 emission) in the traditional process, and realizes decomposition of the silicate rare earth ore, significantly improves the effect of the rear-end leaching process, reduces the acid consumption and the difficulty of waste water treatment compared with the pickling process, the ore slurry flocculation and sedimentation process helps to improve the industrial production efficiency, and the filter cake washing process further improves the leaching rate of valuable elements, realizes the maximized utilization of silicate rare earth concentrate resources under the premise of environmental friendliness, and provides a technical path for industrial utilization of silicate type rare earth ore.

Description

Technical Field

[0001] This invention relates to the field of rare earth metallurgy technology, and more specifically to a method for leaching valuable elements from silicate rare earth ores. Background Technology

[0002] Rare earth minerals, as "strategic resources" for modern industrial and technological development, are far more significant than ordinary minerals. Containing 17 elements, rare earths, though abundant in the Earth's crust, are difficult to extract, making them irreplaceable "industrial vitamins." Industrially produced rare earth concentrates include bastnaesite-monazite mixed concentrate, bastnaesite concentrate, monazite concentrate, and xenotime concentrate. The main rare earth minerals in these concentrates belong to the carbonate and phosphate groups.

[0003] Carbonate rare earth ores (such as bastnaesite) can be decomposed by heating them above their thermal decomposition temperature, producing rare earth oxides and fluorine oxides. Therefore, bastnaesite concentrate is often decomposed using oxidative roasting, during which cerium is oxidized to a +4 valence state. Subsequently, it is leached with sulfuric acid solution to separate the rare earth elements.

[0004] Phosphate minerals (such as monazite) have very stable mineral structures. They are generally decomposed by using strong acids or strong bases as decomposing agents. They are heated to a temperature close to the decomposition temperature of the decomposing agent or below the boiling point. After decomposition, rare earth elements are leached out with dilute acid to achieve the separation of rare earth elements.

[0005] The industrial processing technology for silicate minerals (such as cerium titanate and zeolite) has not yet been rationally solved, but they are currently considered to have potential industrial value.

[0006] The low-grade uranium polymetallic deposits produced in Tongliao, Inner Mongolia, have a variety of valuable elements, with large reserves of rare earth elements, especially heavy rare earth elements. The rare earth minerals are mainly silicate-type rare earth minerals (i.e., Xingan stone). The rare earth concentrates obtained by magnetic separation and flotation are mainly silicate rare earth minerals, and also contain a certain amount of carbonate rare earth minerals and phosphate rare earth minerals.

[0007] Therefore, the present invention aims to provide a new method to achieve efficient leaching of rare earth elements and other associated valuable elements in silicate rare earth concentrates, realize efficient utilization of silicate rare earth concentrate resources, and provide a new technical solution with broad application prospects for the industrial development and utilization of silicate rare earth mines. Summary of the Invention

[0008] This invention addresses the unresolved problem in existing industrial processing techniques for silicate rare earth ores by developing an extraction process involving "low-temperature sulfation roasting—clinker water leaching—slurry flocculation and sedimentation—filter cake washing." This process utilizes potassium ferricyanide at low temperatures to promote sulfuric acid diffusion and mineral phase transformation, while sodium chloride acts as an additive to inhibit silica gel formation and encapsulate rare earth elements. Simultaneously, chloride ions are introduced to enhance subsequent hydrometallurgical processes. Based on these enhancement measures, concentrated sulfuric acid is used to roast and decompose silicate-type rare earth ores at low temperatures, and the roasted clinker water leaching achieves highly efficient leaching of rare earth, beryllium, uranium, and thorium resources from the rare earth concentrate.

[0009] To address the low solid-liquid separation efficiency of leaching slurry, flocculation is used to achieve rapid sedimentation and improve solid-liquid separation efficiency, while filter cake washing further enhances the hydrometallurgical leaching rate of clinker. This method provides an innovative, efficient, economical, and environmentally friendly solution for the leaching and resource recovery of silicate rare earth concentrates.

[0010] To achieve the above objectives, the present invention adopts the following technical solution:

[0011] A method for leaching valuable elements from silicate rare earth ores includes the following steps:

[0012] (1) First, rare earth concentrate preparation. The uranium-containing low-grade rare earth polymetallic ore (801 Mine) is ground to -200 mesh with more than 80% content, and then silicate type rare earth concentrate with a rare earth element enrichment ratio of more than 20 is obtained by magnetic separation and flotation.

[0013] (2) The rare earth concentrate is mixed with concentrated sulfuric acid, potassium ferricyanide and sodium chloride in a certain proportion and then sulfatated and roasted to decompose the rare earth minerals therein, so as to facilitate leaching and obtain clinker.

[0014] (3) The clinker obtained in step (2) is leached by water leaching process. The clinker and water are leached for 1.5 to 3 hours at a liquid-to-solid ratio of (5 to 10): 1 and a temperature of 50 to 80°C to obtain slurry.

[0015] The water leaching process described above can also achieve the effect of acid leaching. Sulfation roasting destroys the crystal structure of the mineral, making the leached slurry prone to mud formation. This not only causes some valuable metals to be adsorbed into the mud, but also reduces the efficiency of solid-liquid separation.

[0016] (4) The leaching slurry obtained in step (3) is subjected to flocculation-filtration. The flocculant is prepared with water to form a flocculant solution with a mass fraction of 0.1%. Then the flocculant solution is added to the slurry, stirred evenly, and poured into a Buchner funnel. The leaching liquid and filter cake are obtained by vacuum filtration.

[0017] (5) The filter cake obtained in step (4) is washed to release the valuable elements adsorbed in the sludge. The filter cake is washed 3 to 5 times with a countercurrent plate. The liquid-solid ratio of the washing liquid to the filter cake is 1:(1 to 2). The washing effect is enhanced by mixing water with oxidant in the first few stages and the washing is done with water in the last stage. After this washing, the leaching rates of rare earth, beryllium, uranium and thorium in the silicate rare earth concentrate reach 96.06%, 98.25%, 75.35% and 87.93%, respectively.

[0018] (6) Decomposition and leaching evaluation: Roasted clinker was leached with water at a liquid-to-solid ratio of 8:1, a leaching time of 4 hours, and room temperature. After the reaction was completed, the slurry was filtered and washed, and the metal content in the filtrate was tested to determine the effect of sulfation roasting. The water leaching and washing process was evaluated by quantitatively analyzing the metal ion concentration to assess the effect of this method on improving the leaching efficiency of rare earth concentrate.

[0019] Preferably, the mass ratio of the rare earth concentrate, concentrated sulfuric acid and potassium ferricyanide in step (2) is (1-3):1:0.01:0.5.

[0020] Preferably, the roasting temperature in step (2) is 160-230°C, the roasting time is 4-6 hours, and the roasting gas atmosphere is air.

[0021] Preferably, the flocculant in step (4) is any one of CZ4002, AZ5002, AZ9020, Z504, FZ3802 and WZ944.

[0022] The key technical points of this invention are: low-temperature sulfation roasting process to decompose silicate rare earth ore, clinker water leaching to extract metal, leaching slurry flocculation-filtration process, and filter cake washing to recover metal. These processes realize the leaching of silicate rare earth, improve leaching efficiency, and reduce waste generation, providing a reference and basis for the industrial application of silicate rare earth ore.

[0023] As can be seen from the above technical solution, compared with the prior art, the present invention has the following beneficial effects:

[0024] (1) Low-temperature enhanced sulfation roasting process effectively decomposes silicate rare earth minerals, avoiding the high energy consumption and equipment corrosion caused by traditional high-temperature roasting.

[0025] (2) Introducing potassium ferricyanide and sodium chloride as auxiliaries promotes the diffusion of sulfuric acid reaction and inhibits the formation of silica gel, thereby enhancing the release of rare earth elements;

[0026] (3) Water immersion is used instead of strong acid leaching, which is green and environmentally friendly and simplifies subsequent wastewater treatment;

[0027] (4) Introduce flocculation sedimentation and filter cake enhanced washing to achieve efficient solid-liquid separation and complete recovery of rare earth elements;

[0028] (5) High leaching rate of multiple elements (REO, Be, U, Th all exceed 90%), with potential for industrial application;

[0029] This invention constructs a green and efficient extraction system consisting of "low-temperature sulfation-enhanced roasting—clinker hydrometallurgy—flocculation sedimentation—filter cake enhanced washing." For the first time, through the regulation of additives and mild reaction conditions, it achieves the efficient and synergistic extraction of multiple valuable elements, such as rare earth elements, beryllium, uranium, and thorium, from silicate-type rare earth concentrates. This method not only solves the problems of high energy consumption, low leaching rate, and heavy environmental burden associated with traditional roasting, but also significantly improves the comprehensive utilization level of rare earth resources, demonstrating significant prospects for industrial application. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0031] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0032] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] Rare earth concentrate preparation in this embodiment of the invention:

[0034] (1) 90% of low-grade uranium polymetallic ore was ground to -200 mesh using a planetary ball mill;

[0035] (2) Enriching rare earth minerals through magnetic separation using a high-gradient magnetic separator;

[0036] (3) The magnetic separation concentrate obtained is processed by a closed-circuit process of one roughing and three sweeping. Under the reagent system of mixed fatty acids as collector, water glass as inhibitor and sodium fluorosilicate and sodium carbonate as modifier, the flotation concentrate obtained is the rare earth concentrate used.

[0037] Enhanced low-temperature sulfation roasting—cooking water immersion in this invention embodiment:

[0038] In a rare earth concentrate: concentrated sulfuric acid: potassium ferricyanide: sodium chloride = (1-3):1:0.01:0.5, the mineral powder and concentrated sulfuric acid are mixed evenly and placed in a muffle furnace for low-temperature sulfation roasting; the roasting temperature is 160-230℃ and the roasting time is different; the clinker after sulfation roasting is soaked in water for 1.5-3 hours under the conditions of liquid-solid ratio (5-10):1 and temperature 50-80℃, and then the slurry is filtered and washed.

[0039] In this embodiment of the invention, leaching slurry flocculation-filtration is performed as follows:

[0040] The flocculant was prepared with water to a concentration of 0.1% for later use. A certain amount of flocculant solution was added to the clinker leaching slurry, stirred evenly, and then poured into a Buchner funnel for vacuum filtration. The flocculant was one of six types: CZ4002, AZ5002, AZ9020, Z504, FZ3802, and WZ944.

[0041] Filter cake washing in this embodiment of the invention:

[0042] The filter cake obtained by vacuum filtration is washed 3 to 5 times with a countercurrent disc. The liquid-to-solid ratio of the washing liquid to the filter cake is 1:1 to 2. The first few stages are acid washed with a mixture of dilute sulfuric acid and oxidant B, and the last stage is washed with clean water.

[0043] Example 1

[0044] The following is a case study of the implementation of traditional high-temperature sulfation roasting treatment for this silicate-type rare earth ore.

[0045] (1) After grinding, rare earth concentrate is obtained by magnetic separation-flotation process;

[0046] (2) Mix the mineral powder and concentrated sulfuric acid in a certain proportion, let it stand at room temperature for 2 hours, and then use high-temperature sulfation roasting treatment. The roasting temperature is 500℃, the roasting time is 4 hours, the leaching liquid-solid ratio is 8:1, the time is 4 hours, and the temperature is 20℃.

[0047] (3) A flocculant was prepared with water to a concentration of 0.1% for later use. A certain amount of flocculant solution was added to the leaching slurry, stirred evenly, and then poured into a Buchner funnel for vacuum filtration.

[0048] (4) The filter cake is washed in a 4-stage countercurrent plate washing. Each stage contains 100mL of water, 95mL of water and 5mL of hydrogen peroxide. The last stage is washed with water.

[0049] The results (Table 1) show that the high-temperature sulfation roasting-clinker water leaching process achieved leaching rates of 91.35%, 98.51%, and 96.44% for uranium, rare earth elements, and beryllium in rare earth concentrate, respectively; the thorium leaching rate could also be increased to 87.89%.

[0050] Table 1 High-temperature sulfation roasting

[0051]

[0052] Example 2

[0053] The following is a case study of using additives to enhance the low-temperature sulfation roasting of silicate-type rare earth ores:

[0054] (1) After grinding, rare earth concentrate is obtained by magnetic separation-flotation process;

[0055] (2) The additives (potassium ferricyanide and sodium chloride), mineral powder and a certain amount of concentrated sulfuric acid were mixed evenly and placed in a muffle furnace for low-temperature sulfation roasting; the roasting temperature was 230℃ and the roasting time was 8h; the leaching liquid-solid ratio was 8:1, the time was 4h and the temperature was 20℃. The effect of acid roasting of rare earth concentrate at 230℃ is shown in Table 2;

[0056] (3) A flocculant was prepared with water to a concentration of 0.1% for later use. A certain amount of flocculant solution was added to the leaching slurry, stirred evenly, and then poured into a Buchner funnel for vacuum filtration. The results are shown in Table 3.

[0057] (4) The filter cake was washed using a 4-stage countercurrent plate washing method, with 100 mL per stage. The last stage was washed with clean water. The results are shown in Table 4.

[0058] Table 2 Low-temperature sulfation roasting

[0059]

[0060] Table 3. Experiment on the effect of flocculant dosage on the filtration improvement of leached slurry.

[0061]

[0062] Table 4 Results of Leach Slurry Washing Test

[0063]

[0064] The results showed that the leaching rates of rare earth elements, beryllium, uranium, and thorium were 97.96%, 99.44%, 92.21%, and 94.11%, respectively, after sulfation roasting at 230℃. The addition of additives enhanced the low-temperature roasting effect, making it comparable to the high-temperature roasting leaching effect. Low-temperature sulfation roasting also consumed less energy and could achieve the decomposition of silicate rare earth ores. The slurry filtration rate showed a pattern of first increasing and then decreasing within the experimental range (flocculator dosage 0–80 g / t). At a flocculant dosage of 20 g / t, the slurry filtration rate reached 226.3 kg·m³. 2 The filtration capacity is more than 3 times higher than that without flocculant; after leaching and washing of rare earth concentrate, the leaching residue yield is about 60%, and the filter cake moisture content is about 33% (wet basis, about 50% dry basis); the total rare earth recovery rate of the leaching-washing process is 91.52%.

[0065] Example 3

[0066] Commonly used decomposition processes for rare earth concentrates include: alkaline decomposition, salt thermal decomposition, hydrochloric acid heated leaching, high-temperature pressurized acid leaching, high-temperature sulfation roasting, and low-temperature sulfation roasting. Research was conducted on the decomposition and leaching process most suitable for silicate-type rare earth ores. The first step, obtaining the rare earth concentrate, follows the same method. The second step employs different decomposition methods.

[0067] Decomposition conditions for the alkaline decomposition method: NaOH concentration was a variable parameter, reaction temperature was 140℃, and reaction time was 6 h; water washing test conditions: washing twice with clean water, liquid-to-solid ratio of 10:1, time 1 h, temperature 90℃; leaching test conditions: HCl solution concentration of 6 mol / L, liquid-to-solid ratio of 10:1, reaction time 2 h, temperature 90℃. The decomposition results of various metals in rare earth concentrates under different alkali dosages at 140℃ are shown in Table 5.

[0068] Table 5 Results of NaOH solution decomposition test (140℃)

[0069]

[0070] As the amount of NaOH increases, the decomposition rate of rare earth minerals gradually increases, and the reaction reaches a basic equilibrium when the alkali dosage is 120%. The decomposition and extraction rates of uranium and thorium in the concentrate are relatively high, reaching over 85%, while the decomposition effect of niobium and zirconium is poor.

[0071] Salt-added thermal decomposition method: (NH₂)₂SO₄ was used for roasting and decomposition. 20g of mineral powder was mixed evenly with a certain amount of (NH₂)₂SO₄ and placed in a muffle furnace for roasting at 500℃ for 5 hours (heating up for 1 hour). After cooling, the roasted clinker was leached with water at a liquid-to-solid ratio of 10:1 for 2 hours at a temperature of 60℃. The leaching slurry was then filtered and washed. The effect of (NH₂)₂SO₄ dosage on the decomposition of rare earth concentrate is shown in Table 6.

[0072] Table 6 Results of the Exploratory Experiment on the Decomposition of (NH4)2SO4 by Roasting

[0073]

[0074] The experimental results show that ammonium sulfate has a certain decomposition effect on rare earth concentrates. With the increase of ammonium sulfate dosage, the leaching rates of rare earth, beryllium, uranium, thorium and other minerals gradually increase, especially the leaching rate of uranium, which can reach 84.67%. However, the extraction rate of the main valuable metal rare earth is low. The ammonium sulfate roasting method is not suitable for silicate-type rare earth concentrates.

[0075] Hydrochloric acid heated leaching method: A leaching experiment was conducted on rare earth concentrate using a heated hydrochloric acid solution. The experimental conditions were a leaching solution-to-solid ratio of 4:1 and leaching at 90℃ for 6 hours. The extraction results of various valuable metals by different concentrations of hydrochloric acid solution are shown in Table 7.

[0076] Table 7 Results of hydrochloric acid leaching test for rare earth concentrate

[0077]

[0078]

[0079] As can be seen from Table 7, the extraction rates of valuable metals such as rare earth, uranium, and beryllium increase slightly with the increase of hydrochloric acid concentration. Under the experimental conditions, the extraction rates of uranium are 83%–87%, thorium is 50%–60%, and beryllium is 62%–76%. At the same time, rare earth is also leached out at a rate of 55%–68%. The hydrochloric acid heating leaching method cannot achieve the purpose of leaching or pre-leaching to remove impurities.

[0080] High-temperature and high-pressure acid leaching:

[0081] The leaching agent was a 100 g / L sulfuric acid solution, the liquid-to-solid ratio was 3:1, the reaction temperature was 180℃, the pressure was 1.52 MPa (oxygen partial pressure 0.5 MPa), and the leaching time was 4 h. The results are shown in Table 8.

[0082] Table 8 Results of High-Temperature and Pressure Acid Leaching Tests on Rare Earth Concentrates

[0083]

[0084] High-pressure and hydrochloric acid leaching yields are roughly equivalent in removing uranium and thorium, while rare earth leaching yields are somewhat lower. However, they still do not achieve the goal of pre-leaching to remove radioactive nuclides.

[0085] High-temperature sulfation roasting:

[0086] The mineral powder was mixed evenly with concentrated sulfuric acid and left to stand at room temperature for 2 hours. The roasting temperature was 700℃ and the roasting time was 4 hours. The leaching liquid-to-solid ratio was 8:1, the time was 4 hours, and the temperature was 20℃.

[0087] Table 9 Results of High-Temperature Enhanced Roasting and Decomposition Tests of Rare Earth Concentrates in Sulfuric Acid

[0088]

[0089] *After roasting, the pH of the water leaching solution is >5. Add concentrated sulfuric acid to adjust the leaching agent to 50g / LH2SO.

[0090] The results showed that the high-temperature calcination at 700℃ decomposed sulfuric acid and sulfates, reducing the acidity and the content of iron, niobium, etc. in the solution. At the same time, due to the high temperature, sintering may have occurred, which also greatly reduced the dissolution rate of valuable metals such as rare earth elements, beryllium, and uranium.

[0091] Example 4

[0092] Example 4 compares the low-temperature sulfation roasting process with and without additives.

[0093] Except for the absence of additives, the low-temperature sulfation roasting was carried out using the same operating steps as in Example 2. The results of the low-temperature sulfation roasting test are shown in Table 10.

[0094] Table 10 Decomposition Test Results of Rare Earth Concentrate under Low-Temperature Sulphation Roasting (with Additives)

[0095]

[0096] Adding additives is beneficial to enhancing the low-temperature sulfation roasting effect of silicate-type rare earth concentrates. Experimental results show that adding additives helps to improve the leaching effect of four valuable elements: rare earth, beryllium, uranium, and thorium.

[0097] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to the method section.

[0098] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those 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 invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for leaching valuable elements from silicate rare earth ores, characterized in that, Includes the following steps: (1) Low-temperature sulfation roasting: rare earth concentrate is mixed with concentrated sulfuric acid and additives, and sulfation roasting is carried out at a temperature of 160-230℃ to obtain clinker; the additives are potassium ferricyanide and sodium chloride; the mixing mass ratio of rare earth concentrate, concentrated sulfuric acid, potassium ferricyanide and sodium chloride is (1~3):1:0.01:0.5; the rare earth concentrate is Xingan stone; (2) Clinker leaching process: mix clean water with clinker and leach at a certain temperature for a period of time to obtain slurry; (3) Leaching slurry flocculation-filtration process: The flocculant is prepared with water to form a flocculant solution with a mass fraction of 0.1%. Then, the flocculant solution is added to the slurry, stirred evenly, and poured into a Buchner funnel. Vacuum filtration is used to obtain leachate and filter cake. (4) Filter cake washing process: The filter cake is washed 3 to 5 times with a counter-current disc. The first 2 to 4 times are washed with water mixed with oxidant to enhance the washing effect, and the last stage is washed with water. The oxidant is hydrogen peroxide or sodium hypochlorite.

2. The method for leaching valuable elements from silicate rare earth ores according to claim 1, characterized in that, The roasting time in step (1) is 4~6h, and the roasting gas atmosphere is air.

3. The method for leaching valuable elements from silicate rare earth ores according to claim 1, characterized in that, Step (2) The liquid-to-solid ratio is (5~10):1, the leaching temperature is 50~80℃, and the leaching time is 1.5-3h.

4. The method for leaching valuable elements from silicate rare earth ores according to claim 1, characterized in that, The flocculant mentioned in step (3) is any one of CZ4002, AZ5002, AZ9020, Z504, FZ3802 and WZ944.

5. The method for leaching valuable elements from silicate rare earth ores according to claim 1, characterized in that, Before step (1), rare earth concentrate pretreatment is also included, specifically: grinding the rare earth concentrate to -200 mesh to account for more than 80%, and obtaining silicate type rare earth concentrate with a rare earth element enrichment ratio of more than 20 by magnetic separation and flotation.

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