Method for gradient separation and comprehensive recovery of resources of mixed rare earth concentrate

Abstract

The application discloses a method for gradient selection and comprehensive recovery of mixed rare earth concentrate, which comprises the following steps: 1) first reaction: reacting the mixed rare earth concentrate with hydrochloric acid, and performing solid-liquid separation to obtain first selection and first selection liquid; 2) second reaction: reacting the first selection liquid with the mixed rare earth concentrate again, adding a calcium-containing inorganic compound into the reaction system to continue the reaction after the reaction is completed, and performing solid-liquid separation to obtain second selection and second selection liquid; 3) recovery selection liquid reaction: reacting the second selection liquid with rare earth chloride to obtain rare earth phosphate solid and calcium chloride solution; and 4) third reaction: reacting the second selection with hydrochloric acid, and performing solid-liquid separation to obtain third selection and third selection liquid; wherein the CaO content in the mixed rare earth concentrate in steps 1) and 2) is 5-15 wt%; and the third selection is a selection concentrate. The method can remove calcium, recover calcium resources, and the rare earth yield is greater than or equal to 99.5%, and comprehensive recovery of resources is realized.

Description

Technical Field

[0001] This invention relates to a method for gradient beneficiation and comprehensive resource recovery of mixed rare earth concentrates. Background Technology

[0002] The Bayan Obo mixed rare earth concentrate is mainly composed of associated minerals such as bastnaesite, monazite, fluorite, apatite, and hematite, and is recognized as a difficult-to-smelt mineral. Due to differences in beneficiation processes, flotation reagents, and on-site operations, the proportions of bastnaesite and monazite in the resulting mixed rare earth concentrate vary, as do the contents of associated minerals such as fluorite and apatite. Since the rare earth minerals in the concentrate are mainly composed of bastnaesite and monazite, their processing methods differ from those for bastnaesite and monazite alone. In recent years, the most studied decomposition methods for mixed rare earth concentrates include: roasting with concentrated sulfuric acid, decomposition of monazite with liquid alkali, decomposition of bastnaesite with sulfuric acid slurry, and high-temperature chlorination. Currently, the Bayan Obo mine mainly uses two processes in industrial production: roasting with concentrated sulfuric acid and decomposition with caustic soda.

[0003] The concentrated sulfuric acid roasting method is a classic process for decomposing rare earth concentrates. Due to its advantages such as simple process, convenient operation, high rare earth recovery rate, low requirements for rare earth grade, and suitability for large-scale continuous production, it is widely used for rare earth extraction from Bayan Obo mixed rare earth concentrate.

[0004] In the liquid alkali decomposition process for mixed rare earth concentrates, the concentrate is first pretreated with hydrochloric acid and sodium sulfate at a low-boiling state for 4-6 hours. The purpose is to remove impurities such as calcium and iron, reduce rare earth loss, and ultimately increase the REO grade to over 65%. The treated concentrate is then decomposed by heating with liquid alkali. This method results in an extremely low REO loss rate. However, a significant problem exists: a large amount of highly acidic wastewater from calcium removal is directly neutralized with the alkali wastewater during the decomposition process and then discharged, resulting in insufficient utilization of the residual acid. The high-grade concentrate obtained contains sodium sulfate and rare earth sulfate double salts. The presence of sodium ions prevents the minerals from being treated using the sulfuric acid decomposition process. Otherwise, after sulfuric acid decomposition, water leaching of the minerals would again form sodium and rare earth double salt precipitates, reducing the rare earth yield. Furthermore, with the recycling of water, sodium will further accumulate, further reducing the rare earth recovery rate.

[0005] CN105668888B discloses a method for the chemical beneficiation of low-grade mixed rare earth concentrate and the comprehensive recovery of wastewater from the beneficiation process. This method involves chemically beneficiating the low-grade concentrate using a mixture of hydrochloric acid solution and an enhanced impurity removal agent. The beneficiation wastewater is then treated with sulfuric acid solution to remove calcium ions, forming calcium sulfate dihydrate. After calcium removal, the wastewater is recycled to treat the low-grade mixed rare earth concentrate. After calcium removal, the recycled wastewater is neutralized stepwise with ammonia or liquid ammonia to recover iron, rare earth elements, phosphorus concentrates, and crude calcium fluoride byproducts. The wastewater is then concentrated by evaporation to obtain ammonium chloride crystals and distilled water. This method has significant advantages in terms of comprehensive resource recovery and acid / alkali consumption. However, it requires the introduction of an enhanced impurity removal agent to remove calcium during the reaction process, and the calcium removal effect is not ideal, with the final CaO content in the beneficiated ore still around 2.5%. Furthermore, the process of recovering rare earths from the beneficiation wastewater is relatively complex and not easily industrialized.

[0006] CN108559842B discloses a method for leaching calcium-strontium rare earth concentrate from Weishanhu Lake using low-concentration hydrochloric acid. This method involves soaking the Weishanhu rare earth concentrate in low-concentration hydrochloric acid and then heating it to react. After the reaction, the solution is filtered, and then Weishanhu rare earth concentrate is added back to the filtered leachate and heated to react again. The liquid obtained after solid-liquid separation is discharged, while the solid phase is reused. This method can essentially remove calcium carbonate from Weishan rare earth concentrate. However, this method is only suitable for treating calcium-containing impurities, primarily calcite, in Weishan rare earth concentrate. It cannot remove calcium-containing impurities such as fluorite and apatite from mixed rare earth concentrates. Furthermore, to ensure effective calcium removal, the liquid-to-solid ratio during the reaction is large, generating a large amount of chemical beneficiation wastewater, increasing the cost of wastewater treatment and making industrialization difficult.

[0007] CN117802312A discloses a chemical beneficiation method for upgrading and reducing the calcium content of mixed rare earth concentrates. This method mainly includes multiple processes such as chemical leaching, separation, and optional drying, with the chemical leaching being carried out in two stages. This method reduces the calcium oxide content in the rare earth concentrate and improves the grade of the mixed rare earth concentrate. However, this method has a significant problem: while it can reduce the calcium oxide content in the rare earth concentrate to about 1% during the upgrading and calcium reduction process, the rare earth yield is only around 95%. In the context of the increasing value of rare earths in the new era, this undoubtedly reduces the utilization value of rare earths and increases production costs.

[0008] CN106801153A discloses a low-cost method for enriching high-grade mixed rare earth concentrates. The method involves leaching a rare earth concentrate with a grade of 40-65 at% obtained from flotation at room temperature using a low-concentration hydrochloric acid solution, separating primary chemical beneficiation and wastewater. The primary chemical beneficiation concentrate is then heated and leached with a freshly prepared hydrochloric acid solution. Washing and separation yield a chemically beneficiated concentrate and a secondary first-stage chemical beneficiation solution. The secondary first-stage solution is then used for further heating and leaching to obtain a new primary chemical beneficiation concentrate. Washing and separation yield a chemically beneficiated concentrate and a secondary second-stage chemical beneficiation solution. This cycle is repeated to separate the primary and secondary beneficiation solutions. While this method can remove calcium, the calcium removal process results in a large amount of rare earth and phosphorus entering the chemical beneficiation solution, leading to a waste of rare earth resources and hindering comprehensive resource recovery. Summary of the Invention

[0009] In view of this, the purpose of this invention is to provide a method for gradient beneficiation and comprehensive resource recovery of mixed rare earth concentrates. This method can remove calcium, recover calcium resources, minimize rare earth loss, achieve a high rare earth recovery rate, and is simple to operate. It can also recover phosphate and calcium chloride solutions separately, thereby achieving comprehensive resource recovery and utilization.

[0010] The present invention achieves the above objectives through the following technical solutions.

[0011] This invention provides a method for gradient beneficiation and comprehensive resource recovery of mixed rare earth concentrates, comprising the following steps:

[0012] 1) Primary reaction: The mixed rare earth concentrate is reacted with hydrochloric acid, and the solid and liquid are separated to obtain primary beneficiation minerals and primary beneficiation solution;

[0013] 2) Secondary reaction: The primary beneficiation solution is reacted with the mixed rare earth concentrate. After the reaction is completed, calcium-containing inorganic compounds are added to the reaction system to continue the reaction. Solid-liquid separation is performed to obtain secondary beneficiation and secondary beneficiation solution.

[0014] 3) Recovery reaction of chemical separation solution: The secondary chemical separation solution is reacted with rare earth chloride to obtain rare earth phosphate solid and calcium chloride solution;

[0015] 4) Tertiary reaction: The secondary beneficiation is reacted with hydrochloric acid, and the solid and liquid are separated to obtain tertiary beneficiation and tertiary beneficiation solution;

[0016] Among them, the CaO content in the mixed rare earth concentrate in steps 1) and 2) is 5-15 wt%; the tertiary beneficiation is a chemical beneficiation concentrate.

[0017] The method according to the present invention preferably further includes the following steps:

[0018] Fourth-stage reaction: Replace the first-stage chemical separation solution with the third-stage chemical separation solution and repeat the reaction in step 2) to obtain the fourth-stage chemical separation solution and the fourth-stage mineral separation solution;

[0019] Recovery reaction of chemical separation solution: Replace the secondary chemical separation solution with the quaternary chemical separation solution and repeat the reaction in step 3) to obtain rare earth phosphate solid and calcium chloride solution;

[0020] Fifth-stage reaction: Replace the second-stage chemical beneficiation with the fourth-stage chemical beneficiation and repeat the reaction in step 4) to obtain fifth-stage chemical beneficiation and fifth-stage chemical beneficiation solution; wherein, the fifth-stage chemical beneficiation is chemical beneficiation concentrate.

[0021] The method according to the present invention preferably further includes the following steps:

[0022] n-stage reaction: Replace the first-stage chemical separation solution with the n-1-stage chemical separation solution and repeat the reaction in step 2) to obtain the n-stage chemical separation solution and the n-stage chemical separation ore;

[0023] Recovery reaction of chemical separation solution: Replace the secondary chemical separation solution with the nth stage chemical separation solution and repeat the reaction in step 3) to obtain rare earth phosphate solid and calcium chloride solution;

[0024] n+1 stage reaction: Replace the secondary chemical beneficiation with the nth stage chemical beneficiation and repeat the reaction in step 4) to obtain n+1 stage chemical beneficiation and n+1 stage chemical beneficiation solution;

[0025] Where n is an even number greater than or equal to 6;

[0026] Among them, the n+1 stage of chemical beneficiation is chemical beneficiation concentrate;

[0027] The n+1 stage chemical separation solution will be further processed in accordance with the n-1 stage chemical separation solution.

[0028] According to the method of the present invention, preferably, in step 1), the concentration of hydrochloric acid is 5-8 mol / L, and the liquid-solid ratio of hydrochloric acid to mixed rare earth concentrate is 0.8-2 mL:1 g.

[0029] According to the method of the present invention, preferably, in step 1), the reaction temperature is 80-95°C and the reaction time is 60-180 min.

[0030] According to the method of the present invention, preferably, in step 2), the liquid-solid ratio of the primary beneficiation solution to the mixed rare earth concentrate is 0.8-2 mL:1 g; the calcium-containing inorganic compound is selected from at least one of calcium carbonate, calcium oxide and calcium hydroxide.

[0031] According to the method of the present invention, preferably, in step 2), the amount of calcium-containing inorganic compound added is 1 to 5 wt% of the mass of the mixed rare earth concentrate.

[0032] According to the method of the present invention, preferably, in step 3), the REO content of the secondary chemical separation solution is less than 1 g / L; the rare earth element in the rare earth chloride is selected from at least one of lanthanum, praseodymium, neodymium and cerium.

[0033] According to the method of the present invention, preferably, in step 4), the concentration of hydrochloric acid is 5-8 mol / L; the weight of the secondary beneficiation is calculated based on the weight of the mixed rare earth concentrate in step 2), and the liquid-solid ratio of hydrochloric acid to secondary beneficiation is 0.8-2 mL:1 g.

[0034] According to the method of the present invention, preferably, in step 4), the reaction temperature is 10-90°C and the reaction time is 60-180 min.

[0035] The method of this invention achieves deep separation of calcium and rare earth elements through a gradient chemical separation process. Simultaneously, by controlling the acidity of the chemical separation solution, rare earth elements in the supernatant are recovered into the slag (the acidity of the chemical separation solution is reduced by adding calcium oxide; the lower acidity allows rare earth elements and phosphorus in the chemical separation wastewater to undergo a precipitation reaction, forming rare earth phosphate precipitates, thus achieving the purpose of rare earth recovery). Unlike traditional chemical separation processes that recover rare earth elements by adding sodium sulfate, this process does not require the introduction of new substances (such as sodium sulfate) to recover rare earth elements and can achieve a rare earth recovery rate of over 99.5%. This invention can fully recover phosphorus lost during the chemical separation process and can also obtain a high-concentration calcium chloride solution by controlling the chemical wastewater (i.e., the chemical separation solution), thereby fully recovering calcium resources in the chemical separation wastewater and saving on wastewater treatment costs. Furthermore, this invention reduces the volume of chemical separation wastewater through a low liquid-to-solid ratio reaction. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the process of the present invention. Detailed Implementation

[0037] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0038] This invention discloses a method for gradient beneficiation and comprehensive resource recovery of mixed rare earth concentrate, comprising the following steps: 1) a primary reaction step of mixed rare earth concentrate with hydrochloric acid; 2) a secondary reaction step of primary beneficiation solution with mixed rare earth concentrate; 3) a recovery step of beneficiation solution; and 4) a tertiary reaction step of secondary beneficiation with hydrochloric acid. It may also include a quaternary reaction step, a quinary reaction step, and an n-stage reaction step or an n+1-stage reaction step (where n is an even number greater than or equal to 6). A detailed description follows.

[0039] <First-order reaction steps of mixed rare earth concentrate with hydrochloric acid>

[0040] The mixed rare earth concentrate is reacted with hydrochloric acid, followed by solid-liquid separation to obtain primary beneficiation and primary beneficiation solution. This process facilitates the removal of calcium-containing minerals. It removes a portion of the calcium from the mixed rare earth concentrate and also preliminarily activates it, making further calcium removal easier.

[0041] In this invention, the mixed rare earth concentrate mainly consists of bastnaesite and monazite, and also contains apatite, fluorite, etc. The mass ratio of bastnaesite to monazite is greater than or equal to 2:1. In the mixed rare earth concentrate of this invention, the REO content is greater than 40 wt%, the P2O5 content is 3–12 wt%, and the CaO content is 5–15 wt%. The mixed rare earth concentrate also contains fluorine (F), with an F content of 5–12 wt%, preferably 7–10 wt%.

[0042] According to one embodiment of the present invention, in the mixed rare earth concentrate, the REO content is greater than 40 wt% and less than 65 wt%, the P2O5 content is 5-12 wt%, and the CaO content is 6-13 wt%. According to a specific embodiment of the present invention, in the mixed rare earth concentrate, the REO content is greater than 45 wt% and less than 65 wt%, the P2O5 content is 7-12 wt%, and the CaO content is 6-11 wt%.

[0043] The main chemical reactions involved in the first-order reaction step are:

[0044] 3REFCO3 + 6HCl = 3CO2↑ + 3H2O + REF3 + 2RECl3; RE represents rare earth elements;

[0045] CaF₂ + 2HCl = CaCl₂ + 2HF;

[0046] Ca5(PO4)3F + 10HCl = 5CaCl2 + 3H3PO4 + HF. The generated HF can be absorbed by spraying to produce hydrofluoric acid.

[0047] In this invention, the concentration of hydrochloric acid can be 5–8 mol / L, for example, 5 mol / L, 6 mol / L, 7 mol / L, or 8 mol / L. The liquid-to-solid ratio of hydrochloric acid to mixed rare earth concentrate is 0.8–2 mL:1 g, preferably 0.9–1.5 mL:1 g, and more preferably 0.9–1 mL:1 g. The reaction temperature of the mixed rare earth concentrate and hydrochloric acid can be 80–95°C, preferably 85–95°C, and more preferably 90–95°C. The reaction time can be 60–180 min, preferably 90–180 min, and more preferably 120–180 min. This facilitates the dissolution of calcium in the hydrochloric acid, increases the REO content of the chemically beneficiated concentrate, and reduces the calcium content in the beneficiated concentrate.

[0048] After the reaction is complete, solid-liquid separation is performed, which can be done by centrifugation or filtration, preferably filtration, to obtain primary beneficiation solution and primary beneficiated ore. In this invention, the primary beneficiated ore can be reacted with 5-8 mol / L hydrochloric acid (the liquid-to-solid ratio of hydrochloric acid to primary beneficiated ore is 0.8-2 mL:1 g) at 10-90°C to obtain low-calcium beneficiated concentrate, and the resulting beneficiation solution can be used for secondary reactions.

[0049] <Secondary reaction steps of primary beneficiation solution and mixed rare earth concentrate>

[0050] The primary beneficiation solution is then reacted with the mixed rare earth concentrate. After the reaction is complete, a calcium-containing inorganic compound is added to the reaction system to continue the reaction, resulting in solid-liquid separation and yielding secondary beneficiation and the secondary beneficiation solution. This reuse of the primary beneficiation solution not only provides preliminary treatment of the mixed rare earth concentrate but also allows for better recovery of calcium chloride solution and phosphorus.

[0051] In this step, the mixed rare earth concentrate mainly consists of bastnaesite and monazite, and also contains apatite, fluorite, etc. The mass ratio of bastnaesite to monazite is greater than or equal to 2:1. In the mixed rare earth concentrate of this invention, the REO content is greater than 40 wt%, the P2O5 content is 3-12 wt%, and the CaO content is 5-15 wt%. The mixed rare earth concentrate also contains fluorine (F) element, with an F content of 5-12 wt%. The mixed rare earth concentrate in this step is basically the same as the mixed rare earth concentrate used above.

[0052] The liquid-to-solid ratio of the primary beneficiation solution to the mixed rare earth concentrate can be 0.8–2 mL:1 g, preferably 0.9–1.5 mL:1 g, and more preferably 0.9–1 mL:1 g. The mixed rare earth concentrate in this step has essentially the same composition as the mixed rare earth concentrate in the primary reaction step, and their weight parts are preferably the same. The reaction temperature between the primary beneficiation solution and the mixed rare earth concentrate can be 50–95°C, preferably 60–90°C, and more preferably 80–90°C. The reaction time can be 60–180 min, preferably 90–180 min.

[0053] In this invention, the calcium-containing inorganic compound is selected from at least one of calcium carbonate, calcium oxide, or calcium hydroxide, preferably calcium oxide. In this step, the amount of calcium-containing inorganic compound added is 1-5 wt% of the mass of the mixed rare earth concentrate, preferably 3-5 wt%, and more preferably 4-5 wt%. The addition of the calcium-containing inorganic compound can, on the one hand, reduce the acidity of the chemical separation solution system, allowing rare earth elements to preferentially precipitate and be recovered, and on the other hand, increase the calcium concentration in the chemical separation solution, facilitating the recovery and utilization of calcium resources. Ultimately, the REO concentration in the secondary chemical separation solution is less than or equal to 1 g / L, preferably less than 1 g / L. Specifically, the REO concentration in the secondary chemical separation solution is 0.1-1 g / L, preferably 0.1-0.6 g / L.

[0054] <Steps for recovering chemical separation solution>

[0055] The secondary chemical separation solution is reacted with rare earth chlorides to obtain rare earth phosphate solid and calcium chloride solution. This allows for the recovery of phosphorus, the production of rare earth phosphate, and a high-concentration calcium chloride solution. The high-concentration calcium chloride solution can then be evaporated and concentrated to obtain calcium chloride as a byproduct.

[0056] In this step, the rare earth element in the rare earth chloride can be selected from at least one of lanthanum, praseodymium, neodymium, and cerium, preferably lanthanum. According to a specific embodiment of the invention, the rare earth chloride is lanthanum chloride. The amount of rare earth chloride added is 5-9 wt% of the weight of the mixed rare earth concentrate in the secondary reaction step, preferably 6-8 wt%. The resulting calcium chloride solution has a CaO content of up to 90 g / L.

[0057] The main chemical reactions involved in this step are as follows:

[0058] RECl3 + H3PO4 = REPO4 + 3HCl.

[0059] <The three-stage reaction steps of secondary mineral processing and hydrochloric acid>

[0060] The secondary beneficiation process involves reacting with hydrochloric acid, followed by solid-liquid separation to obtain tertiary beneficiation and a tertiary beneficiation solution. This yields a tertiary beneficiation concentrate with an REO content of ≥70 wt%. The tertiary beneficiation solution can then be used in a quaternary reaction.

[0061] In this step, the concentration of hydrochloric acid can be 5–8 mol / L, for example, 5 mol / L, 6 mol / L, 7 mol / L, or 8 mol / L. The secondary beneficiation is calculated based on the weight of the mixed rare earth concentrate from the secondary reaction step. The liquid-to-solid ratio of hydrochloric acid to the secondary beneficiation is 0.8–2 mL:1 g, preferably 0.9–1.5 mL:1 g, and more preferably 0.9–1 mL:1 g. The reaction temperature between the secondary beneficiation and hydrochloric acid can be 10–90 °C, preferably 50–90 °C, and more preferably 80–90 °C. The reaction time can be 60–180 min, preferably 90–180 min.

[0062] The CaO content of the obtained tertiary beneficiation is 0.2–2 wt%, preferably 0.5–1 wt%, and more preferably 0.5–0.6 wt%; the REO recovery rate can reach greater than or equal to 99.5 wt%.

[0063] <Fourth-stage reaction step, recovery of chemical separation solution step, and fifth-stage reaction step>

[0064] Replacing the primary chemical beneficiation solution with the tertiary chemical beneficiation solution and repeating step 2) yields a quaternary chemical beneficiation solution and quaternary mineral beneficiation. Replacing the secondary chemical beneficiation solution with the quaternary solution and repeating step 3) yields rare earth phosphate solid and calcium chloride solution. Replacing the secondary mineral beneficiation solution with the quaternary solution and repeating step 4) yields quinary mineral beneficiation and a quinary solution; the quinary mineral beneficiation is the chemical beneficiation concentrate. This allows for the purification of mixed rare earth concentrate using the tertiary chemical beneficiation solution to obtain the chemical beneficiation concentrate (i.e., quinary mineral beneficiation), while simultaneously achieving the recycling of the tertiary solution for comprehensive resource recovery.

[0065] Specifically, the fourth-stage reaction: reacting the third-stage leaching solution with the mixed rare earth concentrate, adding a calcium-containing inorganic compound to the reaction system after the reaction is completed, and continuing the reaction, followed by solid-liquid separation to obtain the fourth-stage leached ore and the fourth-stage leaching solution;

[0066] Recycling leaching solution reaction: reacting the fourth-stage leaching solution with rare earth chloride to obtain rare earth phosphate solid and calcium chloride solution;

[0067] Fifth-stage reaction: reacting the fourth-stage leached ore with hydrochloric acid, followed by solid-liquid separation to obtain the fifth-stage leached ore and the fifth-stage leaching solution.

[0068] The reaction temperature between the third-stage leaching solution and the mixed rare earth concentrate is 50-95 °C, preferably 60-90 °C, more preferably 80-90 °C. The reaction time can be 60-180 min, preferably 90-180 min. The liquid-solid ratio of the third-stage leaching solution to the mixed rare earth concentrate can be 0.8-2 mL:1 g, preferably 0.9-1.5 mL:1 g, more preferably 0.9-1 mL:1 g.

[0069] The calcium-containing inorganic compound is selected from at least one of calcium carbonate, calcium oxide, and calcium hydroxide, preferably calcium oxide. The addition amount of the calcium-containing inorganic compound is 1-5 wt% of the mass of the mixed rare earth concentrate, preferably 3-5 wt%, more preferably 4-5 wt%.

[0070] The rare earth element in the rare earth chloride can be selected from at least one of lanthanum, praseodymium, neodymium, and cerium, preferably lanthanum. According to a specific embodiment of the present invention, the rare earth chloride is lanthanum chloride. The REO concentration in the fourth-stage leaching solution is 0.1-1 g / L, preferably 0.1-0.6 g / L. The weight ratio of the fourth-stage leaching solution to the rare earth chloride is 60-100:5-9, preferably 80-100:6-8. The CaO content of the obtained calcium chloride solution can reach 90 g / L.

[0071] The concentration of hydrochloric acid can be 5-8 mol / L, for example, it can be 5 mol / L, 6 mol / L, 7 mol / L, 8 mol / L. Taking the weight of the fourth-stage leached ore as the calculation basis with the weight of the mixed rare earth concentrate in the third-stage reaction, the liquid-solid ratio of hydrochloric acid to the fourth-stage leached ore is 0.8-2 mL:1 g, preferably 0.9-1.5 mL:1 g, more preferably 0.9-1 mL:1 g. The reaction temperature between the fourth-stage leached ore and hydrochloric acid can be 10-90 °C, preferably 50-90 °C, more preferably 80-90 °C. The reaction time can be 60-180 min, preferably 90-180 min. The CaO content of the obtained fifth-stage leached ore is 0.2-2 wt%, preferably 0.5-1 wt%, more preferably 0.5-0.6 wt%.

[0072] <n-stage reaction step, recycling leaching solution reaction step, and n + 1-stage reaction step>

[0073] Replacing the primary chemical beneficiation solution with the n-1 stage chemical beneficiation solution and repeating step 2) yields an n-stage chemical beneficiation solution and an n-stage chemical beneficiation concentrate. Replacing the secondary chemical beneficiation solution with the n-stage solution and repeating step 3) yields rare earth phosphate solids and calcium chloride solution. Replacing the secondary chemical beneficiation solution with the n-stage solution and repeating step 4) yields an n+1 stage chemical beneficiation concentrate and an n+1 stage chemical beneficiation solution; where n is an even number greater than or equal to 6; the n+1 stage chemical beneficiation concentrate is the chemical beneficiation concentrate. The n+1 stage chemical beneficiation solution is further processed in accordance with the n-1 stage chemical beneficiation solution. This allows the chemical beneficiation solution to be used to process mixed rare earth concentrates and recover calcium chloride solution and phosphate ions; it also allows for further processing of the chemical beneficiation concentrate to obtain a chemical beneficiation concentrate. This is beneficial for further improving the grade (i.e., REO content) of the obtained chemical beneficiation concentrate.

[0074] In some specific implementation schemes, n=6, that is, repeating the reaction of step 2) of the fifth-stage chemical beneficiation solution to obtain the sixth-stage chemical beneficiation solution and the sixth-stage mineral beneficiation solution; repeating the reaction of step 3) of the sixth-stage chemical beneficiation solution to obtain rare earth phosphate solid and calcium chloride solution; repeating the reaction of step 4) of the sixth-stage mineral beneficiation solution to obtain the seventh-stage mineral beneficiation solution and the seventh-stage chemical beneficiation solution.

[0075] In some other specific implementation schemes, n=8, that is, repeating the reaction of step 2) of the seventh-stage chemical beneficiation solution to obtain the eighth-stage chemical beneficiation solution and the eighth-stage mineral beneficiation solution; repeating the reaction of step 3) of the eighth-stage chemical beneficiation solution to obtain rare earth phosphate solid and calcium chloride solution; repeating the reaction of step 4) of the eighth-stage mineral beneficiation solution to obtain the ninth-stage mineral beneficiation solution and the ninth-stage chemical beneficiation solution.

[0076] According to one embodiment of the present invention, the n-stage reaction is as follows: the n-1 stage chemical beneficiation solution is reacted with the mixed rare earth concentrate. After the reaction is completed, a calcium-containing inorganic compound is added to the reaction system to continue the reaction. Solid-liquid separation is performed to obtain the n-stage chemical beneficiation mineral and the n-stage chemical beneficiation solution.

[0077] Recovery reaction of chemical separation solution: react the nth stage chemical separation solution with rare earth chloride to obtain rare earth phosphate solid and calcium chloride solution;

[0078] n+1 stage reaction: The n-stage mineral processing is reacted with hydrochloric acid, and the solid and liquid are separated to obtain n+1 stage mineral processing and n+1 stage mineral processing solution; where n is an even number greater than or equal to 6, the n+1 stage mineral processing solution is further processed in the same way as the n-1 stage mineral processing solution.

[0079] In the n-stage reaction step of this invention, the process parameters are the same as those in the second-stage reaction step. For example, the liquid-to-solid ratio of the n-1 stage chemical separation solution to the mixed rare earth concentrate is 0.8–2 mL:1 g, the reaction temperature is 10–90 °C, and the reaction time is 60–180 min. The amount of calcium-containing inorganic compound added is 1–5 wt% of the mass of the mixed rare earth concentrate. Further details are omitted here.

[0080] The REO concentration in the n-stage chemical separation solution is 0.1–1 g / L, preferably 0.1–0.6 g / L. The process parameters for the reaction step of recovering the chemical separation solution are as described above and will not be repeated here.

[0081] In the n+1 stage reaction step of this invention, the process parameters are referenced from those of the tertiary reaction step. For example, the concentration of hydrochloric acid can be 5–8 mol / L. The n-stage beneficiation is calculated based on the weight of the mixed rare earth concentrate in the n-stage reaction step. The liquid-to-solid ratio of hydrochloric acid to the n-stage beneficiation is 0.8–2 mL:1 g, the reaction temperature can be 10–90 °C, and the reaction time can be 60–180 min. Further details are omitted here. The resulting n+1 stage beneficiation has a CaO content of 0.2–2 wt%, preferably 0.5–1 wt%, more preferably 0.5–0.6 wt%; and a REO content of greater than or equal to 99.5 wt%.

[0082] In this invention, solid-liquid separation can be achieved by centrifugation or filtration, with filtration being preferred.

[0083] <Analytical Methods>

[0084] REO content in mixed rare earth concentrates and chemical beneficiation: analyzed by gravimetric method.

[0085] The F content in the mixed rare earth concentrate was analyzed by distillation.

[0086] P2O5 content in mixed rare earth concentrate: analyzed by bismuth-phosphorus blue spectrophotometry.

[0087] CaO content in mixed rare earth concentrate: analyzed by gravimetric method.

[0088] REO content in the chemical separation solution: analyzed by cerium determination method.

[0089] CaO content in chemical separation solution: EDTA complexometric titration.

[0090] Example 1

[0091] In this embodiment, the mixed rare earth concentrate contains 59.93 wt% REO, 8.5 wt% F, 10.08 wt% P2O5, and 8 wt% CaO.

[0092] Reference Figure 1 Flowchart:

[0093] First-stage reaction: 100 parts by weight of mixed rare earth concentrate were reacted with 6 mol / L hydrochloric acid (i.e., primary hydrochloric acid, solid-liquid ratio of 1 g:1 mL) at 95℃ for 180 min. After the reaction, the mixture was filtered to obtain primary beneficiation solution and primary beneficiated ore. The primary beneficiated ore was further treated with 5 mol / L hydrochloric acid at 90℃ to obtain low-calcium beneficiated concentrate. The resulting beneficiation solution can be used for the second-stage reaction.

[0094] Secondary reaction: The primary beneficiation solution was reacted with 100 parts by weight of mixed rare earth concentrate at 90℃ for 90 min. After the reaction was completed, 4.5 parts by weight of calcium oxide was added to the reaction system and the reaction was continued for another 90 min. After the reaction was completed, the mixture was filtered to obtain secondary beneficiation and secondary beneficiation solution.

[0095] Recovery reaction of the chemical separation solution: 7 parts by weight of lanthanum chloride were added to the secondary chemical separation solution to carry out a precipitation reaction to recover phosphorus from the secondary chemical separation solution, yielding lanthanum phosphate solid and calcium chloride solution. The CaO content in the calcium chloride solution was approximately 90 g / L.

[0096] Tertiary reaction: Secondary beneficiation is reacted with 6 mol / L hydrochloric acid (i.e., tertiary hydrochloric acid, the amount of which is based on the weight of the mixed rare earth concentrate from the secondary reaction, with a solid-liquid ratio of 1 g:1 mL) at 95℃ for 180 min. After the reaction, the mixture is filtered to obtain tertiary beneficiation and tertiary beneficiation solution. Tertiary beneficiation produces a chemical concentrate, namely a low-calcium mixed rare earth concentrate.

[0097] Example 2

[0098] In this embodiment, the mixed rare earth concentrate contains 59.93 wt% REO, 8.5 wt% F, 10.08 wt% P2O5, and 8 wt% CaO. The units of weight parts in this embodiment are the same as those in Example 1.

[0099] Reference Figure 1 Flowchart:

[0100] Fourth-stage reaction: The third-stage chemical beneficiation solution obtained in Example 1 was reacted with 100 parts by weight of mixed rare earth concentrate at 90°C for 120 min. Then, 3.6 parts by weight of calcium oxide was added to the reaction system and the reaction was continued for 60 min. After the reaction was completed, the mixture was filtered to obtain the fourth-stage chemical beneficiation solution and the fourth-stage chemical beneficiation mineral.

[0101] Recovery reaction of chemical separation solution: 9 parts by weight of lanthanum chloride are added to the fourth-stage chemical separation solution to carry out a precipitation reaction to recover phosphorus from the fourth-stage chemical separation solution, and lanthanum phosphate solid and calcium chloride solution are obtained.

[0102] Fifth-stage reaction: The fourth-stage chemical beneficiation is reacted with 7 mol / L hydrochloric acid (the amount of hydrochloric acid is based on the weight fraction of the mixed rare earth concentrate in the fourth-stage reaction, and the solid-liquid ratio is 1 g:1 mL) at 95℃ for 150 min. After the reaction, the mixture is filtered to obtain the fifth-stage chemical beneficiation and the fifth-stage chemical beneficiation solution. The fifth-stage chemical beneficiation is the chemical beneficiation concentrate, namely, low-calcium mixed rare earth concentrate.

[0103] Example 3

[0104] In this embodiment, the mixed rare earth concentrate contains 50.23 wt% REO, 9.5 wt% F, 11.08 wt% P2O5, and 13 wt% CaO. The units of weight parts in this embodiment are the same as those in Example 2.

[0105] Reference Figure 1 Flowchart:

[0106] Sixth-stage reaction (n=6): The fifth-stage chemical beneficiation solution obtained in Example 2 was reacted with 100 parts by weight of mixed rare earth concentrate at 90°C for 120 min. 3.6 parts by weight of calcium oxide was added to the reaction system and the reaction was continued for 60 min. After the reaction was completed, the mixture was filtered to obtain the sixth-stage chemical beneficiation solution and the sixth-stage chemical beneficiation mineral.

[0107] Recovery reaction of chemical separation solution: 6 parts by weight of lanthanum chloride are added to the sixth-stage chemical separation solution to carry out a precipitation reaction to recover phosphorus from the sixth-stage chemical separation solution, and lanthanum phosphate solid and calcium chloride solution are obtained.

[0108] Seventh-stage reaction: The sixth-stage chemical beneficiation process involves reacting the 6-stage mineral processing with 8 mol / L hydrochloric acid (the amount of hydrochloric acid is based on the weight fraction of the mixed rare earth concentrate in the sixth-stage reaction, and the solid-liquid ratio is 1 g:1 mL) at 95℃ for 150 min. After the reaction, the mixture is filtered to obtain the seventh-stage chemical beneficiation process and the seventh-stage chemical beneficiation solution. The seventh-stage chemical beneficiation process yields the chemical beneficiation concentrate, which is a low-calcium mixed rare earth concentrate.

[0109] Table 1

[0110]

[0111] As shown in the table, the REO concentration in the chemical beneficiation wastewater (e.g., secondary, quaternary, and sixth stage chemical beneficiation solutions) can be less than 1 g / L (the REO content in the chemical beneficiation wastewater is 0.5 g / L). The amount of REO in the chemical beneficiation wastewater per ton of mixed rare earth concentrate is 1 m³. 3 Based on these parameters, it can be calculated that the REO yield in the resulting chemical beneficiation (e.g., three-stage, five-stage, and seven-stage chemical beneficiation) is greater than or equal to 99.5%. The calcium chloride solution concentration in the chemical beneficiation wastewater is high, with a CaO content exceeding 90 g / L. The CaO content in the resulting chemically beneficiated ore is less than 1%, and the REO grade is higher than 70%, facilitating subsequent smelting.

[0112] This invention is not limited to the above-described embodiments. Any modifications, improvements, or substitutions that can be conceived by those skilled in the art without departing from the essential content of this invention fall within the scope of this invention.

Claims

1. A method for gradient beneficiation and comprehensive resource recovery of mixed rare earth concentrates, characterized in that, Includes the following steps: 1) Primary reaction: The mixed rare earth concentrate is reacted with hydrochloric acid, and the solid and liquid are separated to obtain primary beneficiation minerals and primary beneficiation solution; 2) Secondary reaction: The primary beneficiation solution is reacted with the mixed rare earth concentrate. After the reaction is completed, calcium-containing inorganic compounds are added to the reaction system to continue the reaction. Solid-liquid separation is performed to obtain secondary beneficiation and secondary beneficiation solution. 3) Recovery reaction of chemical separation solution: The secondary chemical separation solution is reacted with rare earth chloride to obtain rare earth phosphate solid and calcium chloride solution; 4) Tertiary reaction: The secondary beneficiation is reacted with hydrochloric acid, and the solid and liquid are separated to obtain tertiary beneficiation and tertiary beneficiation solution; Among them, the CaO content in the mixed rare earth concentrate in steps 1) and 2) is 5-15 wt%; the tertiary beneficiation is a chemical beneficiation concentrate.

2. The method according to claim 1, characterized in that, It also includes the following steps: Fourth-stage reaction: Replace the first-stage chemical separation solution with the third-stage chemical separation solution and repeat the reaction in step 2) to obtain the fourth-stage chemical separation solution and the fourth-stage mineral separation solution; Recovery reaction of chemical separation solution: Replace the secondary chemical separation solution with the quaternary chemical separation solution and repeat the reaction in step 3) to obtain rare earth phosphate solid and calcium chloride solution; Fifth-stage reaction: Replace the second-stage chemical beneficiation with the fourth-stage chemical beneficiation and repeat the reaction in step 4) to obtain fifth-stage chemical beneficiation and fifth-stage chemical beneficiation solution; wherein, the fifth-stage chemical beneficiation is chemical beneficiation concentrate.

3. The method according to claim 2, characterized in that, It also includes the following steps: n-stage reaction: Replace the first-stage chemical separation solution with the n-1-stage chemical separation solution and repeat the reaction in step 2) to obtain the n-stage chemical separation solution and the n-stage chemical separation ore; Recovery reaction of chemical separation solution: Replace the secondary chemical separation solution with the nth stage chemical separation solution and repeat the reaction in step 3) to obtain rare earth phosphate solid and calcium chloride solution; n+1 stage reaction: Replace the secondary chemical beneficiation with the nth stage chemical beneficiation and repeat the reaction in step 4) to obtain n+1 stage chemical beneficiation and n+1 stage chemical beneficiation solution; Where n is an even number greater than or equal to 6; Among them, the n+1 stage of chemical beneficiation is chemical beneficiation concentrate; The n+1 stage chemical separation solution will be further processed in accordance with the n-1 stage chemical separation solution.

4. The method according to claim 1, characterized in that, In step 1), the concentration of hydrochloric acid is 5-8 mol / L, and the liquid-solid ratio of hydrochloric acid to mixed rare earth concentrate is 0.8-2 mL:1 g.

5. The method according to claim 1, characterized in that, In step 1), the reaction temperature is 80–95℃ and the reaction time is 60–180 min.

6. The method according to claim 1, characterized in that, In step 2), the liquid-to-solid ratio of the primary beneficiation solution to the mixed rare earth concentrate is 0.8–2 mL:1 g; the calcium-containing inorganic compound is selected from at least one of calcium carbonate, calcium oxide, and calcium hydroxide.

7. The method according to claim 1, characterized in that, In step 2), the amount of calcium-containing inorganic compound added is 1 to 5 wt% of the mass of the mixed rare earth concentrate.

8. The method according to claim 1, characterized in that, In step 3), the REO content of the secondary chemical separation solution is less than 1 g / L; the rare earth elements in the rare earth chloride are selected from at least one of lanthanum, praseodymium, neodymium and cerium.

9. The method according to claim 1, characterized in that, In step 4), the concentration of hydrochloric acid is 5-8 mol / L; the weight of the secondary beneficiation is calculated based on the weight of the mixed rare earth concentrate in step 2), and the liquid-solid ratio of hydrochloric acid to secondary beneficiation is 0.8-2 mL:1 g.

10. The method according to claim 1, characterized in that, In step 4), the reaction temperature is 10–90℃ and the reaction time is 60–180 min.

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