Method for treating rare earth ore concentrate through alkaline process

Abstract

The invention discloses a method for treating rare earth ore concentrate by an alkaline process, which comprises the following steps: step 1, melting the rare earth ore concentrate with caustic soda in advance, then adding an alkaline solution for leaching so as to dissolve beryllium element and silicon element in the alkaline solution, and filtering to obtain leachate and insoluble slag; step 2, adding calcium hydroxide into the leachate obtained in the step 1, introducing carbon dioxide gas to precipitate silicon and calcium, and filtering to obtain silicon-calcium slag and filtrate 1; 3, boiling the filtrate 1 obtained in the step 2 to precipitate beryllium, and filtering to obtain basic beryllium carbonate and filtrate 2; and 4, causticizing the filtrate 2 obtained in the step 3 and calcium hydroxide, filtering to obtain calcium carbonate precipitate and filtrate 3, and refluxing the filtrate 3 to the leaching step in the step 1, the filtrate 3 being alkaline. The invention aims to reduce the alkaline treatment cost of the rare earth ore concentrate and improve the emission qualification rate of impurity removal.

Description

Technical Field

[0001] The invention relates to the technical field of rare earth concentrate smelting, and in particular to a method for treating rare earth concentrate by alkali method. Background Art

[0002] Rare earth concentrate refers to the concentrate obtained after preliminary processing of ores containing rare earth elements. Rare earth elements include 17 elements such as lanthanide elements, scandium, and yttrium. These elements mainly exist in the form of minerals in nature, such as monazite and bastnaesite. The extraction process of rare earth concentrate usually includes steps such as ore dressing, crushing, grinding, leaching, extraction, and precipitation. First, the rare earth-containing ore is initially separated through mineral processing; then, the ore is crushed into appropriate sizes and ground to increase the specific surface area of ​​the ore; then, the rare earth elements are dissolved from the ore through a leaching process; finally, the rare earth elements are extracted through chemical methods such as extraction and precipitation to obtain rare earth concentrates. From rare earth concentrates to single rare earth elements, it is generally necessary to smelt rare earth concentrates to extract and separate rare earth elements. The decomposition methods of rare earth concentrates generally include four categories: acid decomposition, alkali decomposition, oxidative roasting and high-temperature chlorination. Among them, the existing acid method for treating rare earth concentrates has a short process flow, strong adaptability to concentrate grades, continuous production, low raw material consumption, and low cost, but the production process produces fluorine-containing sulfuric acid mist waste gas, which is easy to corrode equipment and pollute the environment. The advantages of the existing alkaline method for treating rare earth concentrates are high concentrate decomposition rate, good production environment, and low radioactive waste rate. However, due to the high price of caustic soda, the cost increases and it is only applicable to high-grade rare earth concentrates. There are also a series of problems such as high energy consumption due to long decomposition time and acid-base neutralization processes.

[0003] The invention patent with the existing patent publication number CN114959319A discloses a method for treating solids obtained by the alkaline decomposition process of mixed rare earth concentrate, which includes the following steps: 1) the mixed rare earth concentrate is sequentially subjected to caustic soda decomposition, alkali cake water washing and hydrochloric acid preferential dissolution to obtain rare earth chloride solution and preferentially soluble solids; the rare earth chloride solution is neutralized and impurities are removed by an alkaline reagent to obtain a neutralized rare earth chloride solution and a neutralized solid; the mixture of the neutralized solid and the preferentially soluble solid is repeated for more than two times to obtain a solid to be treated; 2) the solid to be treated is washed with a hydrochloric acid solution N times, N is a natural number of 3 to 9; the HCl concentration in the hydrochloric acid solution is 2.5 to 4.0 mol / L; the washing temperature is 50 to 70°C; 3) washed with water to obtain a discharged solid. Although it can reduce the REO content in the obtained discharged solid. However, the repeated steps of caustic soda decomposition, alkali cake water washing and hydrochloric acid dissolution result in a large consumption of caustic soda, and the discharged solids also contain a certain amount of environmentally polluting metals. Long-term discharge will seriously pollute the soil and the environment. Summary of the invention

[0004] The main purpose of the present invention is to provide a method for treating rare earth concentrate by alkali method, aiming to solve the technical problems of high cost and low qualified rate of discharge of impurities in the existing alkali method for treating rare earth concentrate.

[0005] To achieve the above object, the present invention provides a method for treating rare earth concentrate by alkali method, the method comprising the following steps:

[0006] Step 1, pre-melting the rare earth concentrate with caustic soda, then adding an alkaline solution for leaching, so that beryllium and silicon are dissolved in the alkaline solution, and filtering to obtain a leachate and an insoluble slag;

[0007] Step 2, adding calcium hydroxide to the leaching solution obtained in step 1, and introducing carbon dioxide gas to precipitate silicon and calcium, and filtering to obtain silicon-calcium slag and filtrate 1;

[0008] Step 3, boiling the filtrate 1 obtained in step 2 to precipitate beryllium, and filtering to obtain basic beryllium carbonate and filtrate 2;

[0009] Step 4, causticizing the filtrate 2 obtained in step 3 with calcium hydroxide, filtering to obtain calcium carbonate precipitate and filtrate 3, and reflux the filtrate 3 to the leaching step of step 1, wherein the filtrate 3 is alkaline.

[0010] Optionally, the method further comprises the following steps: adding hydrochloric acid solution to the insoluble slag obtained in step 1 for dissolution, and controlling the pH value after dissolution to be 4-5, so as to precipitate iron, zirconium and niobium elements, and obtaining a soluble slag containing iron, zirconium and niobium and a rare earth chloride solution after filtering.

[0011] Optionally, in step 1, the reaction temperature of the rare earth concentrate and caustic soda melting is 550-750° C., and the mass ratio of the rare earth concentrate to the caustic soda is 1:(1.0-1.4).

[0012] Optionally, in step 1, the alkaline solution is one of sodium hydroxide and potassium hydroxide, and the volume mass ratio of the alkaline solution to the rare earth concentrate is (5-10) L:1 kg.

[0013] Optionally, in step 2, the pH value of the leachate after adding calcium hydroxide is above 13.5.

[0014] Optionally, in step 2, the concentration of the hydrochloric acid solution is 6 to 9 mol / L.

[0015] Optionally, in step 3, the filtrate 1 is boiled for 2 hours.

[0016] Optionally, in step 4, the obtained filtrate 3 is concentrated to a pH value consistent with the alkaline solution in step 1.

[0017] Optionally, the solid-liquid ratio of the insoluble slag to the hydrochloric acid solution is (6-12) kg:1L.

[0018] Optionally, the pH value of the alkaline solution is above 13.5.

[0019] Beneficial effects:

[0020] (1) The present invention adopts an alkaline method to extract rare earth elements, thereby recycling the alkaline solution and effectively reducing the reagent cost;

[0021] (2) Achieve efficient separation of rare earth elements, beryllium and Fe, Zr, Nb, and effectively remove silicon;

[0022] (3) The addition of hydrochloric acid produces rare earth chloride, not simply neutralizing alkali. The hydrochloric acid is effectively utilized and the acid reagent is not wasted.

[0023] (4) The consumed product in the reaction is calcium hydroxide, but it is eventually precipitated out in the form of calcium carbonate and does not enter the product, thereby avoiding the introduction of impurities. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic flow chart of an embodiment of a method for treating rare earth concentrate by alkaline method according to the present invention;

[0025] Figure 2 for Figure 1 The flow chart shown.

[0026] The realization of the purpose, functional features and advantages of the present invention will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0027] It should be understood that the specific embodiments described herein are only used to explain the present invention, and are not used to limit the present invention.

[0028] See also Figure 1-2 The present invention provides a schematic flow diagram of a method for treating rare earth concentrate by alkaline method, the method comprising the following steps:

[0029] Step 1, melt the rare earth concentrate with caustic soda in advance, then add alkaline solution for leaching, so that beryllium and silicon are dissolved in the alkaline solution, and filter to obtain leachate and insoluble slag. Among them, the melting temperature of rare earth concentrate and caustic soda is 550-750°C, preferably 750°C; the mass ratio of rare earth concentrate to caustic soda is 1:(1.0-1.4), preferably 1:1.2, and the pH value of the added alkaline solution is above 13.5, and the volume mass ratio of alkaline solution to rare earth concentrate is (5-10)L:1kg, preferably 10L:1kg, and then in this step, the addition of alkaline solution can dissolve beryllium and silicon in the rare earth concentrate, and at the same time, rare earth elements, iron elements, zirconium elements, and niobium elements exist in the form of insoluble slag of solid compounds, thereby realizing the separation of beryllium, silicon and other rare earth elements.

[0030] Preferably, the alkaline solution is one of sodium hydroxide and potassium hydroxide. Taking the alkaline solution as sodium hydroxide as an example, the reaction involved in the above step 1 is as follows:

[0031] MSiO4 (n-4) +nNaOH→M(OH) n +SiO4 4- +nNa + .

[0032] Among them, the alkaline decomposition of rare earth beryllium concentrate involves two types: silicate type and oxide type. During the alkaline roasting process, the Si-Ob-Si bond of silicate minerals with group structure, chain structure, layer structure and framework structure is replaced by the structure of (Si-OM) during the alkaline melting reaction to generate Na2MSiO4, NaMSiO4, MSiO4 (M is a metal ion, for example, RE 3+ ,Th 4+ , Fe 3+ , Nb 5+ In the action of NaOH on the island-like structure of Na2MSiO4, NaMSiO4, and MSiO4, the replacement of Na ions for M ions is carried out successively. Therefore, the final product of the alkali fusion reaction is M(OH) n and Na4SiO4.

[0033] Step 2, adding calcium hydroxide to the leachate obtained in step 1, and passing carbon dioxide gas to precipitate silicon and calcium, and filtering to obtain silicon-calcium slag and filtrate 1. Among them, the pH value of the leachate after adding calcium hydroxide is above 13.5, and silicon is difficult to precipitate in the form of insoluble matter, and then continuing to pass carbon dioxide gas can reduce the pH value of the filtrate until it drops below 10, and silicon precipitates in the form of calcium silicate. After filtering, silicon-calcium slag is obtained, and beryllium still exists in the filtrate, thereby achieving effective removal of silicon.

[0034] Step 3, boiling the filtrate 1 obtained in step 2 to precipitate beryllium, and filtering to obtain basic beryllium carbonate and filtrate 2. The boiling time is 1 to 2 hours, and the beryllium element generates basic beryllium carbonate precipitation under boiling and alkaline conditions, thereby achieving effective extraction of the beryllium element.

[0035] Step 4, causticizing the filtrate 2 obtained in step 3 with calcium hydroxide, filtering to obtain calcium carbonate precipitate and filtrate 3, and reflux the filtrate 3 to the leaching step of step 1, wherein the filtrate 3 is alkaline, and the causticizing reaction of the filtrate 2 with calcium hydroxide is as follows:

[0036] CO3 2- +Ca(OH)2→CaCO3+2OH - .

[0037] In this step, the filtrate 2 is causticized with calcium hydroxide, and the calcium ions are combined with carbonate ions to form calcium carbonate precipitation. The filtrate 3 is alkaline, and the filtrate 3 solution is returned to the beryllium leaching process, so that the alkaline solution in the process is always recycled.

[0038] Further, hydrochloric acid solution is added to the insoluble slag obtained in step 1 for optimal dissolution, and the pH value after optimal dissolution is controlled to be 4-5, so that iron, zirconium and niobium elements are precipitated, and the optimal dissolution slag containing iron, zirconium and niobium and rare earth chloride solution are obtained after filtration. Wherein, the concentration of the hydrochloric acid solution is 6-9 mol / L, and the solid-liquid ratio of the insoluble slag to the hydrochloric acid solution is (6-12) kg:1L, preferably 9 kg:1L. The addition of hydrochloric acid in this step is used to neutralize the alkali and can also be used to obtain the rare earth chloride solution, thereby expanding the application range of hydrochloric acid and not wasting acid reagents.

[0039] Among them, the reactions involved in rare earth are as follows:

[0040] RE2O3+6HCl→2RECl3+3H2O.

[0041] As well as iron, zirconium and niobium, under the action of 6-9 mol / L hydrochloric acid, they are first reacted and dissolved with hydrochloric acid, and the reactions involved are as follows:

[0042] Fe2 O3+6HCl→2FeCl3+3H2 O;

[0043] ZrO2+4HCl→ZrCl4+2H2O;

[0044] Nb x O y +2yHCl→xNbCl 2y / x +yH2O,Nb x O yIt is the general formula of the corresponding oxides of niobium element Nb2O5, Nb2O3, NbO2, and NbO.

[0045] Furthermore, when the pH value after optimal dissolution is adjusted to 4-5, the dissolved iron, zirconium and niobium elements can be further precipitated to obtain optimal dissolution slag containing iron, zirconium and niobium.

[0046] Further, in order to better illustrate the process and effect of a method for treating rare earth concentrate by alkaline method, the following is described in detail through specific examples, the details are as follows:

[0047] Example 1

[0048] Step 1, pre-melting the concentrate with a rare earth content of 22.7% with caustic soda, with a ore-caustic soda ratio of 1:1.2, and a roasting temperature of 750°C; then adding 10% sodium hydroxide solution for leaching, and filtering to obtain a leachate and an insoluble slag;

[0049] Step 2, adding calcium hydroxide to the leaching solution, and passing carbon dioxide gas to precipitate silicon and calcium, and filtering to obtain silicon-calcium slag and filtrate 1, the silicon content in the slag is 5.95%, and the silicon removal rate is 44.69%;

[0050] Step 3, boiling the filtrate 1 for 2 hours, and filtering again to obtain basic beryllium carbonate and the filtrate 2;

[0051] Step 4, causticizing the filtrate 2 with calcium hydroxide, filtering to obtain calcium carbonate precipitate and filtrate 3, and reflux the filtrate 3 to the sodium hydroxide leaching step.

[0052] Step 5, adding 9 mol / L hydrochloric acid solution to the insoluble slag in step 1 for dissolution, with a solid-liquid ratio of 9:1, and controlling the pH value after dissolution to be 4, so as to precipitate iron, zirconium and niobium elements, and filtering to obtain a soluble slag containing iron, zirconium and niobium and a rare earth chloride solution, with a rare earth leaching rate of 96.2%.

[0053] Example 2

[0054] Step 1, pre-melting the concentrate with a rare earth content of 22.7% with caustic soda, with a ore-caustic soda ratio of 1:1.2, and a roasting temperature of 550°C; then adding 10% sodium hydroxide solution for leaching, and filtering to obtain a leachate and an insoluble slag;

[0055] Step 2, adding calcium hydroxide to the leaching solution, and passing carbon dioxide gas to precipitate silicon and calcium, and filtering to obtain silicon-calcium slag and filtrate 1, the silicon content in the slag is 5.4%, and the silicon removal rate is 38.52%;

[0056] Step 3, boiling the filtrate 1 for 2 hours, and filtering again to obtain basic beryllium carbonate and the filtrate 2;

[0057] Step 4, causticizing the filtrate 2 with calcium hydroxide, filtering to obtain calcium carbonate precipitate and filtrate 3, and reflux the filtrate 3 to the sodium hydroxide leaching step.

[0058] Step 5, adding 6 mol / L hydrochloric acid solution to the insoluble slag in step 1 for dissolution, with a solid-liquid ratio of 9:1, and controlling the pH value after dissolution to be 4, so as to precipitate iron, zirconium and niobium elements, and filtering to obtain a soluble slag containing iron, zirconium and niobium and a rare earth chloride solution, with a rare earth leaching rate of 96.78%.

[0059] Example 3

[0060] Step 1, pre-melting the concentrate with a rare earth content of 22.7% with caustic soda, with a ore-caustic soda ratio of 1:1.2, and a roasting temperature of 750°C; then adding 10% sodium hydroxide solution for leaching, and filtering to obtain a leachate and an insoluble slag;

[0061] Step 2, adding calcium hydroxide to the leaching solution, and passing carbon dioxide gas to precipitate silicon and calcium, and filtering to obtain silicon-calcium slag and filtrate 1, the silicon content in the slag is 5.95%, and the silicon removal rate is 44.69%;

[0062] Step 3, boiling the filtrate 1 for 2 hours, and filtering again to obtain basic beryllium carbonate and the filtrate 2;

[0063] Step 4, causticizing the filtrate 2 with calcium hydroxide, filtering to obtain calcium carbonate precipitate and filtrate 3, and reflux the filtrate 3 to the sodium hydroxide leaching step.

[0064] Step 5, adding 6 mol / L hydrochloric acid solution to the insoluble slag in step 1, with a solid-liquid ratio of 9:1, and controlling the pH value after dissolution to be 5, so as to precipitate iron, zirconium and niobium elements, and filtering to obtain soluble slag containing iron, zirconium and niobium and a rare earth chloride solution, with a rare earth leaching rate of 98.91%.

[0065] Example 4

[0066] Step 1, pre-melting the concentrate with a rare earth content of 22.7% with caustic soda, with a ore-caustic soda ratio of 1:1.2, and a roasting temperature of 750°C; then adding 10% sodium hydroxide solution for leaching, and filtering to obtain a leachate and an insoluble slag;

[0067] Step 2, adding calcium hydroxide to the leaching solution, and passing carbon dioxide gas to precipitate silicon and calcium, and filtering to obtain silicon-calcium slag and filtrate 1, the silicon content in the slag is 5.95%, and the silicon removal rate is 44.69%;

[0068] Step 3, boiling the filtrate 1 for 2 hours, and filtering again to obtain basic beryllium carbonate and the filtrate 2;

[0069] Step 4, causticizing the filtrate 2 with calcium hydroxide, filtering to obtain calcium carbonate precipitate and filtrate 3, and reflux the filtrate 3 to the sodium hydroxide leaching step.

[0070] Step 5, adding 9 mol / L hydrochloric acid solution to the insoluble slag in step 1 for dissolution, with a solid-liquid ratio of 9:1, and controlling the pH value after dissolution to be 4, so as to precipitate iron, zirconium and niobium elements, and filtering to obtain a soluble slag containing iron, zirconium and niobium and a rare earth chloride solution, with a rare earth leaching rate of 96.2%.

[0071] Comparative Example 1

[0072] Step 1, pre-melting the concentrate with a rare earth content of 22.7% with caustic soda, with a ore-caustic soda ratio of 1:1.2, and a roasting temperature of 350°C; then adding 10% sodium hydroxide solution for leaching, and filtering to obtain a leachate and an insoluble slag;

[0073] Step 2, adding calcium hydroxide to the leaching solution, and passing carbon dioxide gas to precipitate silicon and calcium, and filtering to obtain silicon-calcium slag and filtrate 1, the silicon content in the slag is 6.94%, and the silicon removal rate is 14.60%;

[0074] Step 3, boiling the filtrate 1 for 2 hours, and filtering again to obtain basic beryllium carbonate and the filtrate 2;

[0075] Step 4, causticizing the filtrate 2 with calcium hydroxide, filtering to obtain calcium carbonate precipitate and filtrate 3, and reflux the filtrate 3 to the sodium hydroxide leaching step.

[0076] Step 5, adding 6 mol / L hydrochloric acid solution to the insoluble slag in step 1, with a solid-liquid ratio of 9:1, and filtering to obtain soluble slag containing iron, zirconium and niobium and a rare earth chloride solution, with a rare earth leaching rate of 40.95%.

[0077] Comparative Example 2

[0078] Step 1, pre-melting the concentrate with a rare earth content of 22.7% with caustic soda, with a ore-caustic soda ratio of 1:1.2, and a roasting temperature of 350°C; then adding 10% sodium hydroxide solution for leaching, and filtering to obtain a leachate and an insoluble slag;

[0079] Step 2, adding calcium hydroxide to the leaching solution, and passing carbon dioxide gas to precipitate silicon and calcium, and filtering to obtain silicon-calcium slag and filtrate 1, the silicon content in the slag is 6.94%, and the silicon removal rate is 14.60%;

[0080] Step 3, boiling the filtrate 1 for 2 hours, and filtering again to obtain basic beryllium carbonate and the filtrate 2;

[0081] Step 4, causticizing the filtrate 2 with calcium hydroxide, filtering to obtain calcium carbonate precipitate and filtrate 3, and reflux the filtrate 3 to the sodium hydroxide leaching step.

[0082] Step 5, adding 6 mol / L hydrochloric acid solution to the insoluble slag in step 1, with a solid-liquid ratio of 4.5:1, filtering to obtain soluble slag containing iron, zirconium and niobium and rare earth chloride solution, with a rare earth leaching rate of 52.4%.

[0083] Comparative Example 3

[0084] Step 1, pre-melting the concentrate with a rare earth content of 22.7% with caustic soda, with a ore-caustic soda ratio of 1:1.2, and a roasting temperature of 350°C; then adding 10% sodium hydroxide solution for leaching, and filtering to obtain a leachate and an insoluble slag;

[0085] Step 2, adding calcium hydroxide to the leaching solution, and passing carbon dioxide gas to precipitate silicon and calcium, and filtering to obtain silicon-calcium slag and filtrate 1, the silicon content in the slag is 6.94%, and the silicon removal rate is 14.60%;

[0086] Step 3, boiling the filtrate 1 for 2 hours, and filtering again to obtain basic beryllium carbonate and the filtrate 2;

[0087] Step 4, causticizing the filtrate 2 with calcium hydroxide, filtering to obtain calcium carbonate precipitate and filtrate 3, and reflux the filtrate 3 to the sodium hydroxide leaching step.

[0088] Step 5, adding 9 mol / L hydrochloric acid solution to the insoluble slag in step 1, with a solid-liquid ratio of 12:1, filtering to obtain soluble slag containing iron, zirconium and niobium and rare earth chloride solution, with a rare earth leaching rate of 78.32%.

[0089] According to the comparison of the rare earth leaching rates in the above-mentioned Examples 1-4 and Comparative Examples 1-3, the rare earth leaching rates in Examples 1-4 are all greater than the corresponding rare earth leaching rates in the corresponding Examples 1-3. The principle is to adjust the solid-liquid ratio of the insoluble slag to the hydrochloric acid, and then adjust the pH value after the optimal solution, so that the iron, zirconium and niobium elements are precipitated, and the optimal solution slag and rare earth chloride solution containing iron, zirconium and niobium are obtained after filtration. And compared with Comparative Example 1, the concentrate reacts with caustic soda at different temperatures, and the silicon removal rate of the embodiment is greater than that of the comparative example. Then, the silicon is removed efficiently in advance in the embodiment, which can avoid the silicon content affecting the subsequent rare earth leaching rate.

[0090] It should be noted that, in this article, the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or system including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or system. In the absence of further restrictions, an element defined by the sentence "comprises a ..." does not exclude the existence of other identical elements in the process, method, article or system including the element.

[0091] The serial numbers of the above embodiments of the present invention are only for description and do not represent the advantages or disadvantages of the embodiments.

[0092] The above are only preferred embodiments of the present invention, and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A method for treating rare earth concentrate by alkaline method, characterized in that: The method comprises the following steps: Step 1, pre-melting the rare earth concentrate with caustic soda, then adding an alkaline solution for leaching, so that beryllium and silicon are dissolved in the alkaline solution, and filtering to obtain a leachate and an insoluble slag; Step 2, adding calcium hydroxide to the leaching solution obtained in step 1, and introducing carbon dioxide gas to precipitate silicon and calcium, and filtering to obtain silicon-calcium slag and filtrate 1; Step 3, boiling the filtrate 1 obtained in step 2 to precipitate beryllium, and filtering to obtain basic beryllium carbonate and filtrate 2; Step 4, causticizing the filtrate 2 obtained in step 3 with calcium hydroxide, filtering to obtain calcium carbonate precipitate and filtrate 3, and reflux the filtrate 3 to the leaching step of step 1, wherein the filtrate 3 is alkaline.

2. The method for treating rare earth concentrate by alkaline method according to claim 1, characterized in that: The method further comprises the following steps: adding hydrochloric acid solution to the insoluble slag obtained in step 1 for dissolution, and controlling the pH value after dissolution to be 4-5, so as to precipitate iron, zirconium and niobium elements, and filtering to obtain the soluble slag containing iron, zirconium and niobium and the rare earth chloride solution.

3. The method for treating rare earth concentrate by alkaline method according to claim 1, characterized in that: In step 1, the reaction temperature of the rare earth concentrate and caustic soda melting is 550-750° C., and the mass ratio of the rare earth concentrate to the caustic soda is 1:(1.0-1.4).

4. The method for treating rare earth concentrate by alkaline method according to claim 1, characterized in that: In step 1, the alkaline solution is one of sodium hydroxide and potassium hydroxide, and the volume mass ratio of the alkaline solution to the rare earth concentrate is (5-10) L: 1 kg.

5. The method for treating rare earth concentrate by alkaline method according to claim 1, characterized in that: In step 2, the pH value of the leaching solution after adding calcium hydroxide is above 13.

5.

6. The method for treating rare earth concentrate by alkaline method according to claim 2, characterized in that: In step 2, the concentration of the hydrochloric acid solution is 6 to 9 mol / L.

7. The method for treating rare earth concentrate by alkaline method according to claim 1, characterized in that: In step 3, the filtrate 1 is boiled for 1 to 2 hours.

8. The method for treating rare earth concentrate by alkaline method according to claim 1, characterized in that: In step 4, the obtained filtrate 3 is concentrated until the pH value of the alkaline solution in step 1 is consistent.

9. The method for treating rare earth concentrate by alkaline method according to claim 2, characterized in that: The solid-liquid ratio of the insoluble residue to the hydrochloric acid solution is (6-12) kg:1L.

10. The method for treating rare earth concentrate by alkaline method according to any one of claims 1 to 9, characterized in that: The pH value of alkaline solution is above 13.5.

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