Method for decomposing mineral type rare earth ore through sulfating roasting in weak oxidizing atmosphere

Abstract

The invention discloses a method for decomposing mineral type rare earth ore through sulfating roasting in a weak oxidizing atmosphere, which comprises the following steps: S1, mixing the mineral type rare earth ore with concentrated sulfuric acid, and carrying out sulfating roasting decomposition in the weak oxidizing atmosphere to obtain roasted ore and tail gas; s2, leaching the roasted ore obtained in the step S1 by using water, weak acid or a magnesium-containing solution as an ore leaching agent, and filtering to obtain a leaching solution and leaching residues; and S3, the lixivium obtained in the S2 is subjected to neutralization impurity removal and solid-liquid separation treatment, and a sulfuric acid rare earth solution and neutralization impurity removal residues are obtained. According to the method, the mineral type rare earth ore is subjected to sulfating roasting treatment under the weak oxidizing atmosphere, the form of sulfur oxide in the tail gas can be effectively regulated and controlled, and efficient separation and resource recycling of fluorine and sulfur in the tail gas are achieved.

Description

Technical Field

[0001] This invention relates to the field of rare earth metallurgy technology, and in particular to a method for sulfation roasting and decomposing mineral-type rare earth ores in a weak oxidizing atmosphere. Background Technology

[0002] Mineral-type rare earth minerals include bastnaesite, monazite, and xenotime, among which bastnaesite is my country's second largest rare earth resource. Currently, the conventional industrial treatment process for bastnaesite is oxidative roasting-hydrochloric acid leaching-alkali dissolution. The advantages of this process are low investment and no sulfur-containing waste gas is generated, but there are a series of bottleneck problems as follows: (1) The process flow is long, hydrochloric acid and liquid alkali are used alternately, the steps are complicated, and it can only be operated intermittently. (2) The wastewater generation is large (55t / tREO) and is mixed salt wastewater. After the hydrochloric acid leaching residue is treated by alkali conversion, the fluorine element is converted into sodium fluoride, generating a large amount of fluorine-containing wastewater, which is difficult and costly to treat in an environmentally friendly manner. At present, the calcium chloride wastewater generated by extraction is neutralized to produce calcium fluoride slag and sodium chloride-calcium chloride mixed wastewater, and the fluorine resources have not been recovered and utilized. In addition, the sodium carbonate precipitation generates a large amount of sodium chloride wastewater. (3) The gelation during the alkali conversion process makes it difficult to wash, the washing water volume is large, and the addition of a large amount of flocculant affects the subsequent extraction process. (4) Large quantities of radioactive waste are generated, with the vast majority of cerium and thorium elements converted into cerium-thorium slag (0.45 t / t concentrate), and total emissions > 10. 4 Bq / kg; In addition, the rare earth chloride solution obtained by hydrochloric acid dissolution requires stepwise removal of thorium, fluorine, barium, and lead. The impurity removal process is cumbersome and generates numerous types of waste residue (0.12t / t concentrate), of which the total emissions of iron-thorium slag are >4×10 3 Bq / kg, total amount of barium slag and lead slag > 2×10 4 Bq / kg, all of which are radioactive waste residues, and the cost of safe disposal is high. (5) The rare earth yield is low (only 54% excluding cerium enrichment), with less than 10% of cerium forming cerium products, and more than 90% of cerium being produced in the form of cerium enrichment, which cannot be sold as a by-product. In addition, 1-2% of high-value praseodymium and neodymium enter the cerium enrichment, causing losses.

[0003] To solve the above problems, patent CN1667139A discloses a method for decomposing rare earth concentrate, including the following process: (1) mixing rare earth concentrate with concentrated sulfuric acid in a weight ratio of 1:1.1 to 1:1.7; (2) aging the concentrate after mixing with sulfuric acid at 40 to 180°C; (3) roasting the aged concentrate for 1 to 8 hours at a roasting temperature of 150 to 330°C; (4) leaching the roasted ore with water to leach more than 95% of the rare earth and thorium into the solution; then separating thorium and rare earth by extraction, and obtaining thorium nitrate product by washing and back-extraction; after thorium extraction, the solution is precipitated to obtain a rare earth product without thorium; (5) the flue gas produced by roasting is discharged after ammonia defluorination or water washing; (6) the slag after leaching is discharged after water washing. Patent CN104962762A discloses a method for processing bastnaesite, including: (1) ball milling bastnaesite to obtain bastnaesite particles; (2) mixing the bastnaesite particles with concentrated sulfuric acid and quenching them to obtain quenched ore; (3) roasting the quenched ore to obtain roasted sand; (4) slurrying the roasted sand and leaching and filtering it to obtain leachate and leachate residue; (5) extracting the leachate to obtain rare earth and thorium-containing extract; and (6) back-extracting the thorium-containing extract to obtain thorium nitrate. Patent CN106978532A discloses a method for extracting rare earth elements, fluorine, and thorium from fluorine-containing rare earth minerals using concentrated sulfuric acid. The method includes: mixing fluorine-containing rare earth minerals with concentrated sulfuric acid; the single fluorine-containing rare earth mineral or mixed rare earth concentrate contains 50-70% rare earth oxides by mass, the concentrated sulfuric acid contains >90% H2SO4 by mass, and the weight ratio of fluorine-containing rare earth minerals to concentrated sulfuric acid is 1:0.6-1:1.0; calcining the mixture at 120-180°C for 120-300 min; and after leaching the calcined reaction product with water, neutralizing the water extract to a pH of 3.5-4.5 to form a rare earth sulfate solution and an iron-thorium concentrate.

[0004] The above methods all employ concentrated sulfuric acid decomposition, which can effectively process bastnaesite. However, they have the following problems: First, bastnaesite requires a certain amount of time to mature with sulfuric acid before sulfation decomposition, resulting in a long processing time. Second, the amount of residual acid in the roasted ore is difficult to control, and a large amount of residual acid is present when the reaction is terminated, leading to a waste of sulfuric acid. At the same time, the water leaching process requires a large amount of neutralizing agent. Third, it is impossible to fix the radioactive element (thorium) contained in rare earth ores in the solid slag. Although the radioactive element can be converted into high-purity thorium products after entering the solution, the storage cost of thorium is high because the market for thorium is not yet large-scale.

[0005] Baotou mixed rare earth ore is a mixture of monazite and bastnaesite. The mainstream processing technology adopts concentrated sulfuric acid roasting, with a roasting temperature of 250-500℃. At this temperature, the rare earth concentrate sulfation roasting process can convert thorium into thorium pyrophosphate and fix it in the slag, which is conducive to low-cost and safe storage. At the same time, it avoids the problem of high residual acid in low-temperature sulfuric acid roasting. However, there are two major problems: (1) At high temperature, concentrated sulfuric acid decomposes to produce SO3 / SO2 / HF / SiF4 mixed tail gas. At present, the mainstream industrial method is to use water spray absorption to absorb SO3 / HF / SiF4 in the mixed tail gas and convert it into sulfuric acid and fluorine. SO2 gas is further catalytically oxidized to SO3 and then recovered to produce 98% concentrated sulfuric acid product. However, the sulfuric acid and fluorine produced in the mixed tail gas treatment process cannot be used as products. Separation is difficult and costly. Using lime neutralization will cause resource waste and produce a large amount of calcium fluoride waste residue. (2) During the sulfuric acid roasting process, a small amount of cerium in the mineral rare earth ore will be oxidized to stable cerium oxide (CeO2), resulting in a low rare earth yield. Summary of the Invention

[0006] The purpose of this invention is to provide a method for sulfation roasting and decomposing mineral-type rare earth ores in a weak oxidizing atmosphere. The method involves mixing the mineral-type rare earth ores with concentrated sulfuric acid and sulfation roasting and decomposing them under a weak oxidizing atmosphere to obtain roasted ore and tail gas. The roasted ore is then subjected to leaching, neutralization to remove impurities, and solid-liquid separation to obtain a rare earth sulfate solution and leaching residue. By sulfation roasting the mineral-type rare earth ores under a weak oxidizing atmosphere, the form of sulfur oxides in the tail gas can be effectively controlled, achieving efficient separation and resource recovery of fluorine and sulfur in the tail gas.

[0007] To address the aforementioned technical problems, embodiments of the present invention provide a method for the sulfation roasting and decomposition of mineral-type rare earth ores in a weak oxidizing atmosphere, comprising the following steps:

[0008] S1: Mix mineral-type rare earth ore with concentrated sulfuric acid and sulfatate roasting decomposition under a weak oxidizing atmosphere to obtain roasted ore and tail gas;

[0009] S2: The roasted ore obtained in S1 is leached with water, weak acid or magnesium-containing solution as leaching agent, and filtered to obtain leaching solution and leaching residue.

[0010] S3: The leachate obtained in S2 is subjected to neutralization and impurity removal, and solid-liquid separation to obtain rare earth sulfate solution and neutralization and impurity removal residue.

[0011] Furthermore, the weakly oxidizing atmosphere includes: a reducing gas and / or an inert gas;

[0012] The oxygen content is 0.1% to 15%, preferably 5% to 10%.

[0013] Furthermore, the weakly oxidizing atmosphere includes air, and also includes at least one of the exhaust gas, N2, CO2 and CO.

[0014] Furthermore, the exhaust gas includes at least two of the following: SO2, SO3, water vapor, HF, and SiF4, with SO3 accounting for a significant portion of the total SO2 content. x The proportion is less than 20%.

[0015] Furthermore, the tail gas obtained from S1 is absorbed and separated to obtain concentrated sulfuric acid and fluorine-containing acid. The concentrated sulfuric acid is returned to the sulfuric acid roasting process in S1, and the fluorine-containing acid is precipitated to obtain fluoride products.

[0016] Furthermore, the rare earth sulfate solution obtained from S3 is transformed and separated by P507 extraction to obtain a single rare earth chloride solution and a magnesium-containing solution, which is then used for leaching the ore.

[0017] Furthermore, the roasting temperature range for sulfation roasting decomposition under a weak oxidizing atmosphere in S1 is 200℃~450℃, preferably 250℃~350℃, and the roasting time is 2h~12h, preferably 3h~5h.

[0018] Furthermore, the concentration of concentrated sulfuric acid used in the sulfation roasting decomposition under a weak oxidizing atmosphere is 85wt% to 98wt%, preferably 90wt% to 98wt%, and the acid-ore mass ratio is 1.0 to 2.0, preferably 1.2 to 1.5.

[0019] Furthermore, the leaching treatment of the roasted ore is carried out for 1 hour to 6 hours, preferably 2 hours to 4 hours, and the mass ratio of roasted ore to leaching agent is 1:5 to 1:20.

[0020] Furthermore, the leachate is neutralized and purified using at least one of magnesium hydroxide, magnesium oxide, magnesium carbonate, and magnesium bicarbonate.

[0021] The above-described technical solutions of the embodiments of the present invention have the following beneficial technical effects:

[0022] 1. This invention involves sulfation roasting of mineral-type rare earth ores under a weak oxidizing atmosphere, which can effectively control the form of sulfur oxides in the exhaust gas and achieve efficient separation and resource recovery of fluorine and sulfur in the exhaust gas.

[0023] 2. This invention enables controllable sulfur oxide speciation in the tail gas of the sulfation roasting process, promoting the separation of fluorine and sulfur in the tail gas and their conversion into valuable by-products, while reducing tail gas treatment steps and lowering costs. Currently, conventional processes produce tail gas containing over 50% SO3. SO3 and HF / SiF4 are both readily soluble in water and difficult to separate. After water spray absorption, SO3 is converted into sulfuric acid and fluorinated acid. Further pressure filtration and reduced-pressure evaporation yield 70wt% concentrated sulfuric acid, and the gas phase is recovered by condensation to obtain fluorinated acid. SO2, however, has low solubility in water and is more easily separated from HF / SiF4 during water spray absorption. Therefore, this invention controls the sulfuric acid roasting process under a weak oxidizing atmosphere, suppressing SO3 gas generation and promoting SO2 gas generation, thus reducing the proportion of SO3 in the tail gas to a lower percentage of total SO2. x The proportion of SO2 is less than 20%. After water spray absorption, HF / SiF4 gas is converted into fluorinated acid, while SO2 gas is further catalytically oxidized into SO3 and then recovered to produce 98wt% concentrated sulfuric acid product. At the same time, the tail gas treatment process reduces the steps of pressure filtration and vacuum evaporation, thereby reducing the tail gas treatment cost.

[0024] 3. During the sulfation roasting process in a weakly oxidizing atmosphere, all rare earth elements in mineral-type rare earth ores are converted into easily leached RE2(SO4)3 and RE2O3, among which cerium is completely converted into Ce(SO4). x or CeO x (1.5≤x<2), to avoid the formation of stable phase CeO2 and improve rare earth leaching rate. Attached Figure Description

[0025] Figure 1 This is a flowchart of the method for decomposing mineral-type rare earth ores by sulfation roasting in a weak oxidizing atmosphere according to an embodiment of the present invention.

[0026] Figure 2 This is a schematic diagram of the process for sulfation roasting and decomposition of mineral-type rare earth ores under a weak oxidizing atmosphere provided in an embodiment of the present invention. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments and the accompanying drawings. It should be understood that these descriptions are merely exemplary and not intended to limit the scope of the invention. Furthermore, descriptions of well-known structures and techniques are omitted in the following description to avoid unnecessarily obscuring the concept of the invention.

[0028] Please refer to Figure 1 and Figure 2 This invention provides a method for the sulfation roasting and decomposition of mineral-type rare earth ores in a weak oxidizing atmosphere, comprising the following steps:

[0029] Step S1: Mix mineral-type rare earth ore with concentrated sulfuric acid and perform sulfation roasting decomposition under a weak oxidizing atmosphere to obtain roasted ore and tail gas.

[0030] During the sulfation roasting process in a weak oxidizing atmosphere, all rare earth elements in mineral-type rare earth ores are converted into easily leached RE2(SO4)3 and RE2O3, with cerium being completely converted into Ce(SO4). x or CeO x (1.5≤x<2), to avoid the formation of stable phase CeO2, the proportion of Ce(IV) in total Ce is less than 3%.

[0031] Step S2 involves leaching the roasted ore obtained in S1 with water, a weak acid, or a magnesium-containing solution as the leaching agent, and then filtering to obtain the leachate and leaching residue.

[0032] Step S3 involves neutralizing and removing impurities from the leachate obtained in S2, followed by solid-liquid separation to obtain a rare earth sulfate solution and a neutralized residue.

[0033] The above technical solution can effectively control the form of sulfur oxides in the tail gas by sulfation roasting of mineral rare earth ores under a weak oxidizing atmosphere, thereby achieving efficient separation and resource recovery of fluorine and sulfur in the tail gas. Controlling the oxygen content can reduce the SO3 content in the tail gas, promote the separation of fluorine and sulfur in the tail gas and convert them into valuable by-products, and also reduce the cerium oxidation rate and increase the leaching rate.

[0034] Specifically, the weakly oxidizing atmosphere includes: reducing gases and / or inert gases; wherein the oxygen content is 0.1% to 15%, preferably 5% to 10%.

[0035] In the process of sulfation roasting in a weak oxidizing atmosphere, mineral-type rare earth ore decomposes into RE2(SO4)3, while simultaneously generating tail gases such as HF, SiF4, CO2, and water vapor. The specific reactions are as follows:

[0036] 2REFCO3+3H2SO4=RE2(SO4)3+2HF↑+2CO2↑+2H2O↑;

[0037] 3REFCO3=RE2O3+REF3+CO2↑;

[0038] RE2O3+3H2SO4=RE2(SO4)3+3H2O↑;

[0039] CaF2+H2SO4=CaSO4↓+2HF↑;

[0040] SiO2 + 4HF = SiF4↑ + 2H2O↑;

[0041] Rare earth sulfuric acid and concentrated sulfuric acid each decompose to produce SO2, SO3, and H2O vapors as tail gases. The specific reactions are as follows:

[0042] RE2(SO4)3=RE2O3+3SO3↑ or RE2(SO4)3=RE2O3+3SO2↑+1.5O2↑;

[0043] H2SO4=SO3↑+H2O↑;

[0044] Under a weak oxidizing atmosphere (such as CO), the decomposition of rare earth sulfuric acid and concentrated sulfuric acid to produce SO3 gas is suppressed, while the production of SO2 gas is promoted. The specific reaction is as follows:

[0045] Ce2(SO4)3+3CO=Ce2O3+3SO2+3CO2;

[0046] H₂SO₄ + CO = SO₂ + CO₂ + H₂O;

[0047] Under a weak oxidizing atmosphere (when oxygen is insufficient), the further oxidation of Ce2(SO4)3 and Ce2O3 to Ce(SO4)2 and CeO2 is inhibited, while the formation of Ce(SO4)2 is promoted. x CeO x (1.5≤x<2), the specific reactions are as follows:

[0048] Ce₂O₃ + (x - 1.5)O₂ = 2CeO x (1.5≤x<2);

[0049] Ce2(SO4)3 + O2 (minor) → 2Ce(SO4) x (1.5≤x<2).

[0050] Furthermore, the weakly oxidizing atmosphere includes air, and also includes at least one of the exhaust gas, N2, CO2 and CO.

[0051] Preferably, the roasting temperature range for sulfation roasting decomposition under a weak oxidizing atmosphere is 250℃~350℃; the roasting time for sulfation roasting decomposition under a weak oxidizing atmosphere is 3h~5h. In the mineral-type rare earth ore, all rare earth elements are converted into easily leached phases RE2(SO4)3 and RE2O3, wherein Ce(IV) accounts for less than 3% of the total Ce, and the total rare earth yield is greater than 95%; sulfur in the mixed tail gas is converted into SO2, making SO3 a significant portion of the total SO2 in the tail gas. x The proportion is less than 20%. The mixed tail gas is absorbed and post-treated to obtain concentrated sulfuric acid, which is recycled in the sulfation roasting process. The fluorinated acid is treated to obtain fluoride products.

[0052] Preferably, the concentration of concentrated sulfuric acid used in the sulfation roasting decomposition under a weak oxidizing atmosphere is 90wt%–98wt%. In the mineral-type rare earth ore, all rare earth elements are converted into easily leached phases RE2(SO4)3 and RE2O3, wherein Ce(IV) accounts for less than 3% of the total Ce, and the total rare earth yield is greater than 95%. Sulfur in the mixed tail gas is converted into SO2, resulting in SO3 accounting for a significant portion of the total SO2 content in the tail gas. x The proportion is less than 20%. The mixed tail gas is absorbed and post-treated to obtain concentrated sulfuric acid, which is recycled in the sulfation roasting process. The fluorinated acid is treated to obtain fluoride products.

[0053] Furthermore, the acid-to-ore mass ratio during the sulfation roasting and decomposition process under a weakly oxidizing atmosphere is 1.0–2.0, preferably 1.2–1.5. In the mineral-type rare earth ore, all rare earth elements are converted into easily leached phases RE2(SO4)3 and RE2O3, wherein Ce(IV) accounts for less than 3% of the total Ce, and the total rare earth yield is greater than 95%. Sulfur in the mixed tail gas is converted into SO2, resulting in SO3 accounting for a significant portion of the total SO2 content in the tail gas. x The proportion is less than 20%. The mixed tail gas is absorbed and post-treated to obtain concentrated sulfuric acid, which is recycled in the sulfation roasting process. The fluorinated acid is treated to obtain fluoride products.

[0054] Furthermore, the leaching treatment time for the roasted ore is 1h to 6h; the mass ratio of roasted ore to leaching agent is 1:5 to 1:20.

[0055] Furthermore, the neutralization and impurity removal process employs at least one of magnesium hydroxide, magnesium carbonate, magnesium oxide, and magnesium bicarbonate.

[0056] In addition, the exhaust gas includes at least two of the following: SO2, SO3, water vapor, HF, and SiF4, with SO3 accounting for a significant portion of the total SO2 content. x If the proportion is less than 20%, the tail gas is absorbed and separated to obtain concentrated sulfuric acid and fluorine-containing acid. The concentrated sulfuric acid is returned to the sulfuric acid roasting process, and the fluorine-containing acid is treated to obtain fluoride products. At the same time, the rare earth sulfuric acid solution obtained from S3 is transformed and separated by P507 extraction to obtain a single rare earth chloride solution and a magnesium-containing solution. The magnesium-containing solution is recycled for leaching.

[0057] By performing a sulfation roasting process under a weak oxidizing atmosphere, the sulfide form in the tail gas is controlled to SO2 gas, thereby controlling the chemical composition of the tail gas to gases such as SO2 / HF / SiF4. After water spray absorption, the HF / SiF4 gas is converted into fluorinated acid, while the SO2 gas enters the subsequent treatment process to be converted into 98wt% concentrated sulfuric acid product. The sulfur element in the tail gas mainly exists in the form of SO2, making SO3 the main component of the total SO2 in the tail gas. x The proportion is less than 20%, preferably 10%.

[0058] The technical solution of the present invention will be further described below with reference to several embodiments:

[0059] Comparative Example 1

[0060] (1) The mineral-type rare earth ore was decomposed by sulfation roasting in air atmosphere to obtain roasted ore; the concentration of concentrated sulfuric acid used was 90wt%, the acid-ore ratio was 1.5, the roasting conditions were 350℃, and the roasting time was 4h; most of the rare earth elements in the mineral-type rare earth ore were converted into RE2(SO4)3 and RE2O3, of which Ce(IV) accounted for more than 3% of the total Ce.

[0061] (2) The obtained sulfated roasted ore under a weak oxidizing atmosphere was leached with water, filtered to obtain leachate and leaching residue. The roasted ore and water were leached together at a mass ratio of 1:10 for 1 hour. The leachate was neutralized and impurities removed, and solid-liquid separation was performed to obtain rare earth sulfate solution and neutralized residue. The rare earth yield was approximately 92%.

[0062] (3) The SO3 content in the mixed tail gas of the sulfation roasting process accounts for a significant portion of the total SO3 content. x The proportion of sulfuric acid is greater than 50%. The mixed tail gas is absorbed and post-treated to obtain 70wt% concentrated sulfuric acid and 98wt% concentrated sulfuric acid. The mass ratio of the two is about 1:1. The 90wt% sulfuric acid is prepared and recycled for the sulfation roasting process. Fluoride-containing acid is treated to obtain fluoride products.

[0063] Example 1

[0064] (1) The mineral-type rare earth ore is subjected to sulfation roasting decomposition in an atmosphere of at least one or more of the following gases: air and tail gas, N2, CO2 and CO, to obtain roasted ore; the concentration of concentrated sulfuric acid used is 85-98 wt%, the acid-to-ore ratio is 1.0-2.0 times, the roasting conditions are 200-450℃, and the roasting time is 2-12 h; all rare earth elements in the mineral-type rare earth ore are converted into easily leached phases RE2(SO4)3 and RE2O3, wherein Ce(IV) accounts for less than 3% of the total Ce.

[0065] (2) The obtained sulfation roasted ore under a weak oxidizing atmosphere is leached with water, a weak acid, or a magnesium-containing solution. The leaching solution and leaching residue are obtained by filtration. The roasted ore and leaching agent are leached at a mass ratio of 1:5 to 1:20 for 1 to 6 hours. The leaching solution is neutralized and impurities are removed, and solid-liquid separation is performed to obtain a rare earth sulfate solution and a neutralized and impurity-removed residue. The rare earth yield is greater than 95%.

[0066] (3) The sulfur in the mixed tail gas of the weak oxidizing atmosphere sulfation roasting process is converted into SO2, so that SO3 accounts for a larger proportion of the total SO in the tail gas. xThe proportion is less than 20%. The mixed tail gas is absorbed and post-treated to obtain 98wt% concentrated sulfuric acid, which is recycled in the sulfation roasting process. Fluorine-containing acid is treated to obtain fluoride products.

[0067] Other embodiments, comparative examples, and technical effects are detailed in Appendix 1.

[0068]

[0069]

[0070]

[0071]

[0072] The present invention aims to protect a method for sulfation roasting and decomposing mineral-type rare earth ore under a weak oxidizing atmosphere, comprising the following steps: S1: mixing mineral-type rare earth ore with concentrated sulfuric acid and sulfation roasting and decomposing it under a weak oxidizing atmosphere to obtain roasted ore and tail gas; S2: leaching the roasted ore obtained in S1 with water, weak acid or magnesium-containing solution as leaching agent, and filtering to obtain leaching solution and leaching residue.

[0073] S3: The leachate obtained in S2 is subjected to neutralization, impurity removal, and solid-liquid separation to obtain rare earth sulfate solution and neutralization residue. The above technical solution has the following effects:

[0074] 1. This invention involves sulfation roasting of mineral-type rare earth ores under a weak oxidizing atmosphere, which can effectively control the form of sulfur oxides in the exhaust gas and achieve efficient separation and resource recovery of fluorine and sulfur in the exhaust gas.

[0075] 2. This invention enables controllable sulfur oxide speciation in the tail gas of the sulfation roasting process, promoting the separation of fluorine and sulfur in the tail gas and their conversion into valuable by-products, while reducing tail gas treatment steps and lowering costs. Currently, conventional processes produce tail gas containing over 50% SO3. SO3 and HF / SiF4 are both readily soluble in water and difficult to separate. After water spray absorption, SO3 is converted into sulfuric acid and fluorinated acid. Further pressure filtration and reduced-pressure evaporation yield 70wt% concentrated sulfuric acid, and the gas phase is recovered by condensation to obtain fluorinated acid. SO2, however, has low solubility in water and is more easily separated from HF / SiF4 during water spray absorption. Therefore, this invention controls the sulfuric acid roasting process under a weak oxidizing atmosphere, suppressing SO3 gas generation and promoting SO2 gas generation, thus reducing the proportion of SO3 in the tail gas to a lower percentage of total SO2. x The proportion of SO2 is less than 20%. After water spray absorption, HF / SiF4 gas is converted into fluorinated acid, while SO2 gas is further catalytically oxidized into SO3 and then recycled to produce 98% concentrated sulfuric acid product. At the same time, the tail gas treatment process reduces the steps of pressure filtration and vacuum evaporation, thereby reducing the tail gas treatment cost.

[0076] 3. During the sulfation roasting process in a weakly oxidizing atmosphere, all rare earth elements in mineral-type rare earth ores are converted into easily leached RE2(SO4)3 and RE2O3, among which cerium is completely converted into Ce(SO4). x or CeO x (1.5≤x<2), to avoid the formation of stable phase CeO2 and improve rare earth leaching rate.

[0077] It should be understood that the specific embodiments described above are merely illustrative or explanatory of the principles of the invention and do not constitute a limitation thereof. Therefore, any modifications, equivalent substitutions, improvements, etc., made without departing from the spirit and scope of the invention should be included within the protection scope of the invention. Furthermore, the appended claims are intended to cover all variations and modifications falling within the scope and boundaries of the appended claims, or equivalent forms of such scope and boundaries.

Claims

1. A method for sulfation roasting and decomposing mineral-type rare earth ores in a weak oxidizing atmosphere, characterized in that, The following steps are involved: S1: Mix mineral-type rare earth ore with concentrated sulfuric acid and sulfatate roasting decomposition under a weak oxidizing atmosphere to obtain roasted ore and tail gas; S2: The roasted ore obtained in S1 is leached with water, weak acid or magnesium-containing solution as leaching agent, and filtered to obtain leaching solution and leaching residue. S3: The leachate obtained in S2 is subjected to neutralization and impurity removal, and solid-liquid separation to obtain rare earth sulfate solution and neutralization and impurity removal residue.

2. The method for sulfation roasting and decomposing mineral-type rare earth ores in a weak oxidizing atmosphere according to claim 1, characterized in that, The weakly oxidizing atmosphere includes: reducing gases and / or inert gases; The oxygen content is 0.1% to 15%, preferably 5% to 10%.

3. The method for sulfation roasting and decomposing mineral-type rare earth ores in a weak oxidizing atmosphere according to claim 1, characterized in that, The weakly oxidizing atmosphere includes air, and also includes at least one of the exhaust gas, N2, CO2 and CO.

4. The method for sulfation roasting and decomposition of mineral-type rare earth ores in a weak oxidizing atmosphere according to claim 1, characterized in that, The exhaust gas includes at least two of the following: SO2, SO3, water vapor, HF, and SiF4. SO3 accounts for a significant portion of the total SO2 content in the exhaust gas. x The proportion is less than 20%.

5. The method for sulfation roasting and decomposing mineral-type rare earth ores in a weak oxidizing atmosphere according to claim 4, characterized in that, The tail gas obtained from S1 is absorbed and separated to obtain concentrated sulfuric acid and fluorine-containing acid. The concentrated sulfuric acid is returned to the sulfuric acid roasting process in S1, and the fluorine-containing acid is precipitated to obtain fluoride products.

6. The method for sulfation roasting and decomposing mineral-type rare earth ores in a weak oxidizing atmosphere according to claim 1, characterized in that, The rare earth sulfate solution obtained from S3 was transformed and separated by P507 extraction to obtain a single rare earth chloride solution and a magnesium-containing solution. The magnesium-containing solution was then used for leaching the ore.

7. The method for sulfation roasting and decomposing mineral-type rare earth ores in a weak oxidizing atmosphere according to claim 1, characterized in that, The sulfation roasting temperature in S1 is 200℃~450℃, preferably 250℃~350℃; The roasting time is 2h to 12h, preferably 3h to 5h.

8. The method for sulfation roasting and decomposing mineral-type rare earth ores in a weak oxidizing atmosphere according to claim 7, characterized in that, The concentration of concentrated sulfuric acid used in the sulfation roasting in S1 is 85wt% to 98wt%, preferably 90wt% to 98wt%. The acid-to-ore mass ratio is 1.0 to 2.0, preferably 1.2 to 1.

5.

9. The method for sulfation roasting and decomposing mineral-type rare earth ores in a weak oxidizing atmosphere according to claim 1, characterized in that, The leaching time for roasted ore in S1 is 1h to 6h, preferably 2h to 4h; The mass ratio of roasted ore to leaching agent is 1:5 to 1:

20.

10. The method for sulfation roasting and decomposition of mineral-type rare earth ores in a weak oxidizing atmosphere according to any one of claims 1-9, characterized in that, The leachate in S3 is neutralized and purified using at least one of magnesium hydroxide, magnesium oxide, magnesium carbonate, and magnesium bicarbonate.

Images