Method for treating rare earth concentrate leaching waste water

Abstract

The application discloses a treatment method of rare earth concentrate mineralization and selection wastewater, and comprises the following steps: 1) adding an alkaline reagent I and a precipitant I into the rare earth concentrate mineralization and selection wastewater to obtain lead slag and lead-removed supernatant; 2) adding a calcium agent, an alkaline reagent II and a flocculant into the lead-removed supernatant to obtain fluorine slag and fluorine-removed supernatant; 3) electrolyzing the fluorine-removed supernatant to obtain iron slag and iron-removed supernatant; 4) adding a phosphate and a precipitant II into the iron-removed supernatant to obtain rare earth element phosphate precipitate and rare earth-removed supernatant; and 5) evaporating and concentrating the rare earth-removed supernatant to obtain evaporation and concentration liquid, cooling the evaporation and concentration liquid, and performing solid-liquid separation to obtain CaCl2.2H2O crystal and mother liquor. The application can sequentially and directionally separate and recover lead elements, fluorine elements, iron elements, rare earth elements and calcium elements in the rare earth concentrate mineralization and selection wastewater, and avoids cross interference among the elements.

Description

Technical Field

[0001] This invention relates to a method for treating wastewater from rare earth concentrate beneficiation. Background Technology

[0002] When performing atmospheric pressure concentrated alkali decomposition on Bayan Obo mixed rare earth concentrate, chemical beneficiation is typically used to remove impurities such as calcium and iron, reducing rare earth loss. This method involves pretreating the rare earth concentrate with hydrochloric acid and sodium sulfate at a slight boiling state for 4–6 hours, generating a large amount of chemical beneficiation wastewater. The main component of this wastewater is calcium chloride, and it also contains impurities such as rare earth elements, iron, lead, fluorine, and phosphorus, classifying it as high-salt, high-calcium wastewater. In this technical field, the wastewater is typically neutralized to recover some rare earth elements before discharge.

[0003] The main treatment methods for chemical separation wastewater include chemical methods and ion exchange methods. Ion exchange can effectively separate calcium ions, but the resin regeneration process requires the use of regeneration agents, which can cause secondary pollution. Therefore, compared to ion exchange, chemical methods are more commonly used to treat chemical separation wastewater. Chemical methods involve adding certain chemical agents to the wastewater in stages to convert impurity ions into sparingly soluble salts for precipitation or flocculation, thereby removing them.

[0004] CN105668888A discloses a method for the comprehensive recovery of low-grade rare earth concentrate chemical beneficiation and chemical beneficiation wastewater. The method includes: (1) mixing low-grade mixed rare earth concentrate, hydrochloric acid solution and enhanced impurity removal agent in proportion, stirring and dissolving under heating conditions of 90-100℃, and filtering to obtain chemical beneficiation concentrate and chemical beneficiation wastewater with 62%≤REO mass percentage ≤70% and 0.5%≤Ca mass percentage ≤2.5%. (2) adding excess sulfuric acid solution to the chemical beneficiation wastewater to remove calcium ions, and the concentration of hydrogen ions in the mixed solution after adding sulfuric acid is ≥2.5mol / L, producing calcium sulfate dihydrate by-product, and the mass volume concentration of CaO in the chemical beneficiation wastewater after calcium removal is ≤5g / L. (3) The chemical beneficiation wastewater after calcium removal is reused in step (1) to recycle a new batch of low-grade mixed rare earth concentrate. The number of cycles is limited to the CaO mass percentage content in the last calcium-removed concentrate being ≤2.5%. According to the actual low-grade mixed rare earth concentrate, the number of cycles is ≤6 times. (4) After calcium removal from the recycled chemical beneficiation wastewater, the relative concentrations of phosphorus, iron, and rare earth are adjusted with iron salts so that the sum of the molar concentrations of rare earth and iron is 1.0 to 1.5:1.0 with the molar concentration of phosphorus. The pH value is adjusted to 1.0 to 1.5 with ammonia or liquid ammonia. RE, P, and Fe are preferentially co-precipitated. The co-precipitate is combined with the chemical beneficiation concentrate for mineral decomposition, and the three valuable resources of RE, P, and Fe are comprehensively recovered. The solution after removing RE, P, and Fe is further adjusted to pH value of 3.5 to 4.5 with ammonia or liquid ammonia so that the remaining F and Ca in the solution co-precipitate to form crude fluorite product. The neutralized wastewater is concentrated by evaporation to form ammonium chloride crystals and distilled water. This method has significant advantages in comprehensive resource recovery and acid / alkali consumption, but it does not consider the recovery of heavy metal lead, allowing lead ions to migrate throughout the wastewater treatment process and posing a risk of heavy metal pollution. Furthermore, this method generates calcium dihydrate and calcium fluoride, resulting in low economic value.

[0005] CN111018184A discloses a process for treating rare earth wastewater. This method involves acidifying the rare earth wastewater, adding an ammonia nitrogen removal agent and sodium hypochlorite for catalytic oxidation, then adding calcium oxide, controlling the pH value to around 9, and the reaction time to 90–120 minutes. This method can effectively remove COD, ammonia nitrogen, and heavy metal ions from wastewater generated during rare earth extraction, with a high ammonia nitrogen reduction rate. However, the ammonia nitrogen removal agent used in this method is composed of aluminum sulfate, polyvinyl alcohol (PVA1), ferrous sulfate, chelating agent, sodium sulfate, polyepoxysuccinic acid, long-flame activated carbon, and deionized water, resulting in a complex composition, high cost, and potential for introducing new impurities. Furthermore, this method does not achieve the resource utilization of calcium.

[0006] CN119430258A discloses a method for recovering calcium fluoride and rare earths from chemical beneficiation wastewater in rare earth smelting. The method includes: (1) adding alkaline washing water dropwise to the chemical beneficiation wastewater under stirring until the pH is 1.5-4.5, maintaining stirring and aging for 30-60 minutes, performing solid-liquid separation, the obtained liquid is the defluorinated rare earth supernatant, the obtained solid filter cake is washed and dried to obtain calcium fluoride by-product. (2) adding an extractant to the defluorinated rare earth supernatant under stirring, separating the organic phase after separation to obtain a saturated organic phase. (3) adding hydrochloric acid to the saturated organic phase, back-extracting and stirring to separate the aqueous phase and organic phase, continuing to add water to the organic phase for washing, continuing to separate the aqueous phase and organic phase, enriching the organic phase, mixing the aqueous phase, and detecting that the acidity of the mixed aqueous phase is 0.5-1.0 mol / L to obtain rare earth chloride feed solution. (4) Under stirring, carbonate is added to the rare earth chloride solution to adjust the pH to 2.5-3, and solid-liquid separation is performed to obtain solid iron slag and purified rare earth chloride solution. This method treats chemical beneficiation wastewater through a process of preferential fluoride removal and rare earth extraction, achieving the recovery of rare earth and calcium fluoride. However, lead, phosphorus, and iron in the chemical beneficiation wastewater are enriched in calcium fluoride, and the effective separation of elements is not achieved, which limits the secondary utilization of each element. Summary of the Invention

[0007] In view of this, the purpose of the present invention is to provide a method for treating rare earth concentrate beneficiation wastewater, which can sequentially and directionally separate and recover lead, fluorine, iron, rare earth elements and calcium in rare earth concentrate beneficiation wastewater, avoiding cross-interference between elements.

[0008] The present invention achieves the above objectives using the following technical solutions.

[0009] The method for treating rare earth concentrate beneficiation wastewater provided by this invention includes the following steps:

[0010] 1) Add alkaline reagent I to the rare earth concentrate beneficiation wastewater and stir until the pH value of the wastewater reaches 1.5-4; then, add precipitant I to the rare earth concentrate beneficiation wastewater to carry out a precipitation reaction to obtain reaction product I; separate the solid and liquid of reaction product I to obtain lead slag and lead-removed supernatant; wherein, alkaline reagent I is selected from at least one of calcium oxide, calcium hydroxide, and lime milk; the precipitant I is selected from at least one of alkali metal sulfide salts and ammonium sulfide; the molar ratio of the precipitant I to the lead ions in the rare earth concentrate beneficiation wastewater is 1-3:1;

[0011] 2) Add calcium agent to the lead removal supernatant, adjust the pH of the lead removal supernatant to 4-6.5 with alkaline agent II, then add flocculant to a concentration of 0.2-2 mg / L, and react under stirring conditions at 25-95℃ to obtain reaction product II; separate reaction product II into solid and liquid components to obtain fluoride slag and defluorination supernatant; wherein, the calcium agent is selected from at least one of calcium salt, calcium oxide, and calcium hydroxide; the molar ratio of the calcium agent to fluoride ions in the rare earth concentrate beneficiation wastewater is 0.2-0.5:1; the alkaline agent II is selected from at least one of calcium oxide, calcium hydroxide, and lime milk; the flocculant is selected from at least one of PAM and PAC;

[0012] 3) Set the defluoridation supernatant at 10–30 mA / cm². 2 Electrolysis was carried out at a current density, and the mixture was allowed to stand to obtain reaction product III. The reaction product III was then separated into solid and liquid components to obtain iron slag and iron-removed supernatant.

[0013] 4) Add phosphate to the iron removal supernatant, then add precipitant II until the pH of the iron removal supernatant is 4-5, and react at 40-80℃ to obtain reaction product IV; separate reaction product IV into solid and liquid components to obtain rare earth element phosphate precipitate and rare earth removal supernatant; wherein, the phosphate is selected from at least one of ammonium phosphate and alkali metal phosphate; the molar ratio of phosphate ion to rare earth element in rare earth concentrate beneficiation wastewater is 1-2:1; the precipitant II is selected from at least one of ammonia water and alkali metal hydroxide;

[0014] 5) The supernatant containing rare earth elements is evaporated and concentrated until the calcium chloride concentration is 40-60 wt% to obtain the concentrated evaporated liquid;

[0015] The concentrated evaporation solution was cooled at 10–50 °C and the solid and liquid were separated to obtain CaCl2·2H2O crystals and mother liquor.

[0016] According to the processing method of the present invention, preferably, in step 1), the mass concentration of calcium hydroxide in the lime milk is 10-30 wt%; the alkali metal sulfide salt is sodium sulfide.

[0017] According to the processing method of the present invention, preferably, in step 1), the precipitation reaction time is 20 to 60 minutes.

[0018] According to the processing method of the present invention, preferably, in step 1), stirring is performed during the precipitation reaction.

[0019] According to the processing method of the present invention, preferably, in step 2), the calcium salt is selected from at least one of calcium chloride and calcium sulfate; the mass concentration of calcium hydroxide in the lime milk is 10-30 wt%.

[0020] According to the processing method of the present invention, preferably, in step 2), the reaction time is 0.5 to 5 hours.

[0021] According to the processing method of the present invention, preferably, in step 3), the electrolysis time is 20 to 60 minutes.

[0022] According to the processing method of the present invention, preferably, in step 3), the settling time is 5 to 40 minutes.

[0023] According to the processing method of the present invention, preferably, in step 4), the reaction time is 1 to 5 hours.

[0024] According to the processing method of the present invention, preferably, in step 5), the evaporation and concentration is a triple-effect evaporation and concentration; the mother liquor is returned to step 2) as a calcium agent.

[0025] This invention enables the stepwise and targeted separation and recovery of lead, fluorine, iron, rare earth elements, and calcium from rare earth mineralization wastewater, avoiding cross-interference between elements. This invention uses a sulfur-containing precipitant to precipitate lead under low pH conditions, preventing co-precipitation of iron and rare earth elements. This invention uses electrolytic precipitation of iron, utilizing the self-dissolution of Fe at the iron anode. 2+ It replaces added iron salts, reducing the introduction of impurities. Attached Figure Description

[0026] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0027] 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.

[0028] In this invention, "REO" refers to rare earth oxides.

[0029] <Treatment Methods for Wastewater from Rare Earth Concentrate Processing>

[0030] The method for treating rare earth concentrate beneficiation wastewater of the present invention includes a pre-neutralization and lead removal step, a neutralization and fluoride removal step, an electrocoagulation and iron removal step, a phosphate extraction of rare earth steps, and a calcium chloride concentration and crystallization step. These are described in detail below.

[0031] Pre-neutralization and lead removal steps

[0032] Alkaline reagent I was added to the rare earth concentrate beneficiation wastewater and stirred until the pH value of the rare earth concentrate beneficiation wastewater reached 1.5-4; then, precipitant I was added to the rare earth concentrate beneficiation wastewater to carry out a precipitation reaction, and reaction product I was obtained; reaction product I was separated into solid and liquid to obtain lead slag and lead removal supernatant.

[0033] This invention is applicable to the chemical beneficiation wastewater of all types of rare earth concentrates, preferably the chemical beneficiation wastewater of Bayan Obo rare earth concentrate, and more preferably the chemical beneficiation wastewater of rare earth concentrates with the following concentrations of main components:

[0034] Acidity 0.2–2 mol / L, REO 0.1–4 g / L, Ca 25–90 g / L, Pb 0.5–8 g / L, Fe 1–8 g / L, P 5–16 g / L, F 1–8 g / L and Cl 20–120 g / L.

[0035] The acidity of the rare earth concentrate beneficiation wastewater of this invention can be 0.2–2 mol / L, preferably 0.3–1.8 mol / L, more preferably 0.5–1.5 mol / L. The concentration of RE can be 0.1–4 g / L, preferably 0.2–3 g / L, more preferably 0.3–2 g / L. The concentration of Ca can be 25–90 g / L, preferably 28–85 g / L, more preferably 30–80 g / L. The concentration of Pb can be 0.5–8 g / L, preferably 1–7 g / L, more preferably 2–6 g / L. The concentration of Fe can be 1–8 g / L, preferably 2–7 g / L, more preferably 3–5 g / L. The concentration of P can be 5–16 g / L, preferably 7–15 g / L, more preferably 9–14 g / L. The concentration of F can be 1–8 g / L, preferably 1.5–7 g / L, more preferably 2–6 g / L. The concentration of Cl can be 20–120 g / L, preferably 22–115 g / L, and more preferably 24–110 g / L.

[0036] According to one embodiment of the present invention, the alkaline agent I may be selected from at least one of calcium oxide, calcium hydroxide, and lime milk, preferably at least one of calcium oxide and lime milk, more preferably calcium oxide or lime milk. The mass concentration of calcium hydroxide in the lime milk may be 10-30 wt%, preferably 13-28 wt%, more preferably 15-26 wt%.

[0037] According to one embodiment of the present invention, the precipitant I can be selected from at least one of alkali metal sulfide salts and ammonium sulfide, preferably at least one of alkali metal sulfide salts, and more preferably sodium sulfide. In the present invention, the precipitant I can be a salt containing water of crystallization or an anhydrous salt, as long as it can precipitate lead ions, and no particular limitation is made here.

[0038] According to one embodiment of the present invention, the molar ratio of precipitant I to lead ions in rare earth concentrate beneficiation wastewater can be 1 to 3:1, preferably 1.1 to 2.8:1, and more preferably 1.2 to 2.5:1.

[0039] According to one embodiment of the present invention, after adding alkaline agent I, the pH value of the rare earth concentrate beneficiation wastewater can be 1.5 to 4, preferably 1.8 to 3.5, and more preferably 2 to 3.

[0040] A reasonable combination of alkaline reagent I and precipitant I, along with their dosages, can ensure effective precipitation and separation of lead at a lower pH level, while avoiding the co-precipitation of iron and rare earth elements.

[0041] According to one embodiment of the present invention, the precipitation reaction time can be 20 to 60 min, preferably 25 to 55 min, and more preferably 28 to 45 min.

[0042] According to a preferred embodiment of the present invention, after the pH value of the rare earth concentrate beneficiation wastewater reaches 1.5-4, stirring can continue for a certain period of time before adding precipitant I. The stirring time can be 10-60 min, preferably 15-50 min, and more preferably 20-45 min.

[0043] In this invention, stirring can continue during the precipitation reaction.

[0044] In this invention, the stirring speed can be 200-400 rpm, preferably 220-380 rpm, and more preferably 250-350 rpm.

[0045] Reasonable reaction conditions can ensure effective precipitation and separation of lead at a low pH value, while avoiding the co-precipitation of iron and rare earth elements.

[0046] In this invention, the main component of lead slag is lead concentrate (lead sulfide).

[0047] The solid-liquid separation involved in this invention can be achieved by any filtration method or filtration equipment known in the art, and will not be elaborated here. For example, it can be pressure filtration or centrifugal separation. The centrifugal separation speed can be 2000-5000 rpm, preferably 2500-4500 rpm, and more preferably 2700-4000 rpm.

[0048] The water involved in this invention can be any type of water known in the art for the leaching and separation of rare earth elements, which will not be elaborated here.

[0049] Neutralization and defluorination steps

[0050] Calcium agent is added to the lead removal supernatant, and the pH of the lead removal supernatant is adjusted to 4-6.5 with alkaline agent II. Then, flocculant is added to a concentration of 0.2-2 mg / L, and the reaction is carried out at 25-95℃ with stirring to obtain reaction product II. The reaction product II is separated into solid and liquid to obtain fluoride residue and fluoride removal supernatant.

[0051] According to one embodiment of the present invention, the calcium agent may be selected from at least one of calcium salts, calcium oxide, and calcium hydroxide, preferably calcium salts or calcium oxide, and more preferably calcium salts. The calcium salt may be selected from at least one of calcium chloride and calcium sulfate, preferably calcium chloride or calcium sulfate, and more preferably calcium chloride.

[0052] According to one embodiment of the present invention, the molar ratio of calcium agent to fluoride ions in rare earth concentrate beneficiation wastewater can be 0.2 to 0.5:1, preferably 0.25 to 0.45:1, and more preferably 0.3 to 0.4:1.

[0053] According to one embodiment of the present invention, alkaline agent II may be selected from at least one of calcium oxide, calcium hydroxide, and lime milk, preferably at least one of calcium hydroxide and lime milk, more preferably calcium hydroxide or lime milk. The mass concentration of calcium hydroxide in the lime milk may be 10-30 wt%, preferably 13-28 wt%, more preferably 15-26 wt%.

[0054] According to one embodiment of the present invention, the pH value of the lead-removing supernatant can be adjusted to 4 to 6.5, preferably 4.2 to 6.3, and more preferably 4 to 6.

[0055] According to one embodiment of the invention, the flocculant may be selected from at least one of PAM (polyacrylamide) and PAC (polyaluminum chloride), preferably PAM or PAC, more preferably PAM. The flocculant may be added to a concentration of 0.2 to 2 mg / L, preferably 0.5 to 1.8 mg / L, more preferably 0.8 to 1.5 mg / L.

[0056] Reasonable dosages of calcium agent, alkaline agent II, and flocculant can ensure effective precipitation and separation of fluorine, while also helping to avoid co-precipitation of other elements.

[0057] According to one embodiment of the present invention, the reaction temperature can be 25–95°C, preferably 45–90°C, more preferably 60–80°C. The reaction time can be 0.5–5 h, preferably 0.8–4 h, more preferably 1–3 h.

[0058] In this invention, the stirring speed can be 200-400 rpm, preferably 220-380 rpm, and more preferably 250-350 rpm.

[0059] Reasonable reaction conditions can ensure the effective precipitation and separation of fluorine, while also helping to avoid the co-precipitation of other elements.

[0060] In this invention, the main component of the fluorine slag is calcium fluoride.

[0061] Electrocoagulation iron removal steps

[0062] The defluoridation supernatant was kept at 10–30 mA / cm 2 Electrolysis was carried out at a current density, and the mixture was allowed to stand to obtain reaction product III. The reaction product III was then separated into solid and liquid components to obtain iron slag and iron-removed supernatant.

[0063] According to one embodiment of the present invention, the current density for electrolysis can be 10–30 mA / cm². 2 Preferably 12–28 mA / cm 2 More preferably 15–25 mA / cm 2 The electrolysis time can be 20–60 min, preferably 25–55 min, and more preferably 30–50 min.

[0064] According to one embodiment of the present invention, the settling time can be 5 to 40 minutes, preferably 8 to 37 minutes, and more preferably 10 to 35 minutes.

[0065] The electrolysis of the present invention can be carried out in an electrocoagulation reactor, which can be any type of electrocoagulation reactor known in the art, and will not be described in detail here. According to a preferred embodiment of the present invention, the anode of the electrocoagulation reactor is iron, and the cathode is graphite.

[0066] In this invention, reaction product III is Fe(OH)3 flocculents, and the main component of the iron slag is Fe(OH)3. The iron slag can be calcined to generate Fe2O3.

[0067] Limiting the electrolysis conditions to the above range can ensure effective precipitation and separation of iron, while also helping to prevent other elements and impurities from entering the precipitate.

[0068] Phosphate extraction steps for rare earth elements

[0069] Phosphate was added to the iron removal supernatant, followed by the addition of precipitant II until the pH of the iron removal supernatant was 3-5. The reaction was carried out at 40-80℃ to obtain reaction product IV. The reaction product IV was separated into solid and liquid components to obtain rare earth element phosphate precipitate and rare earth removal supernatant.

[0070] According to one embodiment of the present invention, the phosphate may be selected from at least one of ammonium phosphate and alkali metal phosphate, preferably at least one of ammonium phosphate and sodium phosphate, and more preferably ammonium phosphate or sodium phosphate.

[0071] According to one embodiment of the present invention, the molar ratio of phosphate ions in phosphate to rare earth elements in rare earth concentrate beneficiation wastewater can be 1 to 2:1, preferably 1 to 1.5:1, and more preferably 1 to 1.3:1.

[0072] According to one embodiment of the present invention, the precipitant II may be selected from at least one of ammonia water and alkali metal hydroxide, preferably at least one of ammonia water and sodium hydroxide, and more preferably ammonia water or sodium hydroxide.

[0073] According to one embodiment of the present invention, after adding precipitant II, the pH value of the iron removal supernatant can be 3 to 5, preferably 3.2 to 4.8, and more preferably 3.5 to 4.5.

[0074] A reasonable amount of phosphate and precipitant II can ensure the effective precipitation and separation of rare earth elements, improve the purity of rare earth element phosphates, and help avoid co-precipitation of other elements.

[0075] According to one embodiment of the present invention, the reaction temperature can be 40–80°C, preferably 45–75°C, more preferably 50–70°C. The reaction time can be 1–5 h, preferably 1.5–4.5 h, more preferably 1.5–4 h.

[0076] According to a preferred embodiment of the present invention, stirring can also be performed during the reaction process. The stirring speed can be 200-400 rpm, preferably 220-380 rpm, and more preferably 250-350 rpm.

[0077] Reasonable reaction conditions can ensure the effective precipitation and separation of rare earth elements, improve the purity of rare earth element phosphates, and help avoid the co-precipitation of other elements.

[0078] In this invention, rare earth element phosphates can be used in the alkaline decomposition process of rare earth concentrates under normal pressure to achieve the recycling of rare earth elements.

[0079] Calcium chloride concentration and crystallization steps

[0080] The supernatant, after removing rare earth elements, is evaporated and concentrated to a calcium chloride concentration of 40–60 wt% to obtain an evaporated concentrate. The evaporated concentrate is then cooled at 10–50 °C and subjected to solid-liquid separation to obtain CaCl2·2H2O crystals and mother liquor.

[0081] According to one embodiment of the present invention, evaporation concentration can be triple-effect evaporation concentration. Triple-effect evaporation concentration can be implemented in any type of triple-effect evaporator known in the art, and will not be described in detail here.

[0082] In this invention, after evaporation and concentration, the mass concentration of calcium chloride can be 40-60 wt%, preferably 42-58 wt%, and more preferably 45-55 wt%.

[0083] According to one embodiment of the present invention, the cooling temperature can be 10–50°C, preferably 15–40°C, and more preferably 18–30°C. The cooling time can be 0.2–5 h, preferably 0.3–4 h, and more preferably 0.5–3 h.

[0084] Reasonable concentration evaporation and cooling conditions are beneficial to improving the recovery rate of calcium chloride and increasing the purity of the obtained CaCl2·2H2O crystals.

[0085] According to one embodiment of the present invention, the mother liquor can be returned to the neutralization and defluorination step for use as a calcium agent, thereby achieving recycling.

[0086] In this invention, the condensate generated during the evaporation and concentration process can be used to prepare acid solutions in the rare earth concentrate beneficiation and calcium removal process, thereby realizing wastewater utilization and reducing energy consumption.

[0087] <Testing Method>

[0088] REO content was determined by inductively coupled plasma atomic emission spectrometry (ICP-AES).

[0089] Calculation of REO moles: Calculated using equation (1):

[0090] REO molar concentration = REO mass concentration / M (1)

[0091] In the formula, the REO mass concentration is the content of REO, and the unit is g / L; M is the molar mass of the mixed rare earth oxides, specifically 169 g / mol.

[0092] The P content was determined by inductively coupled plasma atomic emission spectrometry (ICP-AES).

[0093] The F content was determined using the fluoride ion selective electrode method.

[0094] The Ca content was determined by inductively coupled plasma atomic emission spectrometry (ICP-AES).

[0095] <Ingredient Description>

[0096] Unless otherwise specified, all raw materials used in the following examples are commercially available products.

[0097] The electrocoagulation reactor is the PREDEST-20 type electrocoagulation reactor manufactured by Asia Environmental Technology (Shanghai) Co., Ltd.

[0098] The triple-effect evaporator is a 100L triple-effect forced circulation wastewater crystallization evaporator manufactured by Liangshan Tairui Chemical Equipment Trading Co., Ltd.

[0099] Example 1

[0100] The concentrations of the main components in the rare earth concentrate beneficiation wastewater used in this embodiment are as follows:

[0101] Acidity 0.68 mol / L, REO 0.325 g / L, Ca 57.23 g / L, Pb 2.54 g / L, Fe 3.87 g / L, P 9.34 g / L, F 2.01 g / L, Cl 94.70 g / L.

[0102] The treatment steps for rare earth concentrate beneficiation wastewater are as follows:

[0103] (1) Pre-neutralization and lead removal: Under stirring at 250 rpm, lime slurry with a Ca(OH)2 mass concentration of 20 wt% was added to 1000 mL of rare earth concentrate beneficiation wastewater, and stirred until the pH of the rare earth concentrate beneficiation wastewater was 2, and stirring was continued for 30 min. Then, 3.55 g of Na2S·9H2O (the molar ratio of Na2S to lead ions in the rare earth concentrate beneficiation wastewater was 1.2:1) was added to the rare earth concentrate beneficiation wastewater to carry out a precipitation reaction for 30 min, and reaction product I was obtained. Reaction product I was separated by pressure filtration to obtain lead slag and lead removal supernatant. In the lead removal supernatant, Pb 2+ The concentration was 0.08 mg / L.

[0104] (2) Neutralization and defluorination: 4.67 g of calcium chloride was added to the lead removal supernatant (the molar ratio of calcium chloride to fluoride ions in the rare earth concentrate wastewater was 0.38:1). The pH of the lead removal supernatant was adjusted to 6 with calcium hydroxide, and PAM was added to a concentration of 1.0 mg / L. The mixture was then reacted at 70 °C and 250 rpm for 1 h to obtain reaction product II. Reaction product II was centrifuged at 3000 rpm to obtain fluoride residue and defluorination supernatant. The main component of the fluoride residue was CaF2, with a purity of 90 wt%. In the defluorination supernatant, F... - The concentration is 5 mg / L.

[0105] (3) Electrocoagulation for iron removal: The supernatant from the defluorination process is added to the electrocoagulation reactor at 15 mA / cm 2 Electrolysis was performed at a current density of 30 min, followed by standing for 10 min to obtain reaction product III. Reaction product III was then centrifuged at 3000 rpm to obtain iron slag and iron-removed supernatant. The iron slag was calcined to produce Fe2O3 with a purity of 95 wt%.

[0106] (4) Phosphate extraction of rare earth elements: Add 0.34 g of ammonium phosphate to the iron-removing supernatant (PO4). 3-The molar ratio of rare earth elements in the wastewater from rare earth mineralization was 1.2:1. NH3·H2O was then added until the pH of the iron-removed supernatant reached 4.2. The mixture was then stirred at 50°C and 250 rpm for 2 hours to obtain reaction product IV. Reaction product IV was then centrifuged at 3000 rpm to obtain a phosphate precipitate of the rare earth elements (REPO4 precipitate) and the rare earth-removed supernatant.

[0107] (5) Calcium chloride concentration and crystallization: The supernatant after rare earth removal was placed in a triple-effect evaporator and concentrated until the CaCl2 mass concentration in the supernatant was 45wt%, yielding a concentrated evaporator. The concentrated evaporator was cooled at 25℃ for 3 hours to precipitate crystals, which were then centrifuged at 3000 rpm to obtain CaCl2·2H2O crystals and mother liquor. The condensate generated during the triple-effect evaporation and concentration process was used to prepare the acid solution in the rare earth concentrate beneficiation and calcium removal process, with a condensate reuse rate of 92%.

[0108] Example 2

[0109] The concentrations of the main components in the rare earth concentrate beneficiation wastewater used in this embodiment are as follows:

[0110] Acidity 1.28mol / L, REO 1.25g / L, Ca 30.44g / L, Pb 1.13g / L, Fe 4.29g / L, P13.57g / L, F 3.4g / L, Cl 24.27g / L.

[0111] The treatment steps for rare earth concentrate beneficiation wastewater are as follows:

[0112] (1) Pre-neutralization and lead removal: Under stirring at 250 rpm, lime slurry with a Ca(OH)2 mass concentration of 20 wt% was added to 1000 mL of rare earth concentrate beneficiation wastewater, and stirred until the pH of the rare earth concentrate beneficiation wastewater was 2, and stirring was continued for 30 min. Then, 1.58 g of Na2S·H2O (the molar ratio of Na2S to lead ions in the rare earth concentrate beneficiation wastewater was 1.25:1) was added to the rare earth concentrate beneficiation wastewater to carry out a precipitation reaction for 30 min, and reaction product I was obtained. Reaction product I was separated by pressure filtration to obtain lead slag and lead removal supernatant. In the lead removal supernatant, Pb 2+ The concentration was 0.046 mg / L.

[0113] (2) Neutralization and defluorination: 6.94 g of calcium chloride was added to the lead removal supernatant (the molar ratio of calcium chloride to fluoride ions in the rare earth concentrate wastewater was 0.35:1). The pH of the lead removal supernatant was adjusted to 4.5 with calcium hydroxide, and PAM was added to a concentration of 1.1 mg / L. The mixture was then reacted at 70 °C and 250 rpm for 1 h to obtain reaction product II. Reaction product II was centrifuged at 3000 rpm to obtain fluoride residue and defluorination supernatant. The main component of the fluoride residue was CaF2, with a purity of 91 wt%. In the defluorination supernatant, F... - The concentration was 7.2 mg / L.

[0114] (3) Electrocoagulation for iron removal: The supernatant from the defluorination process is added to the electrocoagulation reactor at 15 mA / cm 2 Electrolysis was performed at a certain current density for 40 min, followed by standing for 30 min to obtain reaction product III. Reaction product III was then centrifuged at 3000 rpm to obtain iron slag and a supernatant after iron removal. The iron slag was calcined to produce Fe2O3 with a purity of 95.7 wt%.

[0115] (4) Extraction of rare earth elements by phosphate method: Add 1.21g of ammonium phosphate to the iron-removing supernatant (PO4). 3- The molar ratio of rare earth elements in the wastewater from rare earth concentrate beneficiation was 1.1:1. NH3·H2O was then added until the pH of the iron-removed supernatant reached 4.2. The mixture was then stirred at 50°C and 250 rpm for 2 hours to obtain reaction product IV. Reaction product IV was then centrifuged at 3000 rpm to obtain a phosphate precipitate of rare earth elements (REPO4 precipitate) and a rare earth-removed supernatant.

[0116] (5) Calcium chloride concentration and crystallization: The supernatant from rare earth removal was placed in a triple-effect evaporator and concentrated until the CaCl2 mass concentration in the supernatant was 50 wt%, yielding a concentrated evaporator. The concentrated evaporator was cooled at 25°C for 30 min to precipitate crystals, which were then centrifuged at 3000 rpm to obtain CaCl2·2H2O crystals and mother liquor. The condensate generated during the triple-effect evaporation and concentration process was used to prepare the acid solution in the rare earth concentrate beneficiation and calcium removal process, with a condensate reuse rate of 94%.

[0117] Example 3

[0118] The concentrations of the main components in the rare earth concentrate beneficiation wastewater used in this embodiment are as follows:

[0119] Acidity 1.5mol / L, REO 4g / L, Ca 80g / L, Pb 5g / L, Fe 5g / L, P 14g / L, F 5g / L, Cl100g / L.

[0120] The treatment steps for rare earth concentrate beneficiation wastewater are as follows:

[0121] (1) Pre-neutralization and lead removal: Under stirring at 300 rpm, lime slurry with a Ca(OH)2 mass concentration of 20 wt% was added to 1000 mL of rare earth concentrate beneficiation wastewater, and stirred until the pH of the rare earth concentrate beneficiation wastewater was 2.5, and stirring was continued for 30 min. Then, 12.5 g of Na2S·9H2O (the molar ratio of Na2S to lead ions in the rare earth concentrate beneficiation wastewater was 2.17:1) was added to the rare earth concentrate beneficiation wastewater to carry out a precipitation reaction for 40 min, and reaction product I was obtained. Reaction product I was separated by pressure filtration to obtain lead slag and lead removal supernatant. In the lead removal supernatant, Pb 2+ The concentration was 0.05 mg / L.

[0122] (2) Neutralization and defluorination: The mother liquor obtained from the concentration and crystallization of calcium chloride and solid calcium chloride (calculated calcium chloride content of 10.22g) were mixed and added to the lead removal supernatant (the molar ratio of calcium chloride to fluoride ions in the rare earth concentrate wastewater was 0.35:1). The pH of the lead removal supernatant was adjusted to 6.2 with calcium hydroxide, and PAM was added to a concentration of 1.2mg / L. The reaction was then carried out at 75℃ and 250rpm for 1h with stirring to obtain reaction product II. Reaction product II was centrifuged at 3000rpm to obtain fluoride residue and defluorination supernatant. The main component of the fluoride residue was CaF2, and the purity of CaF2 was 92.3wt%. In the defluorination supernatant, F - The concentration was 8.0 mg / L.

[0123] (3) Electrocoagulation for iron removal: The supernatant from the defluorination process is added to the electrocoagulation reactor at 25 mA / cm 2 Electrolysis was performed at a current density of 50 min, followed by standing for 10 min to obtain reaction product III. Reaction product III was then centrifuged at 3000 rpm to obtain iron slag and a supernatant after iron removal. The iron slag was calcined to produce Fe2O3 with a purity of 95 wt%.

[0124] (4) Phosphate extraction of rare earth elements: Add 4.0 g of ammonium phosphate to the iron-removing supernatant (PO4). 3-The molar ratio of rare earth elements in the wastewater from rare earth concentrate beneficiation was 1.13:1. NH3·H2O was then added until the pH of the iron-removed supernatant reached 4.5. The mixture was then stirred at 60°C and 250 rpm for 2 hours to obtain reaction product IV. Reaction product IV was then centrifuged at 3000 rpm to obtain a phosphate precipitate of rare earth elements (REPO4 precipitate) and a rare earth-removed supernatant.

[0125] (5) Calcium chloride concentration and crystallization: The supernatant after rare earth removal was placed in a triple-effect evaporator and concentrated until the CaCl2 mass concentration in the supernatant was 50wt%, yielding a concentrated evaporator. The concentrated evaporator was cooled at 20℃ for 2 hours to precipitate crystals, which were then centrifuged at 3000 rpm to obtain CaCl2·2H2O crystals and mother liquor. The condensate generated during the triple-effect evaporation and concentration process was used to prepare the acid solution in the rare earth concentrate beneficiation and calcium removal process, with a condensate reuse rate of 92%.

[0126] 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 treating wastewater from rare earth concentrate beneficiation, characterized in that, Includes the following steps: 1) Add alkaline reagent I to the rare earth concentrate beneficiation wastewater and stir until the pH value of the wastewater reaches 2-3; then, add precipitant I to the rare earth concentrate beneficiation wastewater and carry out a precipitation reaction for 20-60 minutes to obtain reaction product I; separate the solid and liquid of reaction product I to obtain lead slag and lead-removed supernatant; wherein, alkaline reagent I is selected from at least one of calcium oxide, calcium hydroxide, and lime milk; the precipitant I is selected from at least one of alkali metal sulfide salts and ammonium sulfide; the molar ratio of the precipitant I to the lead ions in the rare earth concentrate beneficiation wastewater is 1.2-2.5:1; 2) Add calcium agent to the lead removal supernatant, adjust the pH of the lead removal supernatant to 4-6 with alkaline agent II, then add flocculant to a concentration of 0.8-1.5 mg / L, and react at 60-80℃ with stirring for 1-3 hours to obtain reaction product II; separate reaction product II into solid and liquid components to obtain fluoride slag and defluorination supernatant; wherein, the calcium agent is selected from at least one of calcium salt, calcium oxide, and calcium hydroxide; the molar ratio of the calcium agent to fluoride ions in the rare earth concentrate beneficiation wastewater is 0.3-0.4:1; the alkaline agent II is selected from at least one of calcium oxide, calcium hydroxide, and lime milk; the flocculant is selected from at least one of PAM and PAC; 3) Set the defluoridation supernatant at 15–25 mA / cm². 2 Electrolysis was carried out at a current density of 30-50 min, and then allowed to stand to obtain reaction product III. The reaction product III was then separated into solid and liquid components to obtain iron slag and iron-removed supernatant. The electrolysis was carried out in an electrocoagulation reactor, and the anode of the electrocoagulation reactor was iron. 4) Add phosphate to the iron removal supernatant, then add precipitant II until the pH of the iron removal supernatant is 3.5-4.5, and react at 50-70℃ for 1-5 hours to obtain reaction product IV; separate reaction product IV into solid and liquid components to obtain rare earth element phosphate precipitate and rare earth removal supernatant; wherein, the phosphate is selected from at least one of ammonium phosphate and alkali metal phosphate; the molar ratio of phosphate ion to rare earth element in rare earth concentrate beneficiation wastewater is 1-1.3:1; the precipitant II is selected from at least one of ammonia and alkali metal hydroxide; 5) The supernatant containing rare earth elements is evaporated and concentrated until the calcium chloride concentration is 40-60 wt% to obtain the concentrated evaporated liquid; The concentrated evaporation solution was cooled at 10–50 °C and the solid and liquid were separated to obtain CaCl2·2H2O crystals and mother liquor.

2. The processing method according to claim 1, characterized in that, In step 1), the mass concentration of calcium hydroxide in the lime slurry is 10-30 wt%; the alkali metal sulfide salt is sodium sulfide.

3. The processing method according to claim 1, characterized in that, In step 1), stirring is performed during the precipitation reaction.

4. The processing method according to claim 1, characterized in that, In step 2), the calcium salt is selected from at least one of calcium chloride and calcium sulfate; the mass concentration of calcium hydroxide in the lime milk is 10-30 wt%.

5. The processing method according to claim 1, characterized in that, In step 3), the settling time is 5 to 40 minutes.

6. The processing method according to claim 1, characterized in that, In step 5), the evaporation and concentration is a triple-effect evaporation and concentration; the mother liquor is returned to step 2) as a calcium agent.

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