Method for recovering calcium fluoride and rare earth using chemical separation wastewater from rare earth smelting

Abstract

The present invention belongs to the technical field of recycling wastewater in rare earth smelting, and specifically relates to a method for recycling calcium fluoride and rare earths using chemical wastewater from rare earth smelting. The method for recycling calcium fluoride and rare earths using chemical wastewater from rare earth smelting described in the present invention comprises the following steps: extracting calcium fluoride to prepare a defluorinated rare earth supernatant stage: under stirring, alkaline water washing water is added dropwise to the chemical wastewater until the pH is 1.5-4.5 to maintain stability, stirring and aging for 30-60min, solid-liquid separation is performed, and the resulting liquid is a defluorinated rare earth supernatant, and the resulting solid filter cake is washed and dried to obtain a calcium fluoride byproduct; the defluorinated rare earth supernatant recovers rare earths; the saturated organic phase extracts and strips rare earths; the chloride rare earth feed liquid purification stage. The method for recycling calcium fluoride and rare earths using chemical wastewater from rare earth smelting provided by the present invention has a high rare earth recovery rate, a high byproduct calcium fluoride yield and a high purity, reduces the waste of rare earth resources, and is simple to operate.

Description

Technical Field

[0001] The invention belongs to the technical field of recycling waste water in rare earth smelting, and in particular relates to a method for recycling calcium fluoride and rare earth by utilizing chemical separation waste water in rare earth smelting. Background Art

[0002] At present, in the rare earth hydrometallurgy process, the chemical separation process plays a vital role as the first key step. This process mainly involves pickling the rare earth concentrate by adding hydrochloric acid, aiming to selectively remove impurity elements such as calcium, lead, zinc, and iron in the concentrate through chemical reactions, so as to ensure the smooth progress of subsequent processing steps and the stability of product quality. However, the introduction of hydrochloric acid in this process inevitably causes some rare earth elements to dissolve in the chemical separation wastewater, resulting in a waste of rare earth resources.

[0003] At present, the main treatment method for chemical dressing wastewater is to discharge it to the environmental protection center for further treatment. However, this treatment method not only fails to effectively recycle the rare earth resources in the wastewater, but also makes the rare earth elements become waste residues along with the sediment during the sewage treatment process, further exacerbating the loss of rare earth resources. According to statistics, taking a company with a daily production capacity of 70 tons of REO (rare earth oxide) as an example, it consumes 170 tons of concentrate every day and produces about 600 cubic meters of chemical dressing wastewater, in which the rare earth content is as high as 1.2 grams per liter. This means that the amount of rare earth lost due to the discharge of chemical dressing wastewater reaches 720 kilograms every day, which poses a severe challenge to the effective utilization of rare earth resources.

[0004] In view of the scarcity and strategic value of rare earth resources, it is particularly important to recover rare earth elements in chemical wastewater. At present, there are two main methods for recovering rare earth elements in chemical wastewater: one is precipitation, but this method is costly and easily produces a large amount of impurity ion precipitation, resulting in a decrease in the quality of the recovered rare earths and making them difficult to reuse; the other is to use organic extractants for extraction and recovery. Although this method has a high rare earth recovery efficiency in theory, the fluorine ions present in the chemical wastewater will cause "ion poisoning" to the organic extraction phase, seriously interfering with the extraction process, resulting in a significant reduction in the extraction effect.

[0005] Therefore, developing a new method that can effectively remove fluoride ion interference and efficiently recover rare earth elements in chemical separation wastewater is of great significance for improving the utilization rate of rare earth resources, reducing resource waste, and promoting the sustainable development of the rare earth industry. Summary of the invention

[0006] The technical problem to be solved by the present invention is to overcome the above-mentioned defects of the prior art and provide a method for recovering calcium fluoride and rare earths by using chemical separation wastewater from rare earth smelting, which has a high rare earth recovery rate, a high yield and high purity of by-product calcium fluoride, reduces the waste of rare earth resources, and is simple to operate.

[0007] The method for recovering calcium fluoride and rare earths by using the chemical separation wastewater of rare earth smelting according to the present invention comprises the following steps:

[0008] Step 1: Extracting calcium fluoride to prepare defluorinated rare earth supernatant

[0009] Under stirring, add alkaline washing water to the chemical wastewater until the pH value is stable at 1.5-4.5 (when the alkaline washing water used is alkaline smelting alkaline washing water, the optimal pH value is 1.5-2, which will avoid the problem of phosphate reacting with calcium in the chemical wastewater to generate calcium phosphate precipitation, and play a role in controlling the production of high-purity calcium fluoride; when the alkaline washing water used is an alkaline solution, the optimal pH value is 4-4.5. Of course, if the cost is not considered, the pH value can also be controlled to 2-4 at this time, without affecting the production of calcium fluoride, and the calcium ions have no effect on the subsequent organic extraction of rare earths), keep stirring and aging for 30-60 minutes (control that no calcium fluoride colloid will appear), perform solid-liquid separation, the obtained liquid is the defluorinated rare earth supernatant, and the obtained solid filter cake is washed and dried to obtain a calcium fluoride byproduct;

[0010] Step 2: Recovering rare earths from the supernatant of defluorinated rare earths

[0011] Under stirring, adding an extractant to the defluorinated rare earth supernatant, taking out the organic phase after separation, and obtaining a saturated organic phase;

[0012] Step 3: Extraction and stripping of rare earths from saturated organic phase

[0013] Add hydrochloric acid to the saturated organic phase, stir and back extract, separate the aqueous phase and the organic phase, continue to add water to the organic phase for washing, continue to separate the aqueous phase and the organic phase, de-enrich the organic phase, mix the aqueous phase, detect the acidity of the mixed aqueous phase to be 0.5-1.0 mol / L, and obtain a rare earth chloride feed solution;

[0014] Step 4: Purification of rare earth chloride solution

[0015] Under stirring, carbonate is added to the rare earth chloride liquid, the pH value is adjusted to 2.5-3, and the solid-liquid is separated to obtain solid iron slag and purified rare earth chloride liquid.

[0016] The chemical separation wastewater in step one has the following components: fluorine content 3500-4500ppm, rare earth content 0.8-1.6g / L, calcium content 18000-26000ppm, lead content 400-600ppm, zinc content 200-500ppm, iron content 300-800ppm, sodium content 60000-80000ppm, chloride ion content 80000-130000ppm, and the remainder is water.

[0017] The alkaline washing water in step one is an alkaline solution or alkaline smelting alkaline washing wastewater; the alkaline solution is a sodium hydroxide solution, a potassium hydroxide solution, a sodium carbonate solution or a potassium carbonate solution, and the alkaline smelting alkaline washing wastewater has a fluorine content of 2000-3000ppm, a phosphate content of 3000-8000ppm, a sodium hydroxide content of 10000-18000ppm, a sodium chloride content of 70000-90000ppm, and the balance is water.

[0018] The extractant in step 2 is the saponified P507 extractant, and the volume of the added extractant is 1 / 4-1 / 15 of the defluorinated rare earth supernatant.

[0019] After the liquid separation in step 2, the organic phase is taken out, and the liquid separation operation is repeated until the rare earth content in the remaining aqueous phase is detected to be 0 g / L. After extraction, the aqueous phase no longer contains rare earth, which proves that all the rare earths are recovered. Then, after the pH is adjusted by carbonate in step 4, the rare earth content in the iron slag is 0 g / L, which proves that the extracted rare earth is completely converted into a rare earth solution, that is, 100% recovery of the rare earth chloride is completed.

[0020] The mass concentration of hydrochloric acid added in step 3 is 30%, and the volume ratio of the saturated organic phase to the hydrochloric acid is 100:5~20.

[0021] In step 3, continue to add water to the organic phase for washing, according to the volume ratio of organic phase: water is 100:10~15.

[0022] In step 3, the rare earth concentration of the mixed aqueous phase detected is 253.5-304.2 g / L (based on the average molecular weight of the rare earth of 169), and the iron content is 6000-10000 ppm.

[0023] The carbonate in step 4 is ammonium bicarbonate, rare earth carbonate, sodium carbonate or sodium bicarbonate. Rare earth carbonate refers to mixed rare earth carbonate or mixed carbonate or single carbonate of rare earth carbonates such as lanthanum carbonate, cerium carbonate, lanthanum cerium carbonate, praseodymium neodymium carbonate, etc.

[0024] The purified rare earth chloride solution obtained in step 4 has a rare earth concentration of 253.5-338.0 g / L (based on the average molecular weight of the rare earth of 169), and an iron content of less than 100 ppm.

[0025] Specifically, the method for recovering calcium fluoride and rare earths by using the chemical separation wastewater of rare earth smelting comprises the following steps:

[0026] Step 1: Extracting calcium fluoride to prepare defluorinated rare earth supernatant

[0027] (1) Take 2L of chemical wastewater and put it in a 3L beaker. Keep it at room temperature. While stirring, slowly add alkaline water washing wastewater until the pH is 1.5-4.5;

[0028] (2) After the addition is complete, keep stirring and aging for 30-60 minutes, and re-measure the pH value if it remains unchanged;

[0029] (3) Solid-liquid separation is performed, and the obtained liquid is the defluorinated rare earth supernatant. The obtained solid filter cake is washed twice with pure water and then dried in an oven at 120°C to obtain a white solid powder, which is the calcium fluoride by-product.

[0030] Step 2: Recovering rare earths from the supernatant of defluorinated rare earths

[0031] (1) Start stirring and add saponified P507 extractant to the defluorinated rare earth supernatant, with the volume added being 1 / 4-1 / 15 of the defluorinated rare earth supernatant;

[0032] (2) Keep stirring for 10-15 minutes, put into a separatory funnel, take out the organic phase, which contains the recovered rare earths, and detect the rare earth content in the aqueous phase to be 0 g / L;

[0033] (3) This step is repeated several times until the organic phase is saturated.

[0034] Step 3: Extraction and stripping of rare earths using saturated organic extraction phase

[0035] (1) Add 30% hydrochloric acid to the saturated organic phase for back extraction, with the back extraction volume ratio being saturated organic phase: hydrochloric acid = 100:5-20, stirring for 20 minutes under this state, and separating the aqueous phase;

[0036] (2) The organic phase is washed once with pure water at a volume ratio of 100:10-15, stirred for 20 min, the separated aqueous phase is mixed with the aqueous phase of step (1), and the acidity of the mixed aqueous phase is detected to be 0.5-1 mol / L to obtain a rare earth chloride solution with a rare earth chloride concentration of 1.5-1.8 mol / L and an iron content of 6000-10000 ppm.

[0037] Step 4: Purification process of rare earth chloride solution

[0038] (1) Adding carbonate to the rare earth chloride solution under stirring to adjust the pH to 2.5-3;

[0039] (2) Solid-liquid separation to obtain solid iron slag and purified rare earth chloride solution (concentration 1.5-1.7 mol / L, iron content below 100 ppm. If treated with rare earth carbonate, the concentration is 1.7-2.0 mol / L, iron content below 100 ppm). The solid is washed three times, the washing water is used for other purposes, and the iron slag enters the waste slag elimination treatment.

[0040] The present invention uses two-step treatment methods to sequentially treat the chemical wastewater to recover rare earths and produce byproduct calcium fluoride, and then completes 100% rare earth recovery through organic extraction. Since fluoride ions will generate calcium fluoride when they meet calcium, but the free state of fluoride ions will increase in a high acid environment, when pH>1.5, fluoride ions will combine with calcium ions, and the residual fluoride ions in the supernatant will be less than 200ppm; the present invention controls the acidic conditions at pH 2.5-3, because there are phosphates in the alkaline water washing wastewater, by controlling pH2.5-3, it is ensured that only calcium fluoride precipitates, and no calcium phosphate precipitates are generated, that is, it will not interfere with the quality of calcium fluoride and will not adsorb rare earth ions; the present invention adds P507 to the rare earth organic extraction phase to extract trivalent cations, and controls fluoride ions <200ppm to avoid the toxicity of anionic fluorine. The present invention controls the pH value by mixing acid and alkaline water, so that the fluoride ions in the acid and alkaline water and the high-content calcium ions in the acid water are precipitated into calcium fluoride until the fluoride is reduced to below 200 ppm, and then the solid and liquid are separated to obtain calcium fluoride, and the defluorinated supernatant is added with an extractant to extract and recover the rare earth.

[0041] Compared with the prior art, the present invention has the following beneficial effects:

[0042] The invention discloses a method for recovering calcium fluoride and rare earths by utilizing chemical separation wastewater of rare earth smelting. Through multi-step treatment, by-product calcium fluoride is first prepared, and then rare earths are extracted and recovered and purified. Alkaline solution is used to adjust pH, and carbonate treatment is used in the process of purifying rare earth chloride solution. Compared with the traditional sewage treatment process, the invention is simple to operate, can recover rare earths, and can obtain high by-product calcium fluoride, thereby increasing the profit. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 The present invention is a process flow chart for recovering calcium fluoride and rare earths from chemical separation wastewater of rare earth smelting. DETAILED DESCRIPTION

[0044] The present invention will be further described below in conjunction with specific embodiments.

[0045] The process flow of the present invention for recovering calcium fluoride and rare earths from the chemical separation wastewater of rare earth smelting is as follows: Figure 1 The room temperature described in the embodiment is 20-25° C. Rare earth carbonate is a normal commercial product and is not affected by its specific type.

[0046] Example 1

[0047] The components of the treated chemical wastewater are: fluorine content 3515ppm, rare earth content 0.82g / L, calcium content 25674ppm, lead content 412ppm, zinc content 323ppm, iron content 796ppm, sodium content 61245ppm, chloride ion content 85267ppm, and the remainder is water.

[0048] The composition of the alkaline smelting alkaline washing wastewater used is: fluorine content 2462ppm, phosphate content 7826ppm, sodium hydroxide content 10246ppm, sodium chloride content 89656ppm, and the balance is water.

[0049] The method for recovering calcium fluoride and rare earths by using the chemical separation wastewater of rare earth smelting comprises the following steps:

[0050] Step 1: Extracting calcium fluoride to prepare defluorinated rare earth supernatant

[0051] (1) Take 2L of chemical separation wastewater and put it in a 3L beaker. Keep it at room temperature. While stirring, slowly add alkaline smelting alkaline water washing wastewater until the pH reaches 1.5;

[0052] (2) After the addition is complete, keep stirring and aging for 30 minutes, and re-measure the pH value.

[0053] (3) Solid-liquid separation was performed, and the obtained liquid was the defluorinated rare earth supernatant. The obtained solid filter cake was washed twice with pure water and then dried in an oven at 120°C to obtain a white solid powder, which was the calcium fluoride by-product. The yield was 88.69% and the purity was 86.46%.

[0054] Step 2: Recovering rare earths from the supernatant of defluorinated rare earths

[0055] (1) Start stirring and add saponified P507 extractant to the defluorinated rare earth supernatant, with the volume added being 1 / 4 of the defluorinated rare earth supernatant;

[0056] (2) Keep stirring for 10 minutes, put into a separatory funnel, take out the organic phase, which contains the recovered rare earths, and detect the rare earth content in the aqueous phase to be 0 g / L;

[0057] (3) This step is repeated several times until the organic phase is saturated.

[0058] Step 3: Extraction and stripping of rare earths using saturated organic extraction phase

[0059] (1) Add 30% hydrochloric acid to the saturated organic phase for back extraction, with the back extraction volume ratio of saturated organic phase: hydrochloric acid = 100:5, stir for 20 minutes in this state, and separate the aqueous phase;

[0060] (2) The organic phase was washed once with pure water in a volume ratio of 100:15, stirred for 20 min, and the separated aqueous phase was mixed with the aqueous phase of step (1). The acidity of the mixed aqueous phase was detected to be 0.74 mol / L, thereby obtaining a rare earth chloride solution with a rare earth chloride concentration of 1.66 mol / L and an iron content of 6453 ppm.

[0061] Step 4: Purification process of rare earth chloride solution

[0062] (1) Adding ammonium bicarbonate to the rare earth chloride solution under stirring to adjust the pH to 3;

[0063] (2) Solid-liquid separation to obtain solid iron slag and purified rare earth chloride liquid. The rare earth chloride concentration was detected to be 1.58 mol / L, the iron content was 46 ppm, and the rare earth content in the iron slag was 0%. The solid was washed three times, and the washing water was used for other purposes. The iron slag entered the waste slag elimination treatment.

[0064] Example 2

[0065] The components of the treated chemical wastewater are: fluorine content 4468ppm, rare earth content 1.59g / L, calcium content 18561ppm, lead content 564ppm, zinc content 489ppm, iron content 304ppm, sodium content 79956ppm, chloride ion content 116566ppm, and the remainder is water.

[0066] The composition of the alkaline smelting alkaline washing wastewater used is: fluorine content 2986ppm, phosphate content 3120ppm, sodium hydroxide content 17686ppm, sodium chloride content 89567ppm, and the balance is water.

[0067] The method for recovering calcium fluoride and rare earths by using the chemical separation wastewater of rare earth smelting comprises the following steps:

[0068] Step 1: Extracting calcium fluoride to prepare defluorinated rare earth supernatant

[0069] (1) Take 2L of chemical separation wastewater and put it in a 3L beaker. Keep it at room temperature. While stirring, slowly add alkaline smelting alkaline water washing wastewater until the pH reaches 1.5;

[0070] (2) After the addition is complete, keep stirring and aging for 60 minutes, and re-measure the pH value.

[0071] (3) Solid-liquid separation was performed, and the obtained liquid was the defluorinated rare earth supernatant. The obtained solid filter cake was washed twice with pure water and then dried in an oven at 120°C to obtain a white solid powder, which was the calcium fluoride by-product. The yield was 89.02% and the purity was 85.01%.

[0072] Step 2: Recovering rare earths from the supernatant of defluorinated rare earths

[0073] (1) Start stirring and add saponified P507 extractant to the defluorinated rare earth supernatant, with the added volume being 1 / 15 of the defluorinated rare earth supernatant;

[0074] (2) Keep stirring for 15 minutes, put into a separatory funnel, take out the organic phase, which contains the recovered rare earths, and detect the rare earth content in the aqueous phase to be 0 g / L;

[0075] (3) This step is repeated several times until the organic phase is saturated.

[0076] Step 3: Extraction and stripping of rare earths using saturated organic extraction phase

[0077] (1) Add 30% hydrochloric acid to the saturated organic phase for back extraction, with the back extraction volume ratio of saturated organic phase: hydrochloric acid = 100:20, stir for 20 minutes in this state, and separate the aqueous phase;

[0078] (2) The organic phase was washed once with pure water at a volume ratio of 100:10, stirred for 20 min, and the separated aqueous phase was mixed with the aqueous phase of step (1). The acidity of the mixed aqueous phase was detected to be 0.98 mol / L, thereby obtaining a rare earth chloride solution with a rare earth chloride concentration of 1.52 mol / L and an iron content of 6124 ppm.

[0079] Step 4: Purification process of rare earth chloride solution

[0080] (1) Adding rare earth carbonate to the rare earth chloride solution under stirring and adjusting the pH to 2.5;

[0081] (2) Solid-liquid separation to obtain solid iron slag and purified rare earth chloride liquid. The rare earth chloride concentration was detected to be 1.51 mol / L and the iron content was 97 ppm. The rare earth content in the iron slag was 0%. The solid was washed three times, and the washing water was used for other purposes. The iron slag entered the waste slag elimination treatment.

[0082] Example 3

[0083] The components of the treated chemical wastewater are: fluorine content 3562ppm, rare earth content 0.81g / L, calcium content 25656ppm, lead content 457ppm, zinc content 214ppm, iron content 772ppm, sodium content 60875ppm, chloride ion content 91274ppm, and the remainder is water.

[0084] The method for recovering calcium fluoride and rare earths by using the chemical separation wastewater of rare earth smelting comprises the following steps:

[0085] Step 1: Extracting calcium fluoride to prepare defluorinated rare earth supernatant

[0086] (1) Take 2L of chemical wastewater and put it in a 3L beaker. Keep it at room temperature. While stirring, slowly add sodium carbonate solution until the pH reaches 4.5.

[0087] (2) After the addition is complete, keep stirring and aging for 30 minutes, and re-measure the pH value.

[0088] (3) Solid-liquid separation was performed, and the obtained liquid was the defluorinated rare earth supernatant. The obtained solid filter cake was washed twice with pure water and then dried in an oven at 120°C to obtain a white solid powder, which was the calcium fluoride by-product. The yield was 88.07% and the purity was 86.62%.

[0089] Step 2: Recovering rare earths from the supernatant of defluorinated rare earths

[0090] (1) Start stirring and add saponified P507 extractant to the defluorinated rare earth supernatant, with the volume added being 1 / 4 of the defluorinated rare earth supernatant;

[0091] (2) Keep stirring for 10 minutes, put into a separatory funnel, take out the organic phase, which contains the recovered rare earths, and detect the rare earth content in the aqueous phase to be 0 g / L;

[0092] (3) This step is repeated several times until the organic phase is saturated.

[0093] Step 3: Extraction and stripping of rare earths using saturated organic extraction phase

[0094] (1) Add 30% hydrochloric acid to the saturated organic phase for back extraction, with the back extraction volume ratio of saturated organic phase: hydrochloric acid = 100:5, stir for 20 minutes in this state, and separate the aqueous phase;

[0095] (2) The organic phase was washed once with pure water at a volume ratio of 100:10, stirred for 20 min, and the separated aqueous phase was mixed with the aqueous phase of step (1). The acidity of the mixed aqueous phase was detected to be 0.57 mol / L, thereby obtaining a rare earth chloride solution with a rare earth chloride concentration of 1.74 mol / L and an iron content of 6288 ppm.

[0096] Step 4: Purification process of rare earth chloride solution

[0097] (1) Under stirring, sodium carbonate is added to the rare earth chloride solution to adjust the pH to 3;

[0098] (2) Solid-liquid separation to obtain solid iron slag and purified rare earth chloride liquid. The rare earth chloride concentration was detected to be 1.68 mol / L, the iron content was 85 ppm, and the rare earth content in the iron slag was 0%. The solid was washed three times, and the washing water was used for other purposes. The iron slag entered the waste slag elimination treatment.

[0099] Example 4

[0100] The components of the treated chemical wastewater are: fluorine content 3612ppm, rare earth content 0.75g / L, calcium content 24328ppm, lead content 407ppm, zinc content 356ppm, iron content 798ppm, sodium content 79897ppm, chloride ion content 11256ppm, and the remainder is water.

[0101] The method for recovering calcium fluoride and rare earths by using the chemical separation wastewater of rare earth smelting comprises the following steps:

[0102] Step 1: Extracting calcium fluoride to prepare defluorinated rare earth supernatant

[0103] (1) Take 2L of chemical wastewater and put it in a 3L beaker. Keep it at room temperature. While stirring, slowly add sodium hydroxide solution until the pH reaches 4.5.

[0104] (2) After the addition is complete, keep stirring and aging for 30 minutes, and re-measure the pH value.

[0105] (3) Solid-liquid separation was performed, and the obtained liquid was the defluorinated rare earth supernatant. The obtained solid filter cake was washed twice with pure water and then dried in an oven at 120°C to obtain a white solid powder, which was the calcium fluoride by-product. The yield was 88.86% and the purity was 86.43%.

[0106] Step 2: Recovering rare earths from the supernatant of defluorinated rare earths

[0107] (1) Start stirring and add saponified P507 extractant to the defluorinated rare earth supernatant, with the volume added being 1 / 4 of the defluorinated rare earth supernatant;

[0108] (2) Keep stirring for 10 minutes, put into a separatory funnel, take out the organic phase, which contains the recovered rare earths, and detect the rare earth content in the aqueous phase to be 0 g / L;

[0109] (3) This step is repeated several times until the organic phase is saturated.

[0110] Step 3: Extraction and stripping of rare earths using saturated organic extraction phase

[0111] (1) Add 30% hydrochloric acid to the saturated organic phase for back extraction, with the back extraction volume ratio of saturated organic phase: hydrochloric acid = 100:5, stir for 20 minutes in this state, and separate the aqueous phase;

[0112] (2) The organic phase was washed once with pure water at a volume ratio of 100:10, stirred for 20 min, and the separated aqueous phase was mixed with the aqueous phase of step (1). The acidity of the mixed aqueous phase was detected to be 0.56 mol / L, thereby obtaining a rare earth chloride solution with a rare earth chloride concentration of 1.71 mol / L and an iron content of 6014 ppm.

[0113] Step 4: Purification process of rare earth chloride solution

[0114] (1) Under stirring, add sodium bicarbonate to the rare earth chloride solution and adjust the pH to 3;

[0115] (2) Solid-liquid separation to obtain solid iron slag and purified rare earth chloride liquid. The rare earth chloride concentration was detected to be 1.64 mol / L, the iron content was 26 ppm, and the rare earth content in the iron slag was 0%. The solid was washed three times, and the washing water was used for other purposes. The iron slag entered the waste slag elimination treatment.

[0116] Comparative Example 1

[0117] This comparative example is the same as Example 1, except that the step 1 of “(1) taking 2L of chemical separation wastewater and placing it in a 3L beaker, keeping it at room temperature, and slowly adding alkaline water washing wastewater from alkali smelting under stirring until the pH value is 1.5” is replaced by “taking 2L of chemical separation wastewater and placing it in a 3L beaker, keeping it at room temperature, and slowly adding alkaline water washing wastewater from alkali smelting under stirring until the pH value is 5”. The other preparation methods are the same.

[0118] The final calcium fluoride byproduct has a yield of 95.16% and a purity of 46.78%.

[0119] In summary, the pH change in step one is too high, resulting in a decrease in the purity of the calcium fluoride byproduct, which cannot meet the sales requirements.

[0120] Comparative Example 2

[0121] This comparative example is the same as Example 2, except that "(1) under stirring, adding carbonate to the rare earth chloride solution and adjusting the pH to 2.5" in step 4 is replaced by "(1) under stirring, adding carbonate to the rare earth chloride solution and adjusting the pH to 3.5", and the other treatment methods are the same.

[0122] The final rare earth chloride concentration detected was 1.37 mol / L, the iron content was 0 ppm, and the rare earth content in the iron slag was 17%.

[0123] In summary, if the pH value in step 4 is adjusted too high, rare earth will be lost, the recovery rate will not reach 100%, and the concentration of purified rare earth will be too low.

[0124] Comparative Example 3

[0125] This comparative example is the same as Example 2, except that "(1) under stirring, adding carbonate to the rare earth chloride solution and adjusting the pH to 2.5" in step 4 is replaced by "(1) under stirring, adding carbonate to the rare earth chloride solution and adjusting the pH to 1.5", and the other treatment methods are the same.

[0126] The final rare earth chloride concentration was 1.53 mol / L, the iron content was 1689 ppm, and the rare earth content in the iron slag was 0%.

[0127] In summary, if the pH value in step 4 is adjusted too low, the iron content of the purified rare earth solution will exceed the standard (the normal standard is below 100 ppm), resulting in excessively high impurity content of the purified rare earth.

[0128] Comparative Example 4

[0129] Compared with the steps of Examples 1 / 2 / 3 / 4, the comparative example removes step 1, extracting calcium fluoride to prepare the defluorinated rare earth supernatant, and the processing methods of other steps are the same.

[0130] Ultimately, no calcium fluoride or fluoride product is produced, the organic phase is poisoned by fluoride ions, an emulsion of useless substances is produced, and the rare earth cannot be recovered.

[0131] Comparative Example 5

[0132] This comparative example is the same as Example 3 / 4, except that the step 4 "(1) take 2L of chemical wastewater and put it in a 3L beaker, keep it at room temperature, and slowly add sodium hydroxide solution / sodium carbonate solution while stirring until the pH is 4.5" is replaced by "(1) take 2L of chemical wastewater and put it in a 3L beaker, keep it at room temperature, and slowly add an equal amount of water while stirring", and the other treatment methods are the same.

[0133] Ultimately, no calcium fluoride or fluoride product is produced, the organic phase is poisoned by fluoride ions, an emulsion of useless substances is produced, and the rare earth cannot be recovered.

Claims

1. A method for recovering calcium fluoride and rare earths from chemical separation wastewater of rare earth smelting, characterized in that: The following steps are involved: Step 1: Extracting calcium fluoride to prepare defluorinated rare earth supernatant Under stirring, alkaline water washing water is added dropwise to the chemical wastewater until the pH value is 1.5-4.5, and stirring and aging is maintained for 30-60 minutes to perform solid-liquid separation. The obtained liquid is the defluorinated rare earth supernatant, and the obtained solid filter cake is washed and dried to obtain calcium fluoride byproduct; The chemical separation wastewater has the following components: fluorine content 3500-4500ppm, rare earth content 0.8-1.6g / L, calcium content 18000-26000ppm, lead content 400-600ppm, zinc content 200-500ppm, iron content 300-800ppm, sodium content 60000-80000ppm, chloride ion content 80000-130000ppm, and the balance is water; Step 2: Recovering rare earths from the supernatant of defluorinated rare earths Under stirring, adding an extractant to the defluorinated rare earth supernatant, taking out the organic phase after separation, and obtaining a saturated organic phase; Step 3: Extraction and stripping of rare earths from saturated organic phase Add hydrochloric acid to the saturated organic phase, stir and back extract, separate the aqueous phase and the organic phase, continue to add water to the organic phase for washing, continue to separate the aqueous phase and the organic phase, de-enrich the organic phase, mix the aqueous phase, detect the acidity of the mixed aqueous phase to be 0.5-1.0 mol / L, and obtain a rare earth chloride feed solution; Step 4: Purification of rare earth chloride solution Under stirring, carbonate is added to the rare earth chloride liquid, the pH value is adjusted to 2.5-3, and the solid-liquid is separated to obtain solid iron slag and purified rare earth chloride liquid.

2. The method for recovering calcium fluoride and rare earths from chemical separation wastewater of rare earth smelting according to claim 1, characterized in that: The alkaline washing water in step 1 is an alkaline solution or alkaline smelting alkaline washing wastewater.

3. The method for recovering calcium fluoride and rare earths from chemical separation wastewater of rare earth smelting according to claim 1, characterized in that: The extractant in step 2 is the saponified P507 extractant, and the volume of the added extractant is 1 / 4-1 / 15 of the defluorinated rare earth supernatant.

4. The method for recovering calcium fluoride and rare earths from chemical separation wastewater of rare earth smelting according to claim 1, characterized in that: After the liquid separation in step 2, the organic phase is taken out, and the liquid separation operation is repeated until the rare earth content in the remaining aqueous phase is detected to be 0 g / L.

5. The method for recovering calcium fluoride and rare earths from chemical separation wastewater of rare earth smelting according to claim 1, characterized in that: The mass concentration of hydrochloric acid added in step 3 is 30%, and the volume ratio of the saturated organic phase to the hydrochloric acid is 100:5~20.

6. The method for recovering calcium fluoride and rare earths from chemical separation wastewater of rare earth smelting according to claim 1, characterized in that: In step 3, continue to add water to the organic phase for washing, according to the volume ratio of organic phase: water is 100:10~15.

7. The method for recovering calcium fluoride and rare earths from rare earth smelting wastewater according to claim 1, characterized in that: In step 3, the rare earth concentration of the mixed aqueous phase detected is 253.5-304.2 g / L, and the iron content is 6000-10000 ppm.

8. The method for recovering calcium fluoride and rare earths from chemical separation wastewater of rare earth smelting according to claim 1, characterized in that: The carbonate in step 4 is ammonium bicarbonate, rare earth carbonate, sodium carbonate or sodium bicarbonate.

9. The method for recovering calcium fluoride and rare earths from chemical separation wastewater of rare earth smelting according to claim 1, characterized in that: The purified rare earth chloride solution obtained in step 4 has a rare earth concentration of 253.5-338.0 g / L and an iron content of less than 100 ppm.

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