Comprehensive utilization method of high-salinity wastewater produced by hydrometallurgical treatment of bastnaesite

Abstract

The invention discloses a comprehensive utilization method of high-salinity wastewater produced by hydrometallurgical treatment of bastnaesite, which comprises the following steps: A, mixing alkaline wastewater and acidic wastewater, neutralizing and clarifying to obtain calcium fluoride and sodium chloride wastewater; b, mixing the sodium chloride wastewater with the precipitation wastewater, adding lime water in an aeration manner to adjust the pH value, hydrolyzing heavy metal ions in the wastewater, and performing solid-liquid separation to obtain filter residues and filtrate which is sodium chloride high-salinity wastewater; and C, adding oxalic acid into the sodium chloride high-salinity wastewater, stirring, standing, carrying out solid-liquid separation, pressurizing, concentrating, recovering hydrochloric acid, and crystallizing to obtain a crystal substance, namely a sodium chloride product. According to the method, fluorine in the wastewater is removed firstly, then the wastewater is recovered into wastewater containing sodium chloride, oxalate is dissolved into the high-salinity wastewater to separate out sodium oxalate and recover hydrochloric acid, so that the content of sodium chloride in the system is greatly reduced, and the recovery efficiency of sodium ions in the wastewater is improved.

Description

Technical Field

[0001] The invention relates to the technical field of rare earth hydrometallurgical wastewater treatment, and in particular to a comprehensive utilization method for high-salt wastewater produced by hydrometallurgical treatment of bastnaesite. Background Art

[0002] At present, the rare earths used in industrial process are generally extracted from rare earth ores and then used in modern production processes. However, in the process of processing rare earth concentrates, a large amount of waste residue and sewage will be generated. Generally, the waste residue has a certain economic value and can be used as a resource after being processed by modern processes. However, due to the complex composition and high treatment cost of sewage, the treatment of sewage cannot meet the zero emission standard. Therefore, in actual production, it can only be discharged after being treated in accordance with industry standards. However, according to the current trend of environmental protection requirements, the requirements for external wastewater will become more and more stringent in the future, so the requirements for external wastewater discharged from rare earth hydrometallurgy will also become more and more stringent.

[0003] The fluorocarbon cerium rare earth concentrate from the Yaoniuping Mine in Mianning County, Liangshan Prefecture, which is currently used in Sichuan, mainly produces three types of wastewater during the treatment of this type of rare earth concentrate: alkaline fluorine-containing wastewater from alkali conversion, acidic heavy metal-containing wastewater from extraction, and high-salt wastewater containing sodium salt from precipitation; and the wastewater obtained after the treatment of these three types of wastewater is mainly high-salt wastewater containing sodium chloride. The current method for treating high-salt wastewater containing sodium chloride is mainly to concentrate and then crystallize sodium chloride. This method consumes a lot of heat energy. At the same time, sodium chloride corrodes the equipment seriously. The produced sodium chloride contains more impurities and the supply direction is relatively narrow. Some companies use the method of acidifying the sodium chloride wastewater with a non-volatile acid, then concentrating and pressurizing it to recover hydrochloric acid and soluble non-volatile salts. The acid is returned to production for use, and the salt can be sold as a product. In this process, the requirements for equipment are relatively harsh. At the same time, the heat energy consumption is relatively large during actual use, and it is poorly applicable in production. Summary of the invention

[0004] The object of the present invention is to provide a comprehensive utilization method for high-salt wastewater produced by hydrometallurgical treatment of fluorocarbon cerium ore in order to solve the shortcomings of the prior art.

[0005] The technical solution adopted by the present invention is as follows: a comprehensive utilization method of high-salt wastewater produced by hydrometallurgical treatment of fluorocarbon cerium ore, wherein the high-salt wastewater includes alkaline wastewater mainly containing sodium fluoride produced by acid-base combined treatment, acidic wastewater produced by extraction, and precipitation wastewater mainly containing sodium chloride produced by precipitation, comprising the following steps:

[0006] A. Mix the alkaline wastewater and the acidic wastewater, neutralize and clarify them, and then filter them. The filter residue is the calcium fluoride product, and the filtrate is the sodium chloride wastewater;

[0007] B. Mixing sodium chloride wastewater with sedimentation wastewater, then adding lime water by aeration to adjust the pH value, so that the heavy metal ions in the wastewater are hydrolyzed, and then adding flocculants for flocculation and sedimentation, and obtaining filter residue and filtrate after solid-liquid separation, wherein the filter residue is heavy metal waste residue and the filtrate is sodium chloride high-salt wastewater;

[0008] C. Add oxalic acid to the sodium chloride high-salt wastewater, stir and let it stand, then separate the solid and liquid, concentrate the filtrate, recover the gas through the concentration exhaust hole to produce hydrochloric acid, condense and crystallize the concentrated filtrate, the crystals are the sodium chloride product, and the crystal water is used as process water.

[0009] Further, the concentration of sodium fluoride in alkaline wastewater needs to be between 4-8 g / L, and the concentration of sodium fluoride can be, for example, 4 g / L, 5 g / L, 6 g / L, 7 g / L, 8 g / L, etc., preferably 5-8 g / L. The concentration of calcium chloride in acidic wastewater needs to be controlled at 200-300 g / L, and the concentration of calcium chloride in acidic wastewater can be 200 g / L, 230 g / L, 250 g / L, 280 g / L, 300 g / L, etc., preferably 250 g / L.

[0010] Furthermore, in step A, the pH value of the mixed solution system needs to be controlled at 6-9 to precipitate more calcium fluoride. The pH value can be 6, 6.5, 7, 7.5, 8, 9, etc.

[0011] Furthermore, in step A, the fluorine content in the obtained sodium chloride wastewater does not exceed 0.08 g / L, so that the residual fluorine ions will not affect the subsequent high-salt wastewater treatment, such as affecting the purity of the precipitated product.

[0012] Further, in step B, lime water is added to adjust the pH value to 8-10 so that the heavy metal ions are fully hydrolyzed, and the flocculant is preferably PAC (polyaluminium chloride).

[0013] Further, in step C, the amount of oxalic acid added is 1-1.05 times the molar amount of sodium ions, preferably 1.05 times.

[0014] Furthermore, in step C, when the filtrate is concentrated, the concentration is stopped when the volume of the filtrate is reduced to 1 / 2 of the original volume.

[0015] Further, in step C, the gas generated during the concentration process is absorbed by a hydrochloric acid recovery device.

[0016] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0017] 1. The present invention rationally plans the wastewater produced in the light rare earth hydrometallurgy process, first removes the fluorine in the wastewater, and then converts the wastewater in the entire hydrometallurgy process into wastewater containing sodium chloride. Soluble and non-volatile oxalate is dissolved in high-salt wastewater to precipitate sodium oxalate. Since sodium oxalate has a low solubility, a large amount of sodium ions in the high-salt wastewater can be precipitated. At the same time, oxalic acid dissociates hydrogen ions and combines with chloride ions. During the concentration process, the hydrogen chloride solution volatilizes, which accelerates the precipitation of sodium oxalate, greatly reducing the content of sodium chloride in the system, improving the efficiency of recovering sodium ions in calcium salt wastewater, and reducing the cost of heat energy required for concentration.

[0018] 2. The present invention uses non-volatile oxalic acid to recover sodium ions in high-salt wastewater and produces hydrochloric acid for production. Compared with other non-volatile acids, oxalic acid has the lowest sodium salt solubility, is less corrosive to equipment, and has low requirements for wastewater treatment equipment. The large amount of sodium oxalate products recovered can not only be sold as alkaline sodium products (calcined to obtain sodium oxide, sodium carbonate, etc.), but also can be reused as a sodium source for rare earth hydrometallurgy, with significant economic benefits. The condensed water obtained can be reused as industrial water or directly discharged to the outside, thereby achieving the purpose of comprehensive utilization. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 The present invention is a schematic flow chart of a comprehensive utilization method for treating high-salt wastewater produced by bastnaesite through hydrometallurgical treatment. DETAILED DESCRIPTION

[0020] The present invention will be described in detail below in conjunction with the accompanying drawings.

[0021] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0022] like Figure 1 As shown, after oxidative roasting, the fluorocarbon cerium rare earth concentrate is treated by an acid-base combined method (actually including hydrochloric acid, liquid alkali, etc.) to obtain a low-cerium liquid, fluorine-containing wastewater and a cerium concentrate (the existing mature process is not repeated here), and the low-cerium liquid is extracted and separated to obtain a single rare earth chloride solution and acidic wastewater, and the single rare earth chloride solution is treated with sodium carbonate precipitation to obtain precipitation wastewater. Therefore, the entire wet smelting process mainly produces the following three types of wastewater: fluorine-containing wastewater, acidic wastewater and precipitation wastewater. In order to comprehensively treat and utilize these wastewaters, the present invention proposes a comprehensive utilization method as follows:

[0023] S1. Neutralize and filter the acidic wastewater and fluoride-containing wastewater, pay attention to control the pH value of the whole system at 6-9, ensure that the fluorine content in the whole system is controlled below 0.08g / L, and produce precipitate calcium fluoride and sodium chloride wastewater during the neutralization reaction, wherein the neutralization reaction formula is:

[0024] F - +Ca 2+ =CaF2↓

[0025] In the above comprehensive reaction process, the sodium fluoride concentration of the fluoride-containing wastewater used is between 4-8g / L, and the calcium chloride concentration in the acidic wastewater is preferably 250g / L; after neutralization and clarification, the calcium fluoride slag is transferred through plate and frame filtration, and the sodium chloride wastewater is discharged into the next wastewater treatment process;

[0026] S2, after mixing the sodium chloride wastewater and the precipitated wastewater, perform heavy metal removal pretreatment, in the heavy metal removal process, add lime water by aeration to adjust the pH value between 8-10, so that the heavy metal ions in the wastewater are hydrolyzed, and then PAC is added to precipitate the hydroxide formed by hydrolysis, flocculate and settle, and then solid-liquid separation is performed to obtain heavy metal waste residue and sodium chloride high-salt wastewater;

[0027] S3, the sodium chloride high-salt wastewater is transferred to a reactor, oxalic acid is added, and the amount of oxalic acid added is 1-1.05 times (preferably 1.05 times) of the molar amount of sodium ions, and then stirred for 15 minutes. After standing for a period of time, some sodium oxalate is precipitated, and the filtrate is transferred to a concentrator after filtration for concentration, and an HCl recovery device is installed at the concentrated gas outlet. When the volume of the concentrated liquid is only about 1 / 2 of the original, the concentration is stopped, and the concentrated filtrate is discharged into a condensation pool for condensation and crystallization. The obtained sodium oxalate crystals are sold as products or directly reused after drying and packaging; the recovered hydrochloric acid is directly used for production, and the remaining crystal water can be directly used as precipitation washing water for recovering free rare earth ions. The reaction formula of the concentration and crystallization reaction is:

[0028] NaCl+H2C2O4==HCl↑+NaC2O4↓

[0029] During the concentration and crystallization process, due to the low solubility of sodium oxalate, some sodium oxalate is precipitated during the addition of oxalic acid, and HCl gas is volatilized. The HCl gas is discharged through the concentration exhaust hole and then recovered by the hydrochloric acid recovery device to produce hydrochloric acid.

[0030] In order to better explain the present invention, some examples are listed below.

[0031] Example 1

[0032] A comprehensive utilization method for treating high-salt wastewater produced by bastnaesite by hydrometallurgical treatment comprises the following steps:

[0033] S1, take 1m 3 Fluoride-containing wastewater, the sodium fluoride concentration in the fluoride-containing wastewater was detected to be 5.2g / L, acidic wastewater was added to the fluoride-containing wastewater for neutralization reaction, and the calcium chloride concentration in the acidic wastewater was detected to be 254.0g / L. The pH value in the solution system was controlled at 7-8. When the fluoride ion content in the solution system was detected to be controlled below 0.08g / L, the addition of acidic wastewater was stopped and clarified and plate-frame filtered to obtain 8.84kg of calcium fluoride slag and 1.008m 3 The purity of calcium fluoride slag is 85.44%, the fluoride ion content in sodium chloride wastewater is 0.072g / L, and the calcium ion content is 0.014g / L (converted to calcium chloride mass);

[0034] S2, sodium chloride wastewater and 0.6m 3 The mother liquor of precipitation was mixed with the wastewater for heavy metal removal pretreatment. In the process of heavy metal removal, lime water was added by aeration to adjust the pH value between 8 and 10, and then PAC was added to precipitate the hydroxide formed by hydrolysis and flocculate and settle, and then solid-liquid separation was performed to obtain 6.22 kg of heavy metal waste slag and 1.574 m 3 Sodium chloride high-salt wastewater, in which the concentration of sodium chloride is 52.20g / L;

[0035] S3, the sodium chloride high-salt wastewater was transferred to the reactor, oxalic acid was added in an amount of 1.05 times the molar amount of sodium ions, and then stirred for 15 minutes, filtered after standing for a period of time, and then the filtrate was transferred to a concentrator for concentration, and an HCl recovery device was installed at the concentrated gas outlet. When the volume of the concentrated liquid was only about 1 / 2 of the original volume, the concentration was stopped, and the concentrated filtrate was discharged into a condensation pool for condensation and crystallization and dried to obtain 71.35 kg of sodium oxalate crystals with a purity of 98.6 4%. In the remaining crystal water, the chloride ion concentration is 12.5 g / L (converted into the mass of sodium chloride), the sodium ion concentration is 36.72 g / L (converted into the mass of sodium chloride), the calcium ion concentration is 0.007 g / L (converted into the mass of calcium chloride), the fluoride ion concentration is 0.042 g / L (converted into the mass of sodium fluoride), and the heavy metal ion concentration is 0.001 g / L (converted into the mass of thorium hydroxide); the condensed water meets the reuse water standard, and the sodium chloride recovery rate reaches 73.44%.

[0036] Example 2

[0037] A comprehensive utilization method for treating high-salt wastewater produced by bastnaesite by hydrometallurgical treatment comprises the following steps:

[0038] S1, take 1m 3Fluoride-containing wastewater, detecting that the sodium fluoride concentration in the fluoride-containing wastewater is 5.8 g / L, adding acidic wastewater to the fluoride-containing wastewater for neutralization reaction, detecting that the calcium chloride concentration in the acidic wastewater is 251.4 g / L, controlling the pH value in the solution system to be controlled at 7-8, detecting that the fluoride ion content in the solution system is controlled to be below 0.08 g / L (converted to the mass of sodium fluoride), stopping adding the acidic wastewater and performing clarification and plate-and-frame filtration to obtain 9.174 kg of calcium fluoride slag and 1025 L of sodium chloride wastewater, the purity of the calcium fluoride slag is 86.33%, the fluoride ion content in the sodium chloride wastewater is 0.038 g / L (converted to the mass of sodium fluoride), and the calcium ion content is 0.011 g / L (converted to the mass of calcium chloride);

[0039] S2, sodium chloride wastewater and 0.5m 3 The precipitation mother liquor wastewater is mixed with the heavy metal removal pretreatment. In the heavy metal removal process, lime water is added by aeration to adjust the pH value between 8 and 10, and then PAC is added to flocculate and settle the hydroxide precipitate formed by hydrolysis, and then solid-liquid separation is performed to obtain 10.15 kg of heavy metal waste residue and 1513 L of sodium chloride high-salt wastewater. The sodium chloride concentration in the sodium chloride high-salt wastewater is 56.15 g / L.

[0040] S3, the sodium chloride high-salt wastewater was transferred to the reactor, oxalic acid was added in an amount of 1.05 times the molar amount of sodium ions, and then stirred for 15 minutes, filtered after standing for a period of time, and then the filtrate was transferred to a concentrator for concentration, and an HCl recovery device was installed at the concentrated gas outlet. When the volume of the concentrated liquid was only about 1 / 2 of the original volume, the concentration was stopped, and the concentrated filtrate was discharged into a condensation pool for condensation and crystallization to obtain 72.02 kg of sodium oxalate crystals with a purity of 98.33% In the remaining crystal water, the chloride ion concentration is 10.37 g / L (converted into the mass of sodium chloride), the sodium ion concentration is 30.55 g / L (converted into the mass of sodium chloride), the calcium ion concentration is 0.007 g / L (converted into the mass of calcium chloride), the fluoride ion concentration is 0.021 g / L (converted into the mass of sodium fluoride), and the heavy metal ion concentration is 0.001 g / L (converted into the mass of thorium hydroxide); the condensed water meets the reuse water standard, and the sodium chloride recovery rate reaches 72.78%.

[0041] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A comprehensive utilization method for high-salt wastewater produced by hydrometallurgical treatment of fluorocarbon cerium ore, wherein the high-salt wastewater includes alkaline wastewater mainly containing sodium fluoride produced by acid-base combined treatment, acidic wastewater produced by extraction, and precipitation wastewater mainly containing sodium chloride produced by precipitation, characterized in that: The steps include: A. Mix the alkaline wastewater and the acidic wastewater, neutralize and clarify them, and then filter them. The filter residue is the calcium fluoride product, and the filtrate is the sodium chloride wastewater; B. Mixing sodium chloride wastewater with sedimentation wastewater, then adding lime water by aeration to adjust the pH value, so that the heavy metal ions in the wastewater are hydrolyzed, and then adding flocculants for flocculation and sedimentation, and obtaining filter residue and filtrate after solid-liquid separation, wherein the filter residue is heavy metal waste residue and the filtrate is sodium chloride high-salt wastewater; C. Add oxalic acid to the sodium chloride high-salt wastewater, stir and let it stand, then separate the solid and liquid, concentrate the filtrate, recover the gas through the concentration exhaust hole to produce hydrochloric acid, condense and crystallize the concentrated filtrate, the crystals are the sodium chloride product, and the crystal water is used as process water.

2. The comprehensive utilization method of high-salt wastewater produced by hydrometallurgical treatment of bastnaesite according to claim 1, characterized in that: The concentration of sodium fluoride in alkaline wastewater is 4-8g / L, and the concentration of calcium chloride in acidic wastewater is 200-300g / L.

3. The comprehensive utilization method of high-salt wastewater produced by hydrometallurgical treatment of bastnaesite according to claim 1, characterized in that: The concentration of sodium fluoride in alkaline wastewater is 5-8g / L, and the concentration of calcium chloride in acidic wastewater is 250g / L.

4. The comprehensive utilization method of high-salt wastewater produced by hydrometallurgical treatment of bastnaesite according to any one of claims 1 to 3, characterized in that: In step A, the pH value of the mixed solution system is controlled to be between 6 and 9.

5. The comprehensive utilization method of high-salt wastewater produced by hydrometallurgical treatment of bastnaesite as claimed in claim 4, characterized in that: In step A, the fluorine content in the obtained sodium chloride wastewater does not exceed 0.08 g / L.

6. The comprehensive utilization method of high-salt wastewater produced by hydrometallurgical treatment of bastnaesite as claimed in claim 5, characterized in that: In step B, lime water is added to adjust the pH to 8-10.

7. The comprehensive utilization method of high-salt wastewater produced by hydrometallurgical treatment of bastnaesite as claimed in claim 6, characterized in that: In step C, the amount of oxalic acid added is 1-1.05 times the molar amount of sodium ions.

8. The comprehensive utilization method of high-salt wastewater produced by hydrometallurgical treatment of bastnaesite as claimed in claim 6, characterized in that: In step C, the amount of oxalic acid added is 1.05 times the molar amount of sodium ions.

9. The comprehensive utilization method of high-salt wastewater produced by hydrometallurgical treatment of bastnaesite as claimed in claim 6, characterized in that: In step C, when the filtrate is concentrated, the concentration is stopped when the volume of the filtrate is reduced to 1 / 2 of the original volume.

10. The comprehensive utilization method of high-salt wastewater produced by hydrometallurgical treatment of bastnaesite as claimed in claim 9, characterized in that: In step C, the gas produced during the concentration process is absorbed by a hydrochloric acid recovery unit.

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