Ionic rare earth separation high ammonium salt wastewater treatment method

Abstract

The invention discloses an ionic rare earth separation high ammonium salt wastewater treatment method, which comprises: adding ammonia water and xanthate to wastewater, carrying out solid-liquid separation, continuously adding phosphate to the liquid, and carrying out solid-liquid separation to obtain impurity-removed wastewater; carrying out evaporative crystallization on the waste water after impurity removal until the volume is reduced to 10-30%, and then carrying out solid-liquid separation to obtain an ammonium chloride product and crystallization mother liquor; and combining the crystallization mother liquor with the high ammonium salt wastewater, and repeating the steps. The invention aims to provide the method for recycling the southern ionic rare earth separation high ammonium salt wastewater, which is simple in process, low in operation cost and good in product quality.

Description

Technical Field

[0001] The present invention belongs to the technical field of wastewater treatment, and particularly relates to a method for treating high-ammonium salt wastewater in ionic rare earth separation. Background Art

[0003] The wastewater from ionic rare earth separation enterprises is high-salt wastewater with high ammonia nitrogen. In almost all the resource utilization processes of rare earth separation wastewater, impurities are removed first and then evaporation crystallization is carried out. Salt products are produced by evaporation crystallization, and the condensed water is reused for wastewater. In order to obtain qualified salt products, deep impurity removal is usually carried out before evaporation crystallization to separate metal impurity ions. Due to the variety of metal impurity ions, multiple impurity removal methods are often combined, resulting in a complex impurity removal process and high cost. Moreover, during the evaporation crystallization process, the wastewater is continuously concentrated, and the concentration of impurity ions in the evaporation mother liquor increases continuously, leading to unqualified product quality in the later stage. Therefore, there is an urgent need for a method for resource utilization of high-ammonium salt wastewater in southern ionic rare earth separation with simple process, low operating cost and good product quality. Summary of the Invention

[0004] The present invention discloses a method for treating high-ammonium salt wastewater in ionic rare earth separation, aiming to provide an economical and simple method for comprehensive utilization of wastewater.

[0005] The high-ammonium salt wastewater in ionic rare earth separation of the present invention is wastewater with the main salt component being ammonium chloride.

[0006] The technical solution of the present invention is as follows:

[0007] 1) Add ammonia water with a concentration of 10 - 15 mol / L to the high-salt wastewater in ionic rare earth separation to adjust the pH of the wastewater to 5 - 7, and then add xanthate. After solid-liquid separation, pretreated wastewater is obtained; wherein, the addition amount of xanthate is such that the molar ratio of xanthate to heavy metal ions in the wastewater is 1 - 3:1;

[0008] 2) To the pretreated wastewater obtained in step 1), add one or several of phosphoric acid, ammonium phosphate, diammonium phosphate, and monoammonium phosphate according to the molar ratio of phosphate radical to calcium ions in the wastewater being 1 - 3:1. Add ammonia water with a concentration of 10 - 15 mol / L to adjust the pH of the wastewater to 7 - 7.5, and then carry out solid-liquid separation to obtain the wastewater after impurity removal and calcium precipitation residue;

[0009] 3) Carry out evaporation crystallization on the wastewater after impurity removal obtained in step 2) at an evaporation crystallization temperature of 60°C - 75°C and a pressure of 10 Kpa - 40 Kpa. Evaporate and concentrate the volume to 10 - 30% to obtain ammonium chloride products and crystallization mother liquor; the crystallization mother liquor is mixed with the high-ammonium salt wastewater in ionic rare earth separation and returned to step 1);

[0010] 4) Add the calcium precipitation residue obtained in step 2) to the ammonium sulfate solution, stir for a period of time, then perform solid-liquid separation to obtain a precipitation residue and a phosphate solution, and return the phosphate solution to step 2).

[0011] The technical concept and beneficial effects of the present invention are as follows:

[0012] Rare earth separation wastewater often undergoes deep impurity removal before evaporation and crystallization. Due to the large variety of metal impurity ions, the impurity removal process is complex, requiring multiple impurity removal agents and multiple steps of impurity removal; during the evaporation and crystallization process, ammonium chloride is easily decomposed into ammonia and hydrochloric acid and enters the condensate water, resulting in the inability to utilize the condensate water; moreover, as the wastewater is continuously concentrated, the concentration of impurity ions increases continuously, leading to unqualified product quality in the later stage. At the same time, the wastewater also contains a certain amount of fluoride ions, which have a relatively large corrosive effect on the evaporation equipment. In order to improve these shortcomings, the present invention starts from the following aspects: 1) By controlling the pH of the wastewater, first form calcium fluoride precipitation with the fluoride ions in the wastewater, and at the same time add xanthate to efficiently precipitate heavy metals; 2) Select substances containing phosphate groups, adjust the pH of the wastewater, and separate most of the impurity metal ions such as Ca in the impurity components in one step; 3) According to the characteristics that ammonium chloride is easily decomposed into ammonia and hydrochloric acid at high temperatures, increase the vacuum degree to reduce the evaporation temperature and avoid the decomposition of ammonium chloride; 4) Return the crystallization mother liquor to be mixed with the high-salt wastewater for rare earth separation to recover ammonium chloride; 5) In order to recycle phosphate, use sulfuric acid to transform the precipitation residue and return the phosphate to precipitate calcium, saving the treatment cost.

[0013] The above process of the present invention realizes the low-cost treatment of high-ammonium salt wastewater for ionic rare earth separation. Specific embodiments

[0014] Example 1

[0015] Into the high-ammonium salt wastewater for ionic rare earth separation containing 120 g / L of ammonium chloride, add 10 mol / L ammonia water to adjust the pH to 7, add xanthate according to the molar ratio of xanthate: heavy metal ions of 1.1:1, and filter to obtain pretreated wastewater; add phosphate to the pretreated wastewater according to the molar ratio of phosphate: calcium ions of 1.1:1, and add 10 mol / L ammonia water to adjust the pH to 7, filter to obtain the wastewater after impurity removal and calcium precipitation residue. In the wastewater after impurity removal, the fluoride ion concentration is less than 20 mg / L, the Ca concentration is less than 50 mg / L, and the concentrations of Pb, Zn, Al, and Fe metal ions are all less than 1 mg / L; then perform MVR evaporation on the wastewater after impurity removal, with the evaporation and crystallization temperature of 60 °C and the pressure of 10 Kpa. After evaporating and concentrating to 13% of the volume, perform crystallization filtration to obtain ammonium chloride products and crystallization mother liquor; finally, mix the crystallization mother liquor with fresh high-salt wastewater for ionic rare earth separation and return it to wastewater treatment. After analysis, the ammonium chloride products meet the industrial product standards. Add the calcium precipitation residue to the sulfuric acid solution, stir, filter to obtain calcium sulfate residue and solution, and return the solution to precipitate calcium.

[0016] Example 2

[0017] To the high-ammonium salt wastewater from ionic rare earth separation containing 130 g / L of ammonium chloride, add 10 mol / L ammonia water to adjust the pH to 5. Add xanthate according to the molar ratio of xanthate:heavy metal ions of 3:1, and filter to obtain the pretreated wastewater. To the pretreated wastewater, add phosphate according to the molar ratio of phosphate:calcium ions of 3:1, and add 10 mol / L ammonia water to adjust the pH to 7.3. Filter to obtain the wastewater after impurity removal and calcium precipitation slag. In the wastewater after impurity removal, the fluoride ion concentration is less than 15 mg / L, the Ca concentration is less than 20 mg / L, and the concentrations of Pb, Zn, Al, and Fe metal ions are all less than 1 mg / L. Then, subject the wastewater after impurity removal to MVR evaporation, with the evaporation crystallization temperature at 70 °C and the pressure at 35 KPa. After evaporating and concentrating the volume to 20%, filter the crystals to obtain ammonium chloride product and crystallization mother liquor. Finally, mix the crystallization mother liquor with the high-salt wastewater from ionic rare earth separation and return it to wastewater treatment. After analysis, the ammonium chloride product meets the industrial-grade product standard. Add the calcium precipitation slag to sulfuric acid solution and stir, then filter to obtain calcium sulfate slag and solution, and the solution is returned for calcium precipitation.

[0018] Example 3

[0019] To the high-ammonium salt wastewater from ionic rare earth separation containing 130 g / L of ammonium chloride, add 15 mol / L ammonia water to adjust the pH to 6. Add xanthate according to the molar ratio of xanthate:heavy metal ions of 2:1, and filter to obtain the pretreated wastewater. To the pretreated wastewater, add phosphate according to the molar ratio of phosphate:calcium ions of 2:1, and add 15 mol / L ammonia water to adjust the pH to 7.5. Filter to obtain the wastewater after impurity removal and calcium precipitation slag. In the wastewater after impurity removal, the fluoride ion concentration is less than 12 mg / L, the Ca concentration is less than 30 mg / L, and the concentrations of Pb, Zn, Al, and Fe metal ions are all less than 1 mg / L. Then, subject the wastewater after impurity removal to MVR evaporation, with the evaporation crystallization temperature at 65 °C and the pressure at 30 KPa. After evaporating and concentrating the volume to 25%, filter the crystals to obtain ammonium chloride product and crystallization mother liquor. Finally, mix the crystallization mother liquor with the high-salt wastewater from ionic rare earth separation and return it to wastewater treatment. After analysis, the ammonium chloride product meets the industrial-grade product standard. Add the calcium precipitation slag to sulfuric acid solution and stir, then filter to obtain calcium sulfate slag and solution, and the solution is returned for calcium precipitation.

Claims

1. A method for treating high-ammonium-salt wastewater from ionic rare earth separation, characterized in that, It includes the following steps: 1) Add ammonia water to the high-salt wastewater from ionic rare earth separation to adjust the pH, and then add xanthate. After solid-liquid separation, the pretreated wastewater is obtained; 2) Add phosphate and ammonia water to the pretreated wastewater obtained in step 1). After solid-liquid separation, the wastewater after impurity removal and calcium precipitation residue are obtained; 3) Evaporate and crystallize the wastewater after impurity removal obtained in step 2). After evaporating and concentrating the volume to 10-30%, ammonium chloride products and crystallization mother liquor are obtained; the crystallization mother liquor is mixed with the high-ammonium salt wastewater from ionic rare earth separation and returned to step 1); 4) Add the calcium precipitation residue obtained in step 2) to the ammonium sulfate solution. After stirring for a period of time and then performing solid-liquid separation, a precipitation residue and a phosphate solution are obtained. The phosphate solution is returned to step 2).

2. The method for treating high-ammonium salt wastewater in ionic rare earth separation according to claim 1, wherein In step 1), the concentration of ammonia water added to the high-ammonium salt wastewater from ionic rare earth separation is 10-15 mol / L.

3. A method for treating high-ammonium salt wastewater in ionic rare earth separation according to claim 1, characterized in that, In step 1), the pH is adjusted to 5-7.

4. A method for treating high-ammonium-salt wastewater in ionic rare earth separation according to claim 1, characterized in that, In step 1), the addition amount of xanthate is such that the molar ratio of xanthate to heavy metal ions in the wastewater is 1-3:

1.

5. A method for treating high-ammonium-salt wastewater in ionic rare earth separation according to claim 1, characterized in that, The phosphate in step 2) is one or more of phosphoric acid, ammonium phosphate, ammonium dihydrogen phosphate, and diammonium hydrogen phosphate.

6. The method for treating high-ammonium salt wastewater in ionic rare earth separation according to claim 1, characterized in that In step 2), the addition amount of phosphate is such that the molar ratio of phosphate to calcium ions in the wastewater is 1-3:

1.

7. A method for treating high-ammonium-salt wastewater in ionic rare earth separation according to claim 2, characterized in that In step 2), add phosphate and ammonia water to the pretreated wastewater until the pH of the wastewater reaches 7-7.5, and then perform solid-liquid separation.

8. A method for treating high-ammonium-salt wastewater in ionic rare earth separation according to claim 1, characterized in that, In step 2), the concentration of ammonia water is 10-15 mol / L.

9. A method for treating high-ammonium-salt wastewater in ionic rare earth separation according to claim 1, characterized in that, In step 3), the evaporation crystallization temperature is 60°C-75°C, and the pressure is 10 Kpa-40 Kpa.