CN105256156B - Process for decomposing fluorine-containing rare earth molten salt waste residues - Google Patents

Abstract

The invention belongs to the field of resource recycling and reuse, and in particular relates to a method for recovering rare earth elements from electrolytic waste residues of fluoride-containing rare earth molten salts by sodium hydroxide alkali conversion and hydrochloric acid dissolution. The present invention comprises the following steps: raw material drying and pulverization of fluorine-containing rare earth molten salt electrolysis waste residue, roasting and alkali conversion, washing the alkali melt to remove fluorine, obtaining calcium fluoride, dissolving with hydrochloric acid, and returning the acid-dissolved feed solution; the important parts of the present invention Low-temperature alkali conversion, calcium fluoride recovery and liquid caustic recovery are carried out in the production process, thus making the present invention more simple in procedure, energy saving and environmental protection, and high primary recovery rate of rare earths compared with other processes (finally, the leaching rate of rare earth elements can reach 98% above) and other outstanding advantages.

Description

A process for decomposing fluorine-containing rare earth molten salt waste slag

technical field

The invention belongs to the field of resource recycling and reuse, and in particular relates to a method for recovering rare earth elements from electrolytic waste residues of fluoride-containing rare earth molten salts by sodium hydroxide alkali conversion and hydrochloric acid dissolution.

Background technique

At present, single rare earth metals and functional rare earth alloys are mainly produced by fluoride system oxidation rare earth electrolytic molten salt process. A certain amount of molten salt waste slag will be produced in the rare earth electrolysis process, and these molten salt waste slags contain 20%-70% rare earth (calculated by REO), and most of the rare earth elements exist in the form of fluoride. At present, the most common method to deal with molten salt electrolysis waste residue is to burn concentrated sulfuric acid at high temperature to remove fluorine, then leach rare earth sulfate with water, and then recover rare earth products through subsequent treatment. This process consumes a lot of acid, has special requirements for equipment, the primary recovery rate of rare earth is about 60% of the total amount, and the use of concentrated sulfuric acid and the treatment of hydrogen fluoride gas generated during the roasting process have special technical requirements, which are prone to accidents. Chinese patent (Application No.: 201010505807.2) discloses a method for recovering rare earth elements from rare earth molten salt electrolysis waste, which uses electrolysis waste and calcium hydroxide in a weight ratio of 1:0.5 to mix 950-1000 ° C and roast, and then use 30 % hydrochloric acid dissolved. This method improves the leaching rate of rare earth, but the roasting temperature is too high, the energy consumption is large, the pot loss is large during burning, and the acid consumption is large due to excessive calcium hydroxide during acid dissolution, and the obtained solution contains a large amount of Ca, Ba, etc. Rare earth elements cause high extraction and separation costs in the later stage.

Contents of the invention

The purpose of the present invention is to provide a process for decomposing fluorine-containing rare earth molten salt waste residue, which is more efficient, energy-saving and environmentally friendly.

Technical scheme of the present invention: a process for decomposing fluorine-containing rare earth molten salt waste residue, comprising the following steps:

A. Drying and pulverizing raw materials of fluorine-containing rare earth molten salt electrolytic waste residue: for wet materials, they should be dried at 150-200°C first, and then crushed into powder by Raymond machine;

B. Roasting and alkali conversion: mix the powder and caustic soda in the step A according to the weight ratio of 1:0.6-0.8, and put it in a bowl, and roast it at 500-600°C for 2-6 hours to convert the rare earth fluoride into the corresponding oxidation Compound and sodium fluoride, after obtaining blocky alkali melt, use Raymond machine to pulverize in time;

C. Fluorine removal by water washing of alkali melt: add alkali melt and water to the washing bucket at a weight ratio of 1:10, wash 3-5 times until the pH value is 7-9, and then press to obtain washing residue;

D. Obtaining calcium fluoride: add milk of lime to the washing solution in step C to make it neutral, press it, wash the slag with dilute hydrochloric acid to keep it neutral, press it again, and dry it at 150-200°C to obtain a content of more than 90%. calcium fluoride;

E. Dissolving with hydrochloric acid: Use concentrated hydrochloric acid to stir the slag of step C in proportion at 70-90°C for 1 hour, then carefully add an appropriate amount of NaClO ₃ and stir for 1 hour until there is no Fe ²⁺ , then use liquid caustic soda to adjust the pH value to 3.5 In addition to Fe ³⁺ , add 2mol/L Na ₂ SO ₄ solution until no white precipitate is formed to remove Ca ²⁺ and Ba ²⁺ ; press, wash, and dry, and the slag mainly contains graphite, ferric hydroxide, and barium sulfate Obtain REO content in the 50-120g/L rare earth chloride feed solution to be separated by subsequent extraction to obtain high-purity rare earth products (extraction process is prior art);

F. Callback of acid solution: add liquid alkali to the washing liquid in step E to adjust the pH value to 12 and sink for 24 hours to extract the supernatant liquid, and the lower layer of turbid liquid is rare earth hydroxide, which can be used as the acid in step E instead of liquid alkali Callback of solution;

In the step E, the washing slag weight and the concentrated hydrochloric acid volume ratio are 1:1.5 tons/cubic meter, and the concentrated hydrochloric acid concentration is the industrial hydrochloric acid of 10mol/L;

The amount of _NaClO3 in step E is determined by the Fe2 ⁺ content of the solution during production, and its actual amount is 1.2 times the theoretical amount, namely: 1.2×6n( _NaClO3 )=n(Fe2 ⁺ ), where n represents the amount of substance.

In step B, the weight ratio of powder to caustic soda is determined by the weight ratio of fluorine in the electrolytic waste residue. If the fluorine content is 0-10%, it is 1:0.6; if the fluorine content is 10-15%, it is 1:0.7; If it is more than 15%, the ratio is 1:0.8.

Described liquid caustic soda is industrial liquid caustic soda, and concentration is 10mol/L.

Described dilute hydrochloric acid concentration is 0.1mol/L.

In step B, the burning temperature is related to the amount of mixed alkali. If the amount of mixed alkali of the same raw material is high, the temperature can be appropriately lowered and the time extended. Low temperature is not conducive to fluorine conversion, and high temperature is good for fluorine conversion, but it is easy to stick to the bowl.

The chemical reaction process of the present invention is as follows:

Alkali conversion of electrolytic waste residue: 2REF ₃ +6NaOH＝RE ₂ O ₃ +6NaF ₃ +H ₂ O

BaF ₂ +2NaOH=BaO+2NaF+H ₂ O

4RE+3O ₂ ＝2RE ₂ O ₃

3Fe+2O ₂ ＝Fe ₃ O ₄

Hydrochloric acid dissolution: RE ₂ O ₃ +6H ⁺ = 2RE ³⁺

Fe ₃ O ₄ +8H ⁺ ＝2Fe ³⁺ +Fe ²⁺ +4H ₂ O

Oxidation: 6Fe ²⁺ +ClO ^3- +6H ⁺ ＝6Fe ³⁺ +Cl ^- +3H ₂ O

Decalcified barium: Ca ²⁺ +S0 ₄ ^2- ＝CaS0 ₄

Ba ²⁺ +S0 ₄ ^2- ＝BaS0 ₄

Adjust pH value and remove iron: Fe ³⁺ +3H ₂ O＝Fe(OH) ₃ +3H ⁺

The advantages of using sodium hydroxide alkali conversion and hydrochloric acid dissolution in the present invention are: (1) the leaching efficiency of rare earth is higher, and the leaching rate can reach more than 98% at one time; (3) Rare earth elements and non-rare earth elements are effectively separated, which facilitates subsequent extraction and separation; (4) Simple operation, more environmentally friendly, and calcium fluoride can be recycled.

Description of drawings

Fig. 1 is a process flow diagram of the present invention.

detailed description

The present invention will be further described below in conjunction with the examples, but the present invention is not limited only to the following examples. (washing slag and concentrated hydrochloric acid ratio in the embodiment: 1:1.5 tons/cubic meter, concentrated hydrochloric acid concentration is the industrial hydrochloric acid of 10mol/L; Liquid caustic soda is industrial liquid caustic soda, and concentration is 10mol/L; Dilute hydrochloric acid concentration is 0.1mol/L L.)

Example 1: 1000Kg of rare earth molten salt waste residue contains 471Kg of rare earth REO, the percentage content of a single rare earth and the test of non-rare earth content are shown in Table 1;

Table 1: Raw material distribution table

project La ₂ O _{3 CeO2} Pr ₆ O ₁₁ Nd ₂ O ₃ Sm ₂ O ₃ Eu ₂ O ₃ Gd ₂ O ₃ Tb ₄ O _{7 Dy2O3 _} quality(%) 2.94 0.07 19.18 76.84 0.07 <0.01 0.53 <0.01 0.22 project Ho ₂ O ₃ Er ₂ O ₃ Tm ₂ O ₃ Yb ₂ O ₃ Lu ₂ O ₃ Y ₂ O ₃ REO _{Fe2O3 _} f quality(%) 0.10 <0.01 <0.01 <0.01 <0.01 <0.01 47.10 7.58 16.57

Production steps:

(1) The molten salt waste slag raw material is crushed into a powder with a particle size of about 100 mesh by a Raymond machine;

(2) Roasting alkali conversion: mix the powder and caustic soda in step (1) evenly in a weight ratio of 1:0.8, and put it in a bowl, and roast it in a push-pull kiln at 550 ° C for 4 hours; Raymond machine crushed to about 100 mesh in time;

(3) Washing of the alkali-melted product: add the alkali-melted product and water to the washing bucket at a weight ratio of 1:10, stir for 1 hour, press to obtain the washing residue, and repeat twice until the washing water pH=8 to obtain the washing residue;

(4) Obtaining calcium fluoride: add milk of lime to the first washing solution in step (3) to make it neutral, press it, wash the slag with dilute hydrochloric acid to keep it neutral, press it again, and dry it at 200°C to obtain the content About 90% calcium fluoride 260Kg;

(5) Dissolving with hydrochloric acid: wash the slag in step (3) with concentrated hydrochloric acid at a ratio of 1:1.5 and stir at 80°C for 1 hour, use an iron test reagent to detect Fe ²⁺ , then carefully add 3.5Kg of NaClO ₃ and stir for 1 hour, Afterwards, adjust the pH value to 3.5 with liquid caustic soda, then add about 4L of 2mol/L Na ₂ SO ₄ solution while measuring until no white precipitate is formed to remove Ca ²⁺ and Ba ²⁺ ; squeeze, wash, and dry to obtain wet pressed Slag 265.5Kg, obtain 5000L of rare earth chloride feed solution containing 92.50g/L of REO, and obtain high-purity rare earth products after subsequent extraction and separation;

(6) Add liquid caustic soda to the second washing liquid in step (5) to adjust the pH value to 12 and sink for 24 hours to extract the supernatant liquid, and the lower layer of turbid liquid is mainly rare earth hydroxide, which can be used in step (5) instead of liquid caustic soda Callback of medium acid solution.

The analysis of production results is shown in Table 2 and Table 3:

Table 2: Analysis and test table of main items of acid-dissolved slag and acid-dissolved feed solution

Table 3: Analysis table of acid solubility rate

Example 2: 850Kg of rare earth molten salt waste slag contains 360Kg of rare earth REO, the percentage content of a single rare earth and the content of non-rare earth are shown in Table 4.

Table 4: Raw material distribution table

Production steps:

(1) The molten salt waste slag raw material is crushed into a powder with a particle size of about 100 mesh by a Raymond machine;

(2) Roasting alkali transfer: Mix the powder and caustic soda in the step (1) evenly at a weight ratio of 1:0.7, put it in a bowl, and roast it in a push-pull kiln at 600°C for 4 hours. The blocky alkali melt obtained was pulverized in time to about 100 mesh with a Raymond machine;

(3) Washing of alkali-melted products: Add the alkali-melted product and water to the washing bucket at a weight ratio of 1:10, stir for 1 hour, and squeeze to obtain washing slag. Repeat 2 times until the washing water pH=9 to obtain the washing residue.

(4) Obtaining calcium fluoride: add milk of lime to the first washing solution in step (3) to make it neutral, press it, wash the slag with dilute hydrochloric acid to keep it neutral, press it again, and dry it at 200°C to obtain the content About 91% calcium fluoride 141Kg.

(5) Dissolving with hydrochloric acid: Use concentrated hydrochloric acid to wash the slag in step (3) and stir at 90°C for 1 hour, use iron test reagent to detect the absence of Fe ²⁺ , use liquid caustic soda to adjust the pH value to 3.5, and then measure While adding about 3L of 2mol/L Na ₂ SO ₄ solution, remove Ca ²⁺ and Ba ²⁺ until no white precipitate is formed. Squeeze, wash, and blow dry to obtain 123.5Kg of wet pressed slag. 4500L of rare earth chloride feed solution was obtained, containing about 78.48g/L of REO, and high-purity rare earth products were obtained after subsequent extraction and separation.

(6) Add liquid caustic soda to the second washing liquid in step (5) to adjust the pH value to 12 and sink for 24 hours to extract the supernatant liquid, and the lower layer of turbid liquid is mainly rare earth hydroxide, which can be used in step (5) instead of liquid caustic soda Callback of medium acid solution.

The production results are analyzed as follows:

Table 5: Analysis and test table of main items of acid-dissolved slag and acid-dissolved feed solution

Table 6: Analysis table of acid solubility rate

Note: The data of waste residue raw materials, acid-dissolved residue, and acid-dissolved liquid analysis test table are all from the test results of a testing center of a research institute in Ganzhou.

Claims (4)

1. A technique for decomposing fluorine-containing rare earth molten salt waste slag is characterized in that: comprising the following steps: A. Drying and pulverizing raw materials of fluorine-containing rare earth molten salt electrolytic waste residue: for wet materials, they should be dried at 150-200°C first, and then crushed into powder by Raymond machine; B. Roasting and alkali conversion: mix the powder and caustic soda in the step A according to the weight ratio of 1:0.6-0.8, and put it in a bowl, and roast it at 500-600°C for 2-6 hours to convert the rare earth fluoride into the corresponding oxidation Compound and sodium fluoride, after obtaining blocky alkali melt, use Raymond machine to pulverize in time; C. Fluorine removal by water washing of alkali melt: add alkali melt and water to the washing bucket at a weight ratio of 1:10, wash 3-5 times until the pH value is 7-9, and press to obtain washing residue; D. Obtaining calcium fluoride: add milk of lime to the water washing solution in step C to make it neutral, press it, wash the slag with dilute hydrochloric acid to keep it neutral, press it again, and dry it at 150-200°C to obtain a content of more than 90%. calcium fluoride; E. Dissolving with hydrochloric acid: Use concentrated hydrochloric acid to stir the slag of step C in proportion at 70-90°C for 1 hour, then carefully add an appropriate amount of NaClO ₃ and stir for 1 hour until there is no Fe ²⁺ , then use liquid caustic soda to adjust the pH value to 3.5 In addition to Fe ³⁺ , add 2mol/L Na ₂ SO ₄ solution until no white precipitate is formed to remove Ca ²⁺ and Ba ²⁺ ; press, wash, and dry to obtain chlorinated The rare earth feed liquid is subjected to subsequent extraction and separation to obtain high-purity rare earth products; F. Callback of acid solution: add liquid alkali to the washing liquid in step E to adjust the pH value to 12 and sink for 24 hours to extract the supernatant liquid, and the lower layer of turbid liquid is rare earth hydroxide, which can be used as the acid in step E instead of liquid alkali Callback of solution; In the step E, the washing residue weight and the concentrated hydrochloric acid volume ratio are 1:1.5 tons/cubic meter, and the concentrated hydrochloric acid concentration is the industrial hydrochloric acid of 10mol/L; The amount of _NaClO3 in step E is determined by the Fe2 ⁺ content of the solution during production, and its actual amount is 1.2 times the theoretical amount, namely: 1.2×6n( _NaClO3 )=n(Fe2 ⁺ ), where n represents the amount of substance. 2. A process for decomposing fluorine-containing rare earth molten salt waste slag according to claim 1, characterized in that: the weight ratio of powder and caustic soda in step B is determined by the fluorine weight ratio in the electrolytic waste residue, if the fluorine content is 0 1:0.6 for -10%, 1:0.7 for 10-15% fluorine, and 1:0.8 for more than 15% fluorine. 3. A process for decomposing fluorine-containing rare earth molten salt waste slag according to claim 1, characterized in that: said liquid caustic soda is industrial liquid caustic soda with a concentration of 10mol/l. 4. A process for decomposing fluorine-containing rare earth molten salt waste slag according to claim 1, characterized in that: the concentration of the dilute hydrochloric acid is 0.1mol/L.