Shown in Figure 1 is a pre-treatment principle process for the intensification of high temperature sulfuric acid roasting to decompose mixed rare earth concentrates in production. The main equipment and technical conditions used in the production process are as follows.
Fig.1 Process flow of high temperature sulfuric acid roasting mixed rare earth concentrate and pretreatment principle
1. Sulfuric acid roasting
The main equipment of the roasting process is a rotary kiln with steel plate rolled and lining anti-corrosion refractory brick. Kiln puzzle combustion chamber, fuel can be used as heavy oil, coal. The length of roasting of the material in the kiln is related to the length, number of revolutions and slope of the kiln. The technical conditions in production are:
Mine: acid (sulfuric acid concentration of 92%) = 1: (1.2 ~ 1.4);
Kiln head temperature 700 ~ 800 ° C;
Kiln tail temperature 220 ~ 270 ° C;
The concentrate decomposition rate is about 93%.
Second, leaching and purification
The hot calcined product from the rotary kiln is slurried in the slurry tank with a washing slag, and the FeCl 3 solution is added, and then transferred to the leaching tank through the pump. The leaching was stirred in a leaching tank while adding MgO to neutralize the residual acid to pH = 3.5 to 4.0, and the slag and the leachate were separated by a plate and frame filter press. In order to increase the rare earth yield, the leaching slag must be subjected to a secondary slag washing operation. The technical conditions in production are:
Solid-liquid ratio (mass: volume) = 1: (10 ~ 15);
Fe/P=2~3;
Leaching time 2~3h;
Leaching temperature; normal temperature;
The neutralization pH is 3.5 to 4.5.
Technical requirements for post-purification leachate:
REO=25～40g/L;
Fe 2 O 3 <0.05 g/L;
PO 4 3 - <0.005g/L;
ThO 2 <0.001 g/L.
Third, solvent extraction transformation
Using bis (2-ethylhexyl) phosphoric acid (i.e., P 204) sulfuric acid extractant solution is extracted into the organic phase of all rare earth, and then to hydrochloric acid was back-extracted, a rare earth sulphate solution may be converted to a rare earth hydrochloric acid solution. In the process of extraction and transformation, impurities such as Ca2+, Mg2+, Fe2+, etc. can be excluded from the raffinate, and the concentration of the rare earth solution is enriched by controlling the concentration and flow rate of the stripping agent. Industrial product according to user requirements, neodymium and samarium are sometimes grouped with the first front in the same extractant prior to transformation, a packet raffinate rare earth element is La ~ Nd. The rare earth element in the stripping solution is a medium-heavy rare earth element after the cerium, and after being precipitated with oxalic acid or ammonium hydrogencarbonate , the cerium , lanthanum and cerium riches can be directly recovered. The raffinate of La~Nd element enters the extraction and transformation process. Both the grouping and the extraction transformation are carried out by fractional distillation. The main technical conditions are as follows.
é’•é’ grading
Series: extraction + washing + back extraction = 7 + 13 + 8 = 28
Organic phase composition: 1mol/LP 204 - kerosene
Stripping agent acidity: 6mol/L hydrochloric acid
La～Nd extraction transformation
series:
Series: extraction + clarification + back extraction = 7 + 2 + 6 = 15
Organic phase composition: peer grouping
La ~ Nd liquid acidity: pH = 1 ~ 4.5
Stripping agent and acidity: 6mol/L HCl
The quality requirements of the stripping solution: REO=250-270g/L, SO42-<0.179g/L, Fe2O3<0.418g/L. If the SO 4 2 - in the extract does not meet the requirements, BaCl 2 can be added quantitatively.
Fourth, evaporation and concentration
The evaporation concentration process is carried out in a steam jacketed heating chamber and an enamel-lined evaporation tank. The technical parameters of the evaporation process are as follows:
The vacuum inside the tank is 6×10 4 Pa;
Evaporation temperature 108 ~ 115 ° C;
The vapor pressure is 0.3 to 0.4 MPa.
5. Preparation of rare earth carbonate
The rare earth carbonate can be directly prepared by adding ammonium bicarbonate to the leachate. The main technical conditions in the production are as follows:
Leaching solution rare earth concentration REO=30～50g/L;
Precipitation temperature 40 ~ 60 ° C;
Stirring speed 60 ~ 80r / min;
Rare earth carbonate requires REO ≥ 43%, Fe 2 O 3 ≤ 0.5%, and SO 4 2 - ≤ 2%.
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