Baking section

Conversion roasting: spodumene concentrate is manually transported from the concentrate warehouse to the bucket elevator and lifted to the concentrate bin. It is then fed into the tail of the lithium carbonate rotary kiln through a disc feeder and a screw feeder. The concentrate is dried using high-temperature gas in the preheating section of the kiln tail. The concentrate undergoes crystal transformation roasting at a temperature of about 1200 ℃ in the calcination section, converting from α - type (monoclinic crystal system, density 3150kg/m3) to β - type spodumene (tetragonal crystal system, density 2400kg/m3, i.e. roasting material), with a conversion rate of about 98% Acid roasting: After cooling in the cooling section, the roasted material is discharged from the kiln head, and then naturally cooled and ground by a ball mill to a particle size of 0.074mm and above 90%. It is transported to the tailings bin of the acid roasting kiln, and then added to the acid mixer by a feeder and a screw conveyor in a certain proportion with concentrated sulfuric acid (above 93%) (concentrated sulfuric acid is calculated as excess lithium equivalent in the roasted material by 35%, and about 0.21 tons of concentrated sulfuric acid are required per ton of roasted material). After mixing evenly, it is added to the acid roasting chamber and subjected to sealed acid roasting at a temperature of about 250-300 ℃ for 30-60 minutes. The β - type spodumene in the roasted material reacts with sulfuric acid, and the hydrogen ions in the acid replace the lithium ions in the β - type spodumene, causing Li2O and SO42- to react with lithium ions in Combine with Li2SO4 that is soluble in water to obtain acidified clinker Slurry leaching and washing: The clinker is cooled and slurried to dissolve soluble lithium sulfate into the liquid phase. To reduce the corrosion of the leaching equipment by the solution, residual acid in the clinker is neutralized with limestone slurry, the pH value is adjusted to 6.5-7.0, and most impurities such as iron and aluminum are removed at the same time. The liquid-solid ratio of the leaching is about 2.5, and the leaching time is about 0.5 hours. The leaching slurry is filtered and separated to obtain the leaching solution, which contains approximately 100g/L Li2SO4 (27g/L Li2O). The filter cake is the leaching residue, with a moisture content of about 35%. The attached solution of leaching residue contains lithium sulfate. To reduce lithium loss, the leaching residue is subjected to reverse stirring and washing, and the washing solution is then returned to the slurry for leaching Purification of leachate: During acid roasting, in addition to alkali metals reacting with sulfuric acid to produce soluble corresponding sulfates, other iron, aluminum, calcium, magnesium, etc. also react with sulfuric acid to produce corresponding sulfates. Although some impurities in the clinker can be removed during the leaching process, the remaining impurities still remain in the leaching solution and need to be further purified to ensure product quality. The purification of leachate adopts the alkalization and calcium removal method, using alkalizing agent lime milk (containing CaO 100-150g/L) to alkalize the leachate, raise the pH value to 11-12, and hydrolyze magnesium and iron into hydroxide precipitation. Then use sodium carbonate solution (containing Na2CO3 300g/L) to react with calcium sulfate to produce calcium carbonate precipitate, thereby removing the calcium in the leachate and the calcium introduced by the alkalizing agent lime milk. The alkaline calcium removal slurry is subjected to liquid-solid separation to obtain a purified solution with a calcium lithium ratio of less than 9.6 × 10-4. The filter cake is the calcium residue, which is returned to the slurry for leaching Purification solution evaporation and concentration: Due to the low concentration of lithium sulfate and low lithium precipitation rate, the purification solution cannot be directly used for lithium precipitation or lithium chloride production. It is necessary to first adjust the pH of the purification solution to 6-6.5 with sulfuric acid, and then evaporate and concentrate it through a three effect evaporator to achieve a lithium sulfate concentration of 200g/L (containing Li2O 60g/L) in the concentrated solution. The concentrated solution is separated by pressure filtration, and the filtrate is ready for use in the next process. The filter cake, which is the residue, is returned to the slurry for leaching.

Lithium carbonate production section

The complete solution and pure alkali solution (containing Na2CO3 300g/L) were added to the evaporation precipitation lithium tank for evaporation precipitation of lithium (boiling and constant temperature for 2 hours). Due to the low solubility of lithium carbonate, it precipitated, with a lithium precipitation rate of about 85%. After lithium precipitation, use a centrifuge to separate primary crude lithium carbonate (containing less than 10% filtrate) and primary lithium mother liquor while hot The primary lithium precipitation mother liquor contains a large amount of sodium sulfate and relatively high lithium sulfate (about 15% of the total amount). Pure alkali solution (containing Na2CO3 300g/L) is added for secondary lithium precipitation to obtain secondary crude product and secondary mother liquor. The mother liquor is neutralized with acid and adjusted with sodium hydroxide to pH, and the by-products anhydrous sodium sulfate and sodium precipitation mother liquor are separated by evaporation crystallization and centrifugation. The anhydrous sodium sulfate is dried by gas flow and packaged to obtain the by-product Yuanming powder. Return the sodium precipitation mother liquor to prepare the mother liquor once The primary crude lithium carbonate and secondary crude product attachment solution contain impurities such as Na2SO4. They are then stirred and washed with clean water at around 90 ℃, and the washing solution is sent to prepare alkali. After washing, the wet refined lithium carbonate is separated by a centrifuge while it is hot. It is then dried by a far-infrared dryer, and magnetic separation is used to remove impurities such as iron wire shavings that fall off the dryer. After that, it is crushed by air flow and packaged for storage This project mainly aims to increase the production capacity of battery grade lithium carbonate. From the perspective of the overall production process, battery grade lithium carbonate and industrial grade lithium carbonate are basically the same, with the difference being that the process control conditions for the evaporation and lithium deposition sections are different. That is, during the evaporation and concentration of the purified liquid, the specific gravity of the finished liquid is measured by a specific gravity meter, and the Li2O concentration in the finished liquid is measured by a flame photometer to ensure that the finished liquid endpoint concentration is within the required range of the process; During lithium deposition, the feeding speed is controlled by adjusting the valve opening through an electromagnetic flowmeter, and the stirring speed of the mixer is controlled by adjusting the motor speed through a frequency converter. The above process control conditions are all key technologies of the company.

Anhydrous lithium chloride section

The finished solution obtained from the roasting section undergoes a double decomposition reaction with calcium chloride solution. After the reaction is complete, CaSO4 · 2H2O is separated and sent for processing to produce CaSO4 product. After separation, a dilute LiCl solution is obtained. β - type active Al2O3, Na2CO3, and NaOH solutions are sequentially added to remove impurities such as SO42-, Ca2+, Mg2+from the dilute LiCl solution. The LiCl concentration is then increased to 400-500g/L through evaporation and concentration. After cooling and filtering, solid NaCl is separated to obtain a concentrated LiCl solution. The concentrated LiCl solution is transported to the refining kettle, and added with the company's own refining agent (the company's patented technology, inorganic components, free of toxic and harmful heavy metals) for replacement reaction with Na+. The ratio of Na+/LiCl in the solution at the end of the reaction is controlled to be less than 30ppm. After separation, LiCl completion solution is obtained, * and then the completion solution is spray dried to obtain anhydrous lithium chloride products with uniform particles.

Technical Parameter