Lithium carbonate production process
Production technology of lithium carbonate
(1) Baking immersion section
Transformation roasting: Spodumene concentrate is artificially sent from the concentrate storage to the bucket elevator to the concentrate bin, and then added into the tail of the lithium carbonate rotary kiln by the disk feeder and spiral feeder. The concentrate is dried with high temperature gas in the preheating section of the kiln tail. The concentrate is roasted in the calcination section at about 1200℃. Density: 3150kg/m3) to β spodumene (tetragonal system, density: 2400kg/m3, that is, the baking material), the conversion rate is about 98%.
Acidizing roasting: After cooling in the cooling section, the baking material is discharged from the kiln head, and then it is processed by natural cooling and ball mill grinding to a particle size of more than 90% 0.074mm, and then transported to the ore bin at the end of acidizing roasting kiln. After that, it is added into the acid mixing machine by feeder and screw conveyor in a certain proportion with concentrated sulfuric acid (more than 93%) (concentrated sulfuric acid is calculated as excess 35% of lithium equivalent in baking material. 0.21t concentrated sulfuric acid is required for each ton of baking material), and then it is added to acidizing roasting chamber for 30 ~ 60min under closed acidizing roasting temperature of 250 ~ 300℃. The β spodumene in the baking material reacts with sulfuric acid, and the lithium ion in β spodumene is replaced by hydrogen ion in acid. Li2O was combined with SO42- to form Li2SO4 soluble in water, and acidified clinker was obtained.
Slurry leaching and washing: the clinker is cooled and slurry, so that the soluble lithium sulfate in the clinker is dissolved into the liquid phase. In order to reduce the corrosion of the solution to the leaching equipment, limestone slurry is used to neutralize the residual acid in the clinker, and the pH value is adjusted to 6.5 ~ 7.0, and most iron, aluminum and other impurities are removed at the same time. The ratio of leaching liquid to solid is about 2.5, and the leaching time is about 0.5h. The leach slurry was filtered and separated to obtain the leach solution containing Li2SO4 100g/L(Li2O 27g/L). The filter cake was the leach residue with a water content of about 35%. The attachment solution of leaching residue contains lithium sulphate. In order to reduce the loss of lithium, the leaching residue is reversed stirred and washed, and the washing liquid is returned to the slurry for leaching.
Purification of leaching solution: in the process of acidizing roasting, in addition to alkali metal can react with sulfuric acid to produce soluble corresponding sulfate, other iron, aluminum, calcium and magnesium can also react with sulfuric acid to produce corresponding sulfate. Although some impurities in the clinker can be removed in the leaching process, the remaining impurities still remain in the leaching solution and need to be further purified to ensure the quality of the product. The leaching solution was purified by alkalization and calcium removal method. The alkalization agent lime milk (containing CaO100 ~ 150g/L) was used to alkalize the leaching solution, and the pH value was raised to 11 ~ 12 to hydrolyze magnesium and iron into hydroxide precipitation. Then sodium carbonate solution (containing Na2CO3 300g/L) was reacted with calcium sulfate to produce calcium carbonate precipitation, so as to remove the calcium in the leaching solution and the calcium brought by the alkalization agent lime milk. The alkalized calcium removal slurry was separated by liquid and solid, and the obtained solution was purified liquid with a calcium-lithium ratio less than 9.6×10-4. The filter cake was calcium slag, which was returned to the slurry mixing leaching.
Evaporation and concentration of purification liquid: due to low concentration of lithium sulfate and low precipitation rate of lithium, the purification liquid can not be directly used for lithium precipitation or preparation of lithium chloride. It is necessary to adjust the purification liquid to pH6 ~ 6.5 with sulfuric acid first, and then concentrate through evaporation and concentration by three-effect evaporator, so that the concentration of lithium sulfate in concentrated liquid can reach 200g/L(including Li2O 60g/L). The concentrated liquid is separated by pressure filtration, and the filtrate is ready for the next process, and the filter cake is returned to the slurry mixing leaching after the filtrate is finished.
(2) Lithium carbonate production section
The finished liquid and pure alkali liquid (including Na2CO3 300g/L) are added into the evaporating lithium precipitation tank for evaporating lithium precipitation (constant temperature for 2h after boiling). The lithium carbonate precipitates due to its low solubility, and the lithium precipitation rate is about 85%. After lithium precipitation, a centrifuge is used to separate a crude lithium carbonate (containing filtrate less than 10%) and a lithium precipitation mother liquor.
The mother liquor of primary lithium precipitation contains a large amount of sodium sulfate and higher lithium sulfate (about 15% of the total). Pure alkali liquor (containing Na2CO3 300g/L) is added for secondary lithium precipitation to obtain secondary crude products and secondary mother liquor. After the mother liquor is neutralized by acid and the pH is adjusted by sodium hydroxide, the by-products anhydrous sodium sulfate and sodium precipitation mother liquor are separated by evaporation crystallization and centrifugation. Anhydrous sodium sulfate was dried by air flow and packaged to produce by-product sodium sulfate. The sodium solution is returned to the mother solution.
A thick liquid lithium carbonate and secondary products attached contains Na2SO4 and other impurities, then wash with clean water to about 90 ℃ for stirring, drove with alkali solution, the centrifuge is used after washing strike isolated wet pure lithium carbonate, then through far infrared drying machine to dry, dry magnetic separation to remove machine fall off the wire scraps of sundry, * after the airflow pulverization, packaging, warehousing.
This project mainly increases the production capacity of battery grade lithium carbonate. Looked from the overall production process, battery grade lithium carbonate and industrial grade lithium carbonate, lithium difference between evaporation and sink two section process control condition is different, the purifying liquid evaporation concentration by hydrometer to determine the destination complete the proportion of liquid and by flame photometer Li2O concentration in the liquid to ensure completion fluid end concentration within the scope of the technical requirements; When lithium sinks, the electromagnetic flowmeter displays and adjusts the different opening of the valve to control the feeding speed, and the motor speed is adjusted by the frequency converter to control the stirring speed of the agitator. The above process control conditions are key technologies of the company.
③ Anhydrous lithium chloride section
CaSO4·2H2O was separated after the double decomposition reaction between the finished solution obtained in the baking and leaching section and the calcium chloride solution. CaSO4 product was prepared by processing. β -active Al2O3, Na2CO3 and NaOH solutions were successively added to remove impurities such as SO42-, Ca2+ and Mg2+ in dilute LiCl solution. After evaporation and concentration, LiCl concentration was increased to 400 ~ 500g/L, and then solid NaCl was separated through cooling and filtration. You get a concentrated LiCl solution. The concentrated LiCl solution is transported to the refining reactor, and the company's own refined preparation (the company's patented technology, inorganic components, does not contain toxic and harmful heavy metals) is added to carry out replacement reaction with Na+, and the ratio of Na+/LiCl in the reaction endpoint solution is controlled to be less than 30ppm. After separation, LiCl completion solution is obtained. * After finishing the liquid spray drying to get uniform particles of anhydrous lithium chloride products.
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