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.

　　Equipment  Configuration

　　Equipment  Model  Quantity