Process For Preparing Lithium Carbonate From Medium & Low Grade Lithium Clay In Yichun City

The lithium clay,which is a mainly material for producing lithium carbonate,contains large amounts of lithium,silicon,potassium and other elements.Lithium carbonate has a variety of industrial uses,and is widely used in ceramics,glass,batteries,atomic energy and other fields.With the rapid development of new energy industry,the demand for lithium resources is increasing.And,it’s more and more important to exploit and use the medium and low grade lepidolite which exist in abundance in Yichun area.In this paper,lithium carbonate from medium and low grade lithium clay via sulfuric acid leaching and roasting was studied.This experiment contains mixing,roasting,leaching,cooling,purification,concentration,carbonization and other steps.This method has the advantages of moderate condition and stable operation process.Two different lithium extraction process routes were compared,a certain amount of lithium carbonate was obtained,but it needs to be improved to increase the yield and purity.Part 1:The Na₂SO₄-H₂SO₄ roasting method was used to treat medium and low grade lithium clay（Li₂O=1.2-1.4%）in Yichun area,the influence of acid concentration,particle size after roasting and mass of sodium sulfate as an additive on the leaching rate was studied.The roasting process was analyzed by TG,XRD,SEM,elemental composition analysis methods,and the influence of Na₂SO₄ as an additive on the leaching process was discussed.Results indicate that,at temperature800℃-1000℃,when acid concentration is 70%,lithium clay particle size is 0.180mm,and mass of sodium sulfate is 100g,the leaching rate reaches 90.0%,which is better than traditional H₂SO₄ roasting method（73.0%）.This process has excellent effects on fixing silicon and aluminum,and can greatly reduce the removal process of silicon and aluminum in traditional leaching process;The main components of roasted residual are Si O₂ and Al₂O₃,which is 59.9%and 20.9%respectively;The additive of sodium sulfate aggravates destruction of original structure of lithium clay ore and can greatly increase the leaching rate of lithium extraction process.The lithium carbonate product has a purity of 99.9%and a yield of 45.0%,which meets the minimum industrial standards.Part 2:The low-temperature roasting method was used to treat medium and low grade lithium clay（Li₂O=1.2-1.4%）in Yichun area,the influence of the ratio of lithium clay:sulfuric acid and stirring time on the leaching rate was studied.The roasting process was analyzed by TG,XRD,SEM,elemental composition analysis methods.and the changes of raw ore before and after roasting in the low-temperature roasting process was discussed.In addition,the influence of potassium sulfate formation the alum for the aluminum removal on the yield of lithium extraction in the purification process was discussed.Results indicate that,at temperature 180℃,the mixing ratio is lithium clay:H₂SO₄:H₂O=1:0.7:0.3,a considerable leaching rate of 84%can be achieved after fully stirring and mixing.The results of the characterization analysis prove that the metal ions in the raw ore can be dissolved under low-temperature roasting conditions,and most of the aluminum ions in the raw ore are also leached and dissolved,because potassium sulfate was added to cool into alum to minimize the lithium loss to the greatest extent in the purification process.The lithium carbonate product has a purity of 91.1%and a yield of 30.0%.Part 3:Recovery of rubidium and cesium from the alum is studied,which is a by-product in the process of lithium extraction,through stepwise crystallization.Results indicate that,the concentration of rubidium and cesium alum increased significantly after first recrystallization at 40℃,and the concentration of cesium oxide increased by 20 times compared with the raw ore.After 6 times of crystallization,the rubidium oxide in the mixed alum is completely separated,and most of the potassium alum and cesium alum remain in the crystal.The method is simple and effective to operate,and can improve the utilization value of by-products.