1. What is lithium carbonate? Classification of lithium carbonate

Lithium carbonate, lithium carbonate, molecular formula Li2CO3, molecular weight 73.891, melting point 720 ℃, boiling point 1342 ℃, density 2.11g/cm3, the appearance of white powder. Is an inorganic compound, colorless monoclinic crystal, slightly soluble in water, dilute acid, insoluble in ethanol, acetone. Used as ceramic, glass, ferrite and other raw materials, components such as spray silver paste, medicine to treat mental depression.

Lithium is the lightest metal in nature. It has physical and chemical properties such as strong electrochemical activity, high specific heat capacity, and large conductivity. It is widely used in the field of new energy materials such as lithium-ion batteries and is known as "industrial monosodium glutamate"; It is one of the elements with application development potential in the 21st century, especially with the rapid development of the new energy industry, lithium has become one of the strategic metal elements supporting the realization of the dual carbon goal.

Classification of 1.1 lithium carbonate

1.1.1 National Standards

For the classification of lithium carbonate, the national standard for general reference is GB/T11075-2013, and the industry standard YS/T582-2013 is generally used for battery-grade carbonic acid. The national standard GB/T11075-2013 is divided into 3 grades according to the different lithium carbonate content, namely Li2CO3-0,Li2CO3-1 and Li2CO3-2.

1.1.2 End use

According to the end use, lithium carbonate can be divided into industrial grade lithium carbonate and battery grade lithium carbonate. The purity of the two is different. The purity of battery grade lithium carbonate is higher than that of industrial grade lithium carbonate. Generally, the lithium carbonate content of 98%-99% is industrial grade lithium carbonate, and the lithium carbonate content ≥ 99.5 is battery grade lithium carbonate. The application scope of industrial-grade lithium carbonate and battery-grade lithium carbonate is also quite different. Battery-grade lithium carbonate is mainly used in new energy lithium batteries, while industrial-grade lithium carbonate is mainly used in traditional ceramics, glass and other industries. Compared with battery-grade lithium carbonate, industrial-grade lithium carbonate has low purity and many impurities, and cannot be directly used as the cathode material of lithium batteries. It can only be applied to lithium batteries after purification and preparation to improve the purity of lithium carbonate. Due to the higher purity of battery-grade lithium carbonate, the price will also be higher than that of industrial-grade lithium carbonate.

Other regulations include: (1) magnetic substance content ≤ 0.0003; (2) moisture content ≤ 0.25; (3) particle size d10 ≥ 1μm,3μm ≤ d50 ≤ 8μm,9μm ≤ d50 ≤ 15μm (4) appearance requirements are white powder, no visible impurities.

2. Lithium carbonate industry chain

The upstream of the lithium carbonate industry chain is the collection of raw materials, mainly divided into lithium mines and salt lakes, lithium mines mainly produce lithium flint ore and lithium mica ore. The middle reaches of the lithium carbonate industry are mainly lithium salt products. Lithium hydroxide produced from spodumene raw ore is processed to obtain industrial grade lithium carbonate and battery grade lithium carbonate; industrial grade lithium carbonate and battery grade lithium carbonate are prepared from lepidolite raw ore; industrial grade lithium carbonate and lithium chloride can be prepared from salt lake brine, wherein lithium chloride can be obtained by recycling lithium extraction technology. The end consumption of lithium carbonate is mainly the application of industrial grade lithium carbonate and battery grade lithium carbonate. Battery-grade lithium carbonate is ultimately used for electronic consumption in downstream industries, and new energy batteries are the most important application direction, while industrial-grade lithium carbonate can be used in lubricants, catalysts, traditional ceramics, glass and other industries, and can also be purified to obtain battery-grade lithium carbonate applied to the new energy industry. Lithium metal can also be used in medicine to treat mental illness.

Upstream production of 2.1 lithium carbonate

2.1.1 Production process

The raw materials of lithium carbonate are generally spodumene, lepidolite and salt lake brine. In recent years, China has been actively developing lithium resources in salt lakes, but the content of magnesium in salt lake brine is very high, and magnesium and lithium are difficult to separate, so lithium ore is generally used to extract.

Lithium extraction from ore and lithium extraction from brine form two production processes due to different raw material routes. As far as reality is concerned, my country's ore lithium extraction technology has great advantages in process and production capacity and has become the current mainstream; while the brine lithium extraction technology has developed relatively slowly, but in recent years Qinghai Salt Lake brine lithium extraction technology has made major breakthroughs. Although Qinghai has already put into production large-scale brine lithium extraction projects, due to resource and cost constraints, domestic lithium carbonate production will still be dominated by ore lithium extraction in the future, and will maintain the pattern for a long time.

China is rich in spodumene mineral resources. Kangding Methylka in Sichuan Province is the second largest spodumene mine in the world, with reserves of up to 1.8877 million tons and high lithium grade, which is easy to exploit and utilize. Yichun City, Jiangxi Province has the largest lepidolite mine in the world. It has been proved that the available lithium oxide resources are more than 2.5 million tons, and about 62.5 million tons of lepidolite concentrate with a lithium oxide grade of about 4% can be produced. The market potential is huge. There are also different processes due to the different content and composition of the raw ore.

(1) Production of lithium carbonate using spodumene

Because of its simple chemical composition, high lithium content and strong chemical inertness, spodumene has always been one of the main ore resources for lithium extraction. The chemical formula and chemical composition of spodumene are shown in the following table.

Lithium ore lithium extraction process generally needs to be crushed, grinding screening high grade lithium concentrate, and then through different process conditions to obtain lithium salt products. According to the different lithium extraction media, the lithium extraction process of spodumene mainly includes six categories, namely: sulfuric acid method, stone 4 limestone method, sulfate method, chloride roasting method, fluorine chemical method and soda ash pressure cooking method. Comprehensive production process, energy consumption and technical process difficulty. At present, the sulfuric acid roasting method is the mainstream production process, and most of the major production enterprises also use the sulfuric acid method to extract lithium.

At present, the production process of lithium carbonate using spodumene is relatively mature. The advantages of this method are: high yield; it can be extracted from ores with low lithium content (1% ~ 1.5%); and the lithium content in the leaching roasting liquid is high (35g/L-55g/L). Disadvantages are: a considerable amount of sulfuric acid and soda ash reaction to generate a lower value of sulfate, adding sulfuric acid for roasting, environmental pressure, exhaust gas treatment investment and operating costs are higher. Therefore, the sulfuric acid method should control the amount of sulfuric acid.

(2) Production of lithium carbonate using lepidolite

Although spodumene is the main raw material for lithium extraction from ore due to its simple element composition, high lithium grade and abundant reserves, the high-cold and high-altitude mining environment limits its industrial development and utilization to a certain extent. China is also rich in lepidolite resources, Yichun, Jiangxi has the world's largest associated lepidolite deposits, and lepidolite contains high value of rubidium and cesium, so the development of efficient lithium extraction process for the comprehensive utilization of lepidolite resources is of great significance. Different from spodumene, lepidolite has complex chemical composition and low lithium grade, accompanied by about 2.14% rubidium and 0.91% cesium. 55% of rubidium and cesium resources in China come from lepidolite. And lepidolite contains 5%-10% fluorine, which will produce lithium loss in the process of lithium extraction and affect the leaching of lithium. Therefore, the development of high-efficiency lithium extraction process from lepidolite requires comprehensive consideration of the recovery of rubidium and cesium and the influence of fluorine.

At present, the main processes of lithium extraction from lepidolite developed in China include sulfate roasting method, limestone sintering method and sulfuric acid roasting method. At present, the more mature sulfate roasting method is applied.