Process for producing lithium carbonate from salt lake brine as raw material

Compared with the preparation of lithium carbonate from spodumene, the production of lithium carbonate from salt lake brine not only has a higher lithium content, but also has abundant resources, low energy consumption, and low product prices. The production of lithium carbonate from salt lake brine has the advantages of low energy consumption and low cost, and has become the development direction of future production of basic lithium products.

Two key indicators: lithium content and magnesium lithium ratio.

Most salt lakes are of high magnesium and low lithium type, and the process technology is difficult. At present, the only lithium salt lakes that have achieved large-scale industrial mining are the Atacama Salt Lake in Chile with low magnesium lithium ratio, the Umbre Murto Salt Lake in Argentina, and the Silver Peak Salt Lake in the United States. The Uyuni Salt Lake in Bolivia is the largest lithium salt lake in the world and has not been extensively exploited.

In recent years, China has also been actively developing lithium resources in salt lakes. The extraction of lithium from brine is mainly carried out in Taijinar Salt Lake and Zabuye Salt Lake. Mining and other salt lake lithium extraction technologies have made rapid progress, and the production scale has rapidly expanded. At present, it has become the main research direction for domestic and foreign companies to develop and produce lithium salts. The main processes for producing lithium carbonate from salt lake brine include evaporation precipitation, calcination, solvent extraction, electrodialysis, aluminate precipitation, adsorption, etc.

1. Evaporation precipitation method

At present, the evaporation precipitation method has achieved industrial production. The main process is:

(1) Using solar energy to evaporate and concentrate lithium containing brine in an evaporation pond;

(2) After the lithium content reaches an appropriate concentration, separation processes such as boron removal, magnesium removal, and calcium removal are carried out;

(3) Add soda ash to precipitate lithium in the form of lithium carbonate.

The advantages of evaporation precipitation method are: simple process; Low energy consumption; Low cost; It is more suitable for brines with low alkaline earth metal content and low magnesium lithium ratio.

2. Calcination method

This production process is a technology proposed for extracting lithium from salt lake brine with high magnesium lithium ratio. Due to the dehydration of MgC12 · 6H2O between 97-554 ℃ and its decomposition into magnesium oxide and hydrogen chloride gas above 550 ℃, lithium chloride does not decompose under these conditions. Based on this principle, scholars such as Jianyuan proposed and completed small-scale experiments in 1996. After calcination, the sintered material is leached. If lithium salt is easily soluble in water, it enters the solution. If magnesium oxide is almost insoluble in water, it remains in the residue. Through the leaching process, impurities such as sulfate ions, magnesium, and a small amount of boron are removed from the leaching solution. After purification of the filtrate, lithium carbonate product can be obtained by evaporation, precipitation, and drying. At present, Jianyuan et al. use lithium bearing bischofite saturated brine after potassium and boron extraction as raw materials, adopt spray drying, calcination, water washing, evaporation concentration, alkali precipitation and other production processes to separate magnesium and lithium from salt lake brine with high magnesium lithium ratio, and obtain high-quality lithium carbonate, high-purity magnesium oxide and by-product industrial hydrochloric acid. The process flowchart is as follows:

The major advantage of this process is the effective comprehensive utilization of salt lake resources, but the disadvantage is that it requires a large amount of water to evaporate, consumes high energy, produces a large amount of hydrogen chloride gas during the calcination process, and causes severe corrosion to equipment. Therefore, equipment selection is of paramount importance in large-scale industrial production.

3. Solvent extraction method

The process of solvent extraction is as follows:

(1) The concentrated brine obtained by stepwise precipitation of sodium chloride, carnallite, and some bischofite from salt lake brine through salt field sun exposure is acidified and enters the extraction tank;

(2) Using tributyl phosphate (TBP) as the extractant, HCl as the counter extractant, FeCl3 as the chelating agent, the extraction process is carried out through multiple stages of counter current extraction washing, counter extraction, acid washing, etc. The residual liquid is discharged and the empty organic phase is returned to the extraction stage for use.

(3) The obtained reverse extraction solution undergoes evaporation concentration, calcination, leaching, impurity removal in the finished product process, followed by evaporation concentration and pure alkali precipitation to produce Li2CO3 product.

The major advantage of this method is that it is suitable for extracting lithium carbonate from high magnesium lithium ratio salt lake brine, and the process is feasible; However, in the extraction process, a large amount of brine needs to be processed, which is highly corrosive to the equipment, resulting in higher requirements for equipment materials during implementation.

4. Electrodialysis

This process is currently a relatively environmentally friendly new process. Ma Peihua and others from the Salt Lake Research Institute of the Chinese Academy of Sciences concentrated lithium containing brine obtained by sun drying and evaporation in salt fields. The brine was then concentrated using a single-stage or multi-stage electrodialysis device and a cation selective ion exchange membrane for circulation (continuous, continuous partial circulation, or batch circulation) to obtain lithium rich and low magnesium brine. Then, through deep impurity removal, refined concentration, and conversion drying, lithium carbonate products can be produced. This process solves the problem of separating magnesium and other impurities from high magnesium lithium ratio salt lake brine. The mass ratio of (Mg/Li) in lithium containing brine is reduced from (1-300): 1 to (0.3-10): 1, and the Li concentration reaches 2-20g/L. The recovery rate of Li is 80%, making it an economical and practical process technology for extracting lithium carbonate from high magnesium lithium ratio brine.

The major advantage of electrodialysis is that it solves the problem of separating magnesium and other impurities from high magnesium lithium ratio salt lake brine, and has become an economical and practical process technology for extracting lithium carbonate from high magnesium lithium ratio brine in Qinghai.

5. Adsorption method

The adsorption production process first uses selective adsorbents to adsorb lithium ions in brine, and then elutes the lithium ions to achieve separation from other ions, facilitating subsequent conversion and utilization processes. For brines with low lithium content, adsorption is a better method. This method has a simple process, high recovery rate, and good selectivity, and has significant advantages compared to other methods. The key to this method is to study adsorbents with excellent performance. The process flow chart is as follows

The advantages of adsorption method are: the production process is relatively simple; Low energy consumption. The disadvantage is that the adsorbents used are mostly in powder form, with poor fluidity and permeability, and a relatively high dissolution rate.