Lithium ore extraction - salt lake lithium ore

Lithium in salt lakes is generally extracted from the old brine left after sodium and potassium production. After lithium enrichment, through evaporation, magnesium removal, and concentration, lithium ions are extracted to generate lithium carbonate.

Salt lakes correspond to different lithium enrichment and lithium extraction processes due to different brine concentrations. The calcination method has high requirements on raw materials, and the concentration of lithium in brine must reach 8-9g/L. This extraction method is suitable for brine resources with high magnesium and lithium content (generally required to reach 2g/L). The precipitation method requires that the mass concentration of lithium ions in the salt lake is greater than 0.5g/L, and when the weight ratio of magnesium to lithium is 1:200/1, the lithium content in the brine of the salt lake is greater than 1g/L. The ion mass concentration is greater than 0.5g/L, and the adsorption method is suitable for 0.1g/L brine.

Currently, there are seven methods for extracting lithium from salt lakes, among which adsorption and electrodialysis are the most widely used in Qinghai. At present, the main international salt lake brine extraction technologies are precipitation method (including carbonate precipitation method, aluminate precipitation method, hydrated lithium sulfate crystallization precipitation method, boron magnesium boron lithium co-precipitation method), calcination leaching method, carbonization method method, solvent extraction method, adsorption method, electrodialysis method, membrane separation method, etc., among which solvent extraction method has not yet achieved large-scale industrial application.

Precipitation method/solar cell method

Also known as the solar cell method, it is often used in salt ponds with high lithium concentrations. Concentrated lithium-rich brine is obtained by evaporating old brine, removing boron, calcium and magnesium ions through acidification or extraction, and obtaining high-lithium brine. Afterwards, a soda ash precipitant is added to separate the lithium from other salts. Li2CO3, isolated directly from the intergranular brine of an alkaline carbonate lake. Disodium hydrogen phosphate was used as a precipitating agent. Lithium and phosphate ions are separated by hydrogen or sodium cation resins. Lithium carbonate precipitated from the concentrated eluate.

Calcination leaching method

The calcination leaching method realizes the extraction of lithium carbonate through steps such as calcination, leaching, and precipitation. The calcination and leaching method is to evaporate the boron-extracted brine to obtain magnesium chloride tetrahydrate. After calcination, magnesium oxide is obtained. Lithium is leached with water, and impurities such as calcium and magnesium are removed with milk of lime and soda ash. The solution is evaporated to about 2% Li. Soda ash was added to precipitate lithium carbonate, and the calcined magnesia slag was refined to obtain a magnesia by-product with a purity of 98.5%.

solvent extraction

After deboronation of the old halogen, add FeCl3 solution to form LiFeCl4, use tributyl phosphate (TBP)-kerosene extraction system to extract LiFeCl4 into the organic phase, form LiFeCl4+2TBP extraction complex, pickle and extract with hydrochloric acid. After evaporation and concentration, roasting, leaching, and impurity removal, anhydrous lithium chloride can be obtained, and finally sodium carbonate is added to generate lithium carbonate.

Adsorption

First of all, the adsorption production process is that the lithium ions in the salt lake brine are adsorbed by a selective adsorbent, and then the lithium ions are eluted to realize the separation of lithium ions from other ions, which is convenient for subsequent transformation and utilization. The key to this process is the lithium adsorbent, which requires that the adsorbent can eliminate the interference of a large number of coexisting alkali metal and alkaline earth metal ions in the brine, selectively adsorb lithium ions in the brine, and have high adsorption capacity and adsorption strength.

Membrane method—electrodialysis and nanofiltration membrane separation

Electrodialysis membrane separation technology has been industrialized in Dongtai Salt Lake, Qaidam Basin. This technology is used to separate salt lake brine with a weight ratio of magnesium to lithium of 1-200. Through one-stage or multi-stage electrodialyzer, adopt monovalent cation selective ion exchange membrane and monovalent anion selective exchange membrane (continuous, continuous partial circulation or batch circulation) process, add soda ash to precipitate lithium carbonate. The resulting mother liquor can be recycled.

This method is suitable for the separation of lithium and magnesium ions in brines with relatively high magnesium and lithium contents. However, the process requirement is that the salt content of the light brine is less than 100g/L, otherwise the separation effect will be poor and the cost will increase greatly. The process is simple to set up, easy to operate, and has no pollution to the environment, but the separation efficiency is not high. The filter membrane has a short service life.

Magnesium-lithium salt lake brine or salt field sun-dried concentrated old brine is electrodialyzed and concentrated through one-stage or multi-stage electrodialyzers, and lithium is concentrated by monovalent cation selective ion exchange membranes and monovalent anion selective ion exchange membranes. Adding soda ash to precipitate lithium carbonate, the mother liquor can be recycled