Introduction to the process steps and characteristics of lithium extraction by lepidolite alkali method!

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The common alkali methodlithium selection process is mainly the limestone roasting method. In addition, based on the characteristics of the ore and process drawbacks, another method has been developed Some new process methods have been introduced, let’s take a look at them together.

1. Lepidolite limestone roasting method

When usedLimestoneWater immersion after roasting the mineral, the lithium concentration in the immersion liquid is low (about 4g·L-1Li₂O), resulting in a huge volume of the mother liquor. It is about 10 to 15 times that of extracting lithium from spodumene using the limestone roasting method. The concentration and recovery of lithium requires a large amount of evaporation and high energy consumption. The main components of the leaching slag are calcium silicate, calcium fluoride, etc. The amount of dry slag per ton of lithium hydroxide monohydrate is more than 40t, and the composition is complex and extremely difficult to apply. Therefore, the pollution of the solid slag is quite serious. The ore is rich in K, Rb, Cs and other valuable elements that enter the leaching solution along with lithium after leaching. After recycling, it can increase the economic benefits of the process.

For the comprehensive recovery of potassium, rubidium and cesium in the leaching solution, most studies pass CO₂ into the lithium extraction mother liquor to crystallize potassium bicarbonate to recover potassium, and then use The sequential precipitation and separation of rubidium and cesium using chlorostannate or ferrocyanide requires a long process, low efficiency, high cost, and high environmental pressure.

Cs and Rb were extracted and separated using 4-sec-butyl-2(α-methylbenzyl)phenol (BAMBP) at different OH-concentrations, and then back-extracted with hydrochloric acid to obtain CsCl and RbCl. , but the extraction agent is expensive and toxic, and the separation coefficient of the extraction system is small. Multi-stage extraction and back-extraction are required to achieve the purpose of separation.

2. Lithium carbonate + sulfuric acid method

In order to reduce the cost of recovering K, Rb, and Cs, there is a new separation method, which is to add sulfuric acid to the mother liquor after lithium carbonate precipitation and boil it. CO₂ is decomposed, and the K₂SO₄ product is obtained after cooling and filtration. Tartaric acid is then added to the filtrate, and after the reaction, the potassium hydrogen tartrate product is obtained by filtration. The secondary filtrate is concentrated and evaporated to dryness to remove tartaric acid radicals, and water and aluminum sulfate are added to precipitate cesium alum and rubidium alum in sequence. The obtained alum salt reacts with barium hydroxide to obtain CsOH and RbOH products.

The total recovery rate of potassium in this process is >99%, and the purity of cesium alum and rubidium alum is >99%. It also has low material loss and low cost. The whole process is non-toxic and pollution-free, and will produce a large amount of waste residue.

3. Lepidolite lime milk pressure cooking method

The lepidolite lime milk pressure cooking method is a new alkaline lithium extraction method. Its main process steps are:

1. High-temperature steam defluorination of lepidolite;

2. Lime milk and defluorinated lepidolite are pressure-cooked at a liquid-to-solid ratio of 4:1 and 159°C;

3. The pressure cooking liquid evaporates to precipitate LiOH·H₂O or the leaching liquid is concentrated and then CO₂ is introduced to precipitate lithium carbonate. Compared with the limestone roasting method, the process has small material flow, less slag production, and is simple in composition and easy to use. However, a large amount of HF gas generated during the pre-defluorination process is difficult to handle, and the solid particles in the slurry refine and expand at high temperatures, making it difficult to filter. The feeding and discharging process is difficult, and the production efficiency is affected.

4. Lithium extraction by alkaline dissolution of lepidolite

Lithium extraction by alkaline fusion is a lithium extraction method that uses sodium hydroxide as a solution. Its main process steps are:

1. Mix lepidolite and 50% NaOH solution at a mass volume ratio (g:ml) of 1:3.5, and react at 190°C;

2. The leachate is diluted and passed through a cation exchange resin Adsorb various alkali metal ions;

3. Elute the resin with dilute sulfuric acid;

4. Add sodium carbonate to precipitate lithium carbonate after the eluate is concentrated.

This process eliminates the need for pre-high-temperature defluoridation and does not have the problem of hydrofluoric acid corroding equipment, and completes the conversion process of potassium, rubidium, and cesium in one go. The mother liquor exchanged with the resin is crystallized and concentrated to prepare high value-added aluminum-silicon products, which increases the economy of the process and reduces the output of polluting waste residue.

The above mainly introduces the process methods and process steps of alkaline extraction of lithium from lepidolite ore. In the actual mineral processing plant, any lithium ore beneficiation needs to be carried out Ore beneficiation test analysis, through analysis, design and customization of suitable lithium ore beneficiation process methods, can we obtain higher lithium concentrate and achieve efficient return on investment.