Extraction de lithium à partir de saumures de lacs salés : Méthode de précipitation

Abstract: With the rapid development of the new energy vehicle and energy storage industries, the demand for lithium—a crucial strategic resource of the 21st century—continues to rise. Nearly 60% of global lithium resources are contained in salt lake brines; compared to spodumene ores, lithium extraction from salt lakes offers the advantages of abundant reserves and lower costs. As a traditional extraction method, precipitation remains widely used in industrial production due to its process simplicity and technological maturity. This paper provides a systematic overview of the principles and process types of the precipitation method, as well as its application in lithium extraction from salt lakes.

Introduction to the Precipitation Method

Les méthode de précipitation est l'une des techniques couramment utilisées pour extraire le lithium des saumures des lacs salés. Le processus consiste à précipiter sélectivement les composés de lithium de la solution de la saumure par le biais de réactions chimiques. Les principe de la méthode des précipitations is to use solar energy to evaporate and concentrate salt lake brine naturally. After removing boron, calcium, and magnesium to remove impurities, a mixture of precipitants or salting-out agents is added to the mother liquor to separate lithium in the form of precipitates. Precipitation extraction of lithium metal has been applied earlier in industry. The process is mature, simple to operate, and highly reliable. However, this method needs better adaptability to brines with high concentrations of alkaline earth metal ions and low concentrations of lithium ions. According to the specific process, the precipitation method is divided into carbonate, aluminate, boron magnesium, and boron lithium co-precipitation. Nous allons présenter ces trois méthodes de précipitation pour l'extraction du lithium des lacs salés.

1. Méthode de précipitation des carbonates 

The carbonate precipitation method involves evaporating and concentrating the lithium-containing brine from the salt lake, adding lime to remove residual calcium, magnesium, and other basic metal impurities, and then adding a sodium carbonate precipitant to prepare lithium carbonate products. The method has low energy consumption and applies to industrial production and extraction. The disadvantage is that lithium selectivity is low, and alkali consumption is relatively high in the production process. After the salt lake brine is naturally evaporated and concentrated by solar energy to make salt, it is separated by segmental crystallization. Then an alkaline precipitant and impurity metal Mg2+ are added to form an insoluble precipitate. Magnesium is removed by solid-liquid separation, and then a specific temperature and alkalinity are maintained. Evaporate and crystallize NaCl, and finally add precipitant soda ash to prepare the lithium carbonate product. Use ammonia water and ammonium bicarbonate to adjust the brine alkalinity and precipitate the impurity magnesium. The removal rate of magnesium is about 98%, and the recovery rate of lithium is above 95%. The carbonate precipitation method has the advantages of simple operation and mature technology. It is currently the most important method for extracting lithium from salt lake brine with a low magnesium-lithium ratio. In the separation and extraction process, problems such as large alkali consumption and poor selectivity limit its industrial application.

2. Méthode de précipitation des aluminates

By reasonably controlling the aluminum-lithium ratio, we obtain aluminum-lithium precipitates first, filter the sediments, calcinate the residues at high temperatures, and immerse the calcined products in water to separate aluminum-lithium. Use a precipitating agent to remove impurities such as calcium and magnesium in the lithium-containing solution, add sodium carbonate after evaporation and concentration for the lithium precipitation reaction, and realize the production of lithium carbonate products. Use AlCl3·H2O and NaOH as raw materials; the aluminum hydroxide precipitation method is used to precipitate lithium selectively, and then the aluminum-lithium coprecipitate is subjected to high-temperature calcination and room-temperature water immersion. After filtration, we obtain a lithium-containing solution. Add NaOH to the solution to remove calcium and magnesium impurities. After that, add sodium carbonate to get lithium carbonate. Generally speaking, the aluminate precipitation method has problems such as high evaporation energy consumption of carbonization liquid and roasting leaching liquid, large freshwater consumption, and complicated process flow.

3. Méthode de co-précipitation du bore magnésium et du bore lithium

Les méthode de co-précipitation bore-magnésium refers to the demagnetization of the brine after the evaporation and concentration of the salt field to precipitate the potassium-magnesium mixed salt, adding an alkaline precipitant to control the pH value at 8-10, and under a specific temperature and pressure, making boron and magnesium co-precipitate. After solid-liquid separation, add NaOH to the mother liquor for deep magnesium removal. Then add soda ash to prepare lithium carbonate products. The recovery rate of lithium in this method reaches 80%-90%.

Les méthode de co-précipitation bore-lithium consiste à éliminer les impuretés de l'ancienne saumure qui a précipité le sodium et le potassium, en ajoutant des précipitants acides tels que l'acide chlorhydrique ou l'acide sulfurique pour réaliser la co-précipitation bore-lithium, afin de réaliser la séparation du lithium et du magnésium. Après le lavage à l'eau du résidu obtenu, les impuretés telles que le magnésium et le calcium sont éliminées en profondeur et, enfin, un précipitant est ajouté pour préparer le carbonate de lithium. Le taux de récupération du lithium atteint 75%-85%.

Les méthode de co-précipitation de bore-magnésium et de bore-lithium est adaptée à l'extraction du lithium à partir de saumures de lacs salés à forte teneur en magnésium et en lithium en Chine. Cette méthode présente des procédures de séparation simples, une bonne opérabilité et un rendement élevé en lithium. Elle offre certaines perspectives d'application industrielle, mais le problème est que les précipités obtenus par la méthode de coprécipitation bore-magnésium sont principalement colloïdaux et que la séparation solide-liquide est difficile. Au cours du processus de séparation, le taux de perte de lithium atteint 15%-20%, ce qui entraîne un gaspillage important de lithium.

Based on the boron-lithium co-precipitation method, boron-lithium co-precipitation is carried out by using the process of primary freezing, evaporation with halogen, primary evaporation, secondary freezing, secondary evaporation, and precipitation of boron-lithium. The recovery rate of boron-lithium in this method is relatively high and has strong practicality. The precipitation process was developed earlier and had the advantages of mature process technology and high operational reliability. However, for the production process in China that uses high-magnesium-lithium ratio salt lake brine as raw material, the alkaline precipitant is generally large, the production cost is relatively high, and there is high & poor selectivity to lithium and other issues.

Il convient de noter que la méthode de précipitation n'est qu'une des nombreuses techniques employées pour l'extraction du lithium. D'autres méthodes, telles que l'extraction par solvant et l'extraction directe du lithium à partir de la saumure, sont également utilisées en fonction des caractéristiques spécifiques de la saumure et du produit final souhaité.

Résumé

As a mature technology for lithium extraction from salt lakes, the precipitation method encompasses various process variants tailored to different brine compositions. The carbonate method is suitable for systems with simple matrices and low magnesium-to-lithium ratios; the aluminate method can handle higher magnesium-to-lithium ratios; and boron-related processes are appropriate for boron-bearing salt lakes. Current research focuses on developing novel precipitants, optimizing precipitation conditions, and enhancing lithium recovery rates to maintain the method’s competitiveness in lithium resource development. With future technological advancements, the precipitation method is expected to overcome existing limitations and play a more significant role in processing brines with high magnesium-to-lithium ratios.

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