Extração de lítio de salmoura de lago salgado: Método de Precipitação

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

O método de precipitação é uma das técnicas comuns utilizadas para extrair lítio de salmouras de lagos salgados. O processo envolve a precipitação selectiva de compostos de lítio da solução de salmoura através de reacções químicas. O princípio do método de precipitação 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. Vamos apresentar estes três métodos de precipitação para a extração de lítio de lagos salgados.

1. Método de precipitação de carbonatos 

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. Método de precipitação de aluminatos

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. Método de co-precipitação de boro magnésio e boro lítio

O método de co-precipitação de boro e magnésio 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%.

O método de co-precipitação boro-lítio refere-se à remoção de impurezas da salmoura antiga que precipitou sódio e potássio, adicionando precipitantes ácidos como ácido clorídrico ou ácido sulfúrico para fazer a co-precipitação de boro-lítio, para realizar a separação de lítio e magnésio. Depois de o resíduo obtido ser lavado com água, as impurezas como o magnésio e o cálcio são profundamente removidas e, finalmente, é adicionado um precipitante para preparar o carbonato de lítio. A taxa de recuperação do lítio atinge 75%-85%.

O método de co-precipitação de boro magnésio e boro lítio é adequado para a produção de extração de lítio a partir de salmoura de lago salgado com elevada relação magnésio-lítio na China. Este método tem procedimentos de separação simples, forte operacionalidade e alto rendimento de lítio. Tem algumas perspectivas de aplicação industrial, mas o problema é que os precipitados obtidos pelo método de co-precipitação de boro e magnésio são maioritariamente coloidais e a separação sólido-líquido é difícil. Durante o processo de separação, a taxa de perda de lítio atinge 15%-20%, resultando num grande desperdício de lítio.

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.

É importante notar que o método de precipitação é apenas uma das várias técnicas utilizadas para a extração de lítio. Outros métodos, como a extração por solventes e a extração direta de lítio da salmoura, são também utilizados, dependendo das características específicas da salmoura e do produto final pretendido.

Resumo

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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