Abstract: Lithium ion sieve can directly extract lithium from salt lake brine and seawater, and it is a promising lithium adsorbent. The preparation and detection methods of manganese oxide lithium ion sieve precursors are introduced, and the development history of ion sieve materials is briefly described.
Lithium is the lightest metal in nature. Lithium and its compounds have a wide range of special uses, including energy, aerospace industry, metal smelting and manufacturing, refrigeration, glass, ceramics, medicine and other industries. In the field of atomic energy, lithium is called new? Energy element? Lithium -6 is the raw material for hydrogen bombs and thermonuclear reactors. Lithium-ion battery has the advantages of high energy, good cycle performance and non-toxicity, and is widely used in portable communication equipment. 2 1 century, lithium carbonate for lithium batteries will exceed 20,000 tons. Lithium-based grease has become the leading product of grease. In addition, lithium carbonate as an emotional corrector can effectively treat manic psychosis. At present, the demand for lithium in the world is increasing, and the consumption of lithium also reflects the development level of a country's high technology.
The global lithium resources are about12.76 million tons, mainly distributed in granite pegmatite deposits and salt lakes. Among them, the lithium reserves in lithium mines are only 400,000 tons, accounting for about 3.0% of the global total reserves, while the share of lithium resources in salt lake brine exceeds 77%. The reserve of lithium in lithium mine is far from meeting the market demand, and the solid mineral resources are constantly exhausted, so the development and utilization of lithium mine resources are facing a major turning point. Exploring the extraction of lithium from salt lake brine, low concentration seawater and groundwater has become an important research topic in chemistry, chemical engineering, materials and other disciplines. The process of extracting lithium from salt lake brine is simple, and the cost is about half of that of extracting lithium from ore. At present, the annual capacity of extracting lithium from salt lake brine abroad is nearly 20,000 tons, accounting for about 40% of the total capacity of lithium salt. Using brine or other liquid mineral resources containing lithium instead of ore to produce lithium salt is the development trend of lithium industry in the world.
First, the development process of ion shielding materials
In 1850, Thompon et al. first systematically studied the ion exchange between Ca2+ and Na2+ in soil and NH+ and K+ in water. The substances with exchange properties were later identified as clay, glauconite zeolite molecular sieve and humic acid. It is generally believed that this is the first discovery of ion shielding materials. At the beginning of 20th century, Harms and others synthesized aluminum silicate gel as ion exchange material and applied it to water softening. However, its selective screening performance is poor, its acid resistance is poor and its performance is changeable. In 1960s, Clearfield A and others discovered that zirconium phosphate can be crystallized, which pointed out a new direction for the development of ion shielding materials. Crystallization makes the polycrystalline structure of these zirconium phosphates determined, and the macroscopic ion shielding and exchange behavior can be explained from the perspective of microstructure. After 1980s, Kenta, Qi Feng, etc. Lithium manganese oxide LiMn2O4 with crystal structure was synthesized, which has special selective adsorption performance for lithium ions.
Second, the prospect of extracting lithium from salt lake brine in China
China is rich in salt lake resources, mainly concentrated in Qinghai, Tibet, Xinjiang and Inner Mongolia. Salt lake brine with large lithium resources and high content is mostly concentrated in Qaidam Basin of Qinghai Province, such as Taijinaier Salt Lake, Yiliping Salt Lake, Chaerhan Salt Lake and Dachaidan Salt Lake, which all have extremely high exploitation value. Zhabuye Lake in Tibet is one of the three major salt lakes with lithium content exceeding one million tons in the world. Therefore, the establishment and development of lithium industry in China Salt Lake can not only transform resource advantages into economic advantages, but also promote and develop the economy in western China, providing ideal materials for the development of high technology in 2 1 century.
3. Method for extracting lithium from salt lake brine
At present, the development and utilization of lithium resources mainly focus on the method of extracting lithium from salt lake brine. The methods of extracting lithium from salt lake brine include evaporation, crystallization, precipitation, flotation, solvent extraction and ion exchange. Evaporative crystallization separation method uses a lot of caustic soda and soda ash, which leads to high cost of lithium salt products; Precipitation and solvent extraction are time-consuming and laborious; The flotation process is complicated; The ion exchange method has the advantages of low cost, simple process and wide application. Therefore, it has become the development direction of separation technology to develop new inorganic ion adsorbents with high efficiency and high selectivity. Manganese oxide with spinel structure not only has high selectivity and large exchange adsorption capacity for Li+, but also has the characteristics of economy and environmental protection, which has become the research focus of scholars at home and abroad.
4. A preparation method of lithium ion screen
At present, the preparation methods of LiMn2O4 precursor for lithium ion screen are mainly divided into solid-phase method and liquid-phase method. Solid state synthesis methods are mainly divided into high temperature solid state method, microwave sintering method and solid state coordination method. Solid phase method is generally simple in operation, short in steps, convenient for large-scale production and easy to realize industrialization, but it consumes a lot of energy and has low yield. Liquid-phase synthesis methods mainly include sol-gel method, precipitation method and hydrothermal method. Liquid phase method generally requires high operation, long reaction steps, uniform particle size, regular morphology and relatively pure crystals. Here are some common methods:
1. High-temperature solid-state reaction method: High-temperature solid-state reaction method is the most commonly used and easy-to-operate method to synthesize the precursor of lithium ion sieve, which is to mix the easily-melted or easily-decomposed compounds of lithium and manganese in a certain proportion, and then bake them at high temperature for a certain period of time to synthesize the required compounds. Among them, the main lithium sources are Li2CO3 and LiOH? H2O, LiNO3 and LiI, etc. Manganese sources mainly include MnO, Mn2O3, MnO2, MnCO3 and Mn(CH3COO)2? 4H2O, etc. The high-temperature solid-state reaction method is simple to operate and easy to industrialize. At the same time, there are some shortcomings: high energy consumption and low productivity; Some lithium salts volatilize, and the original proportion is difficult to grasp; The uniformity of the product is very poor.
2. Microwave sintering method: Microwave sintering method is a widely used method for preparing ceramic materials developed in recent years. It is mainly based on the direct action of microwave on the inside of the material, which is converted into heat energy and heated from the inside of the material, thus shortening the reaction time. Microwave sintering method can control the phase structure of powder by adjusting the power of microwave, which is easy to be industrialized and worthy of attention. But after all, it is a solid-state reaction, and the particle size of the obtained powder can only be controlled above micron level, and the powder morphology is slightly poor.
3. Solid-state coordination reaction method: This method is also developed in recent years, especially suitable for the synthesis of metal clusters and solid complexes. Firstly, the solid metal complex was prepared at room temperature or low temperature, and then the oxide ultrafine powder was prepared by thermal decomposition at a certain temperature. Solid-state coordination reaction method retains the characteristics of simple operation of traditional high-temperature solid-state reaction method, and is superior to it in synthesis temperature, calcination time, product particle size and distribution.
4. Sol-Gel method: also known as Pechini synthesis method, it belongs to liquid phase synthesis method and is based on the principle that some weak acids can form chelates with some cations, and chelates can form solid polymer resins with polyol polymers. Because metal ions can react with organic acids and disperse uniformly in polymer resin to realize atomic mixing, ultrafine oxide powder can be prepared at a lower temperature. The traditional sol-gel method is to hydrolyze metal alkoxide to get sol, and then dry to get gel.
Because of its high cost and complex process, materials workers have made a series of improvements and derived some new methods, such as citric acid coordination method, glycine coordination method, polymer coordination method, polyhydroxy acid coordination method and so on. The preparation of lithium ion screen is mainly to remove lithium ions from the precursor spinel with appropriate stripping agent without destroying the configuration of the precursor spinel, so as to ensure the memory of lithium ions in the obtained lithium ion screen. At present, the main stripping agents used are acidic compounds, such as hydrochloric acid, nitric acid and sulfuric acid. The indexes for evaluating the leaching effect are mainly the leaching rate of lithium and the dissolution loss rate of manganese. It is hoped that the stripping rate of lithium can be maximized and the dissolution loss rate of manganese can be minimized by using excellent stripping agent. Compared with hydrochloric acid, nitric acid and sulfuric acid have strong oxidizability, which will increase the leaching loss of manganese to a certain extent, so most of them use hydrochloric acid with appropriate concentration as stripping agent. However, the same eluent, different concentrations and different elution time have different elution effects. Therefore, when preparing ion sieve, we must choose the best pickling conversion conditions.
Verb (abbreviation of verb) Detection of lithium ion sieve
It is necessary to detect the surface morphology of the prepared ion sieve, that is, to detect the product after lithium is eluted by precursor acid by SEM to obtain the scanning result image. By comparing the scanning images of the precursor structure, we can detect whether the precursor structure is damaged during the acid elution of lithium, and then by comparing the pictures in the literature, we can detect whether the product is spinel crystal structure and whether the crystal form is complete. Then the product (precursor) was detected by XRD, and the scanning result map was obtained. According to the scanning result diagram, it is judged whether the product is spinel LiMn2O4 and whether there are impurities. By comparing with the spectrum in the literature, we can detect whether the product has defects, spinel LiMn2O4, and whether there are impurities.
Conclusion of intransitive verbs
At present, the research on ion sieve is still in the experimental stage. In order to realize its industrialization, we must first solve the problems of granulating and dissolving manganese. At the same time, the actual adsorption capacity of ion sieve must be improved by improving the synthesis method and optimizing the experimental conditions. Manganese oxide lithium ion sieve is a new, efficient and green adsorbent, which has a good application prospect. Therefore, the lithium ion sieve adsorption method of manganese oxide has become an important research direction of extracting lithium from salt lake brine and seawater in the world.