Exploration of resource utilisation process of lithium mica waste residue

With the booming development of new energy industry, the demand for lithium resources is growing. As an important lithium-containing mineral resource, lithium mica produces a large amount of slag in the process of mining and utilisation. If these slags are not handled properly, they will not only cause environmental pollution, but also waste the valuable resources. Therefore, the resource utilisation of lithium mica waste residue has become the key to achieve a win-win situation in terms of environmental and economic benefits.

High-value element extraction process

Lithium mica waste slag contains potassium, lithium, rubidium, cesium, beryllium and other high-value elements, and the extraction of these elements is an important way to enhance the value of waste slag resources.

Acid method is one of the commonly used extraction processes. Taking the sulphuric acid method as an example, the lithium mica ore is first crushed and ground to a suitable particle size, then mixed with concentrated sulphuric acid and reacted at a specific temperature and time, so that the lithium mica reacts with the sulphuric acid to produce products such as lithium sulphate. Afterwards, through water leaching, purification and other steps, impurity ions are removed, and a purer lithium sulfate solution is obtained, and then lithium sulfate crystals are obtained through evaporation and concentration and crystallisation techniques. However, the traditional sulfuric acid method has problems such as high energy consumption, long leaching time and high acid consumption.

Roasting method is also a commonly used elemental extraction process. Commonly, there are chlorination roasting method, limestone roasting method, sulfate roasting method and so on. The lithium mica and sulfate or other compounds are mixed and roasted at a high temperature of 800 - 1000 ℃, which destroys the mineral structure of the lithium mica and releases the lithium element. After cooling and crushing of the roasted product, the soluble lithium compounds are dissolved out by leaching process, and then the lithium compounds are concentrated by removing impurities by chemical reagents, adjusting pH, and evaporation or crystallisation, etc. For example, sulphate roasting is used in the production of lithium mica. For example, the lithium in lithium mica is extracted by sulphate roasting, which can get better extraction effect by roasting for 0.5-2 hours at 850-1000℃.

The extraction of lithium by pressure-boiling method is mainly under the conditions of high temperature, high pressure and the presence of liquid-phase water, through the chemical reaction between sodium carbonate and lithium-containing ores, so that lithium is extracted in the form of lithium carbonate. This process has significant differences in lithium extraction effect for raw materials with different mineral phases, but the lithium extraction efficiency for lithium mica is relatively low.

In addition to the above methods, there are new processes such as microwave-enhanced baking. Microwave-enhanced baking can significantly shorten the heating time, reduce energy consumption, and improve the lithium leaching rate.

Building materials utilisation process

The main components of lithium mica waste residue are quartz and feldspar, etc., which have the characteristics of raw materials for building materials and can be used to prepare a variety of building materials.

In cement preparation, the composition of lithium mine waste is similar to clay raw materials, and can replace part of the clay raw materials for the preparation of cement clinker. Relevant research shows that lithium mine waste can stabilise the M₃S crystal phase and improve the crystallinity of C₃A. Controlling the mixing amount of lithium mine waste <5% to prepare white silicate cement clinker can improve the content of C₃S and C₃A in clinker, reduce the content of f - CaO, and significantly improve the early strength of cement.

When used in the preparation of concrete, lithium mine waste slag to replace part of the cement as concrete admixture, can be a large-scale consumption of waste slag and reduce the pressure on the environment. Sio₂ and Al₂O₃ in the lithium slag can react with Ca(OH)₂ in the cement to generate hydrated calcium silicate gel, thus improving the mechanical properties and durability of concrete. The researchers prepared lithium slag cement paste by replacing 10% - 30% of cement with lithium slag, and tested the various performance indicators of the test block, and found that the incorporation of lithium slag will affect some properties of the cement paste, such as increasing the setting time, reducing the air content, etc., but through the optimisation of the mixing amount and the addition of admixtures, etc., the performance of the concrete can be improved.

In the field of ceramic preparation, lithium mine waste slag is a typical high-silicon, aluminium-rich, alkali-rich solid waste raw material, and its main mineral composition is close to that of traditional ceramic raw materials. Through the acidic lithium slag and silicon carbide and other foaming agents and other additives with the role of the preparation of high-strength, low thermal conductivity of lithium slag-based porous ceramic materials.

In addition, lithium mine waste can also be used to prepare geopolymers. The chemical composition of lithium slag is similar to that of fly ash, which can be used as a silicon and aluminium precursor for single-component geopolymers. Through the use of thermal activation and alkali activation techniques, the heat of hydration of lithium waste mineral polymers can be lowered, and their compressive strength and other properties can be improved.

Green Backfill Process

In order to avoid potential safety hazards in the pits left behind after the end of mining, tailings are usually used as aggregate with binder and water to prepare backfill materials for filling. Paste backfill can be made from crushed and graded tailings, with binder and water added to the mixture, and the prepared paste backfill can be transported to the quarry by gravity or volumetric pump.

Conclusion

The resource utilisation of lithium mica waste residue is of great significance. Through the processes of high-value element extraction, building material utilisation and green backfilling, the reduction, harmlessness and resourcing of waste residue can be achieved, which not only alleviates the environmental pressure, but also promotes the recycling of resources and provides strong support for sustainable development. However, there are still some challenges in the current utilization process, such as the complexity of the waste residue composition, the different nature of the waste residue around the world, the difficulty of utilization, the higher cost, etc. In the future, there is a need for further in-depth research and optimization of the process, to promote the widespread application of lithium mica waste residue resourcing technology and the development of industrialisation.