Lithium, a rare element belonging to the alkali metal group, appears silver-white with a density of 0.534. It has a melting point of 180°C and a boiling point of 1342°C. Lithium is extracted from lithium ores, and this process involves the use of lithium ore dressing technology to obtain qualified lithium concentrates. This article introduces the lithium ore dressing process and common types of lithium minerals.
Lithium Ore Dressing Methods
There are various methods for lithium ore dressing, including manual selection, flotation, chemical methods, combined dressing, splitting, radioactive selection, and particle flotation, with the first four methods being more commonly used.
(a) Manual Selection
Manual selection was a significant ore dressing method for lithium concentrates and spodumene concentrates in the 1950s and 1960s. In 1962, 91% of spodumene concentrates were obtained through manual selection, mainly because lithium ores, mostly from pegmatite deposits, had large, easily manually separable industrial minerals like lithium pyroxene and spodumene. However, manual selection has been gradually replaced by mechanical ore dressing methods due to its high labor intensity, low production efficiency, significant resource waste, and low separation indicators. Nevertheless, in developing countries with cheap labor, manual selection remains a primary method for lithium concentrate production.
(b) Flotation Method
The study and application of the flotation method started early, and it was applied to industrial production of lithium pyroxene concentrates abroad in the 1930s. Lithium pyroxene flotation employs both reverse flotation and positive flotation, while lithium mica is easily floated and commonly subjected to positive flotation.
Research on flotation of lithium pyroxene and spodumene began in China in the late 1950s. Subsequently, research was conducted on lithium mica flotation, lithium beryllium separation, and other lithium beryllium minerals. Process flows for the flotation of spodumene, lithium pyroxene, and lithium mica were developed and applied in the lithium beryllium ore dressing process of newly constructed plants.
(c) Chemical Methods
This method is suitable for salt lake lithium ore to extract lithium salts. It involves evaporating brine on a solar field, leading to the precipitation of sodium and potassium salts. The concentration of lithium chloride is then increased to around 6%, and it is sent to a factory where the soda method is used to transform lithium chloride into solid lithium carbonate products.
Brine-type lithium resources mainly include carbonate-type, sulfate-type, and chloride-type. Currently, the main developments are in the carbonate-type and sulfate-type resources. The technology for development is complex, and it is currently in the production trial stage.
(d) Combined Dressing Method
A single ore dressing method is challenging to remove all impurities and obtain lithium concentrates. Different ore dressing methods need to be adopted for various gangue minerals. In such cases, combined dressing methods are used. Common combined dressing methods include flotation-magnetic separation and gravity separation-flotation-magnetic separation.
To date, scientists have identified over 150 lithium-bearing minerals. The lithium minerals commonly used as industrial raw materials are spodumene, lepidolite, lithium phosphoaluminate, iron lithium mica, and transparent lithium feldspar.
(a) Spodumene
Monoclinic crystal system, often in columnar, platy, and needle-like crystals. Colors range from white, gray, light green to rose, and it is non-magnetic. Spodumene has two crystal types: α and β. When natural spodumene is roasted at 1100°C, it transforms from the α type to the β type, exhibiting thermal cracking properties. Spodumene is found in pegmatite and pneumatolytic-hydrothermal deposits.
(b) Lepidolite
Lepidolite is often found in scaly and foliated aggregates, with colors ranging from rose, purple, light purple, to grayish-yellow, and sometimes colorless. It is non-magnetic and can be found in granite pegmatites, granites, and quartz veins.
(c) Iron Lithium Mica
Iron lithium mica is often produced in flake form, with colors ranging from gray, brown, dark green, to dark purple. It contains approximately 12.5% FeO and exhibits weak magnetism. It is produced in pegmatite and high-temperature quartz veins, and is sometimes found in granites and granite pegmatites.
(d) Lithium Phosphoaluminate
Lithium phosphoaluminate often occurs in irregular blocky and nearly equiaxed shapes, with colors such as gray, yellow-white, and green-white. It typically contains 8-9.5% Li2O, making it the lithium-bearing mineral with the highest lithium content. It is found in granite pegmatites and sometimes in leucogranite and high-temperature quartz veins.
(e) Transparent Lithium Feldspar
Transparent lithium feldspar is often blocky, platy, and needle-like, with colors ranging from white, gray to occasionally pink and green. It is commonly found in granite pegmatites.
Lithium deposits can be classified into three major types: granite pegmatite deposits, pneumatolytic-hydrothermal deposits, and salt lake brine sedimentary deposits. Currently, the world's lithium raw materials mainly come from granite pegmatite and salt lake sedimentary deposits. Notable deposits include the Greenbushes deposit in North Carolina, the Bernic Lake deposit in Canada, and the Salar de Atacama in northern Chile, which are all famous lithium deposits.
