Lithium Extraction Technology of Lithium-rich Clay Mineral Resources

Lithium-rich clay deposits are predominantly derived from carbonate rocks; climatic conditions characterised by alternating wet and dry periods, coupled with a low-salinity transitional marine-terrestrial depositional environment ranging from reducing to weakly oxidising conditions, have created favourable conditions for the enrichment of lithium. In the ore, lithium exists primarily as the distinct mineral kokite, with some adsorbed onto montmorillonite; very little is associated with illite or kaolinite. Furthermore, lithium-rich clay deposits offer the advantages of a wide distribution, thick ore layers and low extraction costs, presenting enormous potential for resource development. The industry has now established a variety of mature lithium extraction processes, primarily comprising four major categories: sulphuric acid leaching, roasting and leaching, field-enhanced leaching, and combined acid-base leaching.

Sulphuric acid leaching is the simplest and most direct lithium extraction technology. It uses dilute sulphuric acid as the leaching reagent, utilising the chemical reaction between the acid solution and the lithium-bearing components in the ore to convert solid lithium ions into soluble lithium sulphate, which is fully dissolved into the leachate, thereby achieving efficient separation and extraction of lithium. The process is simple, efficient and widely applicable.

The roasting-leaching method is the core process for upgrading clay-type lithium ore. It involves roasting and activation to break down the mineral structure, followed by lithium extraction using various leaching methods, and is divided into three sub-processes. The roasting-acid leaching method involves activating the ore through high-temperature roasting, followed by an acid leaching reaction to generate soluble lithium salts, thereby completing the leaching of lithium. The additive roasting-water leaching method involves roasting the ore in a mixture with additives such as limestone, gypsum and sulphates. The reaction between these additives and the lithium-bearing minerals generates soluble lithium salts, which can then be recovered through subsequent leaching with fresh water. The calcination-ion exchange leaching method is better suited to carbonate-type lithium ores. After high-temperature decomposition to activate the minerals, a replacement reaction occurs between the cations in the salt solution and the lithium adsorbed between mineral layers, thereby achieving the leaching and recovery of lithium.

The external field-enhanced leaching method is a new type of high-efficiency lithium extraction technology. It relies on external fields such as ultrasound, microwaves and electric fields to disrupt the stable structure of minerals, activate lithium elements and significantly improve leaching efficiency. Among these, pulsed voltage electric field lithium extraction technology is relatively well-established. By establishing an electric field between an anode and a cathode and adding intercalation agents, a pulsed electric field drives the directional migration of lithium ions between clay mineral layers, causing them to detach from the mineral matrix and ultimately be concentrated and recovered in the cathode zone. This process is environmentally friendly and simple to operate, but is only suitable for ion-adsorption-type clay lithium ores.

The combined acid-base method is a modified, low-cost lithium extraction process that combines the dual advantages of acid and base methods. First, sulphuric acid leaching is employed to produce acid leachate and leaching residue; the residue is then subjected to alkali leaching to obtain alkali leachate. Finally, carbon dioxide is introduced into the alkali leachate to adjust the pH to 8.5–10.5, after which the solution is filtered to precipitate the lithium carbonate product. This process requires minimal equipment, consumes little energy, generates minimal residue, offers controllable parameters and has low production costs, providing an excellent technical pathway for the large-scale, resource-efficient development of lithium-rich clay deposits.