Indium element and indium extraction resin

The wide range of applications of indium has earned it the titles of "industrial vitamin" and "vitamin of alloys". Its most common form of application is C (ITO) - a unique material that is both conductive and transparent. 
(1) Display and Touch Control Field
ITO films are widely used in liquid crystal displays, touch screens, OLED displays and other devices. 70% of the global indium consumption is used in the production of ITO targets. 
(II) Semiconductor Field
High-purity indium possesses unique semiconductor properties. Compounds such as indium phosphide (InP) and indium arsenide (InAs) are used in 5G communication, fiber networks, lasers, and the manufacturing of high-frequency and low-power chips. 
(III) New Energy Field
The photoelectric conversion efficiency of copper-indium-gallium-selenium (CIGS) thin-film solar cells exceeds 22%, and it is internationally recognized as "a very promising new type of thin-film solar cell for the next generation". 
(4) Other Fields Indium can also be used to manufacture low-melting-point alloys, bearing alloys, nuclear reactor control rods, high-vacuum sealing gaskets, etc.

Among the various indium extraction technologies, the ion exchange method stands out due to its high efficiency, environmental friendliness, and recyclability. The main principle is as follows: In this process, indium is adsorbed from the indium-containing solution using ion exchange resins, and then recovered through desorption (washing). The general process typically includes steps such as acid dissolution, ion exchange, washing, and desorption of indium.
(1) The structure and chemical composition of indium extraction resins 
The commonly used indium extraction resins in the wet indium refining industry are mostly macroporous chelating ion exchange resins. Their structure design combines physical strength with chemical selectivity. 
Framework: This framework is made of cross-linked polystyrene polymer material and is produced through suspension polymerization with a large pore structure. This framework is resistant to acids, salts, and abrasion, and can adapt to the extreme environment of high acid and high salt in wet smelting. At the same time, the large pore structure provides a huge specific surface area and rapid ion diffusion channels. 
Functional groups: The functional core of the resin is the chelating functional group, which contains amino phosphonic acid groups. This functional group contains coordination atoms such as O, N, S, and P, which can provide lone pairs of electrons and form stable coordination bonds and ionic bonds with In³⁺ and other metal ions, thereby achieving selective chelation and adsorption of indium ions. For the dedicated resin for indium, its functional groups are specially designed, having an extremely high affinity for trivalent indium ions, while having very weak adsorption for common impurity ions such as Na⁺ and Fe²⁺, thus achieving precise separation. 
Ion type: Industrial resins are usually supplied in sodium type or hydrogen type. When leaving the factory, they are mostly converted to working type (such as sodium type). Users can start using them by simply opening the bag and performing a simple pre-treatment (such as acid transformation or water washing). 
Physical form: The particle size is generally between 0.315 and 1.25 mm, and it is uniformly spherical. The uniform particle size distribution can reduce water flow resistance, ensure bed layer permeability, prevent deviation and blockage, and facilitate the uniform progress of adsorption and desorption processes. 
(2) Working Principle: Selective Adsorption "Molecular Sieve" 
The working principle of the indium resin can be summarized as "precise identification and targeted capture": In acidic leaching solution (usually with pH < 2), indium exists in the form of In³⁺. When the indium-containing liquid passes through the resin column, the specific functional groups on the resin act like a "key", only pairing with the indium ions to form a stable complex. Meanwhile, impurity ions such as zinc, aluminum, and iron will flow out with the waste liquid. 
After adsorption saturation, the resin is desorbed using hydrochloric acid/sulfuric acid as the eluent, and a high-concentration indium-rich solution can be obtained. The desorbed resin undergoes a simple regeneration process, and its adsorption performance can be restored, allowing it to be used in the next round. 
(III) Core Strengths 
High selectivity: The specific functional groups have extremely strong selectivity for In³⁺, enabling the direct extraction of indium from complex multi-metal leaching solutions, significantly simplifying the separation process. 
Strong environmental tolerance: It can operate stably under pH values lower than 2 and even more acidic conditions, with a temperature tolerance of up to 60-80℃. It is suitable for the conventional processes of adsorption in weakly acidic systems and elution in strongly acidic systems. 
Outstanding dynamic performance: The large-pore structure ensures rapid ion exchange, with fast adsorption and desorption rates and high production efficiency. 
High physical and chemical stability: The cross-linked framework and stable functional group bonding method enable it to withstand erosion and pressure changes, and can be repeatedly regenerated for hundreds of cycles.