# A Review on the Recovery and Separation of Gallium and Indium from Waste
## 3 Methods of Recovering Gallium and Indium from Secondary Sources
### Sorption and Ion Exchange
#### 3.4.2 Sorption Using Polymer Resins  
Several ion exchange resins also deserve attention. A porous resin with the trade name XAD-7 impregnated with Cyanex 923 is characterized by a high adsorption capacity towards In(III) [31]. Styrene-divinylbenzene copolymer impregnated with secoctylphenoxyayacetic acid is also a very good indium sorbent. The adsorption process can be carried out in a wide temperature range, at a pH of 3. Unfortunately, only three bed cycles are possible [82]. Strongly basic (with quaternary ammonium functional groups on polystyrene-DVB matrix) gel-type resin (Varion AD) in a chloride form was used to recover indium via ion exchange. A purified indium solution obtained from the anion-exchange procedure was neutralized to a pH 7 via a 5 M NH\({}_{4}\)OH solution to obtain In(OH)\({}_{3}\). It was then redissolved in HCl, obtaining a solution with 72 g/dm\({}^{3}\) In concentration, which was used to electrodeposit pure metallic indium (of 99.9997% purity) using DSA anodes and Ti cathode blanks [39]. IRA-900 is another strong base anion exchange resin. It consists of a macroporous styrene-divinylbenzene matrix that has quaternary ammonium functional groups. This resin can be used to separate and recover indium from a sulfuric acid solution by using the HSO\({}_{3}\)\({}^{-}\)/HSO\({}_{4}\)\({}^{-}\) ligand. Initially, In(III) forms a complex anion with HSO\({}_{3}\)\({}^{-}\)/HSO\({}_{4}\)\({}^{-}\). This complex anion can then be adsorbed by the IRA-900 anion exchange resin through ion exchange. IRA-900 demonstrated the best adsorption selectivity to indium at a concentrations of sodium sulfide and sulfuric acid of 0.5 mol/dm\({}^{3}\). It had an adsorption capacity of 95.56 mg/g at 318 K after 30 min. In contrast, the adsorption capacities of Al, Sr, Fe, Zn, and Cu were weak. The In(III) recovery efficiency was about 99.6%, which indicates that the resin is effective for the separation and recovery of indium from ITO films [83]. Impregnating polymer resins with appropriate solvents allows for or improves the separation of gallium, indium, and zinc from the sulfate solutions. For example, it was proposed to use EHEHPA and D2 EHPA solvents to impregnate HZ-803, a macroporous resin. A solution with a pH of 1 was passed through a first column, in which indium was completely recovered from it. Then, the pH of the solution was raised to 3 and it was directed to a second column, where gallium ions and some zinc ions were adsorbed. To completely separate Ga(III) from Zn(II), the solution, after the regeneration of the second column, had to be passed through a third column [31]. In another study, to recover indium from the spent LCD screens, the efficiencies of nine ion-exchange resins were studied: Lewatit TP207, Amberlite IRC 748, Purolite MTS 9300, Lewatit TP 260, Lewatit SP 112, Amberlite IR 120, Lewatit VP OC 1026, Lewatit TP 272, and Reillex HPQ. Among the tested resins, Lewatit VP OC 1026, which was impregnated with D2 EHPA, was found to be the most selective towards indium in solutions with high concentrations of Al, Ca, and Fe. Optimal leaching conditions were established, which included a H\({}_{2}\)SO\({}_{4}\) concentration of 0.2 M, a pulp density of 50% \(w/v\), a temperature of 70 \({}^{\circ}\)C, and a time of 30 min. Lewatit VP OC 1026 resin was able to adsorb up to 34.6 mg of indium per 1 g of resin from the post-leaching solution with an initial indium concentration of 102 \(\pm\) 7 mg/dm\({}^{3}\) at 25 \({}^{\circ}\)C. Indium could be partially eluted (78%) with a 1 M HCl solution or completely eluted with a 5 M HCl solution. At the end of the regeneration/elution tests, a final solution with an indium concentration of about 242 \(\pm\) 29 mg/dm\({}^{3}\) was obtained, which contained less than 2 mg/dm\({}^{3}\) of other impurities [84]. Polymer resins containing complexing functional groups are another promising solution thanks to their high selectivity towards Ga(III) and In(III) [73].