# A Review on the Recovery and Separation of Gallium and Indium from Waste
## 3 Methods of Recovering Gallium and Indium from Secondary Sources
### Leading
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Acid/Base Concentration** & **Temperature** & **Solid-to-Liquid Phase Ratio (S/L)** & **Time [h]** & **Additional Procedures** & **Leading Efficiency [\%], Type of Waste** & **Ref.** \\
**Concentration** & **Temperature** & **Phase Ratio (S/L)** & **Time [h]** & **Additional Procedures** & **Efficiency [\%], Type of Waste** & **Ref.** \\
**[mol/dm3]** & **Temperature** & **Phase Ratio (S/L)** & **Time [h]** & **Additional Procedures** & **Efficiency [\%], Type of Waste** & **Ref.** \\
4 M HCl & 80 & 10 & 3 &
\begin{tabular}{c} roasting \\ Na\({}_{2}\)CO\({}_{3}\):waste = 1:1 \\ 1000 \({}^{\circ}\)C 4 h \\ \end{tabular} & 93.40 from CIGS & [34] \\
5 M HCl & 75 & 50 & 2 &
\begin{tabular}{c} oxidant addition \\ (H\({}_{2}\)O\({}_{2}\) (A/O = 9:1)) \\ \end{tabular} & 99 from ITO & [38] \\
0.5 M HCl & 80 & 33.33 & 1 & none & \textgreater{}90 from ITO & [39] \\
2 M HCl & 55 & & &
\begin{tabular}{c} Ultrasonication \\ (300 W ultrasonic \\ waves) \\ \end{tabular} & 96.80 from ITO & [45] \\
4 M HCl & - 1 & 200 & 142 s &
\begin{tabular}{c} Microwave \\ (650 W)-ultrasound \\ heating system \\ \end{tabular} & 100 from ITO & [48] \\
0.25 M H\({}_{2}\)SO\({}_{4}\) & 80 & 40 & 2 & none & 99 from ITO & [41] \\
3 M H\({}_{2}\)SO\({}_{4}\) and & 80 & 25 & 3 &
\begin{tabular}{c} oxidant addition \\ (H\({}_{2}\)O\({}_{2}\)) \\ \end{tabular} & 99 from InP & [42] \\
18 M H\({}_{2}\)SO\({}_{4}\) & 68 & - 1 & 0.33 & ultrasonication & 92 from ITO & [46] \\  & & & & pre-leaching & \\
10–11 M NaOH & 95 & 100 & 3 &
\begin{tabular}{c} (4 M HNO\({}_{3}\) at 80 \({}^{\circ}\)C) \\ roasting NaOH \\ or Na\({}_{2}\)CO\({}_{3}\) \\ \end{tabular} & \textgreater{}90 from LED & [51] \\ \hline \hline \end{tabular}  
* not specified.  
\end{table} 
Table 1: Optimal conditions for the leaching of indium from ITO, InP, InAs, and CIGS waste. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Acid/Base Concentration** & **Temperature** [\({}^{\circ}\)C] & **Solid-to-Liquid Phase Ratio (S/L)** & **Time [h]** & **Additional Procedures** & **Leading Efficiency [\%], Type of Waste** & **Ref.** \\
**Concentration** & **Pressure [atm]** & **[g/100 cm3]** & **Time [h]** & **Additional Procedures** & **Efficiency [\%], Type of Waste** & **Ref.** \\
2 M HNO\({}_{3}\) & 60 & - 1 & 2 & none & 99 from GaAs & [17] \\
2 M HNO\({}_{3}\) & 30 & 2 & 2 & none & 98 from GaAs & [29] \\
2 M HNO\({}_{3}\) & 30 & 2 & 2 & none & 99 from GaAs & [39] \\
0.25 M HCl & - 1 & 3.33 & - 1 &
\begin{tabular}{c} NaOH:waste = 10:1 \\ 1000 \({}^{\circ}\)C 8 h \\ \end{tabular} & 73.3 from GaN & [32] \\  & & & & & 1000 \({}^{\circ}\)C 8 h & \\
4 M HCl & 80 & 10 & 3 &
\begin{tabular}{c} Na\({}_{2}\)CO\({}_{3}\):waste = 1:1 \\ 1000 \({}^{\circ}\)C 4 h \\ pre-leaching \\ \end{tabular} & 96.86 from CIGS & [34] \\
6 M NaOH & 95 & 100 & 3 &
\begin{tabular}{c} (4 M HNO\({}_{3}\)) \\ roasting NaOH \\ or Na\({}_{2}\)CO\({}_{3}\) \\ \end{tabular} & \textgreater{}90 from LED & [51] \\
2 M NaOH & 90 & 50 & 3 & oxidation process &
\begin{tabular}{c} 92.65 from Ga \\ rich waste \\ \end{tabular} & [54] \\ \hline \hline \end{tabular}  
* not specified.  
\end{table} 
Table 2: Optimal conditions for the leaching of gallium from GaAs, GaN, and CIGS waste. final efficiencies depending on the LCD pulp density (1% and 2% \(w/v\)) and the use of pure or mixed bacteria. By using the mixed culture of _Acidithiobacillus ferrooxidans_ and _Acidithiobacillus thiooxidans_, high leaching efficiencies of both indium (94.7%) and tin (98.2%) can be obtained [56]. Bio-acid leaching of LED with a high pulp density (40 g/dm\({}^{3}\)) using only a culture of sulfur-oxidizing bacteria (_Acidithiobacillus thiooxidans_) but with a multistep contact bioleaching, allowed for the achievement of 100%, 100%, and 75% extraction efficiencies of Cu, Ni, and Ga, respectively [57]. Indium extraction from spent LED monitors, including bioleaching followed by solvent extraction, stripping, and precipitation, was also possible. At optimized inoculum percentages of _A.