Which of the reaction is suitable for concentrating ore by leaching process?
\( \mathrm{2Cu_2S + 3O_2 \rightarrow 2Cu_2O + 2SO_2} \)
\( \mathrm{Fe_3O_4 + CO \rightarrow 3FeO + CO_2} \)
\( \mathrm{Al_2O_3 + 2NaOH + 3H_2O \rightarrow 2Na[Al(OH)_4]} \)
\( \mathrm{Al_2O_3 + 6Mg \rightarrow 6MgO + 4Al} \)