So the answer is: increase the temperature, stir, extend the leaching time, filter and leach again;
(2) Hydrogen peroxide has strong oxidizability and can oxidize reducing substances, Fe2+ and Cr3+ have reducibility, and Fe2+ and Cr3+ can be oxidized by hydrogen peroxide into high valence ions, which is convenient for separation from impurity ions.
The ionic equation of fe2+ reaction is 2fe2+H2O2+2h+= 2fe3++2h2o, goethite is composed of Fe, H and O, and the chemical formula is 89, so the 1mol of this substance should contain 1mol of Fe, and the mass of H and O is 89-56=33, which indicates that it should contain 2mol and 60.
So the answer is: Fe2+; 2fe 2 ++ H2O 2+2H+= 2fe 3 ++ 2H2O； FeO (oh);
(3) The metal ions in sulfuric acid leaching solution are mainly Cr3+, followed by Fe3+, Al3+, Ca2+ and Mg2+. Because Fe3+ has been precipitated by goethite, NaOH solution is added to make the solution alkaline, and the PH=8 of the solution is 8, and Al3+ and Cu2+ are transformed into precipitates and removed. Part of the precipitate filtered out will be dissolved in enough sodium hydroxide solution, and the reaction involved is Al.
Taking a small amount of supernatant and injecting enough CO2, the corresponding precipitate can be obtained. The reaction involved is AlO2-+2H2O+CO2=Al(OH)3↓+HCO3-.
Therefore, the answers are: Al3+, Cu2+; al(OH)3+OH-= alo 2-+2H2O； alo 2-+2H2O+CO2 = Al(OH)3↓+HCO 3-；
(4) Sulfur dioxide is reducible. After ion exchange in filtrate II, Na2Cr2O7 in the solution is oxidized to sulfuric acid, Na2Cr2O7 oxygen is reduced to CrOH(H2O)5SO4, and sulfuric acid in the aqueous solution reacts to generate sodium sulfate. According to the analysis of atomic conservation, the square formula is written as na2cr2o7+3so2+1H2O ═ 2croh.
According to the equation, when the valence of Cr element decreases by 3, 3NA electrons will be transferred for every generation of 1mol Cr(OH)(H2O)5SO4.
So the answer is:1; 3; 1 1; 2; 1; 3NA。