The answer is: increase the temperature, stirring, prolonging the leaching time, filtering and then leaching again;
(2) hydrogen peroxide has a strong oxidizing property, can oxidize the reductive substances, Fe2+ and Cr3+ have the reducing property, Fe2+ and Cr3+ can be reduced by hydrogen peroxide, and Fe2+ and Cr3+ can be oxidized by Fe2+ and Cr3+, and the metal ions are mainly Cr3+ and Cr3+. and Cr3+ can be oxidized by hydrogen peroxide to high valence ions, in order to facilitate the separation of ions with impurities,
Which Fe2+ reaction of the ionic equation for 2Fe2++H2O2+2H+=2Fe3++2H2O, the needle ferrite constituent elements are Fe, H, O, the amount of the chemical formula for the 89, then 1mol of the substance should contain 1 mol of Fe, then the mass of the H, O for the 89- 56=33, it can be seen that should contain 2molO and 1molH, the chemical formula should be FeO (OH),
So the answer is: Fe2 +; 2Fe2 + + H2O2 + 2H + = 2Fe3 + + 2H2O; FeO (OH);
(3) sulfuric acid leachate of metal ions in the main Cr3 +, followed by Fe3 +, Al3 +, Ca2+ and Mg2+, as Fe3+ to needle ferrite formation has been precipitated, then add NaOH solution to make the solution alkaline, solution PH = 8, Al3+, Cu2+ converted to precipitate removed, filtered out of the precipitate in part of the precipitate will be dissolved in a sufficient amount of sodium hydroxide solution, the reaction involved is Al (OH) 3 + OH - = AlO2 - + 2H2O,
take a small amount of OH)3↓+HCO3-;
(4) sulfur dioxide is reductive, was filtrate Ⅱ through the ion exchange solution Na2Cr2O7 oxidized to sulfuric acid, Na2Cr2O7 oxygen is reduced to CrOH (H2O) 5SO4, sulfuric acid in aqueous solution to generate sulfuric acid reaction to generate sodium sulfate, based on the analysis of the atomic conservation of the analytical writing of the equation of balance for Na2Cr2O7+ 3SO2 + 11H2O ═ 2CrOH (H2O) 5SO4 ↓ + Na2SO4,
By the equation can be seen, the Cr elemental valence decreased by 3, then each generated 1 mol Cr (OH) (H2O) 5SO4, the transfer of 3NA electrons,
Therefore, the answer is: 1; 3; 11; 2; 1; 3NA.