i have the solution with H2SO4 and Na2SO4，FeSO4，CuSO4，etc, how can i separate the solution to fetch H2SO4?

Question

about 3~4mg/l H2SO4 in solution.

Answer 1

Probably you need to check the soubility points of all of compounds. Im guessing that if you cool down the mixture, the Fe and Cu will fall out first.

as for the Na2SO4, maybe you can distill out the h2so4, im only giving guesses as I dont know the boiling points for the compounds.

give it a try

Answer 2

These are all ionic compounds, so distillation will not work. You could add HCl in solution, which will return the hydrogens back to the sulfide salts, then add a precipitation agent to get the metals out.

I don't really know what the point would be; just buy more sulfuric acid if you need it. If it's a neutralization issue, add a weak base until the pH is 7.