The method for calcination of iron sulfides, pyrite, marcasite etc. at a high temperature 900° C. according to the reaction:4FeS2+11O2 →2Fe2O3+8SO2  (1) is known. The escaping gas is converted to sulfuric acid, and a calcine (Fe2O3) is used for production of various iron compounds or applied in ferrous metallurgy to obtain metal iron. However, because of a high residual content of sulfur in the calcine, its application in metallurgy is limited and it is usually dumped. [Short Chemical Encyclopedia, Moscow, 1979].
There is known a method of sulfatization of sulfide materials by their treatment with concentrated sulfuric acid at 200° C.-300° C. [U.S. Pat. No. 1,895,811, 1933, L. EMakovezky, H. Morgan]. This process is described by a reaction:MeS+4H2SO4 →MeSO4+4 SO2+4H2O  (2) where Me —Fe, Ni, Zn, Cu etc.
However, the largest extent of sulfatization (78.4%) of pyrite (FeS2) was achieved at 200° C., the sulfatization extent of copper sulfides was lower.
With temperature increase to 300° C. the reaction of pyrite sulfatization proceeds as follows:FeS2+H2SO4→FeSO4+S0+H2S  (3) 
At a temperature 300° C. sulfuric acid behaves as a strong oxidizer and a portion of iron is oxidized to Fe(III) [S. S. Naboichenko, V. I. Smimov “Hydrometallurgy of copper”, Moscow, “Metallurgiay”, 1974):2FeS2+3H2SO4 →Fe2(SO4)3+S0+3H2S  (4) 
There exists a method for sulfatization of zinc and copper sulfides by their dissolving in sulfuric acid of a high concentration (45-70%) at a temperature below the boiling point of these solutions (for 45% H2SO4-≦130° C.; for 70% H2SO4-≦140° C.). Under these conditions zinc sulfate was obtained (ZnSO4 H2O), sulfatization of copper and iron sulfates proceeded incompletely [U.S. Pat. No. 5,711,922, Jan. 27.1998; O'Brien, Robert N.].
Sulfide ores and concentrates can be also treated with a mixture of sulfuric and nitric acids at 110-170° C. Sulfuric acid concentration is 40-65%. The amount of nitric acid required for sulfatization is 0.5-3.0 moles of HNO3 per 1 mole of sulfides which are contained in the treated material [U.S. Pat. No. 5,484,579, Jan. 16, 1996; O'Brien, Robert N.]. This technology does not provide a complete sulfatization of metal sulfides as well. In addition a complicated problem of utilization of gases SO2 and SO3, which contain nitrogen oxides arises.
All the patents mentioned above deal with a complicated and yet unsolved problem of separation of admixtures of sulfates of such metals as Al, Cu. Zn, Ni etc. from iron sulfates.
Usually the solution of metal sulfates obtained after sulfatization and leaching is oxidized with oxygen of air or by other methods in order to convert Fe2+ to Fe3+ then the solution is adjusted to pH=2, iron precipitates as Fe(OH)3, and the admixtures remain in solution. To obtain iron (III) sulfate, iron hydroxide is again dissolved in sulfuric acid. Extraction of admixtures from the sulfuric acid solution is a complicated problem.
If the solution obtained after sulfatization contains a large amount of copper, the method of cementation with iron scrap is applied. It is described by the following reactions:Fe0Cu2+→Cu+Fe2+  (5) 2Fe3++Fe→3Fe2+  (6) 
Copper precipitates as a metal powder, and iron converts to its bivalent form FeSO4, all admixtures, except for copper, are in solution with iron. Isolation of pure iron sulfate from this solution is a large technological problem.
The present invention is aimed at the development of the method for processing sulfide ores and concentrates, in particular pyrite, performed at lower temperatures than pyrite calcination and which results in the production of highly pure iron sulfates without using additional amounts of reagents for neutralization of strongly acidic solutions.