Method for producing ferrous nitrate and calcium sulfate from waste acid generated during titanium dioxide production through sulfuric acid method

The invention provides a method for producing ferrous nitrate and calcium sulfate from waste acids generated during the production of titanium dioxide through the sulfuric acid method. The waste acids generated during the production of titanium dioxide through the sulfuric acid method are mixed with an excessive amount of ferrous hydroxide to have reaction and produce ferrous sulfate; the reaction liquid is filtered to produce a filtrate mainly containing ferrous sulfate; an excessive amount of calcium nitrate is added to the filtrate mainly containing ferrous sulfate to produce ferrous nitrate and calcium sulfate, and the reaction liquid is filtered to separate ferrous nitrate and a calcium sulfate liquid; the calcium sulfate precipitates are washed, dried and pulverized to obtain a calcium sulfate product; a small amount of ferrous sulfate is added to the ferrous nitrate liquid to neutralize calcium nitrate, and then the reaction liquid is fed to a reduced pressure distiller for reduced pressure distillatio