Treatment and Utilization of Spent Acid that Used in Galvanizing ( Pickling )

                                

                                      1-       6 HCl + Fe₂O₃ ----- 2 FeCl₃ + 3 H₂O 

2-            Fe + HCl  -------- Fe Cl₂ + H₂

 

The main concentration of pickling tank is 16% wt/ wt .

The performance of the tank can't be effective when it reaches 5  wt/ wt .

At this point the iron content is 150 gr / lit . it means you have  ore or iron mine .

There is more than one option to treat this consumed acid :

·        Acid Regeneration : it can be used on or off line by using special type of resins in order to get rid of iron then concentrate  it to reach crystal stage as FeCl₃ and it is necessary to keep Fe content within 10 gr/ lit to reduce dipping time in pickling or acid tank . the second option to treat the consumed acid off line by evaporation or treat it with sulfuric acid as below

3 H₂SO₄ + 2 FeCl₃ ------ 6 HCl +   Fe₂( SO₄)₃

  H₂SO₄ +  FeCl₂ ------  2 HCl +   Fe SO₄

The value of ferric sulfate or ferrous sulfate is very high in water treatment Plant (domestic water treatment or as fertilizer ).

·        The critical issue is the polluted  of consumed acid : it should not contain other metal such as zinc or pickling additive which cant be evaporated by simple purification  .