Treatment of Waste Water from Galvanizing Unit



 Treatment of  WasteWater from  Galvanizing Unit 
                                            مخطط مقترح لمعالجة مياه الجلفنة                                               

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

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                                                                         1-        6 HCl + Fe 2 O 3 ----- 2 FeCl 3 + 3 H 2 O  2-             Fe + HCl  -------- Fe Cl 2 + H 2   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 FeCl 3 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 H 2 SO 4 + 2 FeCl 3 ------ 6 HCl +   Fe 2 ( SO 4 ) 3   H 2 SO 4 +  FeCl 2 ------  2 HCl +   Fe SO 4 The value of ferric sulfa
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Critical Factors of Choosing the Metal for Galvaning

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     There are two factors to be considered : 1 - The iron for galvanizing is a product and not galvanized for the purpose of maintenance. 2- If the option to choose the metal exists, it is desirable to choose iron  that gives us a high quality product within the basic criteria, including: 1- The chemical composition of the metal, especially the content of silicon, carbon and phosphorous .... etc . 2- The surface must be free of organic pollutants (dyes, paints, polymers, bitumen). 3-   No  high corrosion or  pores in the metal surfaces . 4- The thickness of the iron should be consistent and  no significant differences. 5- The design  of products should allow draining of molten zinc.
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Galvanizing Material

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      A-       degreasant   1-    Degreasing: It is  used to remove organic substances or contamination   , the concentration of this material usually  10% wt/wt from tap water  2-    Actually 7.5% has been used in decreasing tank the, the process take place without problem in production 3-    The temperature of the tank is  75 c, there are neutral , alkaline and acidic degreaser .  4-    The dipping time is the same . 5 -    The method of check the concentration is necessary  to improve performance  and to  control .     B- pickling additive   1-     This additive is used as: a- inhibitor agent b- wetting gent c- anti – vaporization agent 2-     1.4% of the concentrated acid is added to the pickling tank from the pickling additive   3-     The use of the pickling additive has taken place with out any problems 4-  they are  harm ful    in case of producing new substances from consumed acid , and same for water treatment ( almost contain heavy  metals  and
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