Reactions:
1.- Na2Cr2O7 + H2SO4 + H2O = 2CrO4H2 + Na2SO4
2.-CrO4H2 + ZnO = ZnCrO4 + H2O
3.- 4ZnCrO4 + 2NaOH + 2H2O = 4ZnO.Na2O.4CrO3.3H2O
Process to obtain a batch of 100 kilograms of HHS Zinc Chromate
Solution "a": Dissolve 62.31 kgs. of sodium bichromate in the double of its weight in water = 124.62 liters.
Add to this solution 15.73 kgs. of concentrated sulfuric acid ( this is 8.49 liters -1,25 times the stoichiometric amount-).
Solution "b": Prepare a suspension of 38.7 kgs. of zinc oxide in about 250 liters of water.
Procedure:
Stirring , pour the solution "a" over the suspension "b". This is done in 20 minutes.
Then, 48.6 liters of sodium hydroxide ( concentration= 48% -4,3 times the stoichiometric amount-) are added until pH is > 10.3
The precipitate is then filtered and slightly washed.
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