Galvanic sector and some industrial processes use hexavalent chromium for chromium plating operations on metal or plastic.
The wastewater, sent to the water purification system, produced with these chromium plating processes has a small percentage of hexavalent chromium that must be chemically reduced from hexavalent to trivalent.
Even after neutralization, the hexavalent chromium remains completely in water solution, in order to flocculate it, it is necessary to carry out a reduction called dechromatation.
Dechromatation in chemical-physical plants takes place with reducing reagents such as sodium bisulphite in the acid field with the following reaction, 4 H2CrO4 + 6 NaHSO3 + 3 H2SO4 = 2 Cr2(SO4)3 + 3 Na2SO4 + 10 H2O the reaction is controlled with special instruments and probes to detect pH and Redox potential.
It is possible to dechromate a wastewater containing hexavalent chromium with ferrous sulphate or ferrous chloride at neutral or alkaline pH, this solution is recommended when the design of the chemical-physical purifier requires the use of primary coagulants and when the concentration of hexavalent chromium is limited.
