Application of sulfites in electroplating wastewater treatment system
Time : 02-22-2016  Traffic:0
In electroplating wastewater treatment system, sodium bisulfite, sodium metabisulfite or sodium sulfite are commonly used as reducing agent to react with hexavalent chromium. Generally, the density of hexavalent chromium in wastewater  and PH value in wastewater are controlled in the range of 100~1000mg/L and 2.5~3 respectively. Now let’s review the specific theoretical amount of the reducing agent.

Typically, the best sodium bisulfite-to-hexavalent chromium ratio should be 4:1, the best sodium metabisulfite- to- hexavalent chromium ratio should be 3:1, and the best sodium sulfite-to-hexavalent chromium ratio should be 4:1. The feeding of the reducing agents should not be excessive so as to avoid feed materials waste and also to avoid potential reacts to form {Cr2(OH)2SO3}2. The reduction reaction time is good to limited to approximately 30 minutes, and PH value of chromium hydroxide precipitate should better be controlled  in the range of 7~8. The precipitants can be selected as lime, sodium carbonate or sodium hydroxide according to the actual situation of the system.

Sulfites reduction technology is widely used in chromium-containing wastewater treatment which is mainly produced by electroplating production, plating solution filtration and waste solution discharge. Separate treatment is needed due to the hexavalent is highly toxic. Sulfite reduction, ferrous sulfate - lime treatment are common methods to reduce hexavalent chromium to trivalent chromium.