Chemical Treatment for Nitrite Nitrogen Removal From Stainless Steel Pickling Liquor Wastewater

Steel pickling produces acidic waste liquor that has a high metal content and contains other compounds, including nitrogen compounds such as nitrite. Most treatment technologies focus on eliminating the hazardous nature of the waste pickling liquor by neutralization with lime. Increasing the pH generates waste sludge and precipitates heavy metals; thus, reducing the hazardous characteristics. Alternative treatment technologies focus on recovering valuable acid and metals. However, few of these treatments remove nitrogen compounds that can cause whole effluent toxicity problems. For this work, chemical treatments for removing nitrite from waste pickling liquor were studied. Sulfamic acid, sodium bisulfite, and sodium hypochlorite (bleach) were used to treat waste pickling liquor from a stainless steel continuous rolling mill. Sulfamic acid was determined to be the most efficient chemical treatment and most environmentally friendly because it completely reduced nitrite to nitrogen gas, while the other treatments produced other nitrogen compounds (nitrous oxide or nitrate). The testing showed that the highest treatment efficiency occurs under acidic conditions and should be performed prior to neutralization.