Closed Loop System for the Treatment of Waste Pickle Liquor.

摘要

The report gives results of a demonstration of the feasibility of converting ferrous sulfate (FeSO4.7H2O)--obtained by low-temperature crystallization from H2SO4waste pickle liquor generated by the acid-cleaning of steel surfaces--to marketable ferric oxide (Fe2O3). A closed-loop system is proposed,consisting of a crystallizer,ion exchange unit,oxidizer,and hydrolyzer. All acids are recycled,and the net effect is that FeSO4.7H2O is consumed and Fe2O3is produced. The FeSO4.7H2O solution was contacted with hydrogen ion exchange resin in a continuous ion exchange unit. Removal of ferrous ion was 90%. About 11-15% by weight H2SO4was generated for recycle to pickling. The resin was regenerated with 4M HNO3,and a ferrous-ferric nitrate solution was produced. This product was heated to 180C and contacted with air to get complete oxidation to the ferric state and to oxidize any byproduct NO2to HNO3. The nitrate solution was then hydrolyzed to Fe2O3and HNO3in a continuous coil autoclave at 205C. The HNO3was about 20% by weight and can be recycled to the ion exchange unit. After drying,the Fe2O3was about 99% pure. A preliminary market survey indicates the product may have a value of $0.10-$0.80per kilogram.