A Case Study on “Reuse of Stainless Steel Finishing Wastewater”

Steel pickling is part of the finishing process in the production of stainless steel, in which oxide and scale are removed from the surface of stainless steel, by dissolution in acid. Steel pickling process produced large quantity of diluted acid which further treated by individual industry or as combined effluent treatment. During the pickling process pickled liquor/s applied on steel surface and due to that metal oxide and scale is removed from the surface of steel and mixed or suspended in the acid solution. When the strength of pickle liquor reduced, it is discarded and is drain out from pickling tanks. This liquid waste is called spent picking liquor (SPL). The pH of SPL is around 1.5 to 2. SPL is hazardous waste as per Environment Protection Act 1986 Government of India. SPL sample was mixed with the concentrated H2SO4 of a particular amount, and this solution was added in the particular amount of iron scrap powder. Then mixture was heated around 100°C and in this heated mixture small amount of concentrated HNO3 was mixed. The solution was put in the furnace for cretin duration at temperature about 900°C. At this temperature all iron oxide converted into ?-Fe2O3 which commercially known as red oxide. The use of SPL to make red oxide not only solves the problem of safe disposal of SPL but also gives the value added product.