Neutralizing acidic wastewater from the pickling process using slag from the steelmaking process : A pilot study in project "Neutralsyra"

Abstract: Properties and origins of two byproducts from steelmaking plants, slag and acidic wastewater, are investigated in this report. The slags' suitability as neutralizing agents of acidic wastewater from the pickling process, with regard to amount of slag required and the environmental impact of the produced byproducts is investigated. Currently, lime concentrate – which is a finite resource – is used as a neutralizing agent at steel production plants. Because one of the most abundant components in slag is calcium oxide, which is also the active neutralizing substance in lime concentrate, slag is a potential neutralizing agent. A total number of eight slags – four slags from Outokumpu Stainless and four slags from Sandvik Materials Technology – are examined and compared to lime concentrate. Theoretical calculations and experimental trials are performed in order to determine if slag is able to neutralize acidic wastewater. The results show that all the slags are able to neutralize acidic wastewater, but not all slags have the same efficiency. The slags from SMT’s AOD-converter and SMT’s landfill are the most efficient in terms of total amount of neutralizing agent required to neutralize acidic wastewater. The results show that approximately four times more dry slag substance is required, when using the most efficient slag than when lime concentrate is used to neutralize acidic wastewater. The environmental and economic implications of the results are discussed.