Use of slag to neutralize acidic waste water

Purpose and goal

The aim of this study was to investigate the possibility of using slag instead of purchased lime to neutralize acids and acidic wastewater from the steel mills. By reusing slag in the neutralization process, as well as reusing the by-product after the neutralization process, it is possible to save raw materials and reduce the landfills. In this study, different slag have been ranked for its neutralization abilities compared with purchased lime to neutralize waste water at the steel industry.

Expected results and effects

Results show that slag can be used to neutralize acids and acid wastewater from steel mills. The experiments show that the most effective slags are landfill slag and slag from the ditch at the slag-yard. The results show that about seven to eight times more slag was needed in comparison with lime to neutralize 1 liter of acidic wastewater within a 30 minute period. The purified water after the neutralization process was analyzed by ICP and the results showed that they were within the target values of all elements.

Planned approach and implementation

In total, 8 different slag types have been selected and evaluated for their abilities to neutralize wastewaters from Sandvik and Outokumpu. Experiments have been conducted to rank the neutralization abilities of the slags and to evaluate the minimum amount of slag needed to neutralize 1 liter of waste water within 30 minutes. The purified water after the neutralization was evaluated for its content of metals. Initial efforts have also been done to P-cleanse the waste water. P-purification is important for reuse the sludge into the steelmaking process after neutralization.