A novel approach for resource utilization of stainless steel pickling sludge via nickel–iron blast furnace molten slag

Stainless steel pickling sludge (SSPS) is a by-product of pickling and passivation treatment of stainless steel in the process of stainless steel production. A novel approach for the treatment of the SSPS using the high-temperature nickel–iron blast furnace molten slag (NBFS) was investigated. The results show that the flow temperature of the slag decreases with the increase in the proportion of SSPS. In a certain range, the flow temperature decreases by about 7 °C when the proportion of SSPS increases by 1%. The computational results from FactSage indicate that the addition of SSPS leads to a reduction in MgO content and an increase in CaO and CaSO₄ contents, which are the reasons for the decrease in the flow temperature. Mortar blocks were prepared by mixing the slag powder prepared by water-quenched slag drying ball milling with 425 Portland cement in a certain proportion. As the proportion of SSPS increased from 0 to 5%, the 7-day strength of mortar blocks increased from 22.32 to 26.98 MPa, and the 28-day strength increased from 37.28 to 41.43 MPa. The 28-day activity index is above 75%, and its activity index meets the requirements of S75 ground granulated blast furnace slag. The industrial application program in the nickel–iron blast furnace with a volume of 550 m³ was also put forward, which provides a new way for realizing the resource utilization of SSPS.