## 1 Introduction  
In 2019, 52 Mt of stainless-steel has been produced worldwide [1], which generated roughly 15 to 17 Mt of slag [2]. Compared to other kinds of by-products, such as Basic Oxygen Furnace (BOF) or Blast Furnace (BF) slags, which are well recycled in state-of-the-art applications, stainless-steel slags are mostly disposed in landfills. As an example, in Sweden only, stainless-steel slags are roughly 20% of the total amount of slags produced during the steelmaking processes. However, they constitute around 70% of the landfilled output [3]. The high concentrations of leachable cancerogenic elements (such as Cr or Ni) in these slags, impedes their use in the common state-of-the-art applications, namely aggregates for road pavements or cement. Therefore, these kinds of slags are mostly disposed in landfills. Landfilling itself constitutes a problem too, because the same phenomenon generates risks of soil and water stream contamination, if not properly mended [4; 5; 6; 7; 8]. In addition, the production of stainless-steel has been steadily growing since the year 2008 [1], resulting in higher volumes of landfilled stainless-steel slags. Thus, it is imperative to find a solution for these kinds of materials, as landfills will progressively get filled. Furthermore, environmental restrictions are projected to tighten in the nearby future, resulting in an increasingly high economic liability for stainless steel producers. One possible solution to the problem is to develop a novel application for these kinds of products. Several studies have already tested mineral by-products for the neutralization and treatment of industrial waste waters [9; 10; 11; 12; 13; 14]. These waste streams can substitute the use of raw materials such as quicklime, which is the standard product used for water treatment, due to the high solubility and alkalinity of CaO. Steel and stainless-steel slags contain high percentages of CaO and MgO, which make them suitable replacements to quicklime. Previous studies [15; 16] demonstrated that several stainless-steel slags could be employed for the neutralization and treatment of waste waters derived by the pickling process in steelmaking. The waste waters contained a dilution of different acids like HF, HCl, HNO\({}_{3}\) and H\({}_{2}\)SO\({}_{4}\), which also presented high levels of dissolved metallic elements. Previous experiments demonstrated that as well as lime, the stainless-steel slags tested could rise the required pH values during the waste waters neutralization processes, while guaranteeing a comparable removal of metallic ions from the liquid phases [15]. However, more systematic investigations are necessary to evaluate the efficiency of various stainless-steel slags in neutralizing the pH of acidic solutions. In fact, it is seen from previous studies [10; 16] that the mineral composition of different slags affects the slags capacity of buffering acidic waters. Mineral dissolution and element leaching are the phenomenon that dictates the reaction of slags and acidic waste waters. The dissolution of mineral phases in aqueous media is a complex phenomenon that varies vastly depending on the various parameters of the environment in which the solid materials are in contact with. The phenomenon is usually studied in terms of leaching behavior of slags, which is a detrimental effect when the material is used in standard applications as cement or asphalt mixtures. In the body of literature analyzed for this study, the pH value of the solution is considered one of the most important factors in the dissolution of the mineral phases. Experimentally, it was demonstrated that the more alkali in the solution, the lower the dissolution of the minerals [17; 18]. This is also in compliance with more theoretical studies that used geochemical models to determine the leaching of mineral phases present in steel slags [19]. In batch tests where the pH is not kept constant, the dissolution of the mineral phases is limited by the increase of the solution's pH value.