## 5 Conclusions and Future Work  
This article shows how the concepts of sustainable production, process eco-design, and waste management can help practitioners in the steelmaking industry to improve the sustainability of their whole sector, by setting a conceptual framework for new technological ideas. The authors used a top to bottom approach by first highlighting a sustainability problem, such as the excessive landfilling of slag in the stainless-steel production. Thereafter, the article continued with presenting a technical application that would follow such guidelines. Furthermore, through a conceptual analysis, a whole re-design of two stainless-steel manufacturing process was presented. Outokumpu Stainless (OTK) and Sandvik Material Technologies (SMT) were used as study cases for such an analysis. The general vision that was described also provides a guideline for future research, explaining the needs for such choices and stressing the importance of acting in such a way. After the theoretical part, experimental trials aimed at testing the applicability of the vision were presented. As a preliminary investigation, two slag samples from each company, their limestone samples, and wastewater were used to perform neutralization trials in small-batch tests. The primary goal of such investigation was to compare the slaked lime used by the companies to their slag. Moreover, the focus was also to try to mimic, as best as possible, some boundary conditions present in the neutralization facilities of both companies, such as the target pH value and the retention time of the reactant dispersed in the wastewater. Additionally, since the goal was to test the by-products for a future industrial application, the minimum number of alterations was done to the samples, and only materials retrieved by the companies were used. In fact, the fewer operations are performed on the samples, the more the materials comply with the state of the art of the process, thus, the lower the economic impact of changes in the process. Additionally, the interest is focused mostly on landfill slags, since they are at their end of life as a product, and utilizing them introduces the least amount of changes to the current production process, while it maximizes the retained value of the byproducts. The results of the experimental part are summarized by the following list:  
* Four slags, two per each steel mill, were prepared with the use of crushing devices and a sieve. They were also characterized based on the PSD, along with two lime samples used in the current neutralization industrial process at OTK and SMT. Wastewaters samples were also acquired from the companies. * All slag samples were tested with a stepwise dosing method, in order to measure the minimum amount of material needed to raise the pH of the industrial acidic wastewaters to a value of \(9\pm 2\) \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & **Cr (mg/L)** & **Ni (mg/L)** & **Mo(mg/L)** & **F(mg/L)** & **Fe (mg/L)** & **Zn (mg/L)** \\ \hline Wastewater & 434 & 358 & 42 & 1230 & 664 & 0.8 \\ OL-1 & 0.08 & 0.18 & 12 & 5.7 & 0.12 & \textless{}0.05 \\ OL-2 & 0.07 & 0.32 & 7.2 & 5.8 & 0.07 & \textless{}0.05 \\ OL-3 & 0.1 & 0.32 & 7.6 & 5.1 & 0.17 & \textless{}0.05 \\ O1-1 & 0.12 & 0.27 & 7.3 & 7.9 & \textless{}0.05 & \textless{}0.05 \\ O1-2 & 0.19 & 0.37 & 9 & 10.5 & \textless{}0.05 & \textless{}0.05 \\ O1-3 & 0.08 & 0.32 & 7.2 & 8.7 & \textless{}0.05 & \textless{}0.05 \\ Threshold & 0.5 & 0.5 & 10 & - & 1 & - \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Results of the AIO for the water purity tests. Two of them, one per company, raised the pH to the target value. The lime samples were also tested with the same method for reference. With this method, approximately 4.4 times the amount of slag was needed, compared to the amount of lime. * The quantities measured during the successful trials in the stepwise dosing trials were used as a benchmark for a second experiment, named single-step dosing.