## 4 Conclusions  
The examined slags produced in the course of the industrially tested Ni-dust and laterite ore fines recycling smelting process could be used in the cement industry for the manufacturing of special type composite Portland or slag cements up to 40% by mass with significant environmental and economic benefits, since the physical and mechanical characteristics of all examined cement products were found to meet the requirements of the regulation set for cements. For the 4-2a, b slags, exhibiting the highest strength results, even higher addition could be most possibly feasible. The present research revealed that the most critical parameter in the compressive strength development of the slag cements is the mineralogical composition of the slag. Increasing slag basicity enhances formation of desired hydraulic calcium silicates, as well as calcium aluminates in presence of adequate alumina. Formation of magnesiowustite solid solutions and iron valence also affect the obtained physical and mechanical properties of the corresponding slag cements, respectively, suppressing potential expansion issues. Rapid cooling enhances slag's cementitious properties. However, the results showed that even in cases where rapid cooling to obtain glassy matrix is not feasible, adjustment of slag analysis to obtain mineralogical phases similar to those met in clinker of OPC, even at higher FeO contents (up to 21 wt.%), can result in production of slag with considerable latent hydraulic properties. These findings indicate that there is also potentially space for improvement in conventional EAF steel slags chemical composition to allow for their wider use in building sector. Overall, this research demonstrated that the recycling of metallurgical wastes, through the reduction smelting route in DC-EAF, provides perspectives for development of zero residues metallurgical recycling processes, since besides the recovery of valuable metals in the liquid bath, produced slag analysis can be adjusted, on one hand in favor of the metallurgical yield of the process and on the other to allow its further utilization in the manufacturing of high added value environmental friendly building materials accountable for less CO\({}_{2}\) footprint; relative to the amount of clinker being substituted. The following are available online at [[http://www.mdpi.com/2076-3417/10/13/4670/s1](http://www.mdpi.com/2076-3417/10/13/4670/s1)]([http://www.mdpi.com/2076-3417/10/13/4670/s1](http://www.mdpi.com/2076-3417/10/13/4670/s1)), Figure S1: Flow sheet of the zero residues production smelting process for metallurgical dusts and ore fines recycling [4]. [PERSON] coordinated the research, designed and carried out the testing, the interpretation of the results and the writing of the manuscript; [PERSON] participated in the interpretation of the results and contributed to the manuscript writing; [PERSON] participated in the interpretation of the results and contributed to the manuscript writing; [PERSON] participated in the interpretation of the results and contributed to the manuscript writing; [PERSON] participated to the manuscript writing; [PERSON] participated in the interpretation of the results and contributed to the manuscript writing. All authors have read and agreed to the published version of the manuscript. **Funding:** The industrial Ni-dust and laterite ore fines smelting trials, in the course of which, the slags were produced were jointly funded by the government of Niedersachsen and Georgsmarienhitute Gmbh steelmaking company. **Acknowledgments:** The present announcement is dedicated to the memory of Ing. [PERSON] for his overall guidance and contribution. The industrial Ni-dust smelting trials and slags production took place in the DC-EAF of Georgsmarienhitute Gmbh steel making company. LARCO GMMS.A. provided the Ni-dust and laterite ore-fines. Manufacturing and testing of the slag cements was performed in the R&D center of TITAN S.A.