**4. Conclusions**

The mobility of Sb in contrasting soils, characterized by a medium–low or high pollution level, was reduced by MSWC addition and/or its residual fraction increased. Although the extent of these phenomena appeared to be dependent on the soil type and contamination level, MSWC amendment implied reduced Sb potential bioavailability, which was supported by increased soil biochemical functioning (DHG and GLU, especially) and the development of microbial communities with improved metabolic potentials and catabolic diversity. The addition of MSWC also alleviated Sb phytotoxicity towards triticale plants, and reduced, in most cases, their Sb uptake by roots. Overall, the MSWC impact on Sb-polluted soils was consistent with its use as an amendment for the recovery of such environments. The reduction in labile Sb concentration in treated soils was likely the key factor boosting soil microbial activity and diversity (and probably abundance). Reasonably, this contributed to the development of a rhizosphere environment, which favored plant growth in amended soils and stimulated Sb translocation from the roots to shoots. This is the first time that triticale has emerged as a potential species for Sb phytoextraction. In this regard, MSWC was revealed to be useful to enhance this capacity, and it appears a promising candidate, in combination with triticale, for assisted Sb (or possibly anionic PTE) phytoextraction programs. Despite a clear role of MSWC in the chemical and biochemical recovery of Sb-polluted soils, its long-lasting effect is currently unknown and should be investigated.

**Supplementary Materials:** The following are available online at https://www.mdpi.com/2571-878 9/5/4/60/s1, Table S1: physico-chemical characteristics of SA and SB before Sb spiking; Table S2: chemical characteristics of the MSWC.

**Author Contributions:** Investigation, methodology, formal analysis, writing—original draft preparation, S.D.; conceptualization, methodology, resources, writing—reviewing and editing, G.G. and P.C.; data curation, software, M.G., M.V.P.; methodology, formal analysis, G.P.L. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the University of Sassari (Fondo di Ateneo per la Ricerca 2020).

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** All data analyzed in this study are available from the corresponding author upon request.

**Conflicts of Interest:** The authors declare no conflict of interest.
