The research investigates the process of synthesis of magnesium master alloy with zinc and yttrium. Based on the analysis of state diagrams and requirements for fluxes for smelting of magnesium alloys, the composition of the saline mixture was chosen. X-ray phase analysis of the molten salt mixture showed that during the melting process, yttrium fluoride partially interacted with sodium and potassium chlorides, forming complex salts: Na 1.5 Y 2.5 F 9 , NaYF 4 , Na 5 Y 9 F 32 , and KY 7 F 22 , which are the source for yttrium recovery. Differential thermal analysis (DTA) determined the temperature ranges and values of thermal effects of melting and crystallization of a mixture of the KCl-NaCl-CaCl 2 -YF 3 salt in the recovery of yttrium compounds by a magnesium-zinc alloy. It was determined that interaction within the system begins at a temperature equal to the initial melting point of zinc, and occurs in the range from 415°C to 672°C. As a result of series of experimental meltings, the basic laws of the synthesis of magnesium-zinc-yttrium master alloys from the selected technological salt mixture, as well as the main factors of the metallothermic process, affecting the degree of yttrium reduction were revealed. The metallographic study of the alloys obtained showed that the samples consisted of solid solutions of Mg x Zn y and intermetallic compounds of Mg x Y y Zn z , which were located along the boundaries of dendritic cells. The proposed method of recovery of yttrium fluoride from the chloride melt allows extracting up to 97.2 % of yttrium.

Earlier studies at the Kevitsa Cu-Ni concentrator plant have indicated that seasonal variations of the properties of the process water affect the oxidation of the surface of the minerals, and further, the pentlandite flotation performance. However, it is not clear whether the differences in flotation performance are solely due to changes in the mineral surface oxidation, and/or also due to surface oxidation-induced changes in the aqueous phase of the pulp. This paper investigates the effects of the mineral surface oxidation of Kevitsa Cu-Ni ore on the properties of the aqueous phase of the slurry. A systematic study was formulated to monitor the surface oxidation related changes in the mill circuit of the Kevitsa concentrator plant. The study was timed to coincide with a seasonally observed drop in the concentrator plant’s flotation performance, which happens during the summer months (June, July, and August). Both physicochemical parameters, as well as sulphur oxyanions in the plant process water, mill discharge, and hydrocyclone overflows were monitored. Also, the bubble size in selected rougher and cleaner cells was monitored. The results show that season-related changes in mineral surface oxidation cause clear differences in the aqueous phase chemistry of the mill circuit. The increased concentration of reduced sulphur species in the mill discharge is an indication of extensive oxidation of the ore during milling. Also, the bubble size of the flotation cells reacts to the observed seasonal change. The findings of the study confirm that the consequences expected, based on the theory of mineral surface oxidation, are observable downstream in the aqueous phase of the milling circuit. Based on these results, it is not yet possible to say whether the poor flotation performance is caused solely by the oxidation of the mineral surface or also by the properties of the aqueous phase of the slurry after milling. However, the results show that the plant needs both to find ways to limit oxidation rates in the summer, and to consider installing a more robust frother, capable of maintaining efficacy during the warm season. The findings of this study may help the plant to develop ways to enable a timely response to changes in the recycled process water quality, to prevent harmful impacts on pentlandite flotation. The former could be achieved by lowering the temperature of the process water and flotation air, whereas the latter could mean using a different frother.