Study of Forms of Compounds of Vanadium and Other Elements in Samples of Pyrometallurgical Enrichment of Ash from Burning Oil Combustion at Thermal Power Plants

Abstract

The results of the processing of ash from the combustion of fuel oil after roasting with the addition of Na2CO3 followed by aluminothermic melting are presented. As a result, metallic nickel and vanadium slag were obtained. Studies of slag, metal, and deposits on the electrode were carried out. The resulting metal contains about 90 wt% Ni. The main phases of scurf on the electrode are a solid solution based on periclase (Mg1–x–y–zNixFeyVzO), sodium-magnesium vanadate (NaMg4(VO4)3), and substituted forsterite (Mg2–x–yFexNiySiO4). The processing of ash made it possible to significantly increase the concentration of vanadium and convert it into more soluble compounds. Vanadium amount increased from 16.2 in ash to 41.4–48.1 V2O5 wt% in slag. The solubility of vanadium was studied during aqueous leaching and in solutions of H2SO4 and Na2CO3. The highest solubility of vanadium was seen in H2SO4 solutions. The degree of extraction of vanadium into the solution during sulfuric acid leaching of ash was 18.9%. In slag, this figure increased to 72.3–96.2%. In the ash sample, vanadium was found in the form of V5+, V4+ compounds, vanadium oxides VO2 (V4+), V2O5 (V5+), and V6O13, and nickel orthovanadate Ni3(VO4)2 (V5+) was found in it. In the slag sample, vanadium was in the form of compounds V5+, V4+, V3+, and V(0÷3)+; V5+ was presented in the form of compounds vanadate NaMg4(VO4)3, NaVO3, and CaxMgyNaz(VO4)6; V3+ was present in spinel (FeV2O4) and substituted karelianite (V2–x–y–zFexAlyCrzO3). In the obtained slag samples, soluble forms of vanadium are due to the presence of sodium metavanadate (NaVO3), a phase with the structure of granate CaxMgyNaz(VO4)6 and (possibly) substituted karelianite (V2–x–y–zFexAlyCrzO3). In addition, spinel phases of the MgAl2O4 type beta-alumina (NaAl11O17), nepheline (Na4–xKxAl4Si4O16), and lepidocrocite (FeOOH) were found in the slag samples.