highly significantp < 0.0001
As presented in Table 7 , the ANOVA results indicate that the factors of models A, B, C, D, AC, BC, BD, CD, A 2 , B 2 , and C 2 are D 2 < 0.05 (at the 95% confidence level, p < 0.05 was considered statistically significant and p < 0.0001 was considered statistically highly significant) [ 14 , 20 , 21 ], indicating that the effects of the nitric acid concentration, leaching temperature, liquid–solid ratio, total pressure, as well as the interactions between these factors and their squared effects on the vanadium leaching efficiency were significant.