The effects of silicon, aluminum, and potassium on alkali- and silicate melt-induced slagging are studied through the addition of aluminosilicate compounds and 30 biomasses to address the coexistent dual slagging during biomass combustion. For alkali-induced slagging mainly caused by alkali metal aerosols, the addition of aluminosilicate compounds, such as kaolin and SiO2, can remove approximately 80%, 40% to 60% of gaseous-K at 1273 and 1088 K, respectively. Although SiO2 is more effective in removing gaseous-K, especially at 1088 K (62.5%), it also exacerbates silicate melt-induced slagging because of its reaction with KCl and the formation of low-melting silicates. Hence, the use of SiO2 should be reconsidered. Initial deformation temperature (IDT) is used as the evaluation index for silicate melt-induced slagging. High IDT reduces the potential for silicate melt-induced slagging occurrence. IDT rises as Al2O3 and SiO2/K2O increase, but decreases as K2O, SiO2, SiO2/Al2O3, and (SiO2 + K2O)/Al2O3 increase. The significant effects of the compounds on IDT follow this sequence: Al2O3 > K2O > SiO2 > SiO2/K2O > SiO2/Al2O3 > (SiO2 + K2O)/Al2O3. A set of criteria to evaluate the potential of silicate melt-induced slagging is proposed. The K2O–SiO2–Al2O3 ternary phase diagram is also constructed based on the ash properties of the 30 biomasses to reflect the true potential of silicate melt-induced slagging. It indicates that the K2O–SiO2–Al2O3 ternary diagram constructed based on pure K2O, SiO2, and Al2O3 underestimates the IDT of pure biomass. Results provide useful guidelines for biomass selection and slagging reduction.