The sustainable utilization of industrial and agricultural wastes as secondary nutrient resources represents an important strategy for resource conservation and circular-economy development. In this study, a nitric acid-assisted extraction process was investigated for the integrated processing of phosphorite beneficiation waste and sunflower ash to obtain a phosphorus–potassium-containing liquid product. The mineralogical, structural, morphological, surface-textural, elemental, and thermal characteristics of the raw materials were examined using XRD, FTIR, SEM–EDX, BET, and TGA analyses to support interpretation of their composition and dissolution behavior. The effects of phosphorite waste-to-sunflower ash ratio, nitric acid concentration, extraction temperature, reaction time, and solid-to-liquid ratio on phosphorus and potassium transfer into the liquid phase were systematically evaluated using a one-factor-at-a-time approach. The preferred operating conditions within the investigated ranges were identified as a phosphorite waste-to-sunflower ash ratio of 100:40 (w/w), an HNO₃ concentration of 57 wt.%, an extraction temperature of 80 °C, a reaction time of 150 min, and a solid-to-liquid ratio of 1:3 (w/v). Under these conditions, the resulting liquid phase contained up to 17.9 g L⁻¹ P₂O₅ and 20.4 g L⁻¹ K₂O. The observed trends were consistent with acid-assisted dissolution of phosphorus-bearing phases and comparatively easier transfer of potassium-containing species from sunflower ash. Because the total initial P and K inventories and the residual nutrient contents of the post-extraction solids were not independently quantified, the measured concentrations were interpreted as indicators of liquid-phase extraction performance rather than absolute recovery efficiencies. The proposed approach demonstrates the feasibility of integrated valorization of phosphorite beneficiation waste and sunflower ash within a single nitric acid-assisted extraction route.