This monograph set out to establish a scientifically sound and industrially practicable route for upgrading three classes of marginal Kazakh phosphate raw materials—phosphate-silica layer rocks from Zhanatas, and low-grade phosphorites from the Akzhar and Shilisai deposits—by means of selective organic-acid leaching. Drawing on a comprehensive suite of chemical, thermodynamic, kinetic, mineralogical, microstructural, and economic assessments, the study provides the following consolidated insights.