Silicate mineral powders (SMP) from weathered granite soil from Kazakhstan are proposed for the desalination of potash brines containing sodium, potassium and chloride ions. Batch adsorption experiments using acid-treated silicate (AS) achieved a Na⁺/K⁺/Cl⁻ recovery of ~13/28/6 mg/g. An isothermal study best fitted the Freundlich and Dubinin–Radushkevich models for Na⁺ and K⁺/Cl⁻. The kinetic data were best modeled by pseudo-second-order kinetics for Na⁺/K⁺ and pseudo-first-order for Cl⁻. Thermodynamic calculations showed spontaneity under natural conditions. For Na⁺/K⁺, physisorption is accompanied by ion exchange. To study the possibility of sorbent reuse, several cycles of K⁺/Na⁺ adsorption–desorption were carried out under optimal conditions. AS selectively adsorbed potassium ions, maintaining a high effectiveness during five cycles providing K-form silicate fertilizers. Leachates of spent AS contain high concentrations of K/Na/Ca/Mg and other microelements essential for plants. Thus, SMP resolve two issues: the desalination of brine and the provision of fertilizer.