Sustainable hard water treatment using talc derived magnesium silicate zeolite evaluated by statistical physics and field validation in Siwa Oasis

Abstract

Groundwater in Egypt’s Siwa Oasis exhibits extreme hardness (total ≈ 3312.6 mg/L as CaCO3; Mg2+ ≈ 609.5 mg/L, Ca2+ ≈ 325.4 mg/L), far above guideline values and problematic for health and infrastructure. We report a sustainable softening approach using magnesium-silicate zeolite (Mg.ZA) synthesized from natural talc via alkali fusion (550 °C, 5 h) and mild hydrothermal conversion, producing LTA-type crystallinity with mesoporosity and high surface area (187 m2/g). Performance was evaluated under batch and fixed-bed (continuous-flow) conditions and interpreted with statistical-physics modeling. In batch at pH 7, Mg.ZA achieved 268.8 mg/g (Ca2+) and 206.9 mg/g (Mg2+), following pseudo-first-order kinetics and Langmuir isotherms, indicating physisorption-dominated, near-monolayer uptake. In fixed-bed tests with synthetic and real Siwa groundwater (flow 5 mL/min; pH ≈ 7; bed depth 1–3 cm), increasing bed depth to 3 cm extended breakthrough and raised dynamic capacities to ~ 279.6 mg/g (Ca2+) and ~ 227.8 mg/g (Mg2+); breakthrough and saturation were defined at 10% and 95%, respectively. Field relevance was demonstrated by treating real Siwa groundwater, reducing Ca2+/Mg2+ to acceptable levels across reuse cycles and confirming regenerability. The statistical-physics analysis quantified multi-ionic site occupancy (n > 2) and Qsat consistent with experiments (~ 269 mg/g Ca2+; ~207 mg/g Mg2+), with low adsorption energies (ΔE < 8 kJ/mol) supporting reversible, multilayer physisorption. Collectively, talc-derived Mg.ZA offers a cost-effective, eco-friendly, and scalable adsorbent capable of softening high-hardness groundwater under realistic conditions, supporting decentralized treatment in arid, resource-limited regions.