Reuse of RO Desalination Plant Reject Brine

In this work we try to study the feasibility of salt production from a reject brine coming from a desalination plant in Skhira in the south of Tunisia, This plant treats 22,008 m³/day of raw water to produce 9984 m³ of fresh water and 12,024 m³ of rejected water and has the advantages of being environmentally friendly and producing commercial products in crystalline, slurry, and liquid forms. The process involves an application of the solubility diagrams in order to valorize the reject brines. These solutions are considered as strongly concentrated brines and containing several elements such as: Na⁺, K⁺, Mg²⁺, Ca²⁺, Cl⁻, and SO₄ ²⁻. This observation leads us to consider the complete hexary system Na⁺, Mg²⁺, K⁺, Ca²⁺/Cl⁻, SO₄ ²⁻//H₂O which includes four quinary systems. A number of physico-chemical analyses were employed (Potentiometry, complexometry, gravimetry, XRD, and SEM). At the end of an isothermal and isobaric evaporation of the reject brine, we could recover various salts (NaCl, KCl, CaSO₄·2H₂O, MgSO₄·7H₂O…) very useful for industry and agriculture.