A new chemical classification system of natural waters for desalination and other industrial uses

Abstract

Natural low-salinity waters (i.e., <3000 mg/l are generally classified according to applications, such as drinking, agricultural or industrial. Most of these classification systems are considered as technically correct rather than a systematic chemical classification of natural water types. The increasing demand on very salty water for modern nontraditional needs (e.g., desalination, nuclear power generation, gas and oil production, salt-water fishing and mineral extraction) requires the development of a new system that can identify, describe and classify natural waters into specific chemical types. Earlier works of the present authors indicated the controlling role of chloride ion molar concentration as a master variable to classify natural waters over a range, on which the current study is based. The proposed water chemical classification system compromises four major water classes: Class A: low chloride (<3 mMol/kg Cl); Class B: medium chloride (3–50 mMol/kg CL); Class C: high chloride (50–500 mMol/kg Cl); Class D: very high chloride (>500 mMol/kg Cl). These four water classes are divided into 14 water types (measured in mMol/kg chloride ions): Type 01: very low fresh, <0.5; Type 02: low fresh, 0.5–1; Type 03: medium fresh, 1–1.5; Type 04: high fresh, 1.5–3; Type 05: low brackish, 3–10, Type 06: medium brackish, 10–25; Type 07: high brackish, 25–50; Type 08: low salty, 50–100; Type 09: medium salty, 100–200 Type 10: high salty, 200–500; Type 11: seawater, 500–600; Type 12: high salty seawater, 600–700; Type 13: sub-brine, 700–800; Type-14: brine, >80. The common chemical characteristic of the major ion combination of each water type was defined in detail, and current applications were also considered. Each water type could be further subdivided in order to accommodate many varieties of chemical combinations under the influence of a given chloride ion concentration. Itwas found that natural waters could have a wide variation in their molar combinations (i.e., sulfate-alkalinity and sodic-calcic nature) under the vertical chloride master variable. Some graphic models for the purpose of hydrochemical and geochemical correlations are also presented. The inorganic fouling potential could be easily indicated at a given chloride molar concentration. The precise chemical categorization of various waters became easier. The relevant hydrochemical indicators provide a valuable techno-economical tool for the earlier prediction of inorganic fouling, proper selection of suitable pretreatment methods, chemicals and equipment for desalination technology (membrane and thermal as well as other industrial applications.