Chemical conversions of salt concentrates from desalination plants

Disposal of the desalination blow-down to the sea has detrimental affects to the benthic environment. The blow-down consists of highly concentrated salts. This work proposes an environmentally beneficial process for the production of some chemicals from the salt concentrates. The process involves a series of chemical reactions to convert the NaCl into Na2CO3, NaHCO3 and NH4Cl. In the initial investigations using a batch gas bubbler, optimum temperature of 22°C and NH3/NaCl ratio of 1.2 were established. At these conditions the highest NaCl conversion of 82.2% was obtained. The economic benefits of the proposed process cannot be immediately evaluated. Further analyses and development are needed. This work has shown preliminary indications of the feasibility of protecting the environment by utilizing the salt concentrates from desalination plant for chemicals production.

We have presented the result of a study of mass transfer (absorption of CO2) with chemical reaction (between CO2 and NH3). The result is promising and could be used for preliminary analysis toward designing the proposed separation process. The separation of the synthetic brine was carried out. The highest conversion of 82.2% NaCl into NaHCO3 and NH4Cl was achieved. It was observed that the optimum NH3/NaCl ratio and reaction temperature were 1.2 and 22°C, respectively. If the sample of brine is taken from the desalination plant, it has to be properly analyzed and characterized. This is necessary in order to know the other cations such as Mg2+ and Ca2+ present in the solution. The main products of the process are sodium bicarbonate (NaHCO3), soda ash (Na2CO3) and water rich in ammonium chloride (NH4Cl). The latter is an effective nitrogenous fertilizer, and its solution is well suited for irrigation and other uses. The proposed method could serve as a means for pollution control by converting the concentrated salt into some useful products.