Effect of a Phosphonate Antiscalant during Eutectic Freeze Crystallization of a Sodium Sulfate Aqueous Stream

Abstract

Reverse osmosis (RO) plants are widely used for recovering potable water from industrial wastewater streams. The RO retentate stream is highly concentrated in salts, thereby limiting further treatment using RO due to increased scaling potential of the salts. Currently, the brine streams are disposed of in evaporation ponds in which pure salts cannot be recovered. This makes eutectic freeze crystallization (EFC) an attractive separation method for purification of such streams because it can recover both pure water and salt. However, antiscalants are present in RO and other industrial wastewater streams as impurities. These could have an effect on the thermodynamics and crystallization kinetics during EFC. This paper focuses on the effect of a phosphonate-based antiscalant on the crystallization kinetics of both ice and Na 2 SO 4 •10H 2 O in a continuous EFC process under subeutectic conditions. It was observed that the salt nucleation rate remained almost constant, while a general decrease in the ice nucleation rate occurred with an increase in antiscalant concentration. A general increase in the growth rates of both ice and salt was observed. A threshold antiscalant concentration in the range 350−500 mg/L was observed, beyond which the effect was reversed. The morphology of salt crystals from both the control and antiscalant-dosed solutions was monoclinic and prismatic. The morphology of ice could not be detected due to agglomeration. Product washing was very effective in removing impurities, suggesting that adsorption occurred by physisorption.

Recovering sodium erythorbate from wastewater through freeze crystallization technology

“…Meanwhile, formation of ice removed liquid water causing salinity of the solution to rise. The increased salinity could suppress the ice point (Himawan, Kramer, & Witkamp, 2006;Peters, Chivavava, Rodriguezpascual, & Lewis, 2016) and generate dead zones (Kawahara, 2002) of ice nucleation at a threshold temperature. As the temperature continues to fall, salt would crystallize which reduces the salinity, therefore allowing ice nucleation to restart.…”

Progressive Freezing Method for Concentrating Tetrahydrofuran (THF) Remained in Grignard Reagent Wastewater

“…In progressive freezing process, ice forms in layers starting from the top of solution and grows along cooling surface. Separation of ice and the concentrated waste can be achieved by discharging the residual solution from below . In suspension freezing process, ice crystals grow in granules and stay in a state of suspension.…”

“…Freezing method has been widely applied and researched in many industrial processes such as extraction, [5] sludge disposal, [6] or salt's recovery. [7] In general, freezing method is mainly applied as either a progressive or a suspension process based on ice growth patterns and ultimate ice morphology. [1] In progressive freezing process, ice forms in layers starting from the top of solution and grows along cooling surface.…”

“…Separation of ice and the concentrated waste can be achieved by discharging the residual solution from below. [7] In suspension freezing process, ice crystals grow in granules and stay in a state of suspension. Separation of ice from concentrated waste requires centrifugation, filtration, or gravity.…”

“…This large difference provides an opportunity for concentrating THF and separating water from their mixture via freezing technology. Freezing method has been widely applied and researched in many industrial processes such as extraction, sludge disposal, or salt's recovery . In general, freezing method is mainly applied as either a progressive or a suspension process based on ice growth patterns and ultimate ice morphology .…”