Investigating the Influence of the Pulsed Corona Discharge Over Hypersaline Water

Abstract

Desalination plant and saltwork production currently produce large quantities of by-product, in the form of bitterns, which is generally regarded as waste. Up to now methods to discard this waste are unsustainable and restricted by high capital costs and non-universal application. Cold atmospheric plasma over liquids has led to various established industrial implementations, as well as promising applications, including chemical analysis, nanomaterials synthesis and plasma medicine. In this study interaction plasma -hypersaline water using cathodic or anodic polarization was investigated. Pulses of 2.3 kV, repeated at a frequency of 1 kHz, were applied to produce a pulsed corona discharge (PCD) over hypersaline water (HSW) surface. It was observed that in cathode polarization, considerable number of metallic cations can be extracted from the solution in the form of precipitate salts, while in anodic configuration, despite having a higher spectral intensity for Na (589.5 nm), it was less efficient in the salt precipitation. The findings of this study suggest that changing polarization also changes the mechanism of plasma interaction, indicating to be an interesting technique to explore selective saline water chemical extraction.

Plasma–Saline Water Interaction: A Systematic Review

“…In the corona discharge configuration, the energy of the discharge is applied to a small A P-L [ 66 ], producing localized acidification, which is then dispersed to uniform the solution [ 25 ]. In general, the reactions as the acidification of the solution, [H + ], is proportional to the discharge voltage [ 69 ].…”

“…Acidification caused by plasma can occur with the injection of ions, which react with species in the saline water, such as salts and hydroxyl, forming H 3 O + [ 71 ]. The mechanism of this process is mainly attributed to two pathways: (i) the interaction between electrons, H 2 O, OH − , and N 2 , resulting in the formation of acids such as HNO 3 and HNO 2 [ 19 , 21 , 49 , 56 ]; and (ii) the ionization of water by energetic particles of the plasma, which lead to an increase in the concentration of H + in the solution, in a controlled atmosphere (absence of N 2 ) [ 25 ]. As acidification occurs initially on the surface and then is homogenized in the volume of the solution, these changes may be more relevant for a higher V/A P-L ratio [ 25 ].…”

“…A cathodic discharge is able to form a Taylor cone on the surface and provide crystallization, because the polarity of the plasma attracts the salt-forming cations to the outermost layer of the liquid. On the other hand, in anodic discharge, the surface layer of the liquid is mainly composed of anions and, since it is bombarded with positive ions, the salt particles are not created or ejected towards the electrode, tending to remain in solution [ 25 ]. Furthermore, the anodic configuration causes a pronounced additional effect of evaporation of the saline water by localized heating, as observed by Alves-Junior et al [ 25 ].…”

“… Macro-research fields of the included studies in this review. Fundamental [ 21 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 50 , 52 , 54 , 58 , 59 ], plasma medicine [ 20 , 22 , 31 , 32 , 38 , 39 , 40 , 48 , 49 , 51 , 55 , 56 , 60 ], engineering [ 24 , 25 , 26 , 53 ], and environmental [ 19 , 23 , 27 , 28 , 29 , 30 , 57 ]. …”

“…When plasma touches the surface of saline water, the reactive species interact with the solvated charges in the saline water and induce additional physicochemical transformations, having as one of the consequences the accelerated and selective crystallization of salts, for example, which opens up possibilities for use in desalination processes, chemical extraction, and others [ 19 ]. To date, the effects of the interaction of plasma with saline water have been reported for sterilization and disinfection [ 20 , 21 , 22 , 23 ]; desalination, precipitation, and crystallization of salts [ 19 , 24 , 25 , 26 ]; catalysis of oxidative processes [ 27 , 28 , 29 ]; decontamination of organic pollutants [ 30 ]; alternative sources of nitrites/nitrates [ 31 , 32 ]; etc. There are different applications and different types of plasma sources, which differ strongly from each other, making it difficult to summarize or even compare the results of different types of sources from a chemical and physical point of view.…”