Changes in Chemical Composition of Dissolved Organic Matter in Solar Ponds From Salt Lake Brine

The abundance and chemical composition of dissolved organic matter (DOM) in the brine of solar ponds influence efficiency of mineral extraction and rates of brine evaporation, and cause undesired odor and color of the products. In this paper, we report an investigation on changes of DOM compositions in solar ponds from salt lake brine through different approaches. The results showed that the DOM was primarily composed of carbohydrates, aliphatic and aromatic compounds. Dissolved organic carbon (DOC) analysis revealed that the concentration of DOC in solar pond increased with exposure time, and up to 15−fold upon evaporation/irradiation of salt lake brine. Analyses with the elemental composition, Fourier transform infrared spectroscopy (FTIR) and cross polarization magic angle spinning (CP/MAS) 13C nuclear magnetic resonance (NMR) indicated that the relative abundance of aliphatic compounds (including functionalized ones) increased in solar pond process, while an opposite phenomenon was observed for carboxylic acid moieties, aromatics and carbohydrates. Pyrolysis−gas chromatography−mass spectrometry (Py−GC−MS) revealed that most of the DOM in salt lake brine contained methylene chain, terpenoid-like, carbohydrate and/or aromatic structures. The presence of some sulfur-containing organics implied some anaerobic biotic decays, but microbiological processes were probably subordinate to photo-induced DOM transformations. In the salt lake brine, exposure-driven decay decreased the abundance of polysaccharides and increased that of mono- and polyaromatic pyrolysis products. Finally, the implications and guidelines for removing DOM from brine in the process of brine resource exploitation were discussed.