Metal binding by dissolved organic matter in hypersaline water: a size
fractionation study using different isolation method
Abstract
The influence of dissolved organic matter (DOM) on mineral extraction
from salt lake brines depend on DOM quality. This study contributes to
our knowledge of DOM’s metal binding behavior in hypersaline
environments by characterization of DOM from lakes in the Qaidam Basin,
i.e., Qarhan Lake (LQDOM), Da Qaidam (DQDOM) and West Ginair Salt Lake
(WGDOM). The DOM was fractionated based on solid phase extraction (SPE)
and ultrafiltration (UF), and the spectral and metal binding behavior of
these fractions were studied by absorption spectroscopy, Pb(II)
titration techniques and fluorescence parallel factor (PARAFAC)
analysis. The results showed that bulk DOM generally contained more
dissolved organic carbon (DOC), lower specific UV absorbance (SUVA254),
higher fluorescence and biological indices, comparable humification
index, and lower condition stability constants compared to the other
nature waters. Compared with UF, SPE-derived DOM exhibited higher DOC
recovery and aromaticity and lower carbohydrate yield. It appears that
the SPE procedure used affects the spectral composition of bulk DOM to a
larger extent than UF. Source and molecular weight (MW)-dependent
differences in abundance and quality of brine DOM was indicated by
higher SUVA254 in high MW DOM, for LQDOM and DQDOM, and humic-like
fluorophores were mainly in high MW-DOM in each lake. Moreover, the high
MW humic-like component exhibited higher metal binding potential than
the bulk and low MW counterparts for LQDOM and DQDOM, while the inverse
was observed for WGDOM. This study revealed the effects of isolation
techniques on interpretation of DOM characteristics, and meanwhile
highlighted the importance of origin- and MW-dependent DOM in
manipulating the behavior, fate, and bioavailability of heavy metals in
salt lake brine.