The sorption of borate by ion exchange using a traditional layered double hydroxide (LDH) is affected by external conditions such as coexisting anions. Hydrotalcite intercalated with d-gluconate (G-LDH) was synthesized through a one-step microwave-assisted treatment and characterized by XRD, TEM, FTIR, TG/DTA and two-dimensional 11B NMR. Several factors that influence sorption of borate were investigated: gluconate content in the LDH, G-LDH dosage, coexisting anions, initial pH of borate solution and sorption temperature. The synthesized adsorbent exhibited a greater borate sorption rate than the traditional hydrotalcite (NO3-LDH) or a boron-specific resin. The maximum sorption capacity was 1.27 mmol/g (obtained by fitting to the Langmuir model). The G-LDH sorption density increased with increasing initial borate concentration and adsorbent dosage. In the presence of 50 mM sulfate, sorption of borate by NO3-LDH significantly decreased and no obvious sorption could be observed, whereas the sorption of borate by G-LDH was maintained at ∼0.57 mmol/g. 11B NMR indicated that the sorption mechanism of borate by G-LDH is mainly through bischelate and monodentate types of complexation with borate. This mechanism is similar to that of CRB05, and fundamentally different from that of NO3-LDH.
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