A rapid and efficient method based on microwave-assisted treatment has been developed for preparing layered double hydroxides (LDHs) using natural dolomite as a magnesium source. The aging temperature was 120°C and the total synthetic time was only within 6 h. The product was fully characterized by elemental composition, powdery X-ray diffraction, and scanning electron microscopy, to be highly pure hydrotalcite with a flaky shape. The synthesized adsorbent exhibited the sorption capacity of 1.34 mmol/kg which is comparable to boron-specific resin. Based on ¹¹B MAS NMR and XRD results, the principal mechanism for borate immobilization on the LDHs is ion-exchange followed by transformation of polyborate into monoborate in a process of drying.