Abstract:With brines from salt lake as raw materials, boric acid was separated and extracted by a combined process of acidification, magnesium precipitation with ammonia, and carbonation. Yield of boron is 72%, purity of crude boric acid product is 72% after drying, and purity of boric acid is 99.52% after recrystallization, which meet the first grade of national standard GB/T 538-2006, under the optimum conditions including acid addition of 0.7%, reaction temperature of 60 ℃, and freezing time of 5.5 h. Leaching rate of boron is 95.52% under the optimum carbonation conditions including excess coefficient of ammonium bicarbonate of 1.4, reaction temperature of 50 ℃, ratio of solid to liquid of 10 g/L, and reaction time of 2 h. With the advantages of simple operation and low cost, this process can separate and purify most of magnesium in brine to obtain high-purity magnesium oxide.