Abstract: A new process of preparation of active magnesium oxide from magnesium sulphate waste water，generated from the treatment of Mg-rich laterite-nickel ore by sulfuric acid process was introduced.Magnesium sulphate waste water was neutralized to a pH about 12 by lime to form magnesium hydroxide solution，and then carbonized by carbon dioxide under micro-pressure to get magnesium bicarbonate.Basic magnesium carbonate precipitate was obtained through thermal decomposition. Finally，active magnesium oxide was obtained from basic magnesium carbonate precipitate after filtering，washing，drying，and calcination processes，and the product indexes of active magnesium oxide met the first grade requirements in standard of HG/T 3928—2007.On the one hand，this new process could resolve the waste magnesium sulfate liquid treatment and opened up a new way of enhancing a resource utilization efficiency for the Mg-rich laterite-nickel ore.On the another hand，it could produce high value-added products.

Key words: magnesium sulfate waste, active magnesium oxide, neutralization, carbonation, calcination