Process for producing high grade hydromagnesite and magnesium oxide

A method of preparing hydromagnesite from a source of magnesium chloride, comprising:

• a) preparing a first brine solution from said source of magnesium chloride, wherein said first brine solution comprises magnesium chloride and calcium chloride;
• b) mixing a sulfate salt into said first brine solution capable of converting said calcium chloride into a calcium sulfate precipitate thereby forming said calcium sulfate precipitate and a second brine solution comprising magnesium chloride;
• c) removing said calcium sulfate precipitate from said second brine solution;
• d) ammoniating said second brine solution, after step c), at a temperature range of about 20° C. to about 60° C. to convert magnesium chloride at least partially into magnesium hydroxide and to form ammonium chloride;
• and
• e) carbonating said magnesium hydroxide while maintaining the reaction temperature at about 20° C. to about 120° C. to form a hydromagnesite precipitate,
• f) wherein said first brine solution contains from about 25% to about 35% by weight magnesium chloride in water,
• g) wherein said mixing of said sulfate salt is carried out at a temperature of about 60° C. to about 90° C.