反应详情

Magnesium hydroxide is prepared in two steps by the process of this invention. In the first step magnesium nitrate is treated by an alkaline substance, preferably by ammonia, in an aqueous medium at a temperature not higher than 85° C., at atmospheric pressure, resulting in forming of basic magnesium nitrate. It was found that it is profitable to use in the first step 1.5- to 6.0-multiple, with advantage 3.0- to 5.0-multiple excess of ammonia, at a temperature of 50° to 75° C. The resulting basic magnesium nitrate decomposes hydrothermally in the second step at a temperature of 110° to 150° C., preferably at 120° to 130° C. and at a pressure not greater than 1.5 MPa, generally at a pressure of 0.3 to 1.3 Mpa. The suspension obtained after the first step is heated in pressure equipment, causing pressure increases, and the temperature is held constant at the required value for one hour. The pressure is gradually reduced by draining the gaseous ammonia off the pressure equipment so that at the end of one hour the pressure drops to 0.3 MPa. After the pressure is relieved, the suspension is cooled down to a temperature of 50° to 60° C., filtered and after washing in demineralized water dried or--if necessary--disengaged by floating in demineralized water and treated by a suitable surface active agent before drying.

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