IT1209181B - Magnesium prodn. from magnesite or dolomite - Google Patents

Abstract

Magnesium is produced from magnesite or dolomite by calcination, leaching with calcium chloride soln. crystallisation of magnesium chloride or carnallite from the leach liquor, followed by drying, melting and electrolytic decomposition to magnesium, the Cl, HCl, CO2 and air released from these last three steps being submerged to absorption with milk of lime with addn. of a catalyst to produce calcium chloride soln. The absorption process comprises (i) a first continuous absorption stage using milk of lime of pH above 10; (ii) a first solids sepn. stage; (iii) a first catalytic reaction stage at pH above 10 using a nickel-, iron- cobalt- or copper-contg. catalyat to decompose hypochlorite ions in the soln. to chloride ions; (iv) a second sepn. stage to recover the catalyst for purificn. and recycling; (v) a second absorption stage in which the soln. from (iv), with addn. of milk of lime, is used for pre-scrubbing the off-gases from the melting step firstly at pH below 3 and then, after further addn. of milk of lime, at pH above 10; (vi) treatment of the soln. from (v) with a reductant to reduce chlorine-oxygen cpds. to chloride ions followed by a third absorption stage, with addn. of solids from (ii), at pH below 3 to absorb the HCl from the drying step; (vii) neutralisation of the soln. from (vi) with milk of lime, followed by a third solids sepn. stage to leave a 30-40% calcium chloride soln. contg. max. 50 ppm. Fe ions and max. 50 ppm. ClO3 ions; and (viii) recycling of the soln. from (vii) to the leaching step.