Pure magnesia prodn. from pre-purified aq. magnesium chloride soln. - by crystallisation of sodium and potassium chloride before thermal decomposition

摘要

Prodn. of highly pure MgO involves thermal decompsn. of MgCl2 obtd. from aq. roughly purified solns. (I) contg. MgCl2 together with KCl and/or NaCL and traces of other impurities, removal of most of these impurities by crystallisation and cooling of the cracking gas (II). (I) is mixed with residual impurities obtd. on cooling (II) and the soln. is cooled, so that crystals of carnallite and NaCl form. These crystals are sepd., then the further purified soln. (III) is conc. by evapn., the vapour being discharged and condensed. The conc. soln is subjected to thermal decompsn. at 750-950 degrees C in the presence of (II) in an amt. corresp. to 18-15 times the amt. of MgO formed (all amts. in mole/unit time), so that the NaCl and KCl vapourise and are carried over with (II). (II) is cooled by direct contact with water or aq. MgCl2 soln. and the resultant soln. is added to (I) and/or (III). The process avoids environmental pollution of waste liquor or dust and does not necessitate costly thermal or other intermediate treatment of the prod., which can be handled easily.