METHOD FOR RECOVERING ALKALI METAL CHLORIDE AND ALKALINE EARTH METAL CHLORIDE FROM WASTE SALT PRODUCED IN HEAT TREATMENT OF BILLET IN SALT BATH

摘要

Recovery of alkali and alkaline earth chlorides (I) from waste salts from heat treatment of steel pts. in salt baths involves dissolving the waste salt components in water, sepg. the insol. residue, destroying cyanides if necessary and fractional crystallisation of the dissolved salts. BaCO3 is sepd. from the residue as BaCl2 by adding HCl and added to the salt soln.. BaCl2 is crystallised from the salt soln. by adding NaCl and CaCl2 in (1-5):1 ratio at -5 to +20 degrees C using 150-350g NaCl and 30-150g CaCl2 to 300 g/l waste salt in soln.. NaCl is crystallised by adding CaCl2 to a concn. of 150-400 g/l at 40-120 degrees C. Residual NaCl and BaCl2 are crystallised by concentrating the soln. by evapn. to a CaCl2 concn. of 5500-900 g/l at 60-120 degrees C. A KCl-CaCl2 double salt is crystallised by further concn. at 60-120 degrees C, then the double salt is dissolved in 20-35% CaCl2 soln. at 35-40 degrees C and KCl is crystallised at 5-20 degrees C. CaCl2 is recovered by evaporating the remaining soln. to dryness.