Process for utilization of the gas washing lye from aluminum electrolysis in cryolite production

Claim 1

A PROCESS FOR THE PRODUCTION OF CRYOLITE, NA3ALF6, FROM FLUORINE AND HYDROGEN FLUORIDE CONTAINED IN THE WASTE GASES FROM THE ELECTROLYTIC PRODUCTION OF ALUMINUM, WHICH COMPRISES TREATING SAID WASTE GASES WITH AN ALKALINE AQUEOUS SOLUTION OF A COMPOUND OF SODIUM TO FORM SODIUM FLUORIDE FROM THE HYDROGEN FLUORIDE CONTAINED IN THE WASTE GASES, SEPARATING THE SODIUM FLUORIDE CONTAINING SOLUTION FROM THE INSOLUBLE IMPURITES THEREIN, TREATING THE FILTERED FLUORIDE SOLUTION WITH ALKALI SOLUBLE HIGHLY REACTIVE ALUMINUM MONOHYDROXIDE, ALOOH, OBTAINED FROM THE DECOMPOSITION OF CLAY WITH SULPHUROUS ACID, THEREBY PRECIPITATING CRYOLITE, NA3ALF6, WITH THE FORMATION OF SODIUM HYDROXIDE IN THE REACTION SOLUTION, TREATING THE REACTION SOLUTION WITH SODIUM BICARBONATE IN AN AMOUNT TO PROVIDE A PH IN THE SOLUTION BETWEEN 8 AND 9 TO THEREBY PRECIPITATE A FURTHER AMOUNT OF CRYOLITE, THE AFORESAID STEPS BEING CARRIED OUT AT A TEMPERATURE RANGING FROM ABOUT 40 TO ABOUT 100* C.; AND REMOVING THE FORMED CRYOLITE FROM THE SOLUTION AND DRYING THE SAME.