Manufacture of Perborate

The operation is semi-continuous. During the electrolysis the solution is cooled to about 11 to 12 °C, the solid sodium tetraborate with which the electrolyte is continuously resaturated is maintained in suspension by stirring the 

The necessary amount of borax, as well as a certain quantity of a suspension of magnesium silicate whioh aots as stabilizer, are introduced simultaneously. After 6 hours a further charge of borax is added into the cell. After another 6 hours half of the electrolyte is again drained off and the whole operation described above is repeated. The voltage aoross the bath varies between 5.6 and 6 V and a daily output of 260—270 kg of perborate per cell corresponds approximately to a 57 % current efficiency. The total enorgy consumption per 100 kg of perborate equals 375 to 390 kw-hr. representing an energy efficiency of about 15 %. 

The separated crystalline perborate is dried in a current of air preheated in a heater to 60—70 °C. The Biittner dryer is very suitable for this operation. The dry perborate powder entrained is separated from the air in a cyclone, then homogenized in mixers and finally soreened. 

As the oooling efficiency of the coil in the oell is reduced with time due to the deposit of salts, it is necessary to discontinue the normal operation of the eleotrolyzer (at intervals of 3—6 weeks) in order to remove the salt deposit on the oooling coil by dissolving in water. 

Perborate is packed in galvanized steel, or wooden, paper lined drums. The commercial product has 97 to 98% NaB02. HgOg. 3 H20, the remainder is sodium tetraborate and carbonate the content of active oxygen varies between 10.1 and 10.2 per cent. 

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