Abstract: Ferrite having a uniform degree of oxidation is produced at a higher rate of ferrite forming reaction by pelletizing a mixture of iron oxide and ferromanganese powders and calcining the mixture at a temperature of 900.degree. C. or higher. Zinc oxide, magnesium oxide and/or nickel oxide may be further added to the mixture, as required.

Abstract: An ion exchanger consisting of crushed lignite or brown coal retaining alkali ions, which is obtained by immersing the particles in a dilute caustic alkali solution. The concentration of the caustic alkali ranges from 2 to 20 weight percent, preferably from 3 to 10 weight percent. Following the treatment with the alkali, the system is washed with an acid with a pH of 3 to 7 to remove the alkali liquid. The resultant lignite has less than 4 meq/g, for instance 2.60 to 3.50 meq/g, of sodium ions and exhibits abilities of ion exchange. By treating the alkali treated lignite with hydrochloric acid or sulfuric acid it is possible to retain hydrogen ions, and by using a solution of a calcium salt such as calcium chloride calcium ions can be retained. Thus, calcium ions or potassium ions may be exchanged with cations of a salt of metal of Group second in the periodic table such as calcium, magnesium, barium and zinc.