Process for recovering molybdate or tungstate from aqueous solutions

A process for bleaching pulp comprising:

• a) reacting said pulp with hydrogen peroxide at a temperature of from 30 to 100° C. and at a pH in the range from 1 to 7, wherein said reaction is performed in an aqueous mixture comprising:
• i) from 0.1 to 5% by weight of said hydrogen peroxide and
• ii) from 10 to 1000 ppm of molybdenum in the form of molybdate or from 200 to 10000 ppm of tungsten in the form of tungstate, in each case based on the mass of dry pulp;
• b) separating the pulp bleached with hydrogen peroxide in step a) from said aqueous mixture to obtain an aqueous solution comprising molybdate or tungstate;
• c) contacting the aqueous solution containing molybdate or tungstate produced in step b) with a water-insoluble, cationized inorganic carrier material at a pH in the range from 2 to 6 to give a carrier material laden with molybdate or tungstate and an aqueous solution depleted in molybdate or tungstate;
• d) separating said carrier material laden with molybdate or tungstate from said aqueous solution depleted in molybdate or tungstate;
• e) contacting said carrier material laden with molybdate or tungstate with a second aqueous solution at a pH in the range from 6 to 14 to give a carrier material depleted in molybdate or tungstate and an aqueous solution comprising molybdate or tungstate, and
• f) separating said carrier material depleted in molybdate or tungstate produced in step c) from said aqueous solution comprising molybdate or tungstate;
• wherein said cationized inorganic carrier material is a cationized sheet silicate selected from the group consisting of bentonites, hectorites and attapulgites and said sheet silicate has been ion-exchanged with a quaternary tetraalkylammonium salt or with a quaternized alkanolamine fatty acid ester.