US 4,016,238 A · Process for the obtention of alumina and phosphate values by the alkaline decomposition of silica-containing aluminum phosphate ores

Abstract

A process for the obtention of alumina and phosphate values by the alkaline decomposition of silica-containing aluminum phosphate ores comprises reducing the ore to a particle size of from about 6 to 13 mm; calcining the ore at a temperature of from 500.degree. to 750.degree. C in order to remove water of crystallization and combined water; grinding the calcined ore to a particle size of from 20 to 60 mesh (U. S. Sieve); treating the calcined and ground ore with an aqueous solution having a concentration of from 20 to 30% by weight caustic alkali at an initial temperature of from 65.degree. to 75.degree. C; quickly filtering the hot suspension thus obtained to remove the solid silica and heavy metal oxides; adding a 50% caustic alkali solution to the filtrate in an amount sufficient to obtain a total concentration of from 10 to 15% by weight of free caustic alkali; cooling the alkaline liquor accompanied by an elutriation action in an elutriator to a temperature of from 5.degree. to 10.degree. C in order to remove the crystallized tribasic alkali phosphate in the form of hydrated crystals which are recovered from the bottom of the elutriator; recovering the supernatant liquor from the top of the elutriator; heating said liquor to a temperature of 75.degree.-85.degree. C to obtain an alkali aluminate solution; and converting said alkali aluminate solution into hydrated alumina [Al(OH).sub.3 ] and then into alumina (Al.sub.2 O.sub.3) by known means. The alkaline liquors obtained therefrom are recycled to the alkaline decomposition step after concentration thereof. The process can be rendered cyclic by converting the tribasic alkali phosphate into phosphoric acid by dissolving the phosphate in water, treating with CaO to form tricalcium phosphate and regenerate the caustic alkali, which is concentrated and recycled to the alkaline decomposition step, recovering the tricalcium phosphate, and reacting the same with sulfuric acid to obtain gypsum and phosphoric acid. The gypsum is reacted with carbon to produce lime and SO.sub.2 by known means for use in the process and the SO.sub.2 released is converted into sulfuric acid to use in the process.

Claims11

Dependent claims

A process for the alkaline treatment of silica-containing aluminum phosphate ores for the recovery of alumina and phosphate values therefrom, which comprises in combination the steps of:

a. calcining the ore at a temperature of at least 500.degree. C;
b. grinding the calcined ore down to a particle size of from 20 to 60 mesh (U.S. Sieve);
c. treating the calcined and ground ore with a caustic alkali lye having a concentration of at least 20% by weight of free caustic alkali to produce a suspension containing solid silica, iron oxide and other heavy metal oxides;
d. quickly filtering the suspension thus obtained to remove the solid silica and other heavy metal oxides originally contained in the ore;
e. adding a concentrated caustic alkali lye of at least 50% free caustic alkali concentration to the filtrate, in an amount sufficient to obtain a total concentration of from 10 to 15% by weight of free caustic alkali in the liquor;
f. cooling the alkaline liquor with the aid of an elutriation action to crystallize the tribasic alkali phosphate;
g. removing the thusly crystallized tribasic alkali phosphate;
and
h. recovering a practically pure sodium aluminate aqueous solution which is thereafter coverted into alumina.

6 more elements

A process for the obtention of alumina and phosphoric acid by the alkaline decomposition of silica-containing aluminum phosphate ores which comprises reducing the ore to a particle size of from about 6 to 13mm;

calcining the ore at a temperature of from about 500.degree. to about 750.degree. C to remove water of crystallization and combined water therefrom;
grinding the calcined ore to a particle size of from 20 to 60 mesh (U.S. Sieve);
treating the calcined and ground ore with a caustic alkali aqueous solution having a concentration of from 20 to 30% by weight free caustic alkali plus small amounts of aluminum and phosphorus compounds derived from the recovery of the caustic liquors in the process, at a temperature of from about 65.degree. to 75.degree. C and for a period of time of from 1 to 1.5 minutes to produce a suspension containing solid silica, iron oxide and other heavy metal oxides;
quickly filtering the hot suspension thus obtained to remove the solid silica and iron oxide and other heavy metal oxides, adding a 50% caustic alkali solution to the filtrate in an amount sufficient to obtain a total concentration of from 10 to 15% by weight of free caustic alkali;
cooling the alkaline liquor in an elutriator to a temperature of from 5.degree. to 10.degree. C to remove the crystallized tribasic alkali phosphate in the form of hydrated crystals which are recovered from the bottom of the elutriator;
recovering the supernatant liquor from the top of the elutriator, which contains most of the aluminum in the form of dissolved alkali aluminate and a small amount in the form of microcrystals of Al.sub.2 O.sub.3.3H.sub.2 O;
heating said liquor to a temperature of from about 75.degree. to 85.degree. C to redissolve the Al.sub.2 O.sub.3.3H.sub.2 O into alkali aluminate;
coverting said alkali aluminate solution into hydrated alumina and then into alumina;
recycling the alkaline liquors obtained from the alumina process to the alkaline decomposition step upon concentration thereof;
filtering the tribasic alkali phosphate hydrated crystals recovered from the elutriator;
redissolving said tribasic alkali phosphate in water;
treating the solution with lime in stoichiometric amounts to form tricalcium phosphate and to regenerate the caustic alkali in the form of an alkaline liquor which is concentrated and recycled to the alkaline treatment step;
recovering the tricalcium phosphate;
reacting the same with sulfuric acid to obtain gypsum and phosphoric acid which is thereafter purified;
reducing the gypsum by means of coal into lime and sulfur dioxide;
recycling the lime to the process for treating more tribasic alkali phosphate;
and converting the sulfur dioxide into sulfuric acid for use in the treatment of more tribasic alkaline phosphate.

14 more elements

Dependencies are inferred from the claim text.

Process for the obtention of alumina and phosphate values by the alkaline decomposition of silica-containing aluminum phosphate ores

Life of this patent

Process for the obtention of alumina and phosphate values by the alkaline decomposition of silica-containing aluminum phosphate ores

Life of this patent

Abstract

Claims11