Process for the production of alumina

Claim 2

A PROCESS FOR THE PRODUCTION OF HYDROUS ALUMINA COMPRISING THE STEPS OF: FORMING AN AQUEOUS SOLUTION OF ALUMINUM SULPHATE HAVING A CONCENTRATION OF AT LEAST 2% BY WEIGHT CALCULATED AS AL2O3, FORMING AN AQUEOUS SOLUTION OF SODIUM ALUMINATE, FORMING A MIXTURE OF THE SOLUTIONS TO PRECIPITATE HYDROUS ALUMINA IN THE FORM OF A SLURRY, HAVING A CONCENTRATION OF FROM 2% TO 7% BY WEIGHT, BY INTRODUCING THE SODIUM ALUMINATE SOLUTION, UNTIL THE MIXTURE REACHES A COMPOSITION OF FROM 10% EXCESS ALUMINUM SULPHATE TO 10% EXCESS SODIUM ALUMINATE, AND UNTIL THE RESULTING SOLUTION HAS A PH IN THE RANGE BETWEEN 7.3 TO 10, AT SUCH A RATE AND WITH SUFFICIENT AGITATION THAT A SUBSTANTIAL PROPORTION OF THE HYDROUS ALUMINA PRECIPITATES UNDER ACIDIC CONDITIONS, WHILST MAINTAINING THE MIXTURE AT A TEMPERATURE WITHIN A RANGE SELECTED FROM THE RANGES 12* TO 35*C AND 45* TO 70*C SEPARATING THE HYDROUS ALUMINA FROM ITS MOTHER LIQUOR AND WASHING THE SEPARATED HYDROUS ALUMINA.

Claim 3

A process as claimed in claim 1 wherein the aqueous solution of sodium aluminate has a concentration of from 2 to 7.5% by weight calculated as Al2O3.

Claim 4

A process as claimed in claim 1 wherein the aqueous solution of aluminum sulphate has a concentration of from 2% to 6% by weight calculated as Al2O3.

Claim 5

A process as claimed in claim 1 wherein the temperature of the reaction mixture is maintained at from 55*C to 70*C.

Claim 6

A process as claimed in claim 1 having an additional step located between the steps of formation of the alurry and separation of the slurry comprising ageing the slurry at a temperature of from 12* to 35*C or 45* to 70*C for a period not exceeding 2 hours.

Claim 7

A process as claimed in claim 1 wherein the hydrous alumina is separated from its mother liquor as a filter cake and the filtercake is washed with water.

Claim 8

A process as claimed in claim 1 wherein the hydrous alumina is separated from its mother liquor as a filter cake, the filter cake is then slurried with water, and a second filter cake is formed from the slurry by filtration.

Claim 9

A process as claimed in claim 1 wherein the hydrous alumina is separated from its mother liquor as a filter cake, and the filter cake is dried at a temperature not exceeding 100*C.

Claim 10

The process as claimed in claim 1 wherein the hydrous alumina is separated from its mother liquor as a filter cake, and the filter cake is then dried and calcined at a temperature from 300* to 400*C.

Claim 11

A process as claimed in claim 1 having an additional step comprising treating the filtercake with a solution containing phosphate ions.

Claim 12

A process as claimed in claim 10 wherein the solution containing phosphate ions is selected from the group consisting of a mixture of aluminum nitrate with monohydrogen ammonium orthophosphate, phophosphoric acid, monosodium phosphate and disodium phosphate.

Claim 13

A process for the production of hydrous alumina comprising the steps of: forming an aqueous aluminum sulphate solution having a concentration of at least 2% by weight calculated as Al2O3, forming an aqueous solution of sodium aluminate, forming a mixture of the solutions to precipitate hydrous alumina in the form of a slurry having a concentration of from 2 to 7% by weight, by introducing the sodium aluminate solution into a body of the aluminum sulphate solution, with sufficient agitation, progressively over a period of from 1 minute to 5 hours until the mixture has a pH of from 7.3 to 10.0, at least half of the hydrous alumina precipitating under acidic conditions, whilst maintaining the mixture at a temperature within a range selected from the ranges 12* to 35*C and 45* to 70*C separating the hydrous alumina from its mother liquor and washing the separated hydrous alumina.

Claim 14

A process for the production of hydrous alumina comprising the steps of: forming an aqueous aluminum sulphate solution having a concentration of at least 2% by weight calculated as Al2O3, forming an aqueous solution of sodium aluminate, forming a mixture of the solutions to precipitate hydrous alumina in the form of a slurry having a concentration of from 2 to 7% by weight, by introducing the sodium aluminate solution into a body of the aluminum sulphate solution, with sufficient agitation, progressively over a period of from 1 minute to 5 hours until the mixture has a pH of from 7.3 to 10.0, at least half of the hydrous alumina precipitating under acidic conditions, whilst maintaining the mixture at a temperature within a range selected from the ranges 12* to 35*C and 45* to 70*C separating the hydrous alumina from its mother liquor and washing the separated hydrous alumina.

Claim 15

A process as claimed in claim 12 wherein, during at least two-thirds of the period of introduction of the sodium aluminate solution mixture has a pH of no more than 7.

Claim 16

A process as claimed in claim 12 wherein the period of formation of the mixture is at least 15 minutes.

Claim 17

A process as claimed in claim 14 wherein the period of formation of the mixture is from 30 to 45 minutes.

Claim 18

A process for the production of hydrous alumina compRising the steps of: forming an aqueous solution of sodium aluminate having a concentration of from 2 to 7% by weight calculated as Al2O3, forming an aqueous solution of aluminum sulphate having a concentration of from 2 to 7.5% by weight calculated as Al2O3, forming a mixture of the solutions wherefrom alumina precipitates forming a slurry having a concentration of from 2 to 7% by weight, by introducing the sodium aluminate solution progressively with sufficient agitation over a period of from 15 minutes to 1 hour, until the mixture has a pH of from 7.3 to 10.0 maintaining acidic conditions during at least two-thirds of the period, maintaining the mixture and slurry at a temperature within a range selected from one of the ranges 12* to 35*C and 45* to 70*C, ageing the slurry for not more than 2 hours, forming a filtercake by filtering the slurry, to a concentration of hydrous alumina calculated as Al2O3 of from 8 to 16% by weight, washing the filtercake with at least its own volume of water and drying the filtercake at a temperature not exceeding 150*C.

Claim 19

A process for the production of hydrous alumina compRising the steps of: forming an aqueous solution of sodium aluminate having a concentration of from 2 to 7% by weight calculated as Al2O3, forming an aqueous solution of aluminum sulphate having a concentration of from 2 to 7.5% by weight calculated as Al2O3, forming a mixture of the solutions wherefrom alumina precipitates forming a slurry having a concentration of from 2 to 7% by weight, by introducing the sodium aluminate solution progressively with sufficient agitation over a period of from 15 minutes to 1 hour, until the mixture has a pH of from 7.3 to 10.0 maintaining acidic conditions during at least two-thirds of the period, maintaining the mixture and slurry at a temperature within a range selected from one of the ranges 12* to 35*C and 45* to 70*C, ageing the slurry for not more than 2 hours, forming a filtercake by filtering the slurry, to a concentration of hydrous alumina calculated as Al2O3 of from 8 to 16% by weight, washing the filtercake with at least its own volume of water and drying the filtercake at a temperature not exceeding 150*C.