Preparation of ultrapure boehmites and/or pseudo-boehmites

A process for the preparation of ultrapure and homogeneous boehmite and pseudo-boehmite, comprising (i) admixing amorphous aluminum hydroxycarbonate with a solution of an acid, a base, a salt, or mixture thereof, with the pH of the reaction medium which results being maintained at a value of less than 11, wherein the amorphous aluminum hydroxycarbonate is prepared by carbonating an alkali metal aluminate with carbon dioxide at a temperature ranging from 0.degree. C. to 60.degree. C. for less than 30 minutes and with the pH of the carbonation reaction medium ranging from 7 to 11.5, and thence filtering and washing the precipitate which results with water until the wash waters have a resistivity in excess of 10.sup.5 .OMEGA.. cm, measured at 20.degree. C., and wherein the molar ratio of the sum of the anions and cations in the mixture, other than H.sup.+ and OH.sup.-, to the equivalent of the aluminum compound, expressed as Al.sub.2 O.sub.3, ranges from 0.01 to 2, (ii) next heating the resulting reaction medium at a temperature of less than 90.degree. C. for a period of at least 5 minutes, and (iii) thence heating the reaction medium resulting from the step (ii) at a temperature ranging from 90.degree. C. to 250.degree. C.