Method of Recovering Gallium From Very Basic Solutions by Liquid/Liquid Extraction

The invention relates to a method of recovering gallium from very basic solutions by liquid/liquid extraction.

In our previously issued U. S. Pat. No. 3,971,843 description is made of the recovery of gallium present in aqueous alkaline solutions which also contain compounds of aluminum and sodium, by liquid/liquid extraction using substituted hydroxyquinolines. The method is applied more particularly to the recovery of the gallium in sodium aluminate lyes from the Bayer process, using .beta. alkenyl 8-hydroxy quinolines. The gallium recovery method described in the aforementioned patent includes a stage of extraction proper and a stage where the solvent is regenerated and the gallium recovered by means of strong acids. There are two preferred ways of carrying out the process, depending ont he acid used and its concentration in the stage where the solvent charged with gallium is regenerated. In the first embodiment, the preferred method of recovering the gallium present in very basic aqueous solutions also containing compounds of aluminum and sodium includes the following phases:

putting the aqueous solution into contact with a water-insoluble substituted hydroxyquinoline in solution in a water-insoluble organic solvent as represented by halogenated or non-halogenated aliphatic and aromatic hydrocarbons, so that the gallium and a certain quantity of sodium and aluminum pass from the aqueous phase to the organic phase

separating the organic phase from the aqueous phase

putting the organic phase into contact with a dilute aqueous solution of an acid to extract the sodium and aluminum from the organic phase, the gallium remaining in solution in the said organic phase

separating the organic phase from the aqueous phase and putting the remaining organic phase into contact with a more concentrated aqueous acid solution, to extract the gallium from the organic phase into the aqueous phase

separating the gallium from the aqueous phase.

The acids used are preferably hydrochloric, sulphuric and nitric acid. The concentration of the dilute aqueous acid solution is preferably from 0.4 M to 0.8 M and the concentration of the more concentrated aqueous acid solution is preferably above 1.6 M. But in cases where hydrochloric acid is used, the concentration is preferably from 1.3 M to 2.2 M and more particularly from 1.6 to 1.8.

In a second embodiment, the preferred method of recovering the gallium comprises the following phases:

putting the aqueous solution into contact with a water-insoluble substituted hydroxyquinoline in solution in a water-insoluble organic solvent as represented by halogenated or non-halogenated aliphatic and aromatic hydrocarbons, in such a way that the gallium and a certain quantity of sodium and aluminum pass from the aqueous phase to the organic phase,

separating the organic phase from the aqueous phase

putting the organic phase into contact with a concentrated aqueous solution of an acid capable of chelating (complexing) the gallium in anionic form, the gallium remaining in solution in the organic phase while the sodium and aluminum pass into the aqueous phase

separating the organic from the aqueous phase and putting the remaining organic phase into contact with a dilute aqueous acid solution, whereby the gallium in the organic phase transfers to the aqueous phase

separating the gallium from the aqueous phase.

The acids used are preferably hydrochloric and hydrobromic acid. The concentration of the concentrated acid solution is preferably from 5 M to 8M and that of the dilute solution from 1.3 M to 2.2 M.

Further it can be considered, if it is desired to obtain the gallium less purified, to operate according to the following steps:

putting the aqueous solution into contact with a water-insoluble substituted hydroxyquinoline in solution in a water-insoluble organic solvent as represented by halogenated or non-halogenated aliphatic and aromatic hydrocarbons, in such a way that the gallium and a certain quantity of sodium and aluminum pass from the aqueous phase to the organic phase,

separating the organic phase from the aqueous phase,

putting the organic phase into contact with an aqueous solution of an acid to transfer the gallium, sodium and the aluminum in the organic phase to the aqueous phase,

separating the aqueous phase from the organic phase,

recovering of the gallium sodium and aluminum.

The acids solutions used are preferably either solutions of sulfuric or nitric acids in the concentration above to 1.6 M, or hydrochloric or bromhydric acids in the concentration from 1.3 M to 2.2 M.

In the gallium extracting stage described in the aforementioned patent, it may be advantageous to add substances with an alcohol function, e.g. heavy alcohols like N-decanol and isodecanol and various heavy phenols as well as various other solvating compounds, e.g. certain phosphoric esters like tributyl phosphate, in the organic extraction phase, in known manner.

The concentration of substituted hydroxy quinoline in the organic phase need not be very high, for even a concentration as low as 2% gives good extraction of gallium, due to the far greater affinity of these chelating agents for gallium than for aluminum and sodium; in practice, however, concentrations in the order of 10% are more favorable and enable the majority of the gallium to be extracted.

Furthermore, although temperature is not a critical parameter for obtaining good results by the method described in U.S. Pat. No. 3,971,843, it is advantageous for the extraction stage to be carried out at a fairly high temperature, in practice below 100.degree. C. and preferably from 50.degree. to 80.degree. C. It may be added that, in industrial practice, the solutions generally treated are aluminate solutions from the Bayer process, particularly solutions described as "decomposed", which are at a temperature in the vicinity of 50.degree. C., and, although this temperature is less favorable than a higher one, it is nevertheless sufficient to give satisfactory extraction yields. Moreover the stage where the solvent is regenerated and the gallium recovered is carried out in such a way that the organic phase is treated with an acid solution to recover the gallium, at a temperature below that of the extraction stage and preferably near ambient temperature.

The very basic solutions treated by the methods described are particularly ones in which the OH.sup.- concentration may go up to 13-14 ions g/l. Thus the sodium aluminate lyes from the Bayer process, which are treated preferably by this method, generally have a composition corresponding to:

Na.sub.2 O : from 100 to 400 g/l

Al.sub.2 O.sub.3 : from 40 to 150 g/l

the so-called "decomposed" lyes generally have a composition such as:

Na.sub.2 O : from 150 to 200 g/l

Al.sub.2 O.sub.3 : from 70 to 100 g/l

In industry, installations used for this method are laid out as follows. The sodium aluminate solution, with its alumina content reduced following its "decomposition", and the organic phase comprising the selected chelating agent, a solvent and possibly substances with an alcohol function and other solvating compounds are passed into a first counter current extracting apparatus. A large proportion of the gallium passes into the organic phase, the proportion depending on the respective flow rates of the two liquids. Aluminum, sodium and certain impurities also pass into the organic phase. In another extracting apparatus, the resulting organic phase is put into contact with a first regenerating solution, comprising a dilute strong acid or a concentrated strong chelating acid; in both cases this leaves virtually only gallium in the organic phase. The latter organic phase is then treated in a third counter current extracting apparatus, where it is put into contact with a strong acid for the purpose of recovering the gallium, and is then washed with water before the organic phase is recycled into the first counter current extracting apparatus. The acid solution, which has recovered the gallium, is then treated to complete its purification, then the gallium is extracted from it.

Further a simple industrial apparatus can be used in the case of the desire for a less purified gallium. Such type of apparatus includes a first apparatus of extraction as described hereinabove, at the exit of this first apparatus the organic phase is treated in a counter current extracting apparatus where it is put into contact with a solution of a strong acid for the purpose of recovering the gallium, sodium and aluminum.

It has been found that extended use of alkenyl 8-hydroxy quinoline in a gallium extracting unit by the methods described in the aforementioned patent leads to their gradual degradation, resulting in a reduction in their extracting power. In accordance with the practice of this invention, it has been discovered that there is a group of certain hydroquinolines which have been found to have a stability which does not deteriorate with prolonged use, and which retain the remarkable initial properties of the alkenyl 8-hydroxy quinolines described in the aforementioned patent for extracting gallium from sodium aluminate lyes.

The present invention represents an important improvement over the process of the aforementioned patent in the method of recovering the gallium contained in very basic aqueous solutions by liquid/liquid extraction, using an organic phase chiefly consisting of water-insoluble substituted hydroxyquinolines and an organic solvent, characterized in that the substituted hydroxyquinolines are selected from the group represented by the general formula: ##STR2## wherein R is an alkyl radical or a hydrogen.

In a preferred embodiment of the invention one of the alkyl radicals R has 5 to 20 carbon atoms. Below about 5 carbon atoms, the substituted hydroxyquinolines, according to the invention, are generally found to have a solubility which becomes too great in an acid or basic medium, thus making their use uneconomical due to the subsequent losses. Above about 20 carbon atoms, the substituted hydroxyquinolines according to the invention have a viscosity which makes them difficult to use.

In another preferred embodiment of the invention, the radical R is located in the 7 position on the 8-hydroxyquinoline ring and the preferred substances used in the method of the invention have the general formula ##STR3## wherein n is preferably between 5 and 20.

The hydroxyquinolines of the invention enable the gallium present in very basic aqueous solutions, particularly in sodium aluminate lyes from the Bayer process, to be almost totally extracted without any loss in the course of time.

The embodiments of the method are those referred to above.

The following examples are given to illustrate the invention.

This example illustrates the degradation of alkenylhydroxyquinolines and the non-degradation of alkylhydroxyquinolines, employed in the practice of this invention, under conditions of basicity equivalent to those of an aluminate lye from the Bayer process.

The following hydroxyquinolines were subjected to a rapid degradation test at 150.degree. C. in a 5M NaOH medium, the test being designed to classify the various products. The degradation rate is measured by chromatographic analysis of the resultant products in the gaseous phase after 24 and 72 hours.

This example illustrates the method of the invention when use is made of hydroxyquinoline A of the formula ##STR7##

The gallium is extracted in an industrial extracting installation operating with continuous counter current flow, as described in this application. A sodium aluminate solution, composed of 90 g per liter Al.sub.2 O.sub.3, 185 g/l Na.sub.2 O and 250 mg/l Ga and an organic phase comprising an 8% solution of A in a 90-10 kerosene-decanol mixture is passed into a first counter current extracting apparatus in counter current flow. The extracting temperature is 50.degree. C., the time of residence 1 hour and the ratio of the phases =1. In the second extracting apparatus, the organic phase is put into contact with a regenerating solution comprising 6 M hydrochloric acid. In the third extracting apparatus, operating at ambient temperature, the organic phase is put into contact with a 1.8 M hydrocholoric acid solution. The gallium recovery rate is a function of the time of operation of the installation. After 1000 hours of operation the gallium recovery rate is found to have maintained its initial value of 75%.

This example is given as a comparison and illustrates the degradation of the gallium recovery rate in the course of time, when operating in the same installation and under the same conditions as in Example 2, using an alkenyl hydroxyquinoline B of the formula ##STR8## The results are as follows:

Furthermore the effectiveness of regeneration by HCL remains excellent. The recycled organic phase, in all cases, contains less than 5 mg/l of gallium before fresh contact with the Bayer lye.

It is obviously possible to extract the gallium with product B. In this case, however, if a suitable gallium extraction rate is to be maintained, more of product B has to be added in the course of extraction, the main disadvantage of this being that it is uneconomical.