AT140567B - Process for removing iron from acidic aluminum salt solutions. - Google Patents

Description

  

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  Process for removing iron from acidic aluminum salt solutions.



   According to parent patent no. 137319, iron is removed from acidic aluminum salt solutions by separating the iron with β-naphthalenesulfonic acid or its soluble salts as the insoluble ferrous salt of this acid and working up iron-free aluminum salts in the filtrate. It is also stated that the β-naphthalenesulfonic acid used can be converted from its ferrous salt into its soluble alkali salt by reaction with alkali metal carbonates and reintroduced into the process. The procedure with alkali salts of β-naphthalenesulfonic acid is disadvantageous when it is a matter of obtaining pure aluminum sulfate free of alkali sulfate and double compounds.



   It has now been found that this inconvenience can be overcome by using them
Salts of β-naphthalene sulfonic acid, the metals of which form sulfates which are sparingly or insoluble at ordinary temperature. The sulphates formed then remain in the residue together with the insoluble ferrous salt of the β-naphthalenesulfonic acid, while the filtrate now only contains the aluminum sulphate, which in turn can easily be obtained in a solid state by crystallization or evaporation.



   As salts to be used in this way, in addition to the barium salt, the calcium salt of β-naphthalenesulfonic acid, in particular, whose solubility in the heat allows smooth conversion with the ferrous sulfate in the starting mixture is possible. These salts also have the merit of being recovered by reacting the regenerated alkali salts of β-naphthalenesulfonic acid with alkaline earth chloride.



     While in the process of the parent patent only salts are used that are soluble at ordinary temperature, and when the ß-naphthalenesulfonic acid is recycled with the help of alkali carbonates, salts are again obtained that form soluble sulfates and consequently merge with the aluminum sulfate into the final solution and they contaminate, the particular advantage achieved in the present process when recirculating or converting the precipitates obtained into the starting materials with the addition of sparingly soluble salts of β-naphthaIinsulfonic acid, for example the calcium or barium salt, is that the precipitates formed can be more easily converted back into the starting materials the filtrates obtained in the reaction are pure solutions.

   



   Another new and beneficial effect is the fact that if an excess of precipitating agent, which is useful for complete iron separation, is used during the felling process, the unused precipitating agent does not pass into the final solution during the filtration, as occurs when using soluble salts, but remains in the filtration residue and possibly returns from there into the cycle.



   Example:
In 100 parts of the Baux; The sulfuric acid solution resulting from the digestion and containing 25 parts of aluminum sulphate and 4 parts of ferric sulphate, 9'5 parts of ß-naphthalenesulphonic acid calcium are introduced.



  At about 800 C, sulfur dioxide is introduced with stirring until the iron has completely precipitated as naphthalenesulfonic iron. After cooling to about 10 ° C., the solution is filtered off from the precipitate consisting of ß-naphthalene sulfonic acid iron and calcium sulfate. The aluminum sulfate is obtained from the filtrate by crystallization, which contains only about 0.01% iron as an impurity.

** WARNING ** End of DESC field may overlap beginning of CLMS **.

 

Claims (1)

PATENT CLAIM: Process for removing iron from acidic aluminum salt solutions according to parent patent No. 137319, which consists in using β-naphthalenesulfonic acid as the salt of metals whose sulfates are sparingly or insoluble at ordinary temperature. ** WARNING ** End of CLMS field may overlap beginning of DESC **.