Patented May 12, 1931 1,804,631 UNITED STATES PATENT OFFICE RALPH. H. McKEE, OF NEW CORPORATIONYORK, N. Y., ASSIGNOR OF NEW YORK TO TENNESSEE CORPORATION, A MANUFACTURE OF SULPHATES No Drawing. Application filed November 1, 1924. Serial No. 747,391. This invention relates to the manufacture of Sulphates, and more particularly to the itate is treated to recover the iron and recovery of sulphates from potassium alum aluminum Sulphates. - - - inous minerals, such as sericite, micacious In a typical embodiment of the invention, 5 shist, and in particular, certain slates such sulfuric acid is diluted to about 40 per as are found in Georgia which have a high cent. strength and run into an acid proof content of sericite. tank having a false filter bottom. While an It has heretofore been attempted to re acid of about 40 per cent. strength is pre cover from these minerals, and similar min ferably used, I find that the strength of the i& erals, the potash and alumina in a soluble acid may be varied from 30 per cent. to 60 form b various furnacing- operations, as per cent. Without materially affecting the 60 set forth in my prior Patents Nos. 869,011 performance of the process. Georgia slate, and 1,222,960. The recovery of the potas Such as that found in the Cartersville area, t sium and alumina by treatment with strong or other potassium aluminous mineral is 5 acids at elevated temperatures has also been ground to about 30 mesh and gradually attempted and other means for obtaining added to the diluted acid. The gradual ad these minerals have also been employed. For dition is for the purpose of permitting every 65 various reasons, the different processes have particle of the slate to become thoroughly not been entirely satisfactory and have not Wet with the diluted acid. As an alterna As20 come into extensive use. tive, the slate may be rapidly added or In the present invention, the mineral from dumped into the acid and subsequently ro which the potassium and alumina are to be stirred. The reaction between the acid and recovered is treated with diluted sulfuric the slate ordinarily will start of itself. If acid of about 34° Baumé (40 percent.). necessary, however, the reaction may be is have found that while strong sulfuric acid started by blowing steam into the portion of from 80 per cent. to 90 per cent. strength of the mass near the bottom of the tank. s reacts incompletely and slowly with such The reaction is strongly exothermic and potassium aluminous minerals, even at ele when once started, will require no additional wated temperatures and even when the min heat to maintain the mass at the boiling L () erals are finely ground, dilute sulfuric acid point of the solution. The reaction will of the character referred to above reacts at normally complete itself in less than 24 lower temperatures and at higher speeds, hours. 80 producing large yields of soluble sulphates. - When the reaction is complete, the outlet A further advantage of the use of the diluted below the false bottom is opened and the hot ut Solution drawn off, placed in a tank and 35 acid is the fact that the mineral does not cooled. The residue is washed with hot have to be finely ground. As a general rule, water and the wash water is kept separate 85 grinding to 20 to 30 mesh is sufficient. Finer from the strong filtrate. The waste residue grinding may be resorted to if desired but is is largely silica, but may contain some slate 40 . objected to because of the increased cost. and other mineral matter which has not After the material has been treated with been acted on by the acid. The filtrate is the acid preferably at a temperature of 100 then cooled, preferably by blowing air 90 to 115° C., the filtrate is removed and cooled through the solution, and the mush of crys and the mush of crystals of potash alum, tals of potash alum, aluminum sulphate and 45 aluminum sulphate and iron sulphate filtered iron sulphate filtered off. The blowing of off. A strong acid is then added to the air through the solution is preferably em filtrate and aluminum sulphate and ferric ployed for cooling, as this causes the salts 95 sulphate separated by precipitation. The to crystallize out in a more readily filterable original precipitate is then reworked to re condition. The filtrate is then strengthened 50 cover the potash alum and the second precip with a strong acid and the whole allowed to stand over night. Ferric sulphate and 00 2 1,804,631 aluminum sulphate are thus precipitated fer to employ contains from 30 to 60 per and the filtrate obtained is diluted with the cent.While of H2SO4.I have described in detail the pre solution from the wash water tank to give ferred practice of my process, it is to be un the desired 40 per cent. strength of acid for derstood that the details of procedure may 70 5 useThe in a firstnew run.precipitate of potash alum,- be widely varied without departing from aluminum sulphate and iron sulphate is the spirit of the invention or the scope of washed with a little cold water or saturated the subjoined claims. aluminum sulphate solution and then dis I1. claim:The process of recovering potassium 75 10 solved in a minimum of hot water. This solution is filtered hot and cooled. The sulphate and aluminum sulphate from po potash alum salt then crystallizes out and tassium and aluminum bearing sericitic sili may be filtered off and sold as such. The cates which comprises treating such silicates potash alum may also be roasted to give in coarsely ground condition with sulfuric. 80 ls potassium sulphate and alumina and the acid2. ofThe from process 30 to of60 recoveringper cent. strength. potassium gases from the roasting will contain sulfur dioxid and sulfur trioxid, which may be re Sulphate and aluminum sulphate from potas covered as sulfuric acid. The solution may sium and aluminum bearing sericitic miner be further cooled to precipitate the alumi als which comprises grinding such minerals 85 20 num sulphate and drying and roasting of to approximately 20 to 30 mesh, and treat this precipitate may be resorted to to obtain ing the ground material with diluted sul alumina and roasting gases containing sul furic3. Theacid. process of recovering potassium fur dioxid and sulfur trioxid. If desired, sulphate and aluminum sulphate from po the potassium alum and the aluminuin sul tassium and aluminum bearing sericitic min 25 phate may be roasted together. When the 3rals which comprises grinding such miner process is performed in this manner, the ils to approximately 20 to 30 mesh, and potassium sulphate is separated from the treating the ground material with sulfuric alumina by leaching with hot water and by acid of from 30 to 60 per cent. strength. evaporating. The alumina after washing In testimony whereof, I affix my signa 9. 5

30, and drying, is ready for the market. ture. - ...- . . . . . The iron and aluminum sulphates in the RALPH. H. McKEE. second precipitate, and in the filtrate from the crystallized aluminum sulphate, are sep arated by drying the mixture and roasting 100 35 at from 475° to 500° C. This will decom pose the iron sulfate, forming iron oxid, but will scarcely affect the aluminum sul phate. The roast gases are treated for the recovery of the sulfur dioxid and sulfur 05 49 trioxid content. The roasted mass is leached with hot water to recover the residue of fer ric oxid. The hot water solution of alumi num sulphate is then evaporated and solidi fied or may be dried and roasted to obtain 10 4 alumina.In place of- the differential roasting- proc ess for separating the iron from the alum inum, the iron may be precipitated from the 50 mixed solution by known methods and the 5 iron free filtrate then worked up for its content of aluminum sulphate. By the term “diluted surfuric acid' as employed in the claims is meant an acid of such a strength as would be obtained by di 20 luting commercial sulfuric acid as made by the lead chamber process and concentrated in a Glover tower. Since commercial sul furic acid so prepared is of approximately 25 60 60 Baumé and contains about 78 per cent. of HSO, it is apparent that the term “di luted sulphuric acid' contemplates a prod uct which is of less than 60 Baumé and contains less than 78 per cent. of HaSO4, and g5 as is set forth above, the acid which I pre