US797323A - Process of making chromates. - Google Patents

Description

Unrrn s'ramns PATENT OFFICE.

PHOUE$TET G l MAKING QT'HQOIVIATE$E fipeeification of Letters Patent.

Patented Aug. 15, 1905.

Application filed May 19, 1905. Serial No. 261,207.

To all whom it may concern:

Be it known that I, PETER HOMER, a subject of the German Emperor, residing at 6 Kaiserstrasse, Bernburg, Germany, have invented certain new and useful Improvements in or Relating to the Decomposition of Chrome- Tron Ore by Alkaline Carbonates; and I do hereby declare the following to be a full, clear, and exact description of the invention, such as will enable others skilled in the art to which it appertains to make and use the same.

The manufacture of alkaline bichromates has been hitherto carried on exclusively by exposing a mixture of finely-ground chromium ore, burnt lime, and alkaline carbonates in furnaces to the action of a strongly-oxidizing flame at bright-red heat, whereby the oxid of chromium contained in the chromium ore was oxidized into chromic acid, which combined with the alkalies and formed chromates.

The following proportions were approximately used: one hundred parts of chromium ore, seventy to ninety parts of soda or potash, and one hundred and twenty-five to one hundred and fifty parts of lime. The lime could be partly replaced by residues from lixiviation obtained in the man ufaeture. In that process the lime first efiected the conversion of the alkaline carbonates into caustic alkalies and then prevented furtherflowing together of the fused chromium-ore mass, which was thus maintained in a loose state and rendered easily accessible to oxidation. This lime, which approximately constituted forty per cent. of the fused mass, had to be carried as ballast, as it were, through the whole of the manufacturing operations and finally caused additional difliculties by necessitating the removal of the residue obtained during the manufacture,since the said residue could not be usefully employed. Unlike the processes hitherto used the object of the process according to this invention is to manufacture alkaline bichromates without the use of additional materials and to obtain a residue which can be used for certain purposes such, for instance, red color or paint.

It is well known that chromium-iron ore can be decomposed by calcining finely-powdered ore with an excess of alkaline carbonate (soda or potash.) This method is, for instance, used in quantitative analysis for determining the quantity of chromic oxid in chrome ore. For manufacturing chromates on a large scale this process has not, however, been used hitherto, as during the calcining the soda or potash used to fuse and the heavy ore sank to the bottom of the thin fluid mass, whereby, on the" one hand, oxidation of the ore became impossible, while, on the other hand, the thin fluid alkali quickly destroyed the hearth.

The reaction between chromium ore and alkaline carbonate at red heatmay, however, be converted into an industrial process by preventing the mass from becoming melted into a thin flux. This is attained by first mixing the ore with a theoretically insufficient quantity of soda or potash, so that only a portion of the ore is converted into chromate, while the remaining portion constitutes to acertain extent an admixture, maintainingthe mass in a loose mixed state,and insures access of the oxygen of the air thereto. The lixiviation residue from this first fused mass is then mixed for the second treatment with soda or potash and again calcined in a reverberatory furnace. The second time as much soda or potash is used as is required to enable the whole oxid of chromium of the chromium ore still contained in the residue to be converted into soluble alkaline chromate. The flowing together of the mass is in this case prevented by the iron oxid contained in the ore, magnesia, and other gangue. This second process takes place at a lower temperature than the first.

The process can be carried out in the following manner: One hundred parts of finely- 3 ground chromlum ore are heated with about; fifty to seventy parts of finely-ground sodaf or potash on the hearth of a reverberatory furnace to a bright-red heat.

During the fusion samples are taken from time to time and analyzed as to their contents of chromic acid. When the proportion of chromic acid in the fused mass ceases to in crease, the mass is removed from the furnace, left to cool, and lixiviated in the well-known manner.

During the process oxid of iron and chromate of alkali are formed in accordance with the following equation:

The cooled fused mass is lixiviated with water and the liquid filtered. The filtrate contains neutral alkaline chromate as well'as small quantities of caustic alkali and is treated in the well-known manner so as to obtain bichromate. The residue consists of undecomposed chrome ore, oxid of iron, and gangue. This residue, which still. contains about half of the chrome ore used in its original state, is either dried and ground or mixed moist with soda or potash or their solutions. This time the proper theoretical quantity of alkali is taken and it is heated for the second time with an oxidizing-flame in a reverberatory furnace, whereby nearly the Whole of the chromium oxid is converted into chromic acid. About fifty to sixty parts of soda or potash must be taken for each one hundred parts of residue. The last residue can be used as red coloring-matter.

The advantages of the process according to this invention over the processes hitherto used lie chiefly in the saving in the cost of burnt lime; in the saving of fuel, since the second oxidation takes place at a lower temperature; in the reduction of the wages bill, as the Vol- 'ume of the mass is considerably reduced, owing to the suppression of the use of lime, and in the possibility ofobtaiuing nearly the theoretical output of chromate, While hitherto such output did not exceed eighty five to ninety per cent. of the theoretical in the most chrome-iron ore with a quantity of alkalinecarbonate insuflicient to decompose the ore, exposing the mixture to the oxidizing action of a flame, cooling the mass, lixiviating it With water and fusing the residue again with alkaline carbonate.

In testimony whereof I have hereunto set my hand and affixed my seal in the presence of the two subscribing witnesses.

PETER RoMER. [n s] Witnesses MARIE SCHNEIDER, ALMA GRAF.