US1491944A - Process of producing chromic-acid solutions - Google Patents

Description

Patented pr. 29, 1924.

PROCESS OF PRODUCING CHRONIC-ACID SOLUTIONS.

Ho Drawing.

To all whom z'tmay concern:

Be it known that ARTHUR W. BURWI'JLL, a citizen of the United States, residing at Poughkeepsie, in the county of Dutchess and State of New York, have invented certain new and useful Improvements in Processes of Producing Chromic-Acid Solutions, of which the following is a specification.

Inan application filed concurrently herewith, Ser. No. 531,281, I have described and claimed a process of oxidizing chromic salt solutions by causing the same to flow successively through the cathode and anode compartments of an electrolytic cell having a porous diaphragm, employing certain precautions having the effect of insuring a high degree of efficiency in the utilization of the current and a continued normal operation of the process. Thus, in said process I preferahly use an anode consisting of cast metal, which may be lead; or a lead-antimony alloy containing a comparatively small proportion -say up to 7 per centof antimony; or a lead-antimon y alloy presenting an vactive face of lead. In said process also I use sufficient excess of chromic salt in the flowing electrolyte to avoid substantial evolution of oxygen at the anode. A preferred form of apparatus for use in connection with the above recess comprises a containing vessel of lead or lead-antimony alloy serving as the anode; a porous cup or vessel functioning as a diaphragm; and a cathode, which may be of sheet lead, within the latter.

According to the present invention I am able toprepare directly from chromic hydroxid, a solution of chromic acid substantially free from sulfuric acid. The apparatus employed may be the same as that used for the oxidation of chromic salt solutions;

as mentioned above; but in the present process it is unnecessary to provide fora continuous flow of solutions.

In practicing the present invention I provide an electrolytic cell having a porous diaphragm of acid resisting material such as filtros, porous earthenware 'or the like.

Both

Application filed January 23, 1922. Serial No. 531,282.

electrodes may be of lead, or a lead-antimony alloy containing about 35-70% of antimony as described above, cast metal being preferably used in either case. The solution surrounding thecathode may consist of dilute sulfuric acid, or alternatively of any soluble sulfate. The anode compartment contains initiall a suspension or magma ol chromic hy roxid in water, slightly acidulated with sulfuric acid, or containing a small addition of a soluble sulf ate such as chromic sulfate, sodium sulfate, etc. Upon passage of the electric current the chromic hydroxid is progressively, and eventually completely, oxidized to chromic acid. Preferably the proportion of chromic hydroxid to water in the original charge is such that the concentration of (110;, in the final solution will approximate but not excecd 1077. Anode current densities of the order of 18 amperes per square foot are preferred, with cathode current densities of the order of 100-200 amperes; 8595 C. is a favorable working temperature. The process is most conveniently operated intermittently; but it is within my invention to provide for continuous or semi-continuous o-poration, the chromic acid solution being withdrawn from. the anode compartment, and the equivalent quantities of chromic hydroxid and water supplied thereto.

I claim i 1. Process of producing chromic acid solutions which consists in subjecting a magma or suspension comprising chromic hydroxid and water to anodicoxidation.

2. Process according to claim 1 in which thedanodes present active surfaces of cast lea v 3. Process according to claim 1 in which the anode consists of a cast alloy of lead and antimony, said alloy containing a relatively small proportion of antimony.

In testimony whereof, I aflix my signature,