US755951A - Process of treating ores. - Google Patents

Description

portion of the ferrous oxid present.

UNITED, STATES Patented March 29, 1904:.

PATENT OFFICE.

PROCESS OF TREATING ORES.

SPECIFICATION forming part of Letters Patent No. 55,951, dated March 29, 1904.

Application filed July 17, 1903. Serial No. 166,008. (No specimens.)

T0 aZl whom, it may concern:

Be it known that I, J OSEPH SMITH, a citizen ofthe United States,residing at San Francisco, in the county of San Francisco and State of California, have invented certain new and useful Improvements in Processes of Treating Ores, of which the following is a specification.

In the modern treatment of gold and silver bearing iron sulfids by the cyanid process it has been found desirable to first reduce the sulfids by grinding or crushing from the coarse grains in which they leave the concentratingtables,so that they will pass a fine-mesh screen, the degree of fineness varying in different cases to suit the working of different sulfids. For economic reasons it is not practicable to crush them in the dry state, and to obtain a speedy and inexpensive operation it is necessary to crush or grind them with water. In the course of this grinding or crushing a certain decomposition occurs, producing ferrous sulfate, (FeSO4,) some free sulfuric acid, (H2SO4,) and ferrous oxid, (FeO,) a partiallyoxidized iron set free from the pyrites. The ferrous sulfate and the free sulfuric acid can be easily neutralized in the usual way with a caustic lime or other alkaline treatment; but the ferrous oxid (FeO) cannot be neutralized or made inactive by lime or by any alkaline treatment, and its presence is productive of an abnormal and excessive consumption of cyanid in the after treatment, the quantity actuallyconsumed beingonly limited by the pro- When attempts have heretofore been made to treat gold and silver bearing iron sulfids, the procedure has been to admit the cyanid solution to them directly after the crushing or grinding and while they were yet in a moist condition. The result'has been that the consumption of cyanid was always high, (in many cases so high as to render the treatment commercially impossible,) the extraction of the precious metals in many cases was very low, and the cyanid solution itself, which should be kept free of the base metals, was rendered foul by the large quantities of ferrous oxid which it was continuously taking into solution. To render this ferrous oxid insoluble in cyanid solutions, thereby preventing such solution.

lutions from becoming charged with base mat ter, to render more effective the extraction of the precious metals, to prevent the destruction of unnecessarily large quantities of the cyanide used as solvents, and to reduce to a minimum the cost of treatment are the objects of the process which constitutes my invention. Under the proper conditions this ferrous oxid is very susceptible of complete oxidation, so as to become a ferric oxid. As ferrous oxid it destroys potassium cyanid by the following formula:

but if oxidized to the ferric-oxid statesviz. E6203 and Fe3O4it becomes insoluble in cyanid solutions, and hence the salt is not affected by the iron during treatment. To secure said oxidation, I proceed in the following way: The sulfids crushed or ground to pass the desired-mesh screen are drained of the water used in crushing, given an alkaline treatment in the usual way, and the whole mass previous to cyaniding is subjected to a drying process with the free access of air, The drying may be performed by a low-fire heat, but preferably by steam heat, no danger of sparking the sulfids attending the latter method. If fire-drying is employed, care must be exercised that no roasting occur, which might produce a decomposition of the unaltered sulfids, and more acid. In all cases the drying should be completed in a moderate length of time, no chance being given the material for further weathering. By this treatment the partial oxidation or rusting of the iron, which commenced during the grinding period, is completed, and the whole of the soluble iron is rendered insoluble and inert in cyanid solutions. The result is that in the after cyanid treatment the cyanid consumption is low, the solution is not contaminated, and the extrac tion of the precious metals is good.

The above-stated facts in relation to the iron can be demonstrated in the following way: When cyanid in solution is destroyed, some metal, base or otherwise, has combined with it chemically and has been taken into so- In cyaniding in the old way without preliminary drying the base entering into ferrous oxid contained in a mass of moist crushed ore, which method consists in applying heat to said mass in the presence of air, previous to its treatment by the cyanid solution.

In testimony whereof Ihave aflixed my signature, in presence of two witnesses, this 7th day of July, 1903.

JOSEPH SMITH.

Witnesses:

F. M. BURT, LI W. SEELY.