Leaching

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    Concentration Tests

    in Leaching

    If the agitation tests on the sample of ore ground to pass 200 sieve are not satisfactory, it will be necessary to try the effect of concentration. For this purpose take about 500 grams of ore, crushed to No. 30 sieve, and carefully pan twice over. The tailing may then be ground in water or cyanide solution as already described and screened wet through a No. 80 or 100 sieve, and again panned.

    Pouring

    in Leaching

    The most usual procedure is to pour the fused charge, slag and all, into a conical mould, and when cool to knock off the bottom and put aside for remelting into a shipping bar. At the Butters Divisadero Company's mill, however, G. H.

    Fluxing the Charge

    in Leaching

    The flux ordinarily used will vary with the composition of the precipitate and in order to determine the best mixture a number of small fusions may be made with varying proportions and the results noted. Borax is the most generally useful reagent but if used in large quantity, it makes the fusion rather expensive. Its place may be taken to some extent by carbonate of soda and sand, utilizing the tendency of bases to form fusible double silicates. For this purpose only sufficient soda should be used to form the second base in the double silicate.

    Alkali Consumption

    in Leaching

    Before making up a bottle charge on an unknown ore it is necessary to ascertain the probable alkali consumption. For this purpose weigh up 4 lots of pulp of about 200 grams each, and add water at a ratio of 3 : 1 , numbering the bottles 1, 2, 3, and 4. Then add slaked lime powder at the rate of 5 Ib. per ton of ore to No. 1, 10 Ib. to No. 2, 15 Ib. to No 3, and 20 Ib. to No 4, and agitate for from 6 to 12 hours. At the end of the period filter off some of the liquor from each and test for alkalinity.

    Method of Working When Using Zinc Shavings

    in Leaching

    The extractor box is a long narrow box made of wood or steel and divided up into from five to ten compartments by partitions, and baffles so arranged that the solution rises through the column of zinc in each compartment and descends through the narrow space between the partition and baffle. A tray whose bottom is composed of iron screening of about J^ inch mesh rests on cleats six inches above the bottom of the box so as to allow space beneath for the collection of the gold and silver sludge as it becomes detached from the zinc.

    PRECIPITATION

    in Leaching

    Whatever method of precipitation be used it is of great importance that the solution should be absolutely clear and free from suspended matter, and in practice it is almost impossible to obtain solution from slime treatment, either by decantation or by means of the various types of slime filter, that is sufficiently clean to give the best results. It is therefore almost always advisable to clarify it by filtration before precipitation.

    Aluminium Precipitation

    in Leaching

    The use of aluminium as a precipitant for gold out of cyanide solutions was patented by Moldenhauer in 1893 but he does not appear to have made any practical use of the process. H. F. Julian experimented with it, in the same year, but soon abandoned the idea. In 1910 S. F. Kirk patrick introduced it at the Deloro Smelter in Canada, applying the metal for the first time in the form of a powder, and achieved a complete success. He later installed it at the O'Brien Mine in Cobalt.

    Action of Oxygen in Precipitation

    in Leaching

    In regard to this question some interesting facts have been noted in connection with the recently devised method for determination of oxygen in working solutions already described in the chapter on " Testing and Analysis of Solutions," page 48. In the course of the article by H. A.

    LABORATORY EXPERIMENTS

    in Leaching

    Small scale experiments are very valuable if carefully and skilfully performed, but may be misleading and inconclusive if the proper precautions are not observed.

    Electrolytic Precipitation

    in Leaching

    This was introduced on a commercial scale as an adjunct to the cyanide process on the Rand for precipitating the weak and low-grade solutions resulting from the treatment of slime by decantation, and was known as the Siemens Halske process. The anodes were of sheet iron enclosed in burlap to prevent short circuiting and the cathodes were formed by hanging four or five sheets of lead foil cut into strips upon a stiff wire, and shaking them till the strips separated and formed a bunchy mass. The anodes were placed about four inches apart and the cathodes occupied the entire space between.