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it is a local invention, yet this method is coming into extended use, and experience on mines such as the East Rand, the Princess Estate, the Geduld Proprietary, the Modder Deep, and the City & Suburban Mining & Estate Co., Ltd., warrants a belief in its future. At the Geduld and Princess the conversion of old plants enabled a true comparison to be made and the improvement in sand residues in strictly comparative experiments on a working scale of 0.05 dwt. at the Princess was much more than confirmed at the Geduld, where there was a greater margin to work on.
With the sand filter table system the dewatered sand is pumped in a stream of weak cyanide solution to the collecting vat where the treatment is also finished and every particle of sand must come into contact with cyanide solution, which is not inevitably the case with any other method. Thus we get the advantages of a preliminary "weak wash” which formerly had to be discontinued because of the time lost, while now the sand is under treatment half an hour after it has left the tube-mill plates.
As far as capital cost is concerned, even with treatment in collecting vats, no great saving can possibly be shown if it be recollected that a longer time of treatment will of necessity be required with a watercollected charge, so that more vats must be installed than are required in the safer filter table method. As regards cost of maintenance and operation, a reference may be made to an extract from the official report on the filter table at the City Suburban. The excellent results there shown with regard to light cost and increased extraction serve to confirm the general experience and justify the adoption of the sand filter table system on the fine new plant at the Modderfontein Deep, the most recent on these fields. In this last instance, of course, no comparison with older systems is possible, but the results obtained were better than anticipated from the preliminary small-scale tests made.
The Dorr collecting vat for slime may have the attributed disadvantage of not being a local engineering product, but so far the real reasons for its absence on modern Rand plants are as follows: (1) The increased capacity for a given area is small, as pointed out by Mr. Bosqui. (2) The extra moisture contained in the underflow involves a loss of about 2c. per ton for cyanide alone (required to bring this extra water up to treatment strength). The figure given by the author for moisture in settled slime in the ordinary collector (50 per cent.) is much too high, and modern plants easily secure a reduction to 40 per cent., and still lower figures are obtained when much very fine sand is present. The use of 70-ft. vats in place of the 56-st. mentioned is also becoming general in pursuit of the successful “large unit” policy. (3) The increased capital
* South African Mining Journal, vol. ix, Part II, p: 739 (Jan. 27, 1912).
and running costs of the Dorr vat have insufficient advantages over the simple method now in use.
The Butters filter system, for the introduction of which our thanks are largely due to Mr. Bosqui, is highly appreciated and would have much more extended use if the slime here were generally of higher value than it is. The extra cost is balanced only by the higher extraction when the original slime value is in the neighborhood of 2 dwt. Take for example the Princess Estate where the average value of the residue is under 10c. and many other mines where it is under 20c., the undissolved gold accounting for more than half of this. In such cases it is clear that the quoted running cost of 6c. to 8c. will leave little margin to pay for the extra capital cost involved. This process is very successful at the Geduld with slime of initial value of 3.5 dwt. and where, by the way, the only continuous use of air-lift vats on current slime is as yet practiced, beside the new plant at the Modder Deep. The East Rand Proprietary Mine vats are used for accumulated slime at present.
The economy in zinc consumption claimed for the Merrill press is not warranted by the figures quoted (0.152 and 0.154 lb. per ton of solution). The average figure for the Rand is about 0.35 lb. per ton of pulp and on some plants 0.25 lb. is maintained. This worked out on a 272 to 1 pulp, the usual ratio, would be 0.14 lb. and 0.10 lb., respectively, per ton of solution. Any economy per ton of pulp shown by the Merrill system must therefore be offset by reduced treatment, and the figures given for gold value of the residual solutions, being distinctly poorer than those obtained with zinc shaving, contribute to the impression that this process, though not without valuable features, will have to seek a welcome elsewhere.
While it must not be overlooked that the presence of zinc increases the stability of cyanide solutions to an extraordinary degree, there is the possibility of adopting some new method if it can show greater security of gold, ease of clean up, and reduction of space, combined with practically complete extraction of the gold value from very dilute solutions.
It has frequently been a matter of regret to the Rand metallurgists that processes and devices apparently successful elsewhere, have proved unsuited to local conditions. Although fresh information of local or oversea origin and development will always be welcome, the present, “conservative" attitude of preferring actual trial to glowing verbal accounts will continue manifest in Rand metallurgical practice.
Gasoline from “Synthetic" Crude Oil.
last 25 years.
Discussion of the paper of WALTER 0. SNELLING, presented at the San Francisco
meeting, September, 1915, and printed in Bulletin No. 100, April, 1915, pp. 695 to 704.
A. C. McLAUGHLIN, San Francisco, Cal.-It seems to me that Mr. Snelling's work, if it is what it appears to be, is one of the most important contributions to petroleum technology that has been brought out in the
If his end products are what they seem to be, he has made a discovery, which, in my judgment, will revolutionize the petroleum industry.
As to industrially carrying out these processes I do not think there is the slightest difficulty, for I have had some work recently where crude oils were handled successfully at a temperature of 750°F. and pressure of 750 lb. per square inch.
WILLIAM A. WILLIAMS, San Francisco, Cal.—What metal did you use, Mr. McLaughlin?
A. C. McLAUGHLIN.-Ordinary seamless tubing, extra strong.
WILLIAM A. WILLIAMS.—Tests were made in Dr. Rittman's experimental plant at Pittsburgh, upon samples of residuum furnished by Mr. Bell, the residuum being the remainder of the crude oil after the lighter fractions had been removed.
After the material had been run through Dr. Rittman's plant, yields of from 43 to 58 per cent. of material, boiling under 150°C. were obtained. The distillate had a peculiar odor, due to the presence of benzene, toluene, and other unsaturated hydrocarbons.
W. N. BEST, New York, N. Y.-What is the difference between the Rittman and the Snelling process or system?
WILLIAM A. WILLIAMS.—The fundamental difference is that reactions take place under relatively higher temperatures and pressures and with none of the oil present in its original or liquid state, while the reactions secured by Mr. Snelling and other investigators have been from the liquids in the presence of some vapors.
Under such conditions as Mr. Snelling operates, the temperatures and pressures used are limited and the flexibility in the control of these variables is extremely limited when compared with the Rittman process.
In making gasoline, Dr. Rittman has found favorable temperatures around 500°C. and pressures around 150 lb. to the square inch. Dr. Rittman has recovered from a 300° distillate as high as 85 per cent. of the original product which contains more than 30 per cent. which will boil under 150°C.
A. C. McLAUGHLIN.-What strikes me as most important, in connection with this Snelling discovery, is that it is so different from all cracking processes worked on during the past 30 years. The process of cracking is not new, and my experience as a refiner taught me that the cracking of oil was analogous to what is accomplished with the microscope, i.e., there is a gain in magnification but a loss in definition; what is gained in the stills is lost in the agitators. Compounds are formed which must be taken out with sulphuric acid.
Now, it appears that Mr. Snelling has produced low-boiling, saturated compounds. If he has done that, he has done something never achieved before, and I regard it as a big advance.
M. L. REQUA, San Francisco, Cal.-Has anybody made any estimate of the cost?
A. F. L. BELL, San Francisco, Cal.—In connection with the tests of which Mr. Williams speaks, I do not know that any estimates have been made of what a practical working plant would cost, since the process is in the experimental stage.
The samples Mr. Williams returned to us were tested at our refinery laboratory and re-run as we do our ordinary tops. The highest distillates that came off, or that we could get off, were about 50°Bé., but they had the same boiling points and corresponded closely, by the Engler test, to the 60°Bé. gasoline refined from crude oils and marketed here. But when the samples were treated with sulphuric acid in the same manner as our ordinary distillates, there was a marked reaction; the sulphuric acid turned the distillates black and threw down an excessive sludge, making it impossible to clean them with sulphuric acid. Clarifying with lye and by filtration was only partially successful. We obtained products of a beautiful red color, and some with green hues. But our samples were so small (only 4 oz.) that we could not determine what process would make them a commercial product. I do not think, however, that they can be treated in the same manner as the ordinary distillates of petroleum. They do not have any of the repugnant odors that the ordinary distillates of petroleum have, when heated to the same temperatures in the ordinary still under atmospheric pressure.
WALTER STADLER, San Francisco, Cal.-In reading over the literature which has come to my notice regarding the Snelling system, it has been observed that most of the oils that have been subjected to the treatment and on which detailed results have been published are those from the eastern United States and from Oklahoma. The crude oils from these regions, as I understand them, are usually composed of saturated hydrocarbons of the paraffine series, or a mixture of such saturated hydrocarbons with unsaturated hydrocarbons of the olefine series.
According to the results noted by Mr. Snelling, the process must virtually consist of converting higher-boiling heavy hydrocarbons of both the paraffine and olefine series into lighter low-boiling hydrocarbons of the paraffine series, since by repeated treatment a crude oil resembling the original oil is each time produced from which low-boiling members without color or odor can be distilled.
In California we are naturally interested in the California oils. As yet, detailed results from California oils subjected to the Snelling process have not been noted by me in the literature put forward. In this regard I may have overlooked something. The bulk of our California crude is entirely different than the Eastern and Oklahoma oils in that it is composed of unsaturated hydrocarbons to a degree of unsaturation frequently greater than in the olefine series, of naphthenes, some of the aromatic hydrocarbons, and minor amounts of the paraffine hydrocarbons.
If from the complicated California oils repeated treatment of the heavy residues will each time yield results comparable with those obtained from the Oklahoma and Eastern oils and give lighter products without color or odor, it will mean considerable for the technology of petroleum. It will mean, at least in part, a virtual reversal of the old cracking process. It will mean a process which the more stable lowerboiling bodies are produced without the use of catalyzers. Results with California oils will therefore be of considerable interest.
A. F. L. BELL.-Our California oils are of asphaltic base, whereas most of the Eastern oils are of paraffine base, but I am under the impression that California oils can be treated as well in the Snelling process as the Eastern oils. I simply judge that from the treatment of the California oils in the Rittman process.
Mr. Williams informed me that he was able to obtain a higher percentage of gasoline from the California oils than from the Eastern oils.
WALTER STADLER.—Were not those samples treated with sulphuric acid, and did you not get large quantities of tar which would indicate cracking ?
A. F. L. BELL.—Yes.
David T. DAY.-I would like to mention two points: First, concerning the specific gravity of the distillates, it seems odd to an Eastern man to obtain gasoline, by means of the Rittman process, the specific gravity of which is very high. The explanation is simple: When these oils crack and as the temperature goes up, more and more of the aromatic series are produced. If the temperature is kept low, so that the oil is just cracked, a different specific gravity is obtained. The specific gravity of all these cracked products is high as compared with neutral gasoline.