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By Clarence F. Zeuch

Mr. Shaw's work showed the dodecyl mercaptan as a very good collector compared with other collectors on Cu-Mo ores, Mo ores, and for Au and Au-Ag ores plus Pt ores. However, as one who has had extensive experience on Cu-Mo ores, the work is not complete in making only a rougher concentrate with a collector; the work must be carried on in making a Cu-Mo separation. Did Mr. Shaw do any of this work? Before trying the dodecyl mercaptan as a Cu-Mo collector for the Cu-Mo ore it would be well to have any new work conducted knowing how the reagent acts on the Mo. Will it allow a good separation? The use of the collector at Palabora was also mentioned. From some earlier literature I thought that the reagent has been used as an oxide Cu collector after the sulfide mineral was floated out. I thought the pH at this point was about 1.5-3.0. I would like to have this point clarified.

Jan 1, 1982

EXCEPT for the material, the same method that you used in alloying gold is used in alloying silver, but its alloy is fine copper. Just as the silver does in gold, so copper in silver diminishes and lowers its fineness and increases its quantity. If half the value is surpassed it is no longer called silver but copper containing silver, as I told you of gold. But in my opinion one could also say silver of 5,4, or 3 leghe or even of one. How- ever, these terms are of no importance for our purpose. It is enough that you suppose that the whole quantity of silver that you have is twelve parts. If you put one part of copper in h with the melt, you will say [74] that you have 11-lega silver and that it is in weight thirteen of the first parts† and so on, when you add two to ten and four to eight, always naming the quantity of the fine silver just as you did with the gold, either

Jan 1, 1942

By Earl L. H. Sackett

This laboratory centrifuge is unique in its low cost and ease of construction, its particular adaptability to problems encountered in an ore dressing laboratory and its simplicity of operation. It will treat a sample of the size ordinarily used in a laboratory flotation test. The centrifuge was designed at the Baroid Sales Division of the National Lead Co., Malvern, Ark., and built in a local machine shop to serve as a laboratory machine which would produce results comparable with those obtained in the large scale centrifugal deslimers in use in our Magnet Cove mill. The apparatus has served quite well in this capacity and has also proved effective as a deslimer on a variety of ore dressing problems. The cost of making this machine was relatively low and it is simple to operate. It is strictly a batch machine, but when operated under proper conditions, gives results which agree quite closely with large continuous-flow machines of the same type. Effective separation of minus 5 and 10 micron material is made in an undispersed pulp in a short time.

Jan 4, 1950

By C. H. Wilson, J. J. Jakosky

In recent years geophysical prospecting methods have become well established as important steps in economically initiating new mining ventures in the field of base-metal exploration, placer mining and water-supply problems. The value of these methods as applied to these problems has been greatly increased by new and improved instruments, and a greater degree of skill in laboratory and interpretative technique. Considerable success has been attained, with subsequent drilling checking the predicted depths within 1 to 5 per cent, on problems requiring information on thickness of fill material, depth to and contour of bedrock, extent and yardage of gravels to be mined, and location of hydrostatic water table. In these applications the geophysical work gives data comparable to drilling, and at a cost of about one-fiftieth that of drilling. Discussion of several surveys with accompanying illustrations showing geophysical methods applicable to both simple and complicated placer problems are contained in the paper. The electrical instruments for measuring electromagnetic field strength and surface potentials are described, and their use, coupled with that of other geophysical instruments in modern field procedure, is noted.:

Jan 1, 1934

Both drilling and production of oil decreased in Rumania during 1935. The drilling totaled 1,042,041 ft. and production 61,973,938 bhl., being a decrease of 8.5 and 1.6 per cent, respectively. Wells completed during the year totaled 198, of which 168 were oil wells, compared with 238 and 215, respectively, of 1934. No important discovery was made during the year. The only new field found was Valea Calugareasca, where the Credit Minier completed a small well on the westward plunge of the anticline. Drilling higher on the structure will probably prove the field to be of greater importance than the results of the discovery well indicate. The only other developments of importance were the extension of the Bucsani field, the opening up of a new area on the northeast of the salt at Moreni by Credit Minier and a minor extension of the West Gura Ocnitei field. At Calinesti, on the cast extension of the Moreni field, exploration work continued and a gas well was completed, but oil in commercial quantities is yet to be found.

Jan 1, 1936

Both drilling and production of oil decreased in Rumania during 1935. The drilling totaled 1,042,041 ft. and production 61,973,938 bhl., being a decrease of 8.5 and 1.6 per cent, respectively. Wells completed during the year totaled 198, of which 168 were oil wells, compared with 238 and 215, respectively, of 1934. No important discovery was made during the year. The only new field found was Valea Calugareasca, where the Credit Minier completed a small well on the westward plunge of the anticline. Drilling higher on the structure will probably prove the field to be of greater importance than the results of the discovery well indicate. The only other developments of importance were the extension of the Bucsani field, the opening up of a new area on the northeast of the salt at Moreni by Credit Minier and a minor extension of the West Gura Ocnitei field. At Calinesti, on the cast extension of the Moreni field, exploration work continued and a gas well was completed, but oil in commercial quantities is yet to be found.

Jan 1, 1936

Canadian owned Lake are carriers will be used again this year in an attempt to make up the deficit caused by the two months steel-strike. Buffalo mills need between 5 million and 6 million tons of ore before the Lakes navigation season ends. Mutual Security Program aid will help reactivate Austria's largest iron ore mine. The Erzberg development is one of the moat important in Europe. MSA announced approval of $500,000 in supplemental financing of equipment. Following the war, the Russians stripped the Erzberg and Radmar deposits of equipment. The he Carborundum Corp. is going to build a $2.44 million plant at Akron, NO.. TOP near Niagara Falls for production of rare metals used by the Atomic Energy Commission. A subsidiary, the Carborundum Metals Co., Inc.,, will produce zirconium, hafnium sponge metals. The pyrochlore rich Sukulu Hills in Eastern Uganda will be mined under a pool arrangement including Tinto Mines, Monsanto Chemicals and Frobisher Mines. The combine will be known as the Uganda Development Corp., Pyrochlore is used in the manufacture of heat-resisting. alloys for Jet engines.

Jan 1, 1952

By R. M. Treco

The effect of small additions of oxygen on the hardness, density, and lattice parameters of high purity zirconium has been investigated. Precision parameter values and density of oxygen-free zirconium are given as: a,, - 3.2258 kX units, C = 5.1373 kX units, O23 = 6.507 g per cc. THE effect of oxygen on the hexagonal-phase lattice constants of pure zirconium is of interest for several reasons. The extensive hardening effect of oxygen noted by previous investigators' must be due in part to the lattice distortion accompanying its introduction and possibly to the preferred position of the oxygen atoms. De Boer and Fast' have shown that oxygen is taken into solid solution in large amounts, appearing to occupy an interstitial position. These authors also found that expansion of the lattice was not uniform since the a axis attained a constant value after the addition of 10 atomic pct while the c axis continued to expand. It was thought in the present work that this expansion of the zirconium lattice with increasing amounts of oxygen

Jan 1, 1954

By W. V. Vietti

Actual field data from several wells are used to illustrate the application of the method of determining the average density of the fluid column in a flowing oil well in the Yates field, Pecos County, Texas. The depths of the wells in the Yates field vary from 900 to 1700 ft., depending on surface elevation and the location of the wells on structure. Production rates over 8000 bbl. per hour have been determined and many wells are capable of producing 2000 bbl. hourly. Gas-oil ratios are usually below 400 cu. ft. per barrel, but a few wells high on structure have produced over 3000 cu. ft. per barrel. Incidentally, tubing wells has cut these high ratios to as low as 400 cu. ft.' By common agreement of the operators all wells making ratios over 400 cu. ft. will be tubed. Daily production of the field is prorated to 110,000 bbl. from an open-flow potential of 5,000,000 bbl. based on hourly open-flow gages.

Jan 1, 1931

By A. F. Baker, E. R. Palowitch, A. W. Deurbrouck

As air-pollution regulations become increasingly more stringent, increased significance is being placed on the amount of sulfur present in coals used for steam generation. These regulations are aimed at minimizing the pollution of the atmosphere with noxious gases such as the sulfur oxides that are formed and emitted when coal is burned. Two meet these future requirements, a definite need exists to reduce the sulfur content of some of the coals used for steam generation. Reducing pyritic sulfur involves liberating the pyrite from the coal and then removing it. The specific gravity of pyrite is high (5.0) compared to that of coal (about 1.2, mineral-free), and standard coal-washing devices, such as wet concentrating tables, will efficiently remove pyrite particles larger than about 100 mesh. Particles below this size will be entrained in the table water and will be carried into the clean coal product. Techniques such as froth flotation are of little benefit for pyrite reduction because the flotation characteristics of pyrite are similar to those of coal.

Jan 6, 1966

(Members are urged to send in for this column any notes of interest concerning themselves or their fellow-members.) Members and guests who registered at Institute headquarters during the period July 10 to Aug. 10, 1915: William H. Rettie, Yonkers, N. Y. Paul S. King, Wilmington, Del. A. J. Eveland, Pachuca, Mexico. E. E. R. Tratman, Chicago, 111. Chang Fu Wang, Shanghai, China. Courtenay Dekalb, Tucson, Ariz. F. H. Fovargue, Terlingua, Tex. Emil Gathmann, Baltimore, Md. W. W. Elmer, Tuttletown, Cal. Henry S. Drinker, E. M., LL. D., has just completed 10 years' service as President of Lehigh University. A notable gathering of alumni, with their wives and daughters, numbering more than 1,000 persons, met in South Bethlehem on June 5. In accordance with the request of Dr. Drinker, no formal celebration was held, but, nevertheless, a spontaneous and enthusiastic expression- of appreciation and affection was voiced by alumni, students and faculty, testifying to the regard felt for Dr. Drinker and extolling the progress made by the University under his guidance.

Jan 9, 1915

By Nicholas Chlumecky

To date information is somewhat limited concerning the strength and bearing capacity of floor strata, which is of great importance where proper roof control is desired. If the bearing strength of strata is not known, the support may be excessively strong in relation to the support capacity of the floor, with the result that strong props sink into the floor strata, giving them dubious value as a roof support. The method described is used to determine how tests are made on dry rock to determine the required support area for the base of props or other structures which may rest on rock strata in mines. Relationships were established for the bearing capacity of rocks which were subjected to loads by means of bearing areas of various sizes ranging from 0.09 sq cm (.014 sq in.) to 700 sq cm (108.5 sq in.). This permits the evaluation of the bearing capacity of rocks by testing small areas for the de- termination of the capacity of larger areas.

Jan 3, 1968

Sixteen executives, technicians and operative personnel from the French mining industry, now touring mining operations in the U.S., will wind up their visit to this country at the AIME Annual Meeting. Traveling under ECA auspices, they will be in Denver on Feb. 5, Salt Lake City, Feb. 8 to 13, Bonne Terre on Feb. 16. Four of the group are engaged in bauxite mining, nine in lead and zinc, two in pyrites mining. All are interested in American mining equipment and methods, and hope to contact manufacturers' representatives in the various areas they visit. A $600,000 manganese pilot plant is expected to be put into operation by Sept. 1, by the Bureau of Mines at Boulder City, Nev. S. R. Zimmerly, chief of the Bureau's metallurgical div. for the region, recently completed the mill design and flow sheet; and the Bureau is awaiting steel priorities before building. Ore from the Artillery Peak area, 60 miles south-west of Kingman, Ariz., will be used in the mill. Construction will be handled by Rex Lloyd of Boulder City.

Jan 2, 1951

By Jerrold Marcus

The peninsula is roughly 700 miles long and 180 miles wide. The southern portion is the American-sponsored Republic of Korea and the northern half is the Soviet-promulgated People's Democratic Republic of Korea. The area of South Korea is almost 40,000 sq miles, about the size of the state of Maine, and contains a population estimated at 22.5 million. Prior to annexation by Japan in 1910, the Korean economy was based on a system of self-sufficient farming units, but with Japanese occupation it was geared to Japanese economy. Emphasis was placed on supplying raw materials for Japanese industry and food surpluses to help feed Japan, and on providing a connecting link with Manchuria, traditionally a major raw material source for Japan. Small metal refineries, ore processing, and semi-finished goods manufacturing units grew into existence in the northern part of Korea, where much of the electric power is generated. Under Japanese domination, the south remained essentially agricultural. Food productivity was increased, although manufacture of elementary consumer goods was stimulated for Japanese markets.

Apr 1, 1956

By N. C. Nissen, J. A. Thomas, A. Illis, K. N. Subramanian

Successful miniplant and laboratory testwork has indicated that high purity selenium can be produced from copper refinery slimes. The recovery technique fits into existing unit operations, and the selenium recovery in the new process was close to 99%. This recovery virtually eliminated any selenium being processed through the smelting stage. In addition, miniplant tests conducted at Inco Metals Co.'s J. Roy Gordon Research Laboratory in Mississauga, Ontario, have demonstrated the reliability of the process with respect to extractions, product quality, filtration characteristics, and effluent disposal. Inco's copper refinery at Copper Cliff, Ontario, produces about 500 t/d of copper with the anode slimes fall typically averaging 0.5% of the throughput. Investigations relating to the treatment of slimes within Inco's R&D have been conducted on several occasions since 1959, when the available alternatives such as acid or alkaline pressure leaching, aqueous or high temperature chlorination, roasting, smelting, etc., were considered. Interest in slimes processing was revived recently to meet increasingly stringent environmental standards and to replace equipment of a relatively old plant.

Jan 11, 1978

By John K. Hammes, Stanley D. Michaelson

Generally, the mining costs reported for the large open-pit operations in the United States and South America lie within the range of $0.20 to $0.30 per ton of material moved. (These operations have strip- ping ratios ranging from 1.5 to 4.0.) Productivities for the larger North American properties are in excess of 200 tons of material per man shift, while those for the South American operations are less than 200 tons per man shift. The most significant variations in cost are in the categories of haulage and general mine cost. Haulage costs vary, as expected, according to the mine elevation, pit profile, crusher location, and accessibility of a dump area, and general cost variations depend largely on the overhead cost items included in this category. Drilling and Blasting Practice The majority of open-pit copper mine production drilling is performed by rotary drills. Hole diameter varies from 6 in. to 12 in., with 9-in. holes being most common, and penetration rates vary from 35 ft to 60 ft per hour.

Jan 1, 1968

By I. C. Edwards, W. J. Dengler, D. F. Lillie

By 1959 the milling plant of Bicr oft Uranium Mines Ltd. had been in operation for two years. During this time many changes, both physical and chemical, had been made in an effort to improve plant efficiency. Investigational work had been facilitated greatly by the fact that the Bicroft mill consists to a large extent of two parallel circuits; however, the number of interrelated variables is great, and it is difficult to measure, let alone control, all of them simultaneously. The Bicroft mill staff feels that much progress has been made, but there is much yet to be done and many questions still to be answered. The Addendum outlines noteworthy developments to the fall of 1960. The property of Bicroft Uranium Mines is located in Cardiff Township in the Highlands of Haliburton County, southeastern Ontario, some 140 miles northeast of the city of Toronto and 70 miles due north of Lake Ontario. The ore-bearing dikes are classed as mafic. nonsegregated, syenite and granite pegmatite. Microline, microline perthite, quartz, sodic plagioclase, and pyroxene or biotite are the main constituents with uraninite, uranothorite, fluorite, titanite, cryolite, calcite, pyrite, pyrrhotite, and molybdenite as important accessories. The mill was designed for a nominal capacity of 1000 tpd with all sections except grinding, leaching, and clarification capable of 1500 tons. Feed was entered to one mill unit on Oct. 29, 1956, and to the second parallel line on November 13. The total feed rate was at 1000 tpd on November 15. The first precipitate was produced on November 12. By August 1958 the average entry had been increased to 1410 tpd without the installation of any additional major equipment. The overall recovery has been greater than 93.0 pct on several months, but a recovery of 92.5 pct appears to be most economical. Operating time for eight months in 1958 has been 97.1 pct although all grinding mills were relined during this period. A generalized flowsheet is shown in Fig. 1 and the plant layout in Fig. 2. The ore is crushed in three stages to -3/8-in. and then is wet ground in two stages to approximately 50 pct -200 mesh. The pulp is thickened to 68 pct solids and agitated by air for 33 hr at a pH of 1.9 as maintained by the addition of 93 pct sulfuric acid. Separation of the uranium-bearing pregnant liquor from the residue is accomplished by five-stage countercurrent decantation (CCD), following which the liquor is clarified for removal of fine slimes. The clarified liquor is treated in the ion exchange equipment in which both the upgrading of the solution and the removal of some impurities is accomplished. Addition of magnesia to the high-grade eluate from ion exchange precipitates the uranium as sodium-magnesium diuranate. After being filtered and dried this precipitate is packaged in drums for shipment. The residue from CCD and the barren solution from ion exchange are neutralized by the addition of lime and pumped to the tailings disposal area. CRUSHING All crushing is done on surface in a conventional three-stage unit consisting of a 36x48-in. Birdsboro Buchanan jaw crusher, a 4 1/4-ft standard Symons cone crusher, and a 4-ft Symons shorthead. Both the two primary and the two secondary screens are 4X 8-ft Symons rod decks. Moisture content of the feed ranges from 3 to 4 pct. In the initial installation the primary screens were equipped with 5/16-in. rods at 1 1/4-in. spacing and the secondaries with 5/16-in. rods at 1/2-in. spacing. With this arrangement the average crushing rate was better than 180 tph. To reduce the work required of the grinding circuit as tonnage was increased, several changes were made in the crushing circuit. By September 1957, both secondary screens had been reduced to 3/8-in. spacing, and rod size had been reduced to 3/16-in. to provide increased open area. Average throughput was reduced to 160 tph. Later, 50 pct of one primary screen was decreased to 1/2-in. opening to better balance the load between the two cone crushers. In May 1958,

Jan 1, 1961

By N. Plint, E. T. Pinkney

Copper segregation developments within the Anglo American Group are described with particular reference to the work of the TORCO Project Team. Some radical differences have been adopted in the mechan-ical approach as compared with methods used by previous workers. Most important among these are the following: (1) The heating unit is a fluidized-bed roaster. (2) A moving bed segregation chamber is used in which a packed bed of heated ore, to which reagents have been added, moves slowly downwards under gravity and is discharged at a controlled rate by means of a suitable valve mechanism. (3) The quantities of reagents used (sodium chloride and some form of carbon) are only a small fraction of those recommended by other investigators. (4) Retention times of only 2 min have been satisfactory for the complete segregation of many types of ore. Project TORCO is the code name given by Anglo American Corp. of South Africa, Ltd., to the investigation undertaken in Zambia to develop a plant capable of treating large tonnages of refractory copper-bearing ores by the segregation process. The process has now been under investigation for six years (1960-66) and during that period work has progressed from bench-scale laboratory tests through small-scale pilot-plant work to a 500-tpd commercial pilot unit. Test work has been carried out mainly on the ores of the Zambian Copperbelt and results have been encouraging. Recoveries on the order of 90% have been obtained on all Copperbelt ores tested with high concentrate grades. PRELIMINARY INVESTIGATION Laboratory scale segregation test work on Nchanga banded sandstone ore and oxidized ore from Kansan-shi was originally conducted by Professor Maurice Rey. SociCtC Miniere et Mktallurgique de Pefiarroya, in 1957. Both ores responded favorably to the process. In November, 1960, the consulting engineers of Anglo American Corp. of South Africa, Ltd., initiated preliminary investigations on the application of the segregation process to Copperbelt ores. In early laboratory work, samples were heated in a closed, externally heated tube furnace for one hour at temperatures ranging from 800 to 830°C. The free moisture content of the ore feed was 4% and reagent additions were 0.5% salt and 1.0% coal. Both salt and coal were pre-crushed to -48 mesh Tyler.* All samples except an ore from the Bancroft mine responded well to the process and recoveries of over 90% were obtained. The presence of dolomite was responsible for the relatively poor recoveries from the Bancroft ore, as tests on one of the other ores with additions of calcite or dolomite confirmed. Recoveries dropped from 94 to 45% Grades of all the rougher flotation concentrates produced were low at 10-15% copper. The laboratory investigation was then followed up on a pilot-plant scale. An attempt was made to carry out the segregation process in a coal-fired 5-ft-diam fluidized-bed roaster. The feed consisted of a banded sandstone from Nchanga to which 0.5% sodium chloride had been added. Reducing conditions were maintained in the roaster by the addition of coal in excess of that required for heating the feed. The excess coal and added salt constituted the segregation reagents and the temperature of the bed was held at approximately 750°C. Recoveries of copper and grades of concentrates were low. The reasons for lack of success were: (1) The reaction is a gaseous one and a fluidized-bed roaster is therefore unsuitable as a segregation unit. (2) Coal in excess of that required for heating was introduced into the fluidized bed and under these conditions some of the copper would be reduced in situ. The term "reduced in situ" is used here to describe any copper mineral reduced to the metallic state in its original site within the ore particles. If this copper is to be recovered by subsequent froth flotation it must first be liberated from the gangue by grinding or some other method which, in practice, is usually not feasible on ores of this type.

Jan 1, 1969

By D. J. Rose, W. M. Armstrong, A. C. D. Chaklader

The wetiability of single crystals of MgO by specimens of vacuum-cast iron was studied using the sessile drop technique in vacuo at 1550ºC. Formation of FeO at the liquid-vapor interface caused the contact angle (6) to decrease from 117 to 65 deg during the first minute. After cooling, all specimens possessed a peculiar annular interfacial deposit of Fe,O,. Within the annulus the interface showed no sign of chemical attack. Chemical reaction occurred where the iron was alloyed with Ti, V, Cr, Nb(Cb), Ta, cmd Zr. Vnriation of 6 with alloy concentration was studied. Although vanadium md chromium improved the wettability of MgO by iron, the effect of Zr, Ti, Nb, and Ta was indeterminable because the 8 derived from sessile drop considerations was that of the metal against a restrictive peripheral volume of liquid oxide wetting the substrate. INTEREST in the nature of metal-ceramic interactions has been stimulated by progressive development of metal-ceramic combinations. One of the more valuable methods used for bond investigation is the sessile drop technique. Recent attempts to improve wettability through solute additions to the drop have revealed that the solute may a) react with the oxide creating new compounds at the solid-liquid interface, b) adsorb at the interface in a monolayer formation, or c) distribute throughout the drop uniformly causing no wettability variation. This work, part m in a series1,2 of investigations of interface reactions between metals and ceramics, embraces a study of the Fe-MgO system. MgO possesses a large negative free energy of formation (-173 kcal per g mole 0, at 1550ºC) compared to FeO at this temperature (-73 kcal per g mole 02). Hence the electronegativity difference between the drop and substrate allows selection from an extensive group of metal solutes with intermediate electronegativity differences that would, in the absence of chemical reactions, be expected to adsorb pre- ferentially at the solid-liquid interface. However, the high oxygen pressure of MgO in vacuo creates an oxidation environment which influences the solute behavior. Recent studies of the Fe-MgO systemJ74 have been restricted by chemical reactions that obscured observations. In view of the current interest in liquid-phase sintering of metal-ceramic combinations under partial oxidizing conditions,5 a more comprehensive study of the Fe-MgO system seemed beneficial. EXPERIMENTAL PROCEDURE 1) Specimen Preparation. Optical-grade MgO single crystals and Ferrovac vacuum-cast iron were used in all experiments. A spectrographic analysis of the iron indicated 0.008 C, 0.05 V, 0.005 Mo, 0.01 Ti, 0.002 S, 0.01 Cr, 0.001 Mg, 0.01 Si, 0.003 A1 (wt pct). The MgO crystals were cleaved along (100) planes into plates approximately 20 by 20 by 1 mm. Following annealing in vactto at 1100°C for 3 hr, surface irregularities were removed by a chemical etch in phosphoric acid at 100°C. The iron rod was machined into small cylinders approximately 0.250 in. in diam and length and these were carefully cleaned in organic and acidic solutions to remove surface impurities. All specimens were weighed to the nearest 0.1 mg. 2) Apparatus. The apparatus described in detail by previous authors1,2 was modified for this work. A Polaroid Land Camera was incorporated into the optical system so that drop measurements at ten-second intervals after melting were possible with ultra-high-speed self-develop ing film. 3) Procedure. The iron cylinders were placed upright on the MgO plates and positioned in the molybdenum susceptor. After furnace assembly the system was pumped down to a vacuum of 1 µ and flushed with H2 at 800°C. The system was again evacuated to 5 x 10-5 mm of mercury and the temperature raised to 1550°C within 2 min. The molten drops were photographed at appropriate time intervals. TWO min after melting the iron vapor pressure caused gas discharge, or corona, within the tube. The specimens were then slowly cooled to room temperature, sectioned and examined metallographi-cally. X-ray identification of interfacial reaction products was attempted by the powder diffraction technique. Alloying elements (Ti, V, Cr, Zr, Ta, Nb) were added to the iron in various concentrations up

Jan 1, 1963

By E. A. von Hahn, T. R. lngraham

The rates of cementation of pd11 on electropolislzed copper cylinders were studied in aqueous perchloric acid solutions at pdII concentrations from 0.02 to 0.1 mM. The cylinders were rotated at various high speeds to reduce the diffusion layer to a minimum thickness. In 0.1 M HClO4 solutions, the cemented palladium is dense, adherent, and shiny. The rate data indicate that there are two stages in the deposition. In the initial stage, the rate of cementation is first order with respect to the pd11 concentration. The second stage is much slower. The first stage is consistent with rate control by the diffusion of pd11 ions to the copper surface, and/or chemical reaction at the surface, and the second stage is consistent with rate control by the diffusion of copper ions from the cop-per surface through the deposit of cemented palladium, out to the main body of solution. In 0.001 M HClO4 solution, only the first stage is evident and the rate is more rapid than at higher acidities. This rate enhancement is attributed to PdOH+ ions that predominate at low acidity and aye more reactive than unhydrolyzed pdII. The deposit is porous and loose. All of the cemented deposits are Pd-Cu alloys rather than pure palladium. Activation energies are 9.5 kcal per mole in 0.1 M HClO4 and 7.4 kcal per mole in 0.001 M HClO4. CEMENTATION or displacement reactions occur between aqueous solutions of metal salts and immersed metals according to the general equation: where M1 is electrochemically the more noble metal. Although these reactions find considerable application in metals recovery processes (e.g., the cementation of copper192 or gold3), in electrorefining processes (e.g., solution purification before electrolysis4,5), and in plating and metal finishing processes,6 few studies have been made of the kinetics of such reactions.7-9 The rates of cementation reactions will depend on one or more of the following factors: a) chemical reactions at the metal-solution interface; b) ionic transport to or away from the interface;'-' and c) the character and adherence of the cemented deposit on the substrate metal,6a,10 because the deposit will inhibit the rate of transport of dissolving ions (M2m+) into the solution. In this investigation, the kinetics of the early stages of cementation were studied to obtain an understanding of the reaction mechanism under conditions in which the deposit was sufficiently thin that its inhibiting effect could be disregarded. To achieve this, very dilute solutions in Mn+ were used. Cementation rates are often fast in the initial stages and transport-contr01led.9 To find conditions under which transport control would shift to chemical control, very high stirring velocities were used to minimize the diffusion-layer thickness. Of the many possible cementation reaction systems, the palladous perchlorate-copper system was chosen for this investigation because it was believed to involve simple ion-for-ion exchange. In addition, there are no interfering side reactions, such as the reduction of hydrogen ions, and anion effects are usually absent in perchlorate solutions. EXPERIMENTAL Materials. Reagent-grade chemicals and redistilled water were used in all experiments. Palladous perchlorate stock solutions (0.02 M) were prepared by dissolving 99.5 pct Pd sponge (Johnson Matthey and Mallory Ltd.) in concentrated nitric acid, adding concentrated perchloric acid, evaporating twice slowly (to prevent PdO precipitation) to a small volume, and diluting in a volumetric flask. To prevent gradual hydrolysis of PdII, the stock solutions were made 0.4 M in HC104. Tests for pdIV (Ref. 11) and C1- were negative. Copper strips were cut accurately from 0.025-in. electrolytic tough pitch sheet, Sample 1 (Mines Branch stock or Canadian Copper Refineries Ltd., Montreal), or from oxygen-free, high-conductivity sheet, Sample 2 (American Metal Climax O.F.H.C. brand, sold by Utility Brass and Copper Corp., Brooklyn). The strips were annealed for 1 hr at 335°C in a stream of purified nitrogen (Union Carbide, Linde Division) which had

Jan 1, 1967