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By Sidney G. Parker, Jack E. Pinnell

Cubic ZnSe crystals have been grown with HCl, HBr, and I, as chemical transport reagents. The growth of large, well faceted crystals is in the order HCl < HBr < I, with some produced by I, transport being 1 cm on an edge. ZnSe:I crystals showed no strain in cross polarized light and were homogeneous as determined by electron microprobe. These ZnSe:I crystals had a mobility at 25°C of about 300 sq cm per v-sec and contained 103 dislocations per sq cm; further, these crystals were pure cubic and showed both photolumi-nescence and photo conductance. Doping was attempted during crystal growth. ZnS and Zn (S,Se) crystals were also grown by I, transport. ZnSe crystals have been grown by most of the common techniques.1"6 Of these, chemical vapor transport as developed by Kaldis2 showed promise of producing high perfection, cubic ZnSe. With chemical transport, crystals can be grown far below the transition temperature for conversion of cubic to hexagonal structure. A small temperature gradient between source and growth region tends to allow near equilibrium growth, which should lead to good crystalline perfection. Because it is necessary to form volatile compounds, halogens or their compounds are extensively used as transport agents. HCl, HBr, and I, were compared as transport agents for growth of ZnSe crystals. Doping during crystal growth was attempted. ZnS and ZnSxSe1-x crystals were also grown by chemical transport. Electrical and optical properties of the crystals were examined. EXPERIMENTAL Fig. 1 is a sketch of the growth apparatus, which was a modification of Kaldis&apos;. A quartz rod which butted against the seed crystal served as a heat sink to promote growth only on the seed. Initially, crystal growth was attempted with ZnSe prepared by wet chemical methods. Because such a material contained oxides and selenates, HC1 reacted with these oxygen compounds to form H2O and no ZnSe transport occurred. Further, this ZnSe contained about 10 ppm Cu plus other impurities. High purity ZnSe, containing small amounts or no oxygen compounds, was prepared by reaction of H2Se with zinc vapors at 600° to 800°C in an atmosphere of palladium diffused H2.7 The ZnSe thus produced was usually copper free and contained only 1 ppm by weight of magnesium as determined by emission spectrographic analysis. G.E.&apos;s electronic grade ZnS, which had about 10 ppm metallic impurities, was used without further treatment. ZnS-ZnSe charges were prepared by mixing the two compounds together, then sintering 24 hr at 1100°C in an H2S ambient. The gases, HBr and HC1, were commercial grade, of 99.9 pct purity, while the I2 was 99.999 pct pure. The single crystal seeds with (111) faces for growth were mechanically held in place by sealing the outer quartz tube to the growth tube. After the charge was introduced, the system was outgassed at l0-5 torr while heated to 500°C. The desired quantities of transport reagents were then sealed off in the system, which had been cooled to 25°C. The growth tubes were inserted into a furnace with the desired temperature and thermal gradient. The system was allowed to cool for 1 to 12 hr from growth temperatures of about 850" to 25°C. The tubes remained stationary during crystal growth. HCl CHEMICAL TRANSPORT GROWTH Preliminary runs with HC1 had a temperature gradient of 100° to 200°C and no seed or heat sink. Only small crystals were obtained in these experiments as

Jan 1, 1970

By Chase Palmer

INTRODUCTION. WHILE the reducing action of organic matter, of ferrous sulphate, and of hydrogen sulphide has frequently been invoked to account for the deposition of native gold and silver from ore-forming solutions, the high efficiency in this respect of certain of the metallic minerals which form the ore itself has not been sufficiently recognized. If a little finely powdered chalcocite is placed. in a test-tube and 2 or 3 cc. of a dilute solution of gold chloride are poured over it, two or three shakes of the tube suffice to remove all the gold from the solution. The color of the solution changes from yellow to pale green, showing that copper is dissolved simultaneously with the precipitation of metallic gold. If a piece of chalcocite is hung in a dilute aqueous solution of silver sulphate (1 normal), a coating of silver begins immediately to form on the mineral, and within a few moments a beautiful silver tree has developed, similar to that formed when metallic zinc is immersed in a similar solution.

Jan 5, 1913

By R. W. Jenkins, O. J. Neslage

The need for mechanized drilling to decrease mining costs has resulted in the development of the jumbo from column-and-bar drill by carriages to hydraulically controlled jib jumbos. Resultant savings from use of improved jumbos have been high enough usually to retire the machinery investment within a year. The jib jumbo unit has been and applied successfully to development and preparation programs and flat-bedded stopes, and an even wider field is forecast for its use.

Jan 5, 1950

By John Birkinbine

FOR two years past the Warwick Furnace, at Pottstown, Pa., has attracted attention by the remarkable work done in it, and a statement giving details of its operation and the unexpectedly short blast of 1880 will be acceptable to every member who studies blast-furnace practice. There are so many interesting features in con¬nection with this blast, and so much to be learned from investigating it, that the results of a thorough examination are offered to the Institute sans theories. In collecting the information, the courtesy of the various officers of the Warwick Iron Company was of material advantage, every facility for investigation being extended and an inspection of records being kindly permitted. In the following description these authoritative data are given in full where practicable, without making the paper too prolix, and the

Jan 1, 1881

By John Birkinbine

For two pears past the Warwick Furnace, at Pottstown, Pa., has attracted attention by the remarkable work done in it, and a statement giving details of its operation and the unexpectedly short biast of 1880 will be acceptable to every member who studies blastfurnace practice. There are so many interesting features in connection with this blast, and so touch to be learned from investigating it, that the results of &apos; thorough examination are offered to the Institute sans theories. In collecting the information, the courtesy of the various officers of the Warwick Iron Company was of material advantage, every facility for investigation being extended and an inspection of records being kindly permitted. In the following description these authoritative data are given in full where practicable, without making the paper too prolix, and the

Jan 1, 1881

By E. E. Carpenter

(San Francisco Meeting, September, 1915) BELIEVING that the results accomplished in the mill of the Churchill Milling Co., Wonder, Nev., during the fiscal year ended Sept. 30, 1914, will be of interest, I am presenting the more prominent facts and figures showing the progress made in treating this ore with especial reference to tonnage, supplies, costs, and extractions. The mill is situated at Wonder, Nev., in the Wonder mining district, 55 miles east from Fallon, Nev., the nearest railroad point. All supplies are hauled this distance by freight teams, this method of transportation having been found more reliable for continuous service than trucks, the price paid for hauling being slightly under one cent per pound. In this mill are treated the ores of the Nevada Wonder Mining Co. ,

Jan 6, 1915

By Carolyn Barnes

The Offshore Technology Conference, the world&apos;s largest technical conference and exhibition on the development of offshore resources and protection of the ocean environment, is sponsored annually in Houston, Texas, by 12 international engineering and scientific societies. This year&apos;s OTC, the seventh, will be held May 5-8 at the Astrodomain, and will be the largest in its history. The technical program for the first meeting in 1969 consisted of 100 papers, an exhibit display of 380 booths, and an attendance of 4300. This year. 280 technical papers are to be presented, and more than 2800 exhibit booths, representing some 1200 companies and nine countries, will be on display for an anticipated audience of 40,000.

Jan 4, 1975

By E. Hornbogen

Discontinuous precipitation in a iron can occur by at least two different mechanisms. These mechanisms are compared, using observations made on an Fe-22 at. pct Zn alloy and an Fe-19.5 at. pct Mo alloy. In the Fe-Zn alloy, precipitation began on grain boundaries. These boundaries moved into the supersaturated solid solution, providing nucleation sites and an easy path for diffusion. The precipitated phase pew as lamellae, perpendicular to the PRECIPITATION reactions are called discontinuous if the nucleation of particles does not occur on individual sites in the supersaturated matrix.&apos; In discontinuous precipitation, nucleation and growth occur on a reaction front that moves into the supersaturated solution and leaves a two-phase aggregate behind. The term cellular precipitation2 has also been used, but the term autocatalytic precipi- moving reaction front. The orientation of the depleted iron differed from that of the supersaturated iron. In the Fe-Mo alloy the growing precipitate particles apparently created dislocations in the growth front which served as nucleation sites. The precipitate grew on (110) planes of the iron, and growth occurred through volume diffision. The depleted iron retained the orientation of the supersaturated solid solution. tation seems to describe the nature of such reactions best. The basic effect of such a precipitation mechanism in a solid is that it is able to move or create sites that can catalyze nucleation. Such sites can be grain boundaries and dislocations. A mechanism of autocatalytic precipitation must, therefore, include some rational process by which a grain boundary may move into the supersaturated matrix or by which dislocations may be generated in front of the reaction. Discontinuous precipitation is always in competition with individual nucleation and growth of par-

Jan 1, 1963

By Allen Rogers

THERE are few natural monopolies comparable with the nitrate industry. Perhaps the only other one is, curiously enough, also an essential fertilizer material, viz., potash, of which the Germans have heretofore held practically a-monopoly due to the existence in their territory of the most important known deposits of potash salts. And although nitrates in minute amounts are found in many desert regions, the only deposits callable of being worked commercially exist in Chile. Combined nitrogen in the oxidized form is an essential for plant life. Nature provides it mainly through the agency of nitrogen-fixing bacteria. But where lands are cropped artificially this supply is too small; and gradually the nitrogen supply becomes exhausted. In order to continue farming, it is necessary to furnish a supply of nitrogenous plant food, and this is clone by putting on various substances containing combined nitrogen. These consist of various animal wastes, ammonium sulphate, the ammonia of which is obtained in the destructive distillation of coal, and Chile saltpeter. The latter is immediately available as a plant food, the nitrogen being in the required form. The other substances must oxidize before they are available. Besides its use as a fertilizer, Chile saltpeter is the source from which the bulk of the nitric acid of commerce is derived. The use of nitric acid in the manufacture of almost, all modern explosives is, of course, well known.

Jan 2, 1918

By Arthur Gray

THE thermal analysis of a metal or alloy is ordinarily made with the aid of heating and cooling curves, in which transitions are indicated by the rapid changes in curvature that accompany .changes in the rate of heat absorption or evolution. Analysis by the method that depends on the change in thermal expansivity is not customary, partly, at least, because of the difficulties involved in making the necessary measurements. However, under certain circumstances, the dilatometric method of analysis may possess advantages over the thermometric method that will justify the additional trouble required. The addition of 1 per cent. of zinc to an alloy has been found to produce, upon the volume changes that take place during transition, effects that suggest the possibility of using the dilatometric method of thermal analysis as a rather sensitive means of obtaining chemical information. Although the illustrations presented in this paper are drawn from data obtained during an investigation of dental amalgams, similar phenomena can doubtless be observed with other alloys. Some of the results found during an investigation made in 19171 have been confirmed by data on the thermal expansivity of amalgams published by Souder and Peters of the Bureau of Standards in reporting tests of dental materials.2 Although the Bureau of. Standards made experiments for the purpose of discovering effects of including zinc as one of the constituents of a dental alloy-a matter much discussed in dental literature but without the presentation of reliable experimental evidence to support the views of ;either side-the reports of the test made by the Bureau give the impression that certain striking phenomena associated with the presence of zinc were not noticed. Among such phenomena are those connected with the conditions that determine whether or not a specimen of amalgam becomes covered with droplets from which crystals develop.

Jan 9, 1920

By J. H. Johns, G. R. Stephan

The Climax mine has a history of dealing with ground control problems caused by major stress concentrations in the orebody. These stress concentrations, called weight, can arise in a variety of ways. The general effects of depth, rock type, and mining method give rise to weight problems, but local geologic features and daily cave line management can have even greater effects. Over the years a number of techniques have been developed for identifying weight problems in advance and for cow with them. These techniques all help us to amid interrupting the pace of cave advance and minimize the loss of production.

Jan 1, 1984

By Robert W. Metcalf

THE name "tripoli" is used to designate a number of more or less similar types of silica of sedimentary origin. Usually they are spoken of as "soft" silicas, and are light, very fine grained, porous, and friable. Structure is microcrystalline or cryptocrystalline. The deposits are the residual product of weathering and occur in massive form, either blocky or in friable masses. Tripoli is the end product of the weathering of siliceous Limestones, cherty limestones, or cherts. Weathering removes the calcium carbon- ate, leaving a finely divided siliceous residue to which the name "tripoli" has been applied. Authorities differ as to whether the chert accumulates first and is converted into tripoli or the tripoli is derived by direct decay from various forms of silica during initial weathering of the Limestone. It has also been asserted that tripolis were formed in situ in essentially their present condition as a flocculent, colloidal silica, but it is now believed by most geologists that varying degrees of pressure, combined with one or more methods of origin, have influenced the characteristics of the deposits. Considerable confusion has existed as to what constitutes tripoli. Owing to the similarity of names, tripolite, a type of diatomaceous earth found originally in Tripoli in northern Africa, has been erroneously called tripoli. Tripoli, however, contains no diatoms, the distinguishing characteristic of diatomaceous earth. The material mined in the Missouri-Oklahoma area has been considered by the trade to be the type material, and many feel that the term "tripoli" should more properly be restricted to the product of this region. Although also designated as soft silica, it would be less misleading, perhaps, if the siliceous material mined in southern Illinois were called amorphous silica. Both the Missouri-Oklahoma and Illinois materials are very high in silica. Different in composition, as it is very much lower in silica content than tripoli or amorphous silica, yet included under the classification of tripoli in Bureau of Mines statistical data, is the small but important output of rottenstone in Lycoming County, Pennsylvania. The principal justification for grouping these three types of silica is similarity of use.

Jan 1, 1949

By T. S. Lundy, F. R. Winslow

DIFFUSION coefficients of Hf181 in the high-tem-perature bcc phase of reactor-grade hafnium were determined at temperatures of 1795° to 1995°C by standard lathe-sectioning techniques. The temperature dependence of the data may be described by an Arrhenius-type expression for this limited temperature interval. However, hafnium is classed with the "anomalous" bcc metals zirconium, titanium, and y uranium by the low values of Do and Q observed in this study. The hafnium metal was received as 1/2-in.-diameter crystal bar. Analyses by the Analytical Chemistry Division of Oak Ridge National Laboratory showed the major impurity to be zirconium— about 2.1 pct. The total interstitial content was about 225 ppm with 190 ppm of this oxygen. The Hf"&apos; was supplied as HfC12 in HC1 solution by the Isotopes Division of Oak Ridge National Laboratory. The hafnium bar was cut into disk-shaped specimens 3/8 in. long. One of the flat faces of each specimen was metallographically treated and then the isotope was deposited by vacuum evaporation from a tungsten filament. A 3 by 3 in. NaI (Tl) crystal with a single-channel analyzer was used for counting y rays with energies of 0.3 to 0.7 Mev. The as-deposited layers of isotope had counting rates of about 200 counts per sec. Specimens were annealed in argon in a tantalum resistance furnace. Temperatures were measured with a microoptical pyrometer calibrated for the particular furnace sighting conditions. All sectioning was done by standard lathe techniques. Section weights were determined on a semimicrobalance. A density of 12.5 g per cu cm was used in determinations of section thicknesses. Activities associated with the various sections were measured and the penetration data were treated using the computer code by winslow.&apos; In all cases, except for specimens annealed at temperatures below 1795°C, normal Gaussian penetration behavior resulted. At lower temperatures, plots of In A(x) vs x2 were nonlinear [~(x) = relative activity at a distance x from the

Jan 1, 1965

By G. P. Hulst

THE Parkes process lead refinery of the International Lead Refining Co., at East Chicago, was built by the International Smelting & Refining Co. to treat the lead bullion produced by its Tooele plant, at Tooele, Utah. The plant was designed and constructed under the direction of the writer. Ground was broken Apr. 16, 1912, and exactly six months later the plant was in operation and lead was being cast. The capacity of the plant, running 25 days per month, is 5,000 tons. The four products of the plant are common lead, corroding lead, antimonial lead, and Doré bullion. The site is an area, 64 acres in extent, lying north of 151st Street, between McCook Avenue and the Canal. The Indiana Harbor Belt Railroad, Baltimore & Ohio Chicago Terminal, and Pennsylvania Railroad enter, the yard at the plant. There are five, storage tracks and space for storing 100 cars in the yard. The main lead to the storage tracks passes over a 100-ton track scale on entering the yard...

Jan 8, 1914

By A. E. Hunt, G. P. Clapp

This paper constitutes in substance a part of a more elaborate chapter, accompanied with extended tables of analyses, prepared for the book of Mr. Fred. H. Whipple on " Water-Supply." In advanee of that use of the material, however, it seemed appropriate to lay a portion of it before the Institute; and this opinion of the authors, the Council, by accepting the paper, has ratified. It may seem at first glance, nevertheless, that a paper dealing chiefly with this subject in its sanitary aspects, and only treating in a subordinate way of the one subject (boiler-scale) usually deemed to concern our professions, is somewhat out of place in our Transactions. But reflection will, we trust, correct this impression. In recent periods, and in continually increasing degree, the managers

Jan 1, 1889

By R. F. Evans, J. M. Avert

Much has been written of the glamour of magnesium from sea water, the Aladdin-like creation of a huge magnesium plant in the Nevada desert using cheap hydroelectric power from Boulder Dam; the marvels of the Hansgirg process for the electrothermal reduction of magnesium oxide by carbon, and the ferrosilicon process for producing magnesium from dolomite. This is the story of the production of magnesium by the electrolytic process, using steam-electric power supplied by a public utility, in a plant at Painesville, Ohio, 30 miles east of Cleveland on the shore of Lake Erie. The story is not without interest, since it involves several unique developments that provide the answer to a question frequently asked: How is it possible to produce magnesium metal economically at such a location as Painesville, Ohio? Basically, the answer lies in making use of facilities already in existence for the production of soda ash, which makes it possible to manufacture magnesium chloride, the principal raw material, cheaply enough to offset the high cost of electric power. To this is coupled the successful conversion of by-product chlorine into a product required for the war program. The source of magnesium for this opera- tion is the enormous surface deposit of high-grade dolomite in the region south of Toledo, within reasonable freight haul of Painesville. This same geological stratum underlies the Painesville plant, but unfortunately at a depth of about 3000 ft.— apparently too great a depth to permit underground mining to compete with the delivered cost of rock from surface quarries in other areas. The cost of dolomite obviously is an important factor, since the rock contains only some 12 per cent magnesium (20 per cent MgO) so that one dollar on the cost of stone means more than $8 in terms of its magnesium content, and more than that in terms of recoverable magnesium metal. Production of Magnesia from Dolomite In the summer of 1941, the Diamond Alkali Co. was well along with construction of a plant intended for the commercial production of refractory and other grades of magnesia from dolomite. The process to be used was designed to make maximum economic advantage of existing plant and operations by tying the production of magnesia in with the manufacture of soda ash in such a way as to make use of the lime [CaO)., value of calcined dolomite. The process finally adopted after a lengthy research and development program has much in common with the old Clerc-Nihoul process, but includes certain innovations found to be necessary or advantageous. Essentially, the process is based upon the following series of reactions:

Jan 1, 1949

By David Baker

Devices for saving labor in immediate connection with the operation of the iron blast-furnace have received comparatively little attention. Machines for hoisting and blowing, always employed in some form, have been improved; but charging, tapping, casting and handling the pig-iron in the beds are still performed chiefly by manual labor. At almost all furnaces, filling is done with the handbarrow of twenty-five years ago; and it is only recently that, here and there, chills have been employed in the cast-house instead of the usual sand-beds, to lessen the labor of handling the pig, as well as to secure its greater purity. The manual labor of opening and closing the tapping-hole has

Jan 1, 1893

By F. R. Conley, D. A. Shock

Solution Mining or In Situ Mining has received increasing attention in the past few years because the method offers many attractive possibilities in improving the environmental impact of mining as well as making feasible the extraction of deeper, low value mineral reserves. This paper will present a brief discussion of the state-of- the-art in total solution, slurry removal and leach mining. As a specific example of utilizing the method, the uranium deposits of South Texas are a type of deposit which have been considered as being amenable to in situ leach mining. The parameters required to ascertain the amenability of such a deposit for in situ leaching will be presented. The hydrological factors which influence the production of the soluble uranium solutions and their displacement will be discussed. Mathematical models for various well configurations have been made and graphic representation will be presented to illustrate various production methods and the resultant hydrological consequences.

Jan 1, 1974

By H. H. Podgurski, J. C. M. Li, Y. T. Chou, F. N. Davis, R. A. Oriani

When an Fe-2 pct A1 alloy is nitrogemted at 500ºC with a gus tnixture (NH3-H2) in which the nitrogen activity has been kept Lou] enough to avoid the formation of iron nitride, a two-phase alloy is generuled which consists of AlN particles and a ferrite phase cotaining a heavy network of dislocations. The amount of nitrogen contained in such an alloy, when equilibrated with the nitrogenating atmosphere, far exceeds both that needed to satisfy the normal solution requirements of a Fe and that needed to convert all of the aluninuwi to AlN. This excess nitrogen is accounted for as being trapped on dislocations, adsorbed at the ferrite -AlN interface, and as an en-Iuznced lattice solubility in strained ferrite. This excessive uptake of nitrogen had previously been attribuled by other investigators to the formation of a nonstoichiornetric aluminum nitride. Isotope exchange experiments revealed various amomts of exchargeable N14 present in the originally nitrided samples that could not be removed by reduction with HS at 500ºC. This exchangeable nitrogen has been identified us that bound to the AlN -ferrite interface. Estimates of inter facial areas in alloys containing -3 pct by weight of A1N are as high as 10 sq m per g of alloy. ThE first1 of this series of papers described the experiments forming the basis for the elucidation of the mechanism of the formation of aluminum nitride particles within an Fe-A1 alloy. It was found that not only are dislocations necessary for the nucleation of the AlN particles but also the nitriding reaction in turn produces a dense network of dislocations in the ferrite matrix. It was also observed that nitrogen in excess of that needed for the formation of stoichiometric AIN is taken up by the alloy without the formation of an iron nitride. The present paper is an analysis of the excess nitrogen sorbed by the nitrided Fe-A1 alloy which considers the structure generated by the formation of the aluminum nitride particles. Because of the high density of dislocations, this system has proved to be quite useful in studying nitrogen-dislocation interactions. Wriedt and Darken2 have already reported such studies in a cold-worked ferritic steel. EXPERIMENTAL Nitrogen Sorption. The specimens of this alloy were cold worked (50 pct reduction) to 0.011 in. thickness and chemically cleaned in a 2:1 concentrated phosphoric acid-50 pct hydrogen peroxide solution before nitrogenation. The flowing nitrogenating atmosphere (11 pct NH3-89 pct H2) was established before the ni- trogenating temperature was reached. The same gravimetric and gas-flow equipment described in an earlier paper1 was also used in this investigation. Changes in nitrogen concentration were followed gravimetrically when establishing the isotherms. In the isotope exchange experiments, concentration changes were followed volumetrically. In some instances chemical analyses (Kjeldahl method) were used to check for material balances in both the gravimetric and volumetric procedures. Our objective was to obtain reversible nitrogen sorption isotherms for alloys equilibrated with NH3-H2 gas mixtures over a large range of nitrogen activity* and temperature. The *Defined as equal to PN H /P3/2 ,where P corresponds to partial pressure in atmospheres. Actually the nitrogen activity, aN, in the alloy equals K PNH3 /p3/2H2, where K is the equilibrium constant for the reaction NH3 = N + 3/2H2. upper limit for nitrogen activity was below that which would produce iron nitride; for reasons which will become apparent later, most of the sorption studies were made in the temperature range between 400" and 500&apos;C. The alloy sample studied most extensively in this investigation was given a series of successive reductions (100 pct H2) and nitrogenating treatments at 500°C to attain a stabilized structure. Presumably some dislocations were lost during these treatments. Throughout most of the sorption studies, temperature was held at ± 1°C and the gas-phase composition was held to k0.2 pet NH3. Based upon the results of numerous diffusion experiments with this alloy* the &apos;Results to be published in a third paper of this series. times chosen for equilibration were considered more than adequate, Nitrogen Isotope Exchange. The first exchange experiments were carried out by circulating a measured quantity of H2 and NH3* (with a predetermined isotopic *The NH3 was synthesized over a synthetic ammonia iron catalyst using H2, and N2, enriched with N15. AS the NH3 was formed it was removed continuously from the gas phase by circulating the mixture through a refrigerated (78ºK) trap. When most of the nitrogen had been converted to NH3, it was distilled from the trap into a glass storage vessel. composition, N15/N14) over a nitrided specimen at 450°C in a closed glass system. Attempts to reach the exchange limit isothermally, i.e., an isotopic ratio (N15/N14) in the gas phase identical with the extractable nitrogen in the nitrided alloy, were futile. The exchange rate between the gas phase and the alloy was too slow, involving many days. To circumvent the slow exchange with the gas phase, measured amounts of N15 and N14 were introduced into the alloy by nitrogenating with an NH3-H2, mixture at 500°C containing an N15/N14 ratio of 7.76; the charged specimens were then sealed by allowing an oxide film to form over them in air, and in this final condition the specimens were subjected to 500°C in vacuum for various times during which isotope exchange was allowed to proceed within the specimen. It was estab-

Jan 1, 1970

By Martin C. Kuhn, Lawrence G. Stevens, J. Mark Richardson

The majority of the world&apos;s known and anticipated reserves of nickel ores are lateritic deposits At present, there are several different process alternatives for recovering nickel and other desired metal values from laterite ores An overview is given of the selective reduction roast/ammoniacal leach process, one of the processes in commercial operation.

Jan 1, 1981