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By James A. Voigt

"The efficient separation of metal species from aqueous streams by precipitation techniques requires a fundamental understanding of the various processes that occur during precipitation. These processes include particle nucleation, particle growth by solute deposition, agglomerate formation, and agglomerate break-up. The application of the population balance approach has been used to develop a kinetic model that accounts for these competing kinetic processes. The usefulness of the model is illustrated through its application to the precipitation of yttrium hydroxynitrate, YHN. The kinetic parameters calculated from the model equations and system specific solution chemistry are used to describe several aspects of the effect of pH on the precipitation of the YHN. Implications with respect to the simultaneous precipitation of more than one cation type are also discussed through use of example systems. The effects of solution chemistry, precipitator design, and solvent choice are considered.IntroductionThe application of precipitation technologies to the separation of metals from solution is widely used. Regardless of its application, be it in such diverse areas as the preparation of metal oxide powders for use in commercial products or as a unit operation in the removal of trace metals during wastewater clean up, the fundamental processes involved are the same. These processes include: nucleation from solution, either homogeneous or heterogeneous; growth from solution with chemical reaction either in solution or at the precipitate/solution interface; growth by particle agglomeration; and particle break-up by collisional or shear forces. The effectiveness of the operation and the properties of the precipitate formed, or ""quality"" of the product, are determined by the competing kinetics of the different processes. The kinetics of the processes, in tum, are determined by system-specific solution chemistries and the conditions used to carry out the precipitation operation. For example, generally, when system conditions are such that the supersaturation driving force for precipitation is very high, growth species normally do not have the time to organize themselves with a high degree of crystallographic order and the precipitate is amorphous. In this case nucleation rates are invariably extremely high and the primary mechanism for growth is the agglomeration of nuclei. Conversely, when the supersaturation levels for the same system are reduced, the kinetics of the nucleation and growth processes also are greatly reduced, and a crystalline precipitate can be formed, since the growth species have time to order on particle surfaces."

Jan 1, 1996

By James A. Voigt

The efficient separation of metal species from aqueous streams by precipitation techniques requires 'a fundamental understanding of the various processes that occur during precipitation. These processes include particle nucleation, particle growth by solute deposition, agglomerate formation, and agglomerate break-up. The application of the population balance approach has been used to develop a kinetic model that accounts for these competing kinetic processes. The usefulness of the model is illustrated through its application to the precipitation of yttrium hydroxynitrate, YHN. The kinetic parameters calculated from the model equations and system-specific solution chemistry are used to describe several aspects of the effect of pH on the precipitation of the YHN. Implications with respect to the simultaneous precipitation of more than one cation type are also discussed through use of example systems: The effects of solution chemistry, precipitator design, and solvent choice are considered.

Jan 1, 1996

By G. Van Weert

Refractory gold ores and auriferous concentrates containing silver tend to form refractory silver jarosites during pressure oxidation. Earlier work with pure Ag2S has shown that the addition of iodine species to the autoclave feed yields cyanide soluble iodargyrite (Agl) instead. Near complete silver extractions from the autoclave product were obtained at a I-/Ag+ ratio of 5 or more. This paper reports on the pressure oxidation and cyanide leaching of two industrial refractory (arseno) pyritic silver-bearing concentrates: 1. from Peru (sulphosalts) and 2. from the USA (pyrite, with acanthite occlusions). While using a I-/Ag+ mol ratio of only 1 in the feed, it has been possible to obtain 98 and 97% Ag extraction from the two autoclave products by cyanide leaching, respectively. This compares to 11 and 54% Ag extraction from the as-received concentrates and 4 and 15% Ag extraction, respectively, after pressure oxidation without KI present. The results of the testwork are discussed in terms of concentrate mineralogy and pressure oxidation conditions.

Jan 1, 1994

By Yasuhiro Konishi, Yoshiyuki Noda

"This paper describes a new processing of rare-earth oxide precursor, in which rare-earth carbonate powders are precipitated directly from emulsions of rare-earth loaded carboxylate solutions, using CO2 gas and water. This synthetic route of rare earth carbonate is a combined process of the stripping and precipitation stages in a conventional solvent extraction. Using this technique, lanthanum carbonate and yttrium carbonate were prepared at temperatures of 10 to 80°C and CO2 pressures of 0.1 to 3.0 MPa for 120 min. The rates of carbonate precipitation in a batch autoclave were sensitive to processing parameters such as CO2 pressure, temperature, and organic-phase composition. The particle size distributions of the carbonate powders were markedly dependent on temperature and C02 pressure.IntroductionSolvent extraction is the most appropriate commercial technology for separation and purification of rare earths. In typical commercial processes, the rare earths are stripped from loaded solvent extractants using aqueous solutions of mineral acid. After adjusting the pH of the aqueous strip solution, the rare earths are precipitated as insoluble powders of oxalates or carbonates, from which oxides can be produced by calcination. Such conventional processing can be simplified when the stripping and precipitation stages are combined by emulsifying rare-earth loaded solvent extractant with aqueous oxalic acid solution. It is likely that the single-stage precipitation stripping results in a marked decline in the consumed amounts of precipitating and neutralizing agents, thereby saving on both running and capital costs.Yoon and Doyle1) first demonstrated that oxalate powders of lanthanum and yttrium are directly precipitated from rare-earth loaded carboxylic acid solvent extractant when contacted with aqueous oxalic acid solution at ambient temperature and atmospheric pressure. Yttrium oxalate pow4ers were also prepared by precipitation stripping of di-(2 ethylhexyl) phosphoric acid. (D2EHPA) extractant using oxalic acid-hydrochloric acid solutions. 2) Moreover, neodymium oxalates were directly precipitated from organic solutions of tertiary aliphatic monocarboxylic acid and 2-ethylhexyl phosphonic acid mono-2- ethylhexyl ester using aqueous oxalic acid solutions, and powder characteristics of the resulting oxalates were compared with those of powders by the conventional solvent extraction routes. 3 • 4) Recently, attention has been directed towards the influence of processing parameters on the particle size distributions of yttrium oxalate precipitates. 5)"

Jan 1, 2000

The aquifer at Phosphate Hill, north-west Queensland, presents special management challenges. The site contains a phosphate rock mine, fertilizer plant and camp. All of the site water is provided by the Duchess Embayment Aquifer, located within the Burke River Outlier of the Georgina Basin. The Duchess Embayment is a triangular shaped, Cambrian marine sedimentary basin consisting of siliceous and calcareous phosphorites, shales, siltstones and sandstones. It is fault-bounded on all sides and has a regional dip of 5¦E. The aquifer is largely confined to the siliceous facies of the Beetle Creek Formation. It has a very flat potentiometric surface and an average thickness of 45 m with confining beds above and below. The siliceous facies derives from weathering of the calcareous phase and is highly transmissive while the calcareous zone itself contains less water and is dependent upon interconnecting fractures for its permeability. Recharge appears to occur where the siliceous facies crops out around the edges of, and within, the Embayment. Aquifer management issues revolve around two points: successful dewatering of the orebody for mining; and efficient management to maintain water quality and ensure supply over the predicted 30-year life of the project. Current operations are extracting water at levels much below that originally estimated. This is having a detrimental effect on mine dewatering with the SWL lowering at a rate slower than anticipated. As a result, ore parcels are now beginning to intersect the water table, providing a major constraint to the mining plan. The aquifer drawdown cone is extensive and very flat so to keep the water table at an appropriate level for mining the management plan will include more aggressive dewatering to lower the level of the entire aquifer. The additional water will either be disposed of downstream or stored in a holding dam or via the use of artificial storage and recharge. Water resource management will also need to maintain the current quality. About 37 per cent of the water currently extracted forms the low chloride supply required by the ammonia plant and the power station. This ratio is expected to remain applicable under any future operating conditions but the low chloride resource is restricted so will require prudent management to enable the supply to continue. At current usage rates aquifer recharge versus use will need careful monitoring to ensure that the resource remains viable in the long-term.

Jan 1, 2003

By Bruce D. Hulman, Robert .. F. Gorman

Introduction Groundwater resource evaluation has historically required extensive field investigative work, usually at great cost. More recently, the advent of the microcomputer has made difficult aquifer and groundwater evaluations comparatively simple and less expensive. A groundwater model is a numeric solution to a set of equations that calculates the water level in an aquifer or other types of water bearing strata. A computer will execute the solution of the set of equations rapidly and thereby permit evaluation of large amounts of hydrogeologic data rapidly. Computer modeling of groundwater resources is very often used to forecast the effects of multiple uses of a single groundwater resource. Modeling of heavily used aquifers has proven to be beneficial for averting problems arising from competitive use of a groundwater resource. This paper describes the work tasks performed in order to evaluate a large alluvial aquifer and thereby predict the hydrologic impact of additional groundwater withdrawal. Purpose and Scope Neyer, Tiseo & Hindo, Ltd. (NTH) was retained to evaluate the groundwater supply potential of the Missouri River alluvium underlying the Fairfax District in Kansas City, Kansas (Figure 1). The proposed groundwater supply is being considered for industrial use as non-contact process water and a heat exchange medium for plant climate control. The anticipated peak groundwater demand is estimated to exceed 30 million gallons per day (MGD) during the summer months, with an average daily demand of nearly 25 MGD. The proposed groundwater supply was to be developed from 15 large-diameter production wells located at positions that would minimize potential interference.

Jan 1, 1987

By Henri Letient, Tom Aley, David Evans

Antamina is a large open-pit copper and zinc mine located within the Central Andes of Northern Peru at an altitude of 4300 masl. The facilities are situated within the headwaters of several watersheds, within the Amazon basin. Nearby villages rely heavily on springs and streams for drinking and irrigation water. The principle source of baseflow during the dry season is from Cretaceous karstic limestone aquifers. Antamina will produce nearly 1.4 billion tonnes of waste rock over its mine life. Finding suitable sites for storing large volumes of waste rock is often a challenging task – especially in karstic, alpine terrain. Detailed hydrogeological investigations are essential for delineating the karstic hydrogeologic watersheds associated with the proposed waste facilities, which are often very different than topographic (hydrologic) watersheds. Contamination vulnerability mapping at Antamina consisted of geological and karst mapping, geophysical surveys, geochemical testing, dye-tracer studies, drilling and aquifer testing. Detailed mapping followed by dye-tracer studies proved to be the most cost-effective methods for characterizing the karst aquifer systems. The results were used to optimize waste rock management at the site to minimize potential impacts on groundwater resources.

Jan 1, 2005

By Alexander R. Troiano, Eugene P. Klier

SINCE the very early work on quenched structures, where the products of the martensite transformation had been recognized, this transformation has provoked much interest and study. Theoretically it was desirable to account for the extreme changes in physical properties resulting from the formation of martensite, as that information might lead to results of practical importance. Desirable information, therefore, was on the kinetics of transformation from austenite to martensite as well as on the physical constitution of the martensite. It has been known for years that certain steels quenched to room temperature will contain persistent austenite as well as martensite. Other important and now well- established features of the martensite reaction are the progress of the reaction on cooling only and the independence of Ar" with cooling velocities exceeding the critical velocity. These facts have been experimentally determined by various methods and investigators. Notable among the early investigators were Tammann and Scheill and Wever and Engel.2 Unfortunately, all investigators did not fully interpret their results, which, coupled with several investigations that yielded conficting results, caused a state of confusion that was not clarified until quite recently. X-ray investigations of martensite in steels3-6 indicate it to be a supersaturated solid solution of carbon in alpha iron. This supersaturation is evident from the appearance of a body-centered tetragonal structure with the addition of sufficient carbon. The dimensions of this tetragonal structure are alinear function of the carbon content within the limits of accuracy of the determinations. Slight tempering of tetragonal martensite leads to the destruction of the tetragonal structure, which is converted to a body-centered cubic structure. This phenomenon has precipitated a controversy concerning the nature and mechanism of the tempering of martensite. The facts in the case have been outlined by Epstein7 and more recently by Antia, Fletcher, and Cohen.8 The significance of Ar" on theoretical grounds is not clear, however, although considerable study has been devoted to its determination. The precise position of Ar" as a function of carbon content was first stated by Greninger and Troianos for steels covering a range of approximately 0.7 to 1.8 per cent carbon. The effect of alloying elements on Ar" has recently been the subject matter of investigation by various methods.

Jan 1, 1945

By C. Bailey Williams

Aragonite "sand," an oolitic lime-stone, is distributed throughout the Bahamas on the Grand Bahama Bank, adjacent to Southeast Florida. Bahamian deposits hold 75-100 billion tons of recoverable Aragonite. Aragonite's precipitation from seawater over 700 years ago assures low contaminates, making it a pure material for such industries as cement, glass, etc. A 90-acre, man-made production island was built south of Bimini, adjacent to ocean shipping channels mining is by cutterhead, suction dredge, dewatering, and stockpiling for further drainage and shipping. Aragonite is transferred to the U. S. East and Gulf Coasts via bulk carriers to points of sale.

Jan 1, 1978

By Ronald P. Wright

ARAMIDS UNDERGROUND COAL MINING

Jan 1, 1993

By Renzo Valdez

Si bien la minería formal es la actividad económica más importante en el Perú, sus proyectos son también los que más conflictos generan entre las compañías mineras y las comunidades campesinas. Este trabajo propone la obligatoriedad de regular el arbitraje de conciencia en los convenios comunitarios como mecanismo adecuado y alternativo de solución a esta clase de conflictos, de manera que se logre satisfacer a ambas partes y se permita el desarrollo de la actividad minera sin mayores pérdidas económicas.

Sep 20, 2019

By James Green

It has often been said that the best contracts written are by people who are suspicious of each other. The Spanish philosopher, Ortega y Gasset, said: "Every contract is an Act of Distrust." The arena for dispute settlement outside of the courts is increasing day by day - contracts, especially construction and civil engineering contracts, are written containing arbitration clauses for settling disputes - the very drafting of standard forms of contract, do in some instances by their very construction, create an ambiguity as to intent and provide a breeding ground for dispute. I come from a land far across the sea - the most southern land before the South Pole. Being a young country, 150 years old, we are still progressing - being far removed from the trouble free zones of the world and nuclear free we enjoy a lifestyle second to none.

Jan 1, 1987

By P. A. Tichauer

Arbitration is a flexible method for dispute resolution that gives control to the disputing parties while still maintaining a clear and well-structured decision making process. It responds to the desires of the parties for a resolution that is fair, binding and enforceable and is guided more by pragmatism, efficiency, effectiveness and equality than by a need to comply with the legal procedures and practices of any single country or jurisdiction. Arbitration is particularly well suited for the resolution of disputes pertaining to international commercial agreements which are often present in the metallurgical sector. This paper provides a simplified outline of the features and advantages of arbitration as well as commentary regarding certain prerequisites in order for arbitration to be binding and enforceable.

Jan 1, 2015

By Dominic T. Jordan, Quinn G. Reynolds, Christopher J. Hockaday, Ian J. Barker

A direct-current (DC) plasma arc furnace is a type of electric furnace used for metallurgical operations. The successful operation of DC furnaces depends to a large extent on gaining a fundamental understanding of the arc phenomenon itself, and ensuring its presence in the furnace at all times. A method for detection of the presence of the arc in a DC circuit is presented, along with discussion of why this may be of value for certain modes of furnace operation such as brush-arc. The theoretical development of the method is presented along with supporting experimental work conducted on large-scale pilot-plant facilities.

Jan 1, 2014

By C E. J de Ronde, I C. Wright

Oceanic subduction-related volcanic frontal arcs extend over 20 000 km within the western Pacific basin and over 21 500 km worldwide, yet they remain largely unexplored with respect to active seafloor mineralization. Systematic exploration of 26 major submarine volcanoes along ~840 km of the Kermadec arc northeast of New Zealand has documented ten (39 per cent) as being hydrothermally active. This frequency of venting is comparable to that on slow-to-moderate rate spreading mid-ocean ridges, which comprise ~80 per cent of the 60 000 km-long global system of spreading centers. The chemistry of fluids discharged from the Kermadec arc volcanoes is moderated by magmatic components in both the gaseous (CO2 + SO2-H2S) and liquid (Fe) phases at very high concentration.The high frequency of venting coupled with chemically rich discharge discovered during this first systematic survey of any arc system forecasts submarine arcs as being important sources of chemicals to the oceans and as potentially lucrative exploration sites for seafloor mineralization. The exploration protocols developed during these surveys include bathymetric mapping of mostly unknown volcanic edifices, followed by detailed water column profiling and sampling to detect and characterize volcanic fluid emission signatures. These procedures are being refined as the survey progresses, both for efficiency and as direct seafloor observations become available for predictive application of water column plume information to guide seafloor mineral exploration.

Jan 1, 2002

By Jeremy P. Richards

Key inputs are volatiles and heat: Slab dehydration: Breakdown of amphibole and serpentine in hydrated oceanic crust releases fluids into mantle wedge, causing metasomatism.

May 1, 2008

ABSTRACT' Mainland Papua New Guinea is formed of a microcontinental / island arc system (?Eocene - latest Oligocene Sepic arc) which in Middle to Late Miocene times was obducted over the northward- moving Australian plate. The sedimentary and volcanic units of this system form part of the Wogamush Group (Aure beds, Mena beds, Omaura Formation, Movi beds, Wogamush beds, Wogamush Formation. Nansananka Conglomerate and other correlates in- eluding cale-alkaline volcanics and carbonate beds). This Sepic event was followed in Pliocene-Present times by the obduction of the Finisterre-Adelbert-Oenake fore-arc or possibly oceanic plateau. Obduction of the Sepic arc produced crustal thickening

Jan 1, 1997

By George E. Cook, Peter C. Levick, Francis M. Wells

"Relationships are established between the peak current of a pulsed, rectangular current waveform and the pulse current duty cycle under conditions of constant arc power. By appropriate choice of these interrelated parameters, it is shown that the arc pressure may be varied over a wide range even though the arc power is held constant. The methodology is suggested as a means of countering the effect of gravity in 5-G welding, while maintaining constant heat input to the weld. Combined with appropriate penetration sensors, the methodology is additionally suggested as a means of controlling penetration. IntroductionBoth low frequency pulsation (typically 0.1 - 20 Hz) and high frequency pulsation (> 100 Hz) are often used with GTA welding. Benefits derived from pulsing include improved weld quality and better process control.Advantages cited for low frequency pulsation include claims that the total heat input to the weld is reduced, the weld bead size is reduced, weld penetration is increased, grain size is reduced, porosity is reduced, weld distortion is reduced, thinner materials can be welded successfully, and the tolerance of the welding process to material and production variations is improved (1-16). With respect to the latter, pulsing aids control of weld bead penetration by increasing the tolerance to component dimensions and joint fit-up. It also reduces the sensitivity to disparities in heat sink, and it helps to reduce distortion in thin section material or distortion attributable to poor clamping. In certain materials it can reduce the sensitivity to surface oxides and to cast to cast compositional variations (16). Low frequency pulsation is also useful in welding thick materials mated by a prepared groove. In these applications the low frequency pulsation is used to obtain proper sidewall fusion as the tungsten electrode is weaved from one side of the groove to the other. In this case the weld current pulsation is synchronized with the cross seam weave pattern, such that the high current pulses occur at each sidewall. This type of low frequency pulsation has proven particularly useful in welding with narrow width groove designs (17-21). Finally, Ecer (22) has shown that the pulsed current arc is more stable against magnetic disturbances than an equivalent constant current arc."

Jan 1, 1986

Over the past seven years, a combination of New Zealand-, Australian- and German-led research voyages using the research vessels Tangaroa, Southern Surveyor, and Sonne respectively, have revolutionised our understanding of the Kermadec-Tonga arc-backarc systems. This convergent margin is the most seismically-active subduction zone system on Earth with convergence rates steadily increasing northwards from the Hikurangi Trench to ~250 mm/year at northern Tonga. In combination with the intra-oceanic setting, factors potentially producing magmatic, tectonic, and hydrothermal variability in this system include an increase in potentially subductable sediment northwards along-strike, intersection of the Louisville Ridge (hot-spot chain) and Osbourn Trough (paleo-spreading centre) with the arc at ~25¦S, and the possibility of Samoan (hot-spot) plume ingression in the northern Lau Basin. The bulk of the magmatism is submarine; whereas only a few emergent (some transient) volcanic islands exist, about 80 submarine volcanic centres of significant size (>1000 m above surrounding sea floor) are present between White Island in the south to north of Tafahi in Tonga. About 35 per cent of these centres are hydrothermally active. Important petrogenetic features of the volcanic rocks along this arc system are the abundance of rhyolite (some quartz-amphibole-bearing), and the outcrop of primitive olivine-clinopyroxene-phyric basalts in satellite cones of the major edifices. Many of the edifices consist of complex caldera systems. Eruptions from and degradation of these edifices were probably tsunamigenic. Many of the hydrothermal systems developed within the edifices are likely destroyed during the sector collapses which are the characteristic edifice degradation mode. There are three backarc spreading systems along this margin: the Havre Trough, Valu Fa-Eastern Lau Spreading Centre, and the nascent Fonualei Rifts. The latter are particularly notable in having captured the entire suprasubduction zone magmatic flux for a distance of about 150 km, shutting down the adjacent volcanic front arc volcanoes.

Jan 1, 2005

The Banda arc, a U-shaped orogenic belt which separates oceanic crust of the Banda Sea from continental crust underlying the Australian- New Guinea shelf, has been interpreted to mark the convergent boundary between the northward-moving Indian Ocean- Australian plate and the Southeast Asian plate (Hamilton, 1979; von der Borch, 1979; Bowin et al., 1980). East of the island of Sumba (Fig. 1), the oceanic crust of the Indian Ocean has been completely subducted and Australian crust is now thrust under the Banda arc. Controversy has centered over the interpretation of the Timor trough as the surface location of subduction and the significance of the Savu Sea between Timor and Flores as either a forearc basin or the continuation of the Java trench (Karig et al., 1987). Two concentric island ridges, called the inner and outer Banda arcs (Hamilton, 1979), separate Australian continental crust from the oceanic crust of the Banda Sea (von der Borch, 1979) (Fig. 1). The inner arc is a typical volcanic island arc composed of calc-alkalic volcanic rocks of Neogene age, while older (Permian and younger) complexly deformed sedimentary and metamorphic rocks make up the outer arc. Timor is the largest and most extensively studied island of the outer arc and is separated from the inner arc by the Savu Sea. The triangular-shaped Savu Sea appears to be a complex forearc basin divided by a series of buried basement ridges (Karig et al., 1987). The outer, convex side of the Banda arc is followed by a major negative bathymetric feature known ne rho Timor trnnnh

Jan 1, 1987