Precious metal extraction

Used industrially for electroplating, precious metal extraction and in the synthesis of dyes, pigments, pharmaceuticals, and pesticides. 

Elemental mercury is used industrially in electric lamps and switches, gauges and controls (e.g. thermometers, barometers, thermostats), battery production, nuclear weapons production, and the specialty chemical industry, including the production of caustic soda. Because elemental mercury has a high affinity for gold and silver, it has been, and continues to be, used in precious metal extraction from ore. Elemental mercury has been used for over one hundred years in mercury-silver amalgam preparations to repair dental caries. Mercury continues to be used in folk remedies and in certain cultural practices, with unknown public health implications. 

The static cylindrical geometry offers a convenient cathode design for small scale operations and has primarily been used for precious metal extraction. Mass transport may be enhanced by the use of tangential manifolds emd the use of a reasonable flow rate. 

Simpler fluorinated 3,5-di(trifluoromethyl) phenyl thiourea derivatives, however, displayed higher solubilities in SC-CO2, at lower operating pressure and proved to be more effective ligands for the extraction of Au. Further studies on the optimisation of ligand design and on the applications of these reagents for precious metal extraction in SC-CO2 in progress. 

Elpatievsky, P.V Lutsenko, T.N. 2000. Mining complex as a factor in the formation of the chemical composition of water. Scientific and practical aspects of non-ferrous and precious metals extraction 2 407-415. Khabarovsk Abstracts of Papers. Intern, conf. 

Sulfur donor extractants are less common, althongh dialkylsulfides have been used in precious metal extraction, and a trialkylphosphine sulfide, R3PS (Cyanex 471X, Cytec Inc., New Jersey), is available commercially. Such sulfur donating extractants will need to be considered when extracting and separating soft metals, such as second- and third-row transition metals (e.g., cadminm, mercury, and palladium). 

Columns are useful for processing low flow rates and for systems that exhibit a tendency to form emulsions. An important benefit of a column contactor is the large number of possible theoretical stages and the ability to operate closer to the operating line rather than the equilibrium curve, thereby maximising mass-transfer kinetics. The settling volume is considerably lower than for the corresponding mixer-settler, so columns are preferred for systems in which solution lock-up and low solvent inventories are important (such as in precious metal extraction systems). Columns take up very little floor space, but require considerable headroom mixer-settler requirements are the opposite (Movsowitz et al. 2001 Fox et al. 1998). 

Other Metals. Because of the large number of chemical extractants available, virtually any metal can be extracted from its aqueous solution. In many cases extraction has been developed to form part of a viable process (275). A review of more recent developments in metal extraction including those for precious metals and rare earths is also available (262). In China a complex extraction process employing a cascade of 600 mixer—settlers has been developed to treat leach Hquor containing a mixture of rare earths (131). 

The concentration of most metals in the earth s cmst is very low, and even for abundant elements such as aluminum and iron, extraction from common rock is not economically feasible. An ore is a metallic deposit from which the metal can be economically extracted. The amount of valuable metal in the ore is the tenor, or ore grade, usually given as the wt % of metal or oxide. Eor precious metals, the tenor is given in grams per metric ton or troy ounces per avoirdupois short ton (2000 pounds). The tenor and the type of metallic compounds are the main characteristics of an ore. The economic feasibihty of ore processing, however, depends also on the nature, location, and size of the deposit the availabihty and cost of a suitable extraction process and the market price of the metal. 

The raw precious metal concentrate is totally dissolved in hydrochloric acid—chlorine solution to form the soluble chloride ions of each of the metals. Silver remains as insoluble silver chloride and can be filtered off. Gold, in the form of [AuClJ, is extracted with, eg, tributyl phosphite or methyl isobutyl ketone. Base metals are also extracted in this step, and are removed from the organic phase by scmbbing with dilute hydrochloric acid (HCl). Iron powder is then used to reduce the gold species and recover them from the organic phase. 

J. E. Hoffmann, "Recovery of Selenium from Electrolytic Copper Refinery Slimes," in V. Kudryk, D. A. Corrigan, and W. W. Liang, eds.. Precious Metals Mining Extraction and Processing H, TMS, Warrendale, Pa., 1983. 

Reclamation, Disposal, and Toxicity. Removal of poisons and inorganic deposits from used catalysts is typically difficult and usually uneconomical. Thus some catalysts are used without regeneration, although they may be processed to reclaim expensive metal components. Used precious metal catalysts, including automobile exhaust conversion catalysts, are treated (often by the suppHers) to extract the metals, and recovery efficiencies are high. Some spent hydroprocessing catalysts may be used as sources of molybdenum and other valuable metals. 

Uses. The extraction or cyanidation of precious metal ores was the first, and is stiU the largest, use for black cyanide (71). The leaching action of the cyanide results from the formation of soluble cyanide complexes. 

The use of mercury for extracting precious metals by amalgamation has a long history and was extensively used by Spain in the sixteenth century when her fleet carried mercury from Almaden to Mexico and returned with silver. However, environmental concerns have resulted in falling demand and excess production capacity. It is still used in the extraction of gold and in the Castner-Kellner process for manufacturing chlorine and NaOH (p. 72), and a further major use is in the manufacture of batteries. It is also used in street lamps and AC rectifiers, while its small-scale use in thermometers, barometers and gauges of different kinds, are familiar in many laboratories. 

Plants handling aqua regia Aqua regia is used extensively in the extraction and refining of the precious metals, and tantalum, as one of the few metals resistant to this medium, is used for dissolution/evaporation pans, reactor lids and all immersed ancillary equipment. 

The use of mercury for extracting silver and gold from their ores has been known for many centuries. Gold and silver form amalgams with liquid mercury, which is then distilled away to leave the pure precious metal. The... 

Nathaniel Arbiter and Kenneth N. Han, eds., Gold- Advances in Precious Metals Recovery, Mineral Processing and Extractive Metallurgy Review, vol. 6,1990. 

The slime is recovered and heated in a brick-lined tank to melt the sulfur. The molten sulfur is filtered in a heated stainless-steel pressure filter to separate remaining nickel sulfide pieces and insoluble precious metals, and cast into moulds. The residue is remelted and cast into anodes, the resulting anode slime is now a relatively concentrated precious metal residue and is treated for the extraction of individual metals. 

Yordanov, A. T. Roundhill, D. M. Solution extraction of transition and post-transition heavy and precious metals by chelate and macrocyclic ligands. Coord. Chem. Rev. 1998, 170, 93-124. 

Rimmer, B. F. Refining of gold from precious metal concentrates by liquid-liquid extraction. Chemistry Industry... 

Ohto, K. Nagata, J. Honda, S. Yoshizuka, K. Inoue, K. Baba, Y. Solvent extraction of precious metals with an organoaminophosphonate. Solvent Extr. Ion Exch. 1997, 15, 115-130. 

The first example of luminescence emission from solids, of which written documents exist, date from the Italian Renaissance, originating from the accidental discovery around the year 1600 (1602 or 1603) by a Bolonian shoemaker and alchemist, called Vincencio Casciarolo or Casciarolus. He melted heavy bricks, close to his house, hoping to extract precious metals from them. 

Hybinette A process for extracting nickel from sulfide ores. The nickel ore that occurs in Canada is a mixture of the sulfides of nickel, copper, and iron. Several methods have been used to separate these metals. In the Hybinette process, the ore is first smelted in a blast furnace, yielding a nickel-copper matte (i.e., a mixture of their lower sulfides). This is roasted to remove sulfur and leached with dilute sulfuric acid to remove copper. The resulting crude nickel oxide is used as the anode of an electrochemical cell. The nickel deposits on the cathode, which is contained in a cloth bag. Precious metals collect in the anode slime. The process was invented by N. V Hybinette in 1904 and operated at the Kristiansand refinery, Norway, from 1910. 

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