Silver recovery efficiency

In comparison with the silver recovery/removal efficiencies of the chemical recovery cartridge (CRC) method, the hydroxide precipitation method, and the sulfide precipitation method shown in Table 6, the two precipitation methods appeared to be a better choice than the CRC method. 

Tsunogai and Nozaki [6] analysed Pacific Oceans surface water by consecutive coprecipitations of polonium with calcium carbonate and bismuth oxychloride after addition of lead and bismuth carriers to acidified seawater samples. After concentration, polonium was spontaneously deposited onto silver planchets. Quantitative recoveries of polonium were assumed at the extraction steps and plating step. Shannon et al. [7], who analysed surface water from the Atlantic Ocean near the tip of South Africa, extracted polonium from acidified samples as the ammonium pyrrolidine dithiocarbamate complex into methyl isobutyl ketone. They also autoplated polonium onto silver counting disks. An average efficiency of 92% was assigned to their procedure after calibration with 210Po-210Pb tracer experiments. 

The jarosite process separates icon(III) from zinc in acid solution by precipitation of MFe2(0H)g(S0 2 where M is an alkali metal (usuaUy sodium) or ammonium (see Fig. 2) (40,41). Other monovalent and hydronium ions also form jarosites which are found in the precipitate to some degree. Properly seeded, the relatively coarse jarosite can be separated from the zinc-bearing solution efficiently. The reaction is usuaUy carried out at 95 0 by adding ammonia or sodium hydroxide after the pH has been adjusted with calcine and the iron oxidized. The neutral leach residue is leached in hot acid (spent + makeup) with final acidity >20 g/L and essentiaUy aU the zinc, including ferrite, is solubilized. Ammonium jarosite is then precipitated in the presence of the residue or after separating it. If the residue contains appreciable lead or silver, they are first separated to avoid loss to the jarosite waste solids. Minimum use of calcine in jarosite neutralization is required for TnaxiTniiTn recovery of lead and silver as weU as zinc and other metals. 

The present procedure evolved from our previous work on the conversion of allenals, allenones, and allenylcarbinols to furans and 2,5-dihydrofurans with catalytic silver nitrate (AgN03) in acetone.5-10 It has also been shown that allenylcarbinols can be converted to 2,5-dihydrofuran under these conditions.11 0- and y-Alkynyl allylic alcohols can also be isomerized to furans under strongly basic conditions with potassium tert-butoxide in tetrahydrofuran-tert-butyl alcohol-18-crown-6 or hexamethylphosphoramide (KO-t-Bu in THF-t-BuOH-18-crown-6 or HMPA).12 The AgNOa/silica gel method is milder, faster, and more efficient than the previously reported procedures.13 Moreover, it offers the potential advantage of catalyst recovery and possible applicability to a flow system in which a packed column, protected from light, could serve as the reactor.4... 

R.M. Izatt, D.W. McBride, Jr., P.R. Brown, J.D. Lamb and J.J. Christensen, The influence of halocarbon solvent on macrocycle-mediated cation transport through liquid membranes, J. Membr. Sci., 1986, 28, 69 H. Parham and M. Shamsipur, Highly selective and efficient transport of mercury as Hg(N02)42 ion using Ba2+-18-crown-6 as carrier, ibid., 1994, 86, 29 A. El. Bachiri, A. Hagege and M. Burgard, Recovery of silver nitrate by transport across a liquid membrane containing dicyclohexano 18 crown 6 as a carrier, ibid., 1996, 121, 159. 

There are also cyanide baths that are used for the recovery of silver and gold. These baths contain cyanide anions and other salt anions, and several cations that are used for the efficient and more effective recovery of these precious metals and for electroplating purposes. 

The smelter primarily makes a return from the treatment charge, plus any free metals derived from recoveries achieved for lead and precious metals above the recoveries implied in the terms. For instance it may be possible to achieve 98 per cent lead recovery, giving three per cent free metal. Silver and gold recoveries may also significantly exceed the terms values, depending on process efficiencies. 

Silver normally reports to lead bullion during smelting but will also report to any matte formed. It is the most valuable by-product metal contained in primary lead bullion and efficient recovery is of key importance. 

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