As the price of silver nitrate increases and chemistry department budgets tighten, the recovery of silver from silver residues of analytical laboratory experiments becomes a necessity rather than a luxury. Although many methods have been proposed, most are complex2 and/or are limited by the anions present in the residue.3 ***7The following recovery procedure was selected, after many experiments, as the most efficient and profitable method. It is based upon the traditional ore refining method of forming the impurities into alow melting slag.Silver residue (a mixture of AgCl, Ag2(CN)2, AgSCN, Agl, AgBr, and Ag2CrOi) was dried in an oven at 110°C until it lost its moist appearance. The oven employed here and the furnace used later in the procedure were hooded because of the toxic reaction products formed from the chloride, thiocyanate, and cyanide ions present in the precipitate. This safety precaution is strongly recommended. If the residue is not predried, the mixture sputters when placed in the furnace. The dried residue was intimately mixed with an equivalent amount of potassium carbonate assuming the residue consists entirely of AgCl. Potassium carbonate, rather than sodium carbonate, was chosen because it forms a slag with a lower melting point. It was determined that the more intimate mixtures of K2C03 and residue gave higher yields. When the ingredients were ground in a ball mill for two hours, we obtained 95% recovery from a silver chloride sample, whereas a casual strirring of the ingredients resulted in only a 60-70% yield.The mixture was placed in a clay crucible and baked in a furnace at 1000°C. At this temperature the reduced silver melts, forming a puddle at the bottom of the crucible. When the reaction is carried out at lowrer temperatures, a sponge-like silver is obtained that has impurities trapped in its porous structure. The crucible is filled no more than three-fourths full as some foaming occurs.The furnace floor was protected by a sheet of asbestors which had been preheated at 1000°C for 2 hr to remove combustibles. The furnace was hooded because COCl2 is formed. The reaction wras considered complete when the temperature had returned to 1000°C.
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