Procedure for recovering elemental silver from silver residues

Abstract

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.

Recovery of Silver Nitrate from Silver Chloride Waste

“…Several methods to recycle AgCl into Ag or AgNO 3 have been proposed in the literature, but many are lengthy or require specialized equipment. These methods include conversion by ion exchange, the use of small amounts of AgCl on the order of milligrams, , electrodeposition with cyanide salts, use of extreme temperatures, − forming potentially explosive ammoniacal solutions of silver, − and forming additional environmentally toxic waste byproducts. − However, two promising methods were identified that use only commonly available equipment and materials, have a simple procedure, and are relatively safe. These methods are most likely to achieve the ultimate goal of alleviating financial and environmental burdens.…”

A Study To Reduce Chemical Waste Generated in Chemistry Teaching Laboratories

“…The title of the analytical chemistry experiment is “Equivalency Testing of Potentiometric Titration vs. Indicator Titration for the Determination of Silver Ion Concentration.” The potentiometric titrations produce AgCl, while the indicator titrations produce AgSCN. Steed and Hayes demonstrate the recovery of elemental silver from AgCl and AgSCN residues by mixing the dried residues with an equal amount of potassium carbonate. The mixture is then ground using a ball mill for 2 h, before being baked in a clay crucible in a furnace at 1000 °C.…”

Recovery of silver and cobalt from laboratory wastes

“…A variety of procedures for recovering silver from silver halide residues have been reported; however, these methods usually suffer from serious drawbacks, limiting their general application. The use of high temperature reactions (500-1000°C) (2,3) or hazardous materials (cyanides, silverammonia solutions) (4, 5) is undesirable. The following method is based on previous procedures (6,7) in which common, inexpensive laboratory reagents are utilized.…”