Silver recovery from dental amalgam wastes

Abstract

Alloys made with mercury and other metals are known as amalgam. Dental amalgams are important alloys having mercury (Hg≈40-50%) as a main component and include silver (≈22-39%), tin (≈12-18%) and copper (≈2-18%). Considering the content of dental amalgams, due to the combination of silver, tin and copper in the structure, they have high economic value.1,2 The mixing of silver and other elements and mercury is known as amalgamation. During this process, metallic powders are dissolved in the mercury along the surfaces, and this process leads to the formation of new phases in the structure. These new solid phases result in the plastic state of amalgam. At the end of amalgamation, resulting phases are rigid. The metallurgical phases that are occurred as a result of these reactions are shown in detail in Table 1.3 The metallurgical properties belonging to these phases are complex and the final phase varies according to the content of the starting alloy. In case of Ag-Sn alloy containing copper below 4%, amalgam become harder and stronger but more brittle. In contrast, if the alloy contains copper about 4-5%, separate Cu3Sn phases form in the structure. These phases increase the workability of amalgam and decrease the fragility.3 Basic reactions which occur during amalgamation are as follows: