title: Recovery of silver residues from dental amalgam.
abstract: Dental amalgam residues are probably the most important chemical residues generated from clinical dental practice because of the presence of heavy metals among its constituents, mainly mercury and silver.
  
  
  OBJECTIVE
  The purpose of this study was to develop an alternative method for the recovery of silver residues from dental amalgam.
  
  
  METHODS
  The residue generated after vacuum distillation of dental amalgam for the separation of mercury was initially diluted with 32.5% HNO3, followed by precipitation with 20% NaCl. Sequentially, under constant heating and agitation with NaOH and sucrose, the sample was reduced to metallic silver. However, the processing time was too long, which turned this procedure not viable. In another sequence of experiments, the dilution was accomplished with concentrated HNO3 at 90 degrees C, followed by precipitation with 20% NaCl. After washing, the pellet was diluted with concentrated NH4OH, water and more NaCl in order to facilitate the reaction with the reducer.
  
  
  RESULTS
  Ascorbic acid was efficiently used as reducer, allowing a fast reduction, thus making the procedure viable.
  
  
  CONCLUSIONS
  The proposed methodology is of easy application and does not require sophisticated equipment or expensive reagents.
authors.affiliation: Department of Biological Sciences, Bauru School of Dentistry, University of São Paulo, Bauru, SP, Brazil.
authors.forename: Heloísa Aparecida Barbosa da Silva
authors.initials: HA
authors.lastname: Pereira
authors.forename: Flávia Godoy
authors.initials: FG
authors.lastname: Iano
authors.forename: Thelma Lopes
authors.initials: TL
authors.lastname: da Silva
authors.forename: Rodrigo Cardoso
authors.initials: RC
authors.lastname: de Oliveira
authors.forename: Manoel Lima
authors.initials: ML
authors.lastname: de Menezes
authors.forename: Marília Afonso Rabelo
authors.initials: MA
authors.lastname: Buzalaf
mesh_terms: D001205:Ascorbic Acid / Q000737:chemistry; D003723:Dental Amalgam / Q000737:chemistry*; D018057:Dental Waste; D052918:Environmental Restoration and Remediation / Q000379:methods*; D005590:Fractional Precipitation / Q000379:methods; D017744:Medical Waste Disposal; D017942:Nitric Acid / Q000737:chemistry; D019163:Reducing Agents / Q000737:chemistry; D012834:Silver / Q000302:isolation & purification*; D012965:Sodium Chloride / Q000737:chemistry; D012972:Sodium Hydroxide / Q000737:chemistry; D013395:Sucrose / Q000737:chemistry
chemical_list: D018057:Dental Waste; D017744:Medical Waste Disposal; D019163:Reducing Agents; D012834:Silver; D017942:Nitric Acid; D012965:Sodium Chloride; D012972:Sodium Hydroxide; D013395:Sucrose; D003723:Dental Amalgam; D001205:Ascorbic Acid