Recovery of silver residues from dental amalgam.
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.
Pereira
Heloísa Aparecida Barbosa da Silva
HA
Department of Biological Sciences, Bauru School of Dentistry, University of São Paulo, Bauru, SP, Brazil.
Iano
Flávia Godoy
FG
da Silva
Thelma Lopes
TL
de Oliveira
Rodrigo Cardoso
RC
de Menezes
Manoel Lima
ML
Buzalaf
Marília Afonso Rabelo
MA
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
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