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Umeda H.,Akita University | Umeda H.,Yokohama Metal Co. | Sasaki A.,Yokohama Metal Co. | Takahashi K.,Yokohama Metal Co. | And 2 more authors.
Kagaku Kogaku Ronbunshu | Year: 2010

The strongly acidic wastewaters generated in the process of refining and recycling of precious metals are generally treated by hydrometallurgical routes. For example, wastewaters containing precious metals such as gold, platinum, palladium and silver at concentrations of around 10 mg/L, and other metals such as copper and iron at concentrations ranging from several mg/L to more than 10,000 mgg/L, are usually treated by neutralization. However, wastewaters containing a large amount of ammonium ion (NH 4 +) cannot be treated by general methods of neutralization due to the formation of metal-ammine complexes with increasing pH. The objective of this work is to recover trace precious metals in strongly acidic wastewater containing a large amount of ammonium ions. When wastewater was neutralized at pH 6, the majority of metals such as copper, lead and iron were precipitated, while precious metals were not precipitated. After neutralization, precious metals remaining in the filtrate were precipitated by NaBH 4 reduction at pH 7.5. In the case of platinum in particular, the reduction was improved by deammoniation with sodium hydroxide. Precious metals were concentrated in copper-metal by combining neutralization, deammoniation, reduction and fusion. Recoveries of gold, silver, and palladium were more than 91%, whereas that of platinum was about 71%. © 2010 The Society of Chemical Engineers, Japan. Source

Haga K.,Akita University | Tongamp W.,Akita University | Takasaki Y.,Akita University | Shibayama A.,Akita University | And 3 more authors.
International Journal of the Society of Material Engineering for Resources | Year: 2010

Effluent waters from metallurgical refining process are usually treated by hydrometallurgical processes incorporating leaching, cementation, electrowinning, precipitation to extract and recover precious and base metals from municipal solid wastes. In the current study, we focused on the possibility of recovering previous metals namely; (Cu, Au, In, Pd, Pt) from the effluent water by cementation and solvent extraction steps. Fe, Al, and Zn powders were used for precious metal cementation, and LIX-84I, D2EHPA, and TBP as organic extractants with kerosene were used in solvent extraction. 99% of Cu, 96% of Pd, 85% of Au were recovered by Fe powder at (Fe/Cu) mole ratio of 2, and 99.6% of Cu, 99.5% of Pd were recovered by Al powder at (Al/ Cu) mole ratio of 2. Also 85% of In and 90% of Au were recovered by solvent extraction using D2EHPA and TBP, respectively. © 2010 Soc. Mater. Eng. Resour. Source

Umeda H.,Akita University | Umeda H.,Yokohama Metal Co. | Sasaki A.,Yokohama Metal Co. | Takahashi K.,Yokohama Metal Co. | And 3 more authors.
Materials Transactions | Year: 2011

Generally, trace precious metals remaining in wastewaters generated from the refining process of precious metals are not recovered, due to a relatively high processing cost as well as various technical problems. Recovery of precious metals from wastewaters is very important for the conservation of resources and the protection of environment. However, wastewaters containing a large amount of ammonium ion (NH4 +) cannot be treated by general neutralization operation, due to formation of metal ammine complexes with increasing pH. In this study, the possibility of recovering precious metals and other valuable metals from wastewaters by various traditional metallurgical processes such as cementation, neutralization and reduction, were investigated. A recovery of 99% Copper (Cu), 96% Palladium (Pd), and 85% Gold (Au) by cementation using Iron (Fe) powder, and 99.6% Cu, 99.5% Pd by cementation using Aluminum (Al) powder was achieved. However, complete recovery of all valuable metals by a one-step cementation process was not possible. On the other hand, precious metals and other valuable metals including Copper and Indium, etc., were precipitated by combining neutralization, deammoniation and reduction processes. Results showed that the recovery of Platinum (Pt) in the reduction process was improved by adding deammoniation step. Finally, precious metals are concentrated in the crude copper metal by fusion process. The recovery of Au, Ag, Pd was more than 91%, and that of Pt was about 71%. © 2011 The Japan Institute of Metals. Source

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