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Heavy Metals/Cyanide Treatment
Published in Paul N. Cheremisinoff, Handbook of Water and Wastewater Treatment Technology, 2019
Some typical cyanide wastes include Cyanide-bearing plating solutions and sludges (some treated sludges may be reprocessed to recovery metals; sludges of no value may require subsequent treatment by the encapsulation process)Sodium cyanidePotassium cyanideCalcium cyanideBarium cyanide (the treated waste requires subsequent treatment by the sulfate precipitation process)Hydrogen cyanide (in aqueous solution)Nickel cyanidePotassium silver cyanide (sludges generated may be reprocessed to recover silver)Silver cyanide (sludges generated may be reprocessed for silver recovery)Miscellaneous cyanides
Microcircuitry and Remote Monitoring
Published in Martha J. Boss, Dennis W. Day, Air Sampling and Industrial Hygiene Engineering, 2020
However, the presence of silver cyanide presents an additional concern. The silver cyanide complex when oxidized can precipitate as Silver chloride (a white precipitate)Silver oxide (a black precipitate) Silver oxide is preferred; it is denser than silver chloride with the result that its removal from the wastewater is easier. Higher oxidizing conditions favor the oxide formation; lower oxidizing conditions favor the chloride formation.
Metal Recovery Processes
Published in C. K. Gupta, T. K. Mukherjee, Hydrometallurgy in Extraction Processes, 2017
When the metal zinc is brought into contact with gold or silver cyanide solution, one encounters four important occurrences, namely dissolution of zinc, precipitation of gold/silver, evolution of hydrogen, and consequent increase of alkalinity of the solution. These effects can be well explained based on the following reactions that take place during cementation: () K Au(CN)2+2KCN+Zn+H2O→K2Zn(CN)4+Au+H+KOH () Zn+4KCN+2H2O→K2Zn(CN)4+2KOH+H2
Pyrimidine derivative-based cyanide-free silver electroplating bath
Published in Transactions of the IMF, 2022
Atiqah Binti Jasni, Sachio Yoshihara, Fumio Aiki, Hideki Watanabe
Silver nitrate, AgNO3 (99.8%) and potassium cyanide, KCN (95.0%) were purchased from FUJIFILM Wako Pure Chemical Corporation. 5,5-dimethylhydantoin (> 98.0%) was acquired from X.T.Y ENVIRON-TECH Co., Ltd.. Uracil (>97.0%) was obtained from Kanto Chemical Co., Inc.. Thymine (>98.0%) from Tokyo Chemical Industry Co., Ltd., potassium hydroxide, KOH (95.5%) from Nippon Soda Co., Ltd., nitric acid, HNO3(67.5%) from Saitama Yakuhin Co., Ltd., and silver cyanide (>99.0%) was obtained from Tanaka Precious Metal Corporation. The average molecular weights of the polyethyleneimine (PEI) (branched polymer, FUJIFILM Wako Pure Chemical Corporation) used in the experiments were 600, 1800 and 10,000, and these were denoted as PEI-600, PEI-1800 and PEI-10000, respectively. All chemicals were used as received. Aqueous solutions were prepared with deionised water.
Application of resins with functional groups in the separation of metal ions/species – a review
Published in Mineral Processing and Extractive Metallurgy Review, 2018
Rene A. Silva, Kelly Hawboldt, Yahui Zhang
In alkaline cyanide solutions, quaternary ammonium groups favor the sorption of Au as aurocyanide (i.e., Au(CN)2−) and Ag as silver cyanide (i.e., Ag(CN)2−) species and other base metals cyanides species such as Cu(CN)32−, Zn(CN)42−, Ni(CN)42−, Co(CN)53−, and Fe(CN)64 – (Kotze et al. 2005). The high strength of quaternary ammonium groups reduces the selectivity over target ion species in multi-ionic solutions; hence, quaternary ammonium resins are inconvenient for the purification of metal solutions (Fedyukevich and Vorob’ev-Desyatovskii 2016; X Dai et al. 2010). In multi-ionic solutions, high-value metal species (e.g., Au(CN)2− and Ag(CN)2−) compete with base metals for the finite number of deposition sites in the resin. Instead, resins containing quaternary ammonium groups are recommended for purification of liquid media. In particular cases, quaternary ammonium resins’ selectivity on anions can be achieved depending on the geometrical configuration of the target species. The geometrical configuration of quaternary ammonium groups allows for preferable adsorption of metal complexes with linear geometry over other configurations such as trigonal planar and tetrahedral alignments (Kotze et al. 2005). However, this enhancement in selectivity by geometrical configuration is minor and not significant with respect to the degree of selectivity required by resins in industrial processes.
Towards industrial implementation of glycine-based leach and adsorption technologies for gold-copper ores
Published in Canadian Metallurgical Quarterly, 2018
J. J. Eksteen, E. A. Oraby, B. C. Tanda, P. J. Tauetsile, G. A. Bezuidenhout, T. Newton, F. Trask, I. Bryan
Glycine (NH2–CH2–COOH) is a stable amino acid that has various aqueous ionic forms, i.e. the cationic glycinium ion (NH3–CH2–COOH+) in acidic solutions, the neutral zwitterion (NH3+–CH2–COO−), and the anionic glycinate (NH2–CH2–COO−) ion in alkaline solutions, demarcated by two pKa values at 2.34 and 9.6. While glycine can be decomposed by some micro-organisms or destroyed by strong oxidants, it is stable in the water stability band in the pH–Eh diagram at alkaline pH in the anionic glycinate form. Glycine has a high solubility in water of around 250 g L−1 at 25°C, a density of 1.607 kg t−1, molar mass of 75.07 g mol−1 and a melting point of 233°C (with decomposition). It therefore has a much higher stability (as glycinate anion) than the cyanide or thiosulphate anions. It shows a low but measurable pH-dependent adsorption on clays (montmorillonite specifically) as indicated by Ramos and Huertas [3]. One should compare this to gold and silver cyanide complex preg-robbing on clays [4]. It forms moderately strong complexes with most chalcophile base metals and precious metals under appropriate pH, temperature and redox conditions.