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Heavy Metals
Published in Abhik Gupta, Heavy Metal and Metalloid Contamination of Surface and Underground Water, 2020
Silver (Ag), a precious metal, has an atomic number of 47, an atomic weight of 107.868, and a density of 10.50 g cm–3. Many lead, zinc, and copper ores are argentiferous, that is, these contain argentite or silver sulfide (Ag2S). Silver is extracted as a by-product from the mining of these three metals. However, being a precious metal, even small amounts of silver fetch a lucrative price. Silver is also an essential constituent of calaverite, which is a gold telluride [(AuAg)Te2]. Silver, alloyed with copper to make it hard, is used for making cutlery, utensils, coins, ornaments, and jewelry. Among the other uses of silver, silver vats are used during the production of acetic acid, vinegar, and cider, because of the resistant nature of silver to acetic acid. It is also used in silver solders, dental amalgams, batteries, ceramic paints, and other items. Silver also acts as a catalyst in the synthesis of formaldehyde and acetaldehyde. The property of silver halides of reacting to light instantaneously makes them invaluable in the production of films, plates, and photographic printing paper. Silver nitrate (AgNO3) is an important laboratory reagent in analytical chemistry, and is used for making mirrors, photography, silver plating, dyeing, and numerous other uses ranging from indelible inks and water disinfectant to antiseptic ointments and astringents (Encyclopaedia of Occupational Health and Safety 2012). Silver has very strong antimicrobial properties, and nanosilver compounds are expected to revolutionize the use of silver in antimicrobial formulations.
Characterization and Gold Extraction of Gold-bearing Dust from Carbon-bearing Gold Concentrates
Published in Mineral Processing and Extractive Metallurgy Review, 2022
Pan Cao, Shuanghua Zhang, Yajie Zheng
Refractory gold ores are gold ores whose gold extraction by direct cyanidation is less than 80% even after fine grinding (González-Anaya, Nava-Alonso and Pecina-Treviño 2011; Gudyanga et al. 1999).These ores are naturally resistant to gold recovery because their inherent chemical reasons (e.g., insoluble gold telluride) or physical properties (e.g., gold encapsulated, robbed from the pregnant solution by carbonaceous matter) (Amankwah and Pickles 2009; Dyer et al. 2017; González-Anaya, Nava-Alonso and Pecina-Treviño 2011; Ilankoon et al. 2020; Mubarok et al. 2017; Seitkan and Redfern 2016; Soltani et al. 2019). Gold in these refractory gold ores can be effectively leached and recovered only after pretreatment (Ma et al. 2010; Pedroza et al. 2012). The main pretreatment methods of refractory gold ores include oxidation roasting, pressurized oxidation, ultrafine grinding, and biological oxidation (Hashemzadehfini et al. 2011; Li et al. 2006; McDonald and Muir 2007; Tanaka et al. 2014; Wang et al. 2016; Xu et al. 2015; Yu et al. 2015).
Oxidative Decomposition of Silver Telluride (Ag2Te) Using Hypochlorite in Different Acid Environments
Published in Mineral Processing and Extractive Metallurgy Review, 2022
V.M. Rodríguez-Chávez, J.C. Fuentes-Aceituno, F. Nava-Alonso
The use of chlorine, hypochlorite and hypochlorous acid as oxidants have been widely studied for other gold leaching systems including the carbonaceous ores (Anuar et al. 2021; Baghalha 2007; Davis, Tran and Young 1993; Hasab, Rashchi and Raygan 2013a, 2013b, 2014; Jeffrey, Breuer and Choo 2001; Jha 1987; Nam et al. 2008). The chlorine and hypochlorite containing systems have also been applied to treat ores containing Pt, Pd, Au, Ag with tellurium (Safarzadeh, Horton and Van Rythoven 2017; Sahu et al. 2020). In the particular case of gold dissolution, Baghalha (2007) studied the effect of pH on the gold dissolution with the chlorine/hypochlorite system, reporting that at pH = 8 the dominant species is the hypochlorite ion (ClO−) and that the gold leaching rate is slow; when the pH is below 7.5 the predominant species is the hypochlorous acid (HClO), a stronger oxidant, and the gold leaching rate is faster (Figure 1). The leaching with chlorine species is faster than cyanide leaching, and the environmental control of the chlorine process is simpler (Li et al. 2015). The treatment with chlorine species could be an interesting option for gold-telluride ores, as the dissolved gold remains in solution complexed with the chloride ions, and an additional leaching stage (cyanide or any other leaching agent) is no more necessary (Ahtiainen, Liipo and Lundström 2021; Aromaa et al. 2015). Filippou, St-Germain and Grammatikopoulos (2007) mentioned that a pretreatment of gold telluride minerals in the presence of hypochlorite in alkaline media promotes the leaching kinetics of tellurium leaving behind metallic gold which can be easily recovered by cyanidation.