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Chemical Bonding
Published in Alan Cottrell, An Introduction to Metallurgy, 2019
Coordination compounds and complex ions have great value in chemical metallurgy. The volatile nickel carbonyl Ni (CO)4 compound provides the basis of the Mond process for extraction of nickel (cf. § 8.8). The formation of complex ions often provides a means for getting sparingly soluble substances into solution. The stability of the AuCl4− ion is responsible for the ability of aqua regia (HCl + HNO3) to dissolve gold. Complexes with the cyanide ion CN− are important in electrodeposition (cf. § 9.4) and also in the extraction of gold and silver.
Greener and Sustainable Approach for the Synthesis of Commercially Important Epoxide Building Blocks Using Polymer-Supported Mo(VI) Complexes as Catalysts
Published in Arup K. Sengupta, Ion Exchange and Solvent Extraction, 2017
Misbahu Ladan Mohammed, Basudeb Saha
The molybdenum content of the prepared catalysts was analyzed using a Perkin–Elmer AAnalyst 200 spectrophotometer. A sample of each polymer-supported complex (~0.1 g) was grounded to a fine powder and digested in 15 mL aqua regia for 3 days. Aqua regia is a mixture of concentrated HNO3 and HCl in the volume ratio of 1:3. The resulting mixture was diluted to 100 mL with distilled water and the Mo content was analyzed using an atomic absorption spectrophotometer (AAS). The Mo content of the Ps.AMP.Mo and PBI.Mo catalysts and the corresponding ligand:Mo ratio are given in Table 3.1.
Development of in-situ electro-generated chlorine leaching and its application to the leaching of platinum
Published in Geosystem Engineering, 2022
Min-Seuk Kim, Rina Kim, Kyeong-Woo Chung, Jae-Chun Lee
Leaching valuable metals into a solution is generally the first step in a hydrometallurgical treatment for ores and secondary resources. Hydrochloric or sulfuric acids can leach the most valuable metals, such as Ni, Co, Zn, and Fe, because of the lower standard electrode potential of the metals than hydrogen. However, because of their high standard electrode potential, precious metals, such as Au and PGMs, do not react with hydrochloric or sulfuric acid. Aqua regia is one of the potent leaching agents to dissolve precious metals. It is the molar mixture of three parts concentrated hydrochloric to one part concentrated nitric acid, resulting in the generation of solid oxidizers, such as nitrosyl chloride (NOCl) and chlorine (Cl2), and vigorously attacks precious metals. Aqua regia leaching was a high-speed and low-cost process generally used in small and medium-scale plants for gold (Geoffroy & Cardarelli, 2005). However, it produces unavoidable toxic fumes of nitrogen oxides (NOx), and strong air pollution regulation makes aqua regia leaching no longer a low-cost process. In aqua regia leaching, nitrate has to be eliminated by heat drying before separation and purification processes, and aqua regia hardly dissolves rhodium except in finely divided form.
Recent advances on hydrometallurgical recovery of critical and precious elements from end of life electronic wastes - a review
Published in Critical Reviews in Environmental Science and Technology, 2019
Manivannan Sethurajan, Eric D. van Hullebusch, Danilo Fontana, Ata Akcil, Haci Deveci, Bojan Batinic, João P. Leal, Teresa A. Gasche, Mehmet Ali Kucuker, Kerstin Kuchta, Isabel F. F. Neto, Helena M. V. M. Soares, Andrzej Chmielarz
In the case of precious metals, aqua regia allows the highest gold dissolution rate among different leaching agents, but it is applied usually at laboratory scale because of the strong oxidation and high-corrosion power which limits its industrial applications. Furthermore, management of the highly acidic wastewaters is very difficult. Over the last century, cyanide leaching has been widely used to recover gold from gold minerals and secondary sources its high efficiency and relatively low cost. The main drawback of this method is the production of a huge amount of cyanide contaminated wastewaters, which can lead to a serious damage to people and the environment: for this reason, this method is being gradually replaced by other methods.