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Hydrometallurgical Waste Production and Utilization
Published in Sehliselo Ndlovu, Geoffrey S. Simate, Elias Matinde, Waste Production and Utilization in the Metal Extraction Industry, 2017
Sehliselo Ndlovu, Geoffrey S. Simate, Elias Matinde
Leaching or dissolution is the first process step involved in the hydrometallurgical extraction of metals from ores or any other metal-bearing material. This step involves contact of the value-containing mineral or any metal-bearing material with different chemical reactants known as the leaching solution or the lixiviant. The dissolution process can involve different mechanisms such as simple chemical reactions (acid–base), complexation, redox, dissolved organic matter and microbiological activities. The dissolution process can only take place under appropriate conditions, and most metals are extractable at very low pH and high potentials or high pH and moderate potential. However, the choice of the leaching solution usually depends on the type of materials to be leached, the solubility of the material in the leach solution, the cost of and ease of access to the specific reagent and its regeneration capabilities. The lixiviants can be water, acids, alkalis, salts or, as in modern processes, a biological solution containing microorganisms. Water is the cheapest of all reagents but has limited use since not many minerals are water soluble. It is mainly used for dissolving naturally occurring sodium and potassium salts such as carbonates, chlorides, sulphates and nitrates. It is also used for the leaching of calcines obtained after sulphatizing and chloridizing roasting.
The Use of Small Particle Catalysts in Pursuit of Green and Sustainable Chemistry
Published in Ahindra Nag, Greener Synthesis of Organic Compounds, Drugs and Natural Products, 2022
As a primary process in hydrometallurgy, leaching transfers desired metals from a mineral or ore containing metals to an aqueous solution provides a means to concentrate the metals. The term lixiviant is used in hydrometallurgy to describe a liquid medium that can selectively extract the desired metal from an ore or metal mixture. It has been discovered that lixiviant compositions of dihalogen/S,S-ligands, N,N′-dimethylperhydrodiazepine-2,3-dithione (Me2dazdt) in the presence of iodine (I2) for recovery of precious and noble metals from a non-ferrous metal fraction derived from shredded waste electronic equipment (Scheme 9.22).242
Characteristics and Processing of Copper Refinery Anode Slime
Published in Hossain Md Anawar, Vladimir Strezov, Abhilash, Sustainable and Economic Waste Management, 2019
Navneet Singh Randhawa, Jhumki Hait
Recently Yang et al extracted the Au, Ag and Pd from decopperized anode slime by different pretreatments and different lixiviants. Different lixiviants including cyanide, chloride, thiourea and thiosulfate etc. were tested (Yang et al., 2015). Oxidizing roasting pretreatment for 120min at 625 °C removes 82.18% and 98.52% of S and Sb, respectively. Subsequent leaching of the calcined slime in the alkaline medium results in the dissolution of 46.40% Cu and 98.48% Pb. The recovery of Au, Ag and Pd was 99.48%, 97.69%, 94.79% by cyanide leaching, and 95.01%, 79.84%, 96.59% by chloride leaching, and about 95.21%, 95.66%, 48.79% by thiourea/thiosulfate leaching.
Dissolution kinetics studies of kaolin ore as raw material for mesoporous silica by acid leaching
Published in Canadian Metallurgical Quarterly, 2023
Abdullah S. Ibrahim, Alafara A. Baba
In obtaining the aforementioned industrial raw materials, the traditional routes involving sol–gel, templating and sometimes the hydrothermal techniques which suffer from the high cost of templates and industrial chemicals as well as hazardous waste generation from template removal are widely used [6,7]. However, the selective chemical activation of kaolinite is explored. In this practice, lixiviants are used to selectively remove part of the starting material by exploiting the solubility difference in the leaching solution [8]. This often increases the specific surface area along with the elimination of impurities including partial dissolution of the external layers [5]. For example, Okada et al. [9] prepared porous silica from thermal-activated kaolinite with 20% mass sulphuric acid at 90°C for 0.5–5 h with moderate stirring. The results revealed a decrease in the alumina content and an increase in the specific surface area with increasing time. Panda et al. [10] and Lenarda et al. [11] prepared porous materials using kaolin with the high surface area by sulphuric acid treatment and the solid products have potential as promising adsorbent and catalytic utilisations.
Hydrochloric acid regeneration in hydrometallurgical processes: a review
Published in Mineral Processing and Extractive Metallurgy, 2018
Caitlyn McKinley, Ahmad Ghahreman
Chloride leaching flowsheets have been developed for laterite ores, manganese nodules, low-grade tin ores, ilmenite upgrading, copper from chalcopyrite, nickel from pyrrhotite, lead/zinc/sulphur concentrates, nickel/copper/sulphur concentrates, rare earth element ores and pickling oxide scales with varying levels of commercialisation having been achieved (Peek 1996; Bedrossian & Connell 2014; Park et al. 2015; Rao et al. 2015). In most of the above processes, a proportion of the hydrochloric acid or chloride anion is consumed by gangue minerals - producing stable chloride complexes. Hydrochloric acid being an expensive reagent, vital to the commercialisation of those processes is the regeneration of the chloric anion, whether it is hydrochloric acid or a hydrochloric acid/metallic salt solution (Harris & White 2015). Recycling the lixiviant benefits the processes both economically by reducing the amount of the make-up acid required, and environmentally by producing less acidic waste. The use of make-up acid can be very expensive, with 6 M hydrochloric acid being approximately $300 USD per tonne in North America. In some processes, such as those in ilmenite leaching operations, the hydrochloric acid/calcium chloride lixiviant is easily regenerated by recovering the valuable metals as insignificant impurity accumulation occurs (Das et al. 2013). However, other processes require more complex regeneration techniques and the economic, environmental and social impacts of these methods must be carefully analysed.
Comparative investigation of leaching of zinc from wastes of the zinc alloy production process
Published in Mineral Processing and Extractive Metallurgy, 2021
Hassan Koohestani, Elahe Sadat Khatami, Kazem Babaei
Much research has been carried out successfully to leach zinc oxide by acid and basic agents. These studies have been done using different lixiviants such as ammonia (NH3), sodium hydroxide (NaOH), sulfuric acid (H2SO4), hydrochloric acid (HCl), etc. (Muzenda and Simate 2011). Leaching of zinc ores containing oxidised minerals with sulfuric acid and its kinetics has been studied in recent years. He et al. (He et al. 2010; Li et al. 2010; Xu et al. 2010) investigated the pressure leaching. In their studies, the effects of parameters such as lixiviant concentration, particle size, solution temperature, air pressure, leaching time and the solid/liquid ratio were investigated and the optimum conditions were determined.