Silver Recovery from Assorted Spent Sources

Toxicology of Silver Ions

Syed Sabir

• Publisher: WSPC (EUROPE)
• Year: 2018
• ISBN:
  9781786344595
• Topic: Tecnología e ingeniería
• Subtopic: Ingeniería química y bioquímica

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Silver holds three world records; it has the lowest contact resistance, highest electrical conductivity and the best thermal conductivity of all metals. The element's physical strength, brilliance and malleability leads to its many uses from electronics to optical applications.

A new 'silver rush' has occurred following the recent discovery that silver, when divided to form particles at the nano scale, can take on new properties. Meanwhile, there has been an increase in regulations against environmental pollution of silver ions toxicity, which have caused numerous diseases and disorders in the marine, microbial, invertebrate and vertebrate community (including humans). Both of which have led to a great interest in silver recovery for both environmental toxicity and an economic point of view.

Comprised of ten chapters, this book draws attention to the most advance technologies in silver recovery and recycling from various spent sources, which will appeal to research scientists and metallurgists. The state of the art in recovery of silver from different sources by hydrometallurgical and bio-metallurgical processing and varieties of leaching, cementing, reducing agents, adsorbents, and bio-sorbents are highlighted in this book.

--> Contents:

• Introduction (Syed Sabir)
• Leaching of Silver Contained in Mining Tailings. A Comparative Study of Several Leaching Reagents (Eleazar Salinas-Rodríguez, Juan Hernández-Ávila, Eduardo Cerecedo-Sáenz, Alberto Arenas-Flores, Ma Isabel Reyes-Valderrama, Edmundo Roldán-Contreras and Ventura Rodríguez-Lugo)
• Adsorption and Recovery of Silver from Aqueous Solutions (Emanuelle Dantas de Freitas, Thiago Lopes da Silva, Meuris Gurgel Carlos da Silva and Melissa Gurgel Adeodato Vieira)
• The Biogenic Synthesis of Silver Nanoparticles as a Method for Recovering Silver from Secondary Sources Using Extracts from Indigenous Australian Plants (Derek Fawcett, Sridevi Brundavanam and Gérrard Eddy Jai Poinern)
• Electrochemical Recovery of Silver from Waste Solutions (Victor Reyes-Cruz, María Aurora Veloz Rodríguez, José Angel Cobos Murcia and Gustavo Urbano Reyes)
• Recovery of Silver from Industrial Wastes: Strategies and Technologies (M Chakankar, U Jadhav and H Hocheng)
• Silver Recovery Methods from Photographic Wastes (Nuri Nakiboğlu)
• Recovery of Silver from E-wastes Using Acidothiourea (Katsutoshi Inoue, Biplob Kumar Biswas, Manju Gurung, Hidetaka Kawakita, Keisuke Ohto and Shafiq Alam)
• Silver Extraction and Recovery with Macrocyclic and Tripodal Compounds (Keisuke Ohto,Yuki Ueda, Ramachandra Rao Sathuluri, Hidetaka Kawakita, Shitaro Morisada and Katsutoshi Inoue)
• Environmental Impacts of Silver from Spent Nanosources (Marija Ljubojević, Mirta Milić and Ivana Vinković Vrček)

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--> Readership: Students, researchers, chemists, metallurgists, environmental scientists and electronic waste recovery experts. -->
Keywords:Silver;Silver Recovery;Toxicology;Inorganic Chemistry;Silver IonsReview:0

Chapter 1

Introduction

Syed Sabir

Chemical Engineering Department, King Saud University
P.O. Box 800, Riyadh-11421, Saudi Arabia
[email protected]; [email protected]

1.1 Silver: Historical Perspective

Silver is a precious and durable transition metal, which occurs as a minor constituent, is 67^th in abundance among the metals by weight in the earth’s crust, with an average concentration of approximately 0.1 mg/kg [1], is found worldwide, and is a member of group 1B of the Periodic Table. The name silver is derived from different sources — the ancient name of silver refers to its bright white color; the Hebrew term originates from the verb “to be white”, and the Roman and Greek terms come from the terms “argentum” and “argyros”, respectively, which mean “to be shining”. It seems that the word “argenos” is of Aryan origin and “arg” is of Sanskrit origin (i.e., “clear”). However, in Latin, “argentum” stands for the element silver [2]. This metal was known to ancient civilizations along with other metals, viz. gold, copper, iron, tin, lead, and mercury [3]. The physical beauty of silver has made this precious metal highly desirable to many civilizations, past and present. The metal’s mechanical properties of ductility and malleability, and its high electrical and thermal conductivities, have also made it suitable for a wide range of industrial applications. The singular beauty of silver was well known, and it has been used by humans for over 6,000 years and has played significant roles in various aspects of human life [4, 5]. The use of silver in ornaments, utensils, daggers, pottery, and trade in the ancient Aegean period, and as the basis of monetary systems by ancient people living in the Indus Valley (i.e., in Harappa and Mohenjo-Daro cities), is supported by archaeological evidence [6–10]. Interestingly, many ancient cultures used silver and silver compounds as natural anti-microbial agents in numerous traditional medicinal preparations. Several studies have revealed that nanometer-scale silver particles have unique and potent anti-bacterial and anti-inflammatory properties that can promote faster wound healing. Importantly, in recent years, several bacterial and fungal species have developed immunity against many routinely used antibiotics. Therefore, there is an imperative need to develop new antimicrobial agents to fight these antibiotic-resistant strains. Thus, nanoforms of silver have been extensively studied and incorporated into a wide range of wound dressings and pharmaceutical preparations to prevent bacterial growth. Furthermore, due to the efficacy of nanosilver, it has also been used as a disinfectant agent in a variety of food/beverages containers and in water purification systems.

In pre-historic metallurgy, attention was focused mainly on metals such as lead, silver, copper, and iron, which may have witnessed social changes, the development of the civilization, and mastery of new weapons and articles during the ancient Aegean period. Native silver is relatively rare in the Middle East, and it is believed that the bulk of ancient silver was separated from lead by the process known as cupellation, which may have been discovered in the pre-history period of metallurgy [8]. However, the earlier pre-history in the subcontinent supported the use of copper, gold, silver, and iron. For centuries, the British, French, and Portuguese have developed trade with India and the Far East in silver or gold for their aesthetic value as well as their rarity [6]. The global demand of silver has been escalating progressively with the increasing consumption of electronic and electrical equipment (EEE) [11, 12]. Global silver mine production declined in 2016 for first time in 14 years by 0.6% to a total of 885.8 million ounces [13].

1.2 Silver Occurs Naturally

Silver is a naturally occurring element in the earth’s crust, generally present in fairly low concentrations [14]. However, silver is present as minor and trace constituents of a great variety of minerals, which are listed by Boyle [2]. The most common silver-containing minerals are native silver (Ag), acanthite (Ag₂S), pyrargyrite (Ag₃SbS₃), proustite (Ag₃AsS₃), tetrahedrite tennanite [(Cu,Fe,Ag)₁₂ (Sb,As)₄S₁₃], chlorargyrite (AgCl), argentite, and argentojarosite [AgFe₃(SO)₂ (OH)₆] [15]. Most silver is produced as a by-product of copper, gold, lead, and zinc refining, whereas some amount of silver is extracted by Parkes and cyanidation processes. There are a number of places named after silver, for example, Argentina or the Rio de la Plata in South America. Canada (9%), Australia (9%), Soviet Union (7%), and Chile (7%) were traditionally the main silver-producing countries in the world [16], although today’s main silver-producing countries are Peru, México, and China [7]. Silver production worldwide reached more than 2,700 tons in 2009 — there is now an estimated reserve of 550,000 tons in the earth’s crust, but in 2014, the global production of silver reached 877.5 million ounces [17]. About 700 tons are consumed annually in heterogeneous catalysis (e.g., production of ethylene oxide and formaldehyde, purification of diesel emission gases), more than that used for jewelry [7]. Literature study indicates that the acidity of an indigenous rock has a pronounced effect on the silver concentration in rocks. Boyle [2] suggests that basic rocks contain a maximum amount of silver, with the concentration decreasing with increasing acidity. This makes perfect sense from a chemical standpoint since silver is most soluble in acidic condition. In the recent years, while the natural resources of silver are decreasing, the cost of silver productions has risen rapidly, and the market price of silver has undergone a spectacular rise in spite of its increased applications in numerous fields such as photography, radiography, electronics, photonics, electrical, catalysis, batteries, jewelry, silverware, dental material, biomedicine, medicines, disinfectants in wastewater treatment, food/beverages processes, etc. [18–22]. Among its wide applications, its anti-microbial activity is of great interest.

With the growth of all these industries, the recovery and removal of silver have been intensely studied because its present market demand poses an acute problem in the recovery of silver from spent sources through new economically efficient and environmentally clean technologies [23]. The recent interest in using eco-friendly and cost-effective recovery methods to reduce pollution levels offers an important secondary source of silver. Using plants to extract and recover silver from mine tailings, contaminated soils, and wastes from other sources (i.e., radiographic film and electronics) is an alternative and different method from conventional mining and extraction processes. Meanwhile, there has been a phenomenal increase in the regulations against environmental pollution caused by silver ion toxicity in the marine, microbial, invertebrate, and vertebrate community (including humans) through chains, which has caused numerous diseases and disorders [24–27]. Therefore, there is great concern in the recovery and removal of monovalent silver ion (Ag⁺) from industrial effluents and spent sources, up to ppm level [28]. Moreover, there is a great interest in silver recovery from both environmental and economic points of view [29, 30].

1.3 Natural Sources

Generally, silver metal is obtained from natural sources as a co-product of gold and by-product of zinc, copper, antimony, lead, etc. [19, 31] through conventional open pit as well as underground methods. Silver is most commonly associated with the ores of Au, Cu, Pb, and Zn [32]. The silver-containing base metal ores are crushed and concentrated by flotation methods. The recovery methods are, however, different for ores of lead, zinc, copper, and gold.

Lead concentrates with silver content ranging between 0.08% and 0.12% are sintered and then smelted with coke in a low shaft blast furnace. The hard lead produced from the blast furnace, containing impurities such as copper, antimony, zinc, bismuth, nickel, etc., is pyro-refined in refining kettles in stages. The silver present in hard lead (0.15–0.25%) is separated from the melt by Parkes process involving the addition of zinc into the melt. After thorough mixing of zinc into the molten mixture of lead and silver, the bath is allowed to cool down. The top crust of silver–zinc–lead alloy containing 4–5% silver is removed using a Howard press, which helps in squeezing out the mechanically entrained lead. The silver–zinc–lead alloy is charged into a retort furnace, where zinc is condensed in the adjacent condenser and the retort bullion, containing 7% silver and lead, is cast out. In the next stage, lead is recovered by oxidation to litharge (lead oxide) lying behind enriched silver (996 fineness) in the cupellation furnace. In the year 2010, about 30.72 tons (0.72 M oz) of silver was recovered from lead/zinc concentrates.

Silver content in copper concentrates is in the range of 100–150 g/t" of concentrate. Almost all the silver present in the copper concentrates return to the anode copper in the smelter, since the silver loss through discard slag in the smelter is comparatively small. Silver is also recovered from gold ores by the cyanidation method in which ground gold ores are leached by a dilute cyanide solution. Zinc dust is used to precipitate the gold and silver from the cyanide solution. The precipitate is melted in a furnace to produce a doré metal.

In recent years, the extraction and recovery of silver was carried out either by hydro- or bio-metallurgical routes [33]. Leaching represents the first step of the hydrometallurgical route, and the recovery of silver by different techniques, including cementation, chemical precipitation, adsorption, bio-sorption, electrocoagulation, electrowinning, ion exchange, and solvent extraction, are very important cost-effective methods of extraction from various silver-containing sources.

1.4 Secondary Silver-bearing Raw Materials

Silver-containing materials originate from diverse sources, such as manganese silver ore, refractory antimony ore, silver sulfide concentrates, lead–zinc sulfide concentrates, mining wastewater, spent photography/radiography films, electronic and electrical materials, discarded jewellery, silverwares, brazing alloys, catalysts, batteries, dental amalgam, orthopedic materials, spent bleach-fixing photographic/radiographic solutions, electroplating solutions, and metallurgical processing solutions. Processing of such sources is, therefore, complicated. However, the basic processing technology is shown in Fig. 1.

1.5 Scope of the Book

The aim of this book is to provide a summary and comprehensive overview of the silver-containing sources and technical approaches in silver recovery. In addition, processing techniques for the recovery of silver from spent sources ...

Table of contents

• Cover Page
• Title
• Copyright
• About the Editor
• Acknowledgments
• Contents
• Chapter 1. Introduction
• Chapter 2. Leaching of Silver Contained in Mining Tailings: A Comparative Study of Several Leaching Reagents
• Chapter 3. Adsorption and Recovery of Silver from Aqueous Solutions
• Chapter 4. The Biogenic Synthesis of Silver Nanoparticles as a Method for Recovering Silver from Secondary Sources Using Extracts from Indigenous Australian Plants
• Chapter 5. Electrochemical Recovery of Silver from Waste Solutions
• Chapter 6. Recovery of Silver from Industrial Wastes: Strategies and Technologies
• Chapter 7. Silver Recovery Methods from Photographic Wastes
• Chapter 8. Recovery of Silver from E-wastes Using Acidothiourea
• Chapter 9. Silver Extraction and Recovery with Macrocyclic and Tripodal Compounds
• Chapter 10. Environmental Impacts of Silver from Spent Nanosources
• Index