Silver

From GoldRefiningWiki
Jump to: navigation, search

Silver is a white precious metal with a lot of interesting properties. It's been one of the coin metals as far as humans have used coins.

Contents

Type of scrap

Silver is used in a number of different areas, all from coinage and jewellery to photographic processes. With the advent of digital photography the supply of photographic scrap have dwindled to almost nothing, but still there are old archives with exposed film and left over chemicals.

Silver alloys

Different alloys have been used for different objects of silver.

Sterling silver

The most common alloy used for silver jewellery and silverware. It contains 92.5% silver and 7.5% copper, It can be run in a silver cell directly but would foul the electrolyte quickly.

Silver coinage

Silver coinage have a long story, just as long as we have made coins. In many countries silver coins were made for circulation up until late 1960:es, usually with a silver content as low as 40%. Older silver coins usually contains higher contents of silver than later ones. Today no silver coins are made for circulation, it is only commemorative and medal issues that are made today. Be aware that some coins have a collectors value a lot higher than the melt value.

Contact points

Silver is the metal with lowest resistance and doesn't tarnish so easily. It can form sulfides in an atmosphere rich in sulfur but that is still conducting current and relays can be made to be self cleaning. Some common alloys used in relays and contact points is pure silver, silver palladium, silver with tungsten and gold plated silver in low current applications.

Photographic waste

Silver halides are used as a light sensitive substance, When exposed and developed the exposed silver halide is turned into silver metal and the excess is removed in the liquids. Sources of silver for the refiner is unexposed film and paper, developed film and paper and used fix from the development process. Many photo shops have silver filters on outgoing waters and they can contain more or less silver.

Electronic waste

In electronics silver have a number of different usages. As an alloy metal in MLCC metal layers, as a braze for brazing components, as surface treatments of circuit boards, as a part of lead free solders, as a container of older tantalum electrolyte capacitors, as screen printed conductors on mylar in keyboards and several other usages.

  • Carbon brush, a contact part for transferring electricity to rotating parts. Often made from pure carbon but sometimes with copper or silver up to 80% of the weight. Metal infused carbon is usually used where large current at low voltage is transferred, for example in large motors and generators, especially in wind turbine generators.

Refining silver

Silver can be refined in several ways, via silver chloride or other means, but most commonly is the electrolytic silver cell as it produces high purity silver with simple means.

Chemical reactions

Silver dissolved in nitric acid.

Ag + 2HNO3 = AgNO3 + H2O + NO2

Videos

Silver in the waste stream

Silver is one of the RCRA 8 metals so if it is in the waste stream it can inflict higher costs for treatment.

The EPA Limits for silver both in water and solid waste is 5ppm (mg/l)

References

Personal tools
Google AdSense