What is Silver?
Silver (Ag) is a metallic element, excellent conductor of heat and electricity. Its physical and chemical properties as well as its rarity (the average concentration of silver in the earth's crust is 0.1 ppm) make it a highly desirable mineral for use in jewelry, alloys, electrical and electronic components; in addition, it is used in water treatment as a disinfectant.
It is most present in the oxidation state +1 and less frequently in the oxidation state +2. A higher degree of oxidation is very rare. The most important silver compounds from the point of view of drinking water are; silver nitrate (AgNO3, CAS No. 7761-88-8) and silver chloride (AgCl, CAS No. 7783 90-6).
Silver in water.
In groundwater sources we can find silver values between 0.1 – 9 µg / L, although on some occasion’s wells have been found with concentrations of 30 – 40 µg / L. While in surface water sources silver concentrations vary between 0.1 – 4 µg / L. In treated water, the main source of silver is bacteriostatic activated carbons (silver impregnated).
Chronic exposure to low concentrations of silver can produce argyria, an abnormal condition in which silver becomes lodged in the skin and hair, causing it to turn bluish-gray. Pigmentation of the eye is considered the first sign of widespread argyria. It is difficult to determine the lowest dose that may lead to the development of argyria. Other than this condition, no other adverse health effects are known.
How do you remove silver from water?
In its ionic form, silver is recovered by ion exchange resins in the treatment of industrial waste. Other effective methods are coagulation with ferric sulfate (pH 7 – 9), coagulation with alum (pH 6 – 8), and lime softening.
Last updated 14/02/2020.