![]() Another abundant aqueous species is the silver bisulfide complex AgHS (Purcell & Peters 1998, pp. Inorganic complexes found in sea water include AgHS0, and chlorine complexes such as AgCI2″, AgCI32′, AgCI due to salinity. The most common speciation of silver in sea water involves complexes of chlorine which is relatively high in seawater. On the contrary, freshwater inflow may cause significant variations of seawater. Common complexes of silver when it is dissolved in seawater The pH of seawater varies over a very narrow range of 8.0 ± 0.7 thus the inorganic composition of seawater shows minimal spatial and temporal variation in chemical constituents. The pyrometallurgical oxidation process is usually used if the impurities present have a greater affinity for oxygen than the metal itself. The impurities are oxidized and removed by the blast air (Butts & Coxe 1967). In Cupellation method, the impure silver is heated in oval shaped crucible made of bone ash or cement where a blast of air is passed over the heated molten mass. Impure silver is refined by electrolytic methods or by cupellation methods which involves removing impurities by absorption or vaporization. Other impurities suggested are flux or residual slag. The impure silver is usually associated with unchanged ore, other metal which are produced in similar methods, non-metals such as silicon, carbon as well phosphorous. Silver obtained from metallurgical processes is impure. The parkes method is used in separating silver from lead or copper ores. Silver is precipitated when the solution is brought in contact with metallic aluminum or zinc turnings as illustrated In lixiviation methods, the ore is dissolved in a solution of salt such as sodium cyanide. Mercury is then removed from the amalgam by distillation leaving silver metal. During the amalgamation process, liquid mercury is added to the crushed ore and an amalgam of silver-mercury is formed. A number of metallurgical processes have been used to extract silver from its ore of other metals. This converts the sulfides to sulfates and the metallic silver is precipitated. Metallurgy of silver The recovery of silver from its ores involves roasting the ore in the furnace. Epithermal and mesothermal gold deposits also harbor silver as a by-product. Most deposits in which silver are the main economic mineral are epithermal quartz veins of five element (Ni-Co-As-Ag-Bi) veins. ![]() In addition, silver is commonly formed in a wide variety of hydrothermal deposits and is associated with gold and the base metals such as copper, lead and zinc (Addicks 1940). It also has some excess silver in 0.01 to 0.31% weights. Pyrargyrite is known from both deposit types and usually contains an admixture of 0.1 to 0.9% and sometimes Fe, Zn and Se 0.1 to 0.4% weight. Other widespread silver minerals are canfieldite from tin-silver polymetallic deposit type and selenocanfieldite, both hosted by galena ore. The group of high silver Fe-freibergite is pertinent only to sulhostibnite deposit type having two or three known mineral generations and serves as an indicator for high silver ore (Purcell & Peters 1998, pp. Silver bearing tetrahedrite is heterogenous in both deposit types but more heterogenous in sulphostibnite deposit types. There are three varieties of Fe-freibergite, Ag-Fe-tetrahedrite and Ag-tetrahedrite with the predominance of Ag and Fe. They consist of Fe and Ag bearing tetrahedrite that usually contains Zn admixture. Silver bearing-fahlores are silver-bearing ores of the volcanogenic deposit type. Silver combines with many elements, it, therefore, occurs as an essential element in over 100 minerals and it is a minor constituent in many more. ![]() ![]() The main silver-bearing minerals are acanthite and its higher temperature forms argentite, electrum, tetrahedrite, Pyrargyrite and native silver.
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