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Agitation can be accomplished by external pumps or physical agitation such as a <br /> rotating electrode. <br /> Current or voltage control, can be manual or automatic. Automatic controllers use a Yi• <br /> variety of sensing methods such as conductivity or electronic sensing to detect the il.o <br /> feeding of film in the attached processing equipment. The principle of control is to <br /> have a higher current in the unit when film is being processed and thus releasing silver <br /> to the fix solution. A lower current is desirable when less silver is available in the fixer <br /> solutions. <br /> 3. Factors which affect the Operation and Efficiency of Electrolytic Silver Recovery <br /> Units <br /> a. Silver Concentration ft <br /> Recovery efficiency is directly related to silver concentration in the fixer. The <br /> higher the silver concentration, the higher the plating efficiency, the lower the <br /> concentration, the lower the efficiency. When silver concentration is below 1 gram <br /> per liter, plating efficiency and plating current fall off rapidly, reducing the M <br /> recovery rate of the electrolytic unit. <br /> b. Type of Fixer <br /> The type of fixer can greatly affect the electrolytic recovery process and the type <br /> of electrolytic cell required. For example, bleach-fix solutions require equipment <br /> of special design, and etch additives in graphic arts fixer require special <br /> consideration. <br /> c. Sulfite Concentration IC <br /> A sufficient amount of sodium sulfite must be present in the fixer for the <br /> electrolytic process to work properly. Sodium sulfite is consumed during the <br /> plating process. <br /> d. pH it <br /> The pH of the fixer has a direct relationship on plating efficiency of the recovery <br /> cell. With typical conventional x-ray and graphic arts fixers, a pH of 4,5 to 5.5 is <br /> ideal. For bleach/fix solutions the ideal range is a pH of 7.2 to 7.8. <br />