Fixers

The solutions we offer are based on two main technologies electrolytic silver recovery from fixer solutions and cascade fixing. In what follows we will give more teclmical details about these teclmologies. We will clarify the key-factors to obtain reliable and more ecological solutions for the silver in the rinsing water. 

In both preceding cases, the demands to the electrolysis unit are limited, since there is no need to keep the silver content in the fixer tank constantly low. A steady state silver concentration in the fixer between 3 and 5 g/1 is acceptable, since this causes no substantial loss of fixation speed. 

The primary goal of fixer desilvering is to remove silver from the fixer solution. This desilvering occurs at the cathode, and in good desilvering units, it is performed with an efficiency of well above 90%. 

At the anode, a chemical oxidation reaction is bound to take place. In normal fixers, sulfite (SOj ) is oxidized and acid (H ) is released as a consequence of this oxidation. Due to the decrease of the sulfite concentration and the decrease in the pH, the fixing solution becomes unstable and sulfur precipitation starts to occur when the pH of the fixer decreases below 4.0. In the case of hardening fixers, there is also an upper limit to the pH, since aluminum-hydroxides starts to precipitate when the pH exceeds 5.0. 

It is clear that the freight value depends on the type and amount of film and how the production is spread over time. Figure 3 shows 2 simulations of silver concentration in fixer for different processing regimes. In one case, 10 m of film is processed over 3 hours. In another case, 10 m of film is processed over 16 hours. It is clear that the silver level in the fixer not only depends on the amount of film processed, but also on the distribution of the working load. The simulated daily freight values are 44 and 16 mgW respectively. ... 

In case of cascade fixation, an additional fixing step is used to lower the silver concentration in the fixer which is carried over to the rinse section, as is shown in Figure 4. 

Figure 4 Schematic representation of silver concentration and fixer flow for cascade fixation.

The process is designed such that virtually all silver is fixed in the first fixing step. The fixer in the first fixer section has a typical silver concentration of 7 g/1. The silver in the second fixer section originates from the carry-over from the first fixing section, and a typical silver concentration is 0,4 g/1. Hence, the silver carried over to the rinsing section will be substantially lower. 

It is used as the fixer in photography under the name hypo . 

Silver Thiosulfate. Silver thiosulfate [23149-52-2], Ag 2 y is an insoluble precipitate formed when a soluble thiosulfate reacts with an excess of silver nitrate. In order to minimize the formation of silver sulfide, the silver ion can be complexed by haUdes before the addition of the thiosulfate solution. In the presence of excess thiosulfate, the very soluble Ag2(S203) 3 and Ag2(S203) 3 complexes form. These soluble thiosulfate complexes, which are very stable, are the basis of photographic fixers. Silver thiosulfate complexes are oxidized to form silver sulfide, sulfate, and elemental sulfur (see Thiosulfates). 

Sulfur Complexes. Silver compounds other than sulfide dissolve in excess thiosulfate. Stable silver complexes are also formed with thiourea. Except for the cyanide complexes, these sulfur complexes of silver are the most stable. In photography, solutions of sodium or ammonium thiosulfate fixers are used to solubilize silver hahdes present in processed photographic emulsions. When insoluble silver thiosulfate is dissolved in excess thiosulfate, various silver complexes form. At low thiosulfate concentrations, the principal silver species is Ag2(S203) 2j high thiosulfate concentrations, species such as Ag2(S203) 3 are present. Silver sulfide dissolves in alkaline sulfide solutions to form complex ions such as Ag(S 2 Ag(HS) 4. These ions are... 

Na[AuClJ, per mole of silver haHde. Coordination compounds are used as emulsion stabilizers, developers, and are formed with the weU-known thiosulfate fixers. Silver haHde diffusion transfer processes and silver image stabilization also make use of coordination phenomena. A number of copper and chromium azo dyes have found use in diffusion transfer systems developed by Polaroid (see Color photography, instant). Coordination compounds are also important in a number of commercial photothermography and electrophotography (qv) appHcations as weU as in the classic iron cyano blueprint images, a number of chromium systems, etc (32). 

While couplings are typically sized and chosen based on the before mentioned requirements, they can take on another role, that of a torsional fixer. 

Photographic fixer. Kodak tropical acid hardening-fixing bath F5 or equivalent. 

Develop the plate in the usual manner in the darkroom, say for 9 minutes with Ilford ID-2 developer at 18 °C, then rinse it rapidly with water, and place it in the fixer (Kodak F5) for ca 20 minutes at 18 °C. Remove the plate from the fixer, wash it with running water for at least 30 minutes, wash with distilled water, and dry in the air. 

Phosphine, amino-rhodium complexes catalysts, hydroformylation, 6,261 Phosphine, 3-aminopropyldimethyl-photographic fixer, 6,100 Phosphine, bis(2-carboxyethyl)methyl-photography... 

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