Chrome recycling

For the Germanakos tannery, which has a chrome recycling capacity of 12 m3/d, the approximate... 

This is a favorable process because the side reaction products, nitrogen and water, are not pollutants and the sodium sulfate can be recovered and sold. Also, all of the wash water used to remove the sodium sulfate from the chrome oxide can be recycled. 

In conventional chrome tanning processes 20 to 40% of the chrome used is discharged into wastewaters. In the new process 95 to 98% of the waste Cr3+ can be recycled. 

In addition to the heavy metals stated in Table 22.10, ferro- and ferricyanide are also part of the pollutants in the wastewater generated in a chrome pigment plant. These wastes are generally combined and treated through reduction, precipitation, equalization, and neutralization to be followed by clarification and filtration processes. Most of the heavy metals are precipitated using lime or caustic soda at specific pH. Chromium is reduced by S02 to a trivalent form, wherein it is precipitated as chromium hydroxide at specific pH. Sodium bisulfide is also employed to precipitate some of the metals at a low pH. The treated water is recycled for plant use while the sludge is sent to landfills (Figure 22.7). 

Recovery and Recycling of Toxic Chrome at Germanakos SA Tannery Near Athens, Greece... 

Methane sulfonic acid is used as an electrolyte for electroplating of tin onto sheet steel, for plating tin and tin/lead alloy onto nickel or other base metal substrates in the manufacture of lead frames and bump-contacts for microelectronic devices.It can also be used for copper deposition during the manufacture of microprocessors. Other alkanesulfonic acids have also found use in electroplating applications. Disodium methanedisulfonate and other alkanedisulfonate salts are used in chrome plating.As discussed previously, several processes for the recovery and recycle of alkanesulfonic acids from spent metal plating baths have been described. 

Chrome tanning is the most important tanning method in leather production. The effluents from the tannery house contain a considerable amount of chromium. A limit to the chromium discharge is mandated by pollution regulations in almost every country. It is necessary to recycle chrome tanning materials from the effluents. The most common way of recovering the spent chromium salts is by precipitation (Thorstensen, 1993). The pH of the effluents may be raised to the precipitation point of the chromium salts, which precipitate as a hydrated chromium oxide. 

Ion exchange can be useful for heavy metal removal, particularly for nickel, zinc, copper, or chrome, where the metals can be recovered from the regenerating solution and recycled to the process or sold. Ion exchange has also been applied to treatment of streams containing complexing agents or their compounds, that would interfere with a precipitation process. 

Prior to the processing of any lithium battery for recycling, the battery s material safety data sheet should be reviewed, and, if necessary, a complete analysis should be performed to determine the waste products. Components and chemicals are unique to each manufacturer and not each type of lithium battery. Many are similar but none are identical. Compoimds that can cause serious concern if overlooked include chrome, arsenic, fluorine, mercury, organic solvents, asbestos, lithium, and others. At the end of this chapter are two typical battery analyses performed by Toxco Inc., exemplifying the... 

Inner valve parts of 18-8 stainless steel in HF acid service have been found to give very good operation. One valve on recycle acid service with an 11-13 chrome steel inner valve and stem was badly corroded. Because of stem corrosion in HF acid service, it is recommended that 18-8 stainless steel not be used but that monel stems or carbon steel stems be used. 

In the lower temperature range - from approximately 220 to 260°C - copper-rich catalysts are used whereas in the temperature range up to about 360° C, low-copper, high-zinc catalysts are used. As a temperature higher than 380° C could not be permitted even on applying the old zinc/chrome catalysts, one can assume that operation is carried out with a recycle gas/feed gas ratio of about 4.5 to limit a temperature rise from 220 to about 380° C. If one continues such deliberations under this prerequisite, one notes that about 70 % of the reaction heat can be recovered. 

If chemical reclamation is the objective, process segregation is necessary. This is particularly true when chrome is to be recovered from rinse waters. Cyanide rinses, copper and nickel plating rinses, and alkahne or acid rinses must be removed from the chrome rinse waters. The rinse waters containing the chrome will first pass through a cation-exchange unit where the chrome-bath impurities, such as copper, nickel, and trivalent chromium, are removed.The hexavalent chromium is removed in the anion-exchange unit. If so desired, since the water has been deionized, it can be recycled as high-purity rinse water. 

The alloy shown in Table 10 7 is sometimes called 15/3 Chrome/Moly Iron, or 16% chrome. It is a martensitic white iron of moderate erosion resistance. It is used for the casting of pumps for a number of applications such as carbon in pulp circuits, coal transfer pumps, sewage treatment, and some newspaper recycling pumps. 

The recovered protein fractions, practically chromium-free, can be used in a wide range of formulations for the production of adhesives, cosmetics, films, animal feed and fertilizers. The isolated residue containing chromium and organic matter (chrome cake) has the potential to be recycled into the tanning process by treatment with sulfuric acid [263]. 

Decreased use of chrome by automobile and small-appliance manufacturers and mandated recycling of chromium wastes in the electroplating industry have led to a decline in Na2S04 produced from this source. 

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