Chromium liquors

Table ZSAnalytical determinations of samples coming from the integrated UF/NF process of exhausted chromium liquor...

Despite increasing environmental pressure, including legislation, to minimize the discharge of toxic Cr(vi) species in effluent, the above processes continue to operate using chromium liquors. Indeed, in specific applications, it is often difficult to replace the chromium-containing liquors with alternative process solutions. Hence, it has become increasingly attractive to recycle these liquors or to find suitable treatments prior to disposal. 

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Because these variables have a very pronounced effect on the current density required to produce and also maintain passivity, it is necessary to know the exact operating conditions of the electrolyte before designing a system of anodic protection. In the paper and pulp industry a current of 4(KX) A was required for 3 min to passivate the steel surfaces after passivation with thiosulphates etc. in the black liquor the current was reduced to 2 7(X) A for 12 min and then only 600 A was necessary for the remainder of the process . From an economic aspect, it is normal, in the first instance, to consider anodically protecting a cheap metal or alloy, such as mild steel. If this is not satisfactory, the alloying of mild steel with a small percentage of a more passive metal, such as chromium, molybdenum or nickel, may decrease both the critical and passivation current densities to a sufficiently low value. It is fortunate that the effect of these alloying additions can be determined by laboratory experiments before application on an industrial scale is undertaken. 

The technology developed involves the recovery of chromium from the spent tannery liquors and its reuse. 

Reuse minimal K062, Spent pickle liquor Hazardous components lead, nickel, chromium Total generation about 6 million t/yr Reuse some recycled... 

Pickling done before coating may use a mildly acidic bath such spent liquor is not considered hazardous. Waste pickle liquor flows typically range between 10 and 20 gal/t of pickled product. Rinsewater flows may range from less than 70 gal/t for bar products to more than 1000 gal/t for certain flat-rolled products. The principal pollutants in rinsewater include TSS, dissolved iron, and metals. For carbon steel operations, the principal metals are lead and zinc for specialty and stainless steels the metals include chromium and nickel.15... 

Spent pickle liquor in the acid pickling wastewaters is listed as hazardous waste K062, regulated under RCRA, as it contains considerable residual acidity and high concentrations of dissolved iron salts.2 Exhausted pickling baths are mainly composed of nitrate (150 to 180 g/L), fluoride (60 to 80 g/L), iron (III) (30 to 45 g/L), chromium (III) (5 to 10 g/L), and nickel (II) (3 to 5 g/L). 

Spent pickle liquor is considered a hazardous waste (K062) because it contains considerable residual acidity and high concentrations of dissolved iron salts. For example, spent pickle liquor and waste acid from the production of stainless steel is considered hazardous. The hazardous constituents in K062 are lead, nickel, and hexavalent chromium. Waste pickle liquor sludge generated by lime stabilization of spent pickle liquor is not considered hazardous unless it exhibits one or more of the characteristics of hazardous waste. An estimated 6 million tons of spent pickle liquor are generated annually in the U.S.1... 

Treatment of Liquors Containing Dissolved Chromium cf. Refs. [10,133]... 

The complex formed when a mordant dyeing is aftertreated in a dichromate solution is retained by the wool in preference to the unmetallised mordant dye, which may desorb to some extent during the treatment. The latter is rather unstable in an oxidising solution and quinonoid by-products are often formed. If the chromium complex of the dye is formed from the desorbed dye in solution, this will further complicate the composition of the aftertreatment liquor. Thus reuse of mordant dyeing and aftertreatment baths is not an option. Furthermore, 100% rejection of dichromate ions would be required if the permeate of a membrane process treating the effluent was to be recycled [42]. 

The SRS process is versatile in chlorate plant production. The design and operating conditions can be adapted to meet the need of the different plant requirements, e.g. production of R8 solution with reduced chromium, recovery of chlorate from the purge liquor sent to effluent, or removal of sulphate from the liquor loop. 

Filter off the formed crystals and dry them on filter paper. Choose a well formed crystal of the alum, fasten it with the aid of a thin thread or hair to a glass rod and lower it into the mother liquor. Watch how the crystal grows several days. Examine the shape of the chromium potassium alum crystals under a microscope and compare it with that of potassium aluminium alum crystals. What will happen if crystals of potassium aluminium alum are lowered into a saturated solution of chromium potassium alum. 

The most popular tanning solution in current use is termed 33% basic chromium(III) sulfate and corresponds to the empirical formula CrOHSCV In older procedures, chromate was often reduced at the plant using glucose/sulfuric acid mixtures. At present, 33% basic chromium sulfate is provided as either a solution (chrome liquor) or as a commercially available powder,120 of constant, but at present slightly uncertain, chemical composition. 

Chromium pentaphenyl carbonate,1 [(C6H5)5Cr]2C03.6H20, occurs when the concentrated aqueous mother-liquors from the preparation of the base are exposed to the air in an ice-chest. It forms orange-coloured plates, sintering at about 108° C. and melting indefinitely at 118° to 119° C. A mono- and a di-hydrate are also known. 

Recovering chromium salts from spent tanning liquors has been carried out with an integrated process based on preliminary UF followed by NF [23]. 

For this oxidation the spent liquors, consisting of sulphates of potassium and chromium and also free sulphuric... 

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