Metal sludge

Once the life-cycle inventory has been quantified, we can attempt to characterize and assess the eflfects of the environmental emissions in a life-cycle impact analysis. While the life-cycle inventory can, in principle at least, be readily assessed, the resulting impact is far from straightforward to assess. Environmental impacts are usually not directly comparable. For example, how do we compare the production of a kilogram of heavy metal sludge waste with the production of a ton of contaminated aqueous waste A comparision of two life cycles is required to pick the preferred life cycle. 

This shift in emphasis by the mining iadustry has led to the development and use of a variety of improved techniques, in particular the commercial avadabihty of several metal specific extractants. These techniques are particularly useful in the separations and recycling of metals from metal sludges and metal salt solutions. 

Heavy Metals Removal. Heavy metals should be removed prior to biological treatment or use of other technologies which generate sludges to avoid comingling metal sludges with other, nonhazardous sludges. 

You would indicato a discharge to a POTW In Part III, Section 6.1.1 and the location of the POTW in Part II, Section 1.1. You would also indicate the release of the metal sludge to an offsite land disposal facility In Part III, Section 6.2.1. 

Residuals Produced Resulting metal sludges from the chemical precipitation process may require further treatment prior to disposal. The effluent pH may require an adjustment before it may be discharged. Dissolved inorganics present in the effluent may pose a problem for direct discharge. 

Structural surface inhomogeneity influences the anodic dissolution process in the case of metals with appreciable activation polarization. As a rule, segments with perturbed structure dissolve more rapidly than ordered segments. In a number of cases this causes crystallites to break away from the electrode surface and form metal sludge. 

Use treatment technologies (such as ion exchange, evaporation, and electrolytic metal recovery) that do not use standard precipitation/clarification methods that generate heavy metal sludges. 

It is ineffective or only marginally effective for the claimed use (e.g., using certain heavy metal sludges in concrete when such sludges do not contribute any significant element to the concrete s properties). 

In a steel product manufacturing plant involving acid pickling operation, disposal of hazardous metal sludge is the most expensive engineering task, and treatment of pickling liquor and rinse water is the second most expensive engineering task. 

After treatment has proceeded for a period of time, either the coating reaches its maximum capacity to remove metals or the filter requires backwashing. At this time, the column can be backwashed to recover particulate metals from the column, and an acidic solution can be used to recover the adsorbed metals, thereby regenerating the column. Because the ferrihydrite is trapped on the sand particles, only the contaminant metals and nonferrihydrite are released. Thus the need to dispose of large amounts of iron oxide with the metal sludge, one of the main drawbacks of a conventional treatment process, is eliminated. 

Rosenbaum, S.W. September 1989. "Hydrometallurgical Recycling of Metal Sludge."... 

Electronic parts makers, platers and other metal finishers require clean water rinses to remove plating chemicals from parts prior to the next process. The rinse water is sometimes expensive or in short supply. Furthermore, if the water is of poor quality, it must be pre-treated prior to use. The water is discarded after one use with conventional waste treatment, precipitation and clarification and a hazardous mixed metal sludge is generated which must be shipped to a hazardous waste landfill. 

There are approximately 13,000 job and captive metal finishing shops and printed board shops in the USA. Almost all of these companies have installed waste water treatment systems to comply with the Clean Water Act (CWA). As a result, these companies generate toxic metal sludges which are regulated by the Resource Conservation and Recovery Act (RCRA). Compliance with these two Federal laws, in addition to laws passed by local, county and state regulatory agencies, can require industry to spend 10 to 15% of their sales dollar on compliance. 

The recovery of valuable metals and metal alloys from hazardous metal sludges is technically and economically viable. Small quantities of excess slag are produced and this slag can be recycled into concrete blocks. The E.P. and TCLP leachate limits are met with the slag. 

The CBI process is an endothermic, physical-chemical bonding of metal ions to alumina-silicate crystals in a high temperature environment. The process is accomplished in two stages proportioning and mixing of the additive material with the metal sludge and thermal processing. 

After being dropped into a sludge pit, the steam-still residue is washed with water to remove sodium chloride. The remaining lead metal sludge is then recycled by drying, smelting and sodium addition — to make NaPb alloy. 

Stabilization/solidification of hazardous liquids and sludges by combination of the waste with Portland cement to form a cement paste has been studied as a way to minimize environmental impact. The structure of the paste resists physical attack and the alkaUne nature of the material resists chemical attack, making the technique attractive as a disposal alternative for heavy metal sludges. 

T. M. Brown, Column Leach Testing of Heavy Metal Sludges Stabilized/Solidified with Portland Cement An Investigation of Release Meehanisms, M. S. Thesis, Univ. of New Hampshire, Durham, NH (1984). 

Wastes from metal sludges (approximately 0 to 150 kg/Mg product)... 

An Evaluation of Factors Affecting the Stabilization/Solidification of Heavy Metal Sludge... 

The "water-alcohol" method utilizes isopropyl alcohol to decompose metallic soaps. The mixture is then centrifuged to yield clean oil and a watery metallic sludge. Alcohol is recovered for reuse. 

Alkaline Heavy Metals sludge Released to Atmosphere... 

---