Lead, removal from wastewaters

Lead Removal from Wastewaters Using Chabazite Tuff... 

COLELLA AND PANSINI Lead Removal from Wastewaters... 

The previous considerations and the knowledge of the high selectivity of chabazite for lead (11) suggest research on the possible use of Campanian tuff (namely chabazite tuff) (12) for lead removal from wastewater. Recent studies have emphasized the good behaviour of the tuff either in equilibrium (E. Torracca, P. Galli, private communication) or dynamic tests, carried out with model solutions of only lead (M. Pansini, C. Colella, to be published). 

P-06 - Investigation of lead removal from wastewater by Iranian natural zeolites using Pb as a radiotracer... 

Removal of lead from water is performed generally by precipitation as carbonate or hydroxide with or without coagulation. Chelation with EDTA, nitrilotriacetic acid, or other agents is another usual treatment followed by recovery using precipitation, electrolysis, or chemical oxidation (Borrell-Damian and Ollis, 1999). However, most of these treatments are expensive, and some other ways of lead elimination from wastewater are necessary to be developed. 

Somerset et al. [20] have studied the process of the hydrothermal conversion of fly ash into zeolites (viz., Faujasite, Sodalite and zeolite A) and their application for removal of mercury and lead ions from wastewater. It has also been reported that a dose of zeolites of the order of 5-20 g/1 can result the removal of Pb and Hg by 95 and 30 %, respectively, from the acid mine drainage (AMD) at an average pH of 4.5. 

Somerset, V., Petrik, L., Iwuoha, E. Alkaline hydrothermal conversion of fly ash precipitates into zeolites The removal of mercury and lead ions from wastewater. J. Environ. Manage. 87(1), 125-131 (2008)... 

The facility wastewater monitoring program does not determine the concentration of lead and lead compounds in the scrubber discharge water, and releases to the surface impoundment (releases to land) must be calculated using mate-riai balance information. These releases to land are determined from the amount of lead removed by the scrubber (using the efficiency data provided by the scrubber manufacturer). The volume of the scrubber blowdown Is found to be 1,500 pounds per year. Enter the estimate of the amount of lead and lead compounds released to surface Impoundments in the space provided in Part III, Section 5.5.3 of the form. Because releases of lead to the surface Impoundment are greater than 999 pounds per year, you must enter the actual calculated amount in column A.2 of Section 5.5.1. The basis for the estimate of releases to the surface impoundment, entered in column B of Section 5, is mass balance calculations (code C). 

Precipitation is often applied to the removal of most metals from wastewater including zinc, cadmium, chromium, copper, fluoride, lead, manganese, and mercury. Also, certain anionic species can be removed by precipitation, such as phosphate, sulfate, and fluoride. Note that in some cases, organic compounds may form organometallic complexes with metals, which could inhibit precipitation. Cyanide and other ions in the wastewater may also complex with metals, making treatment by precipitation less efficient. A cutaway view of a rapid sand filter that is most often used in a municipal treatment plant is illustrated in Figure 4. The design features of this filter have been relied upon for more than 60 years in municipal applications. 

Removability of Toxic Organic Pollutants from Wastewater in the Primary Lead Subcategory... 

A major disadvantage of the Wacker chemistry using chloride catalysts is the production of chlorinated byproducts such as chloroethanal. These have to be removed since they are toxic and cannot be allowed in the wastewater. In the small recycle loop the catalyst solution is heated to 160 °C which leads to decomposition of chlorinated aldehydes under the influence of the metal chlorides. The traces going over the top in the gas/liquid separator have to be removed from the wastewater by different means. The toxicity inhibits biodegradation. Chlorine free catalysts have been studied but have not (yet) been commercialised. 

When we look at biological systems, the problem of re-release is particularly critical. In wastewater treatment Nitrogen control and Phosphorous control have been identified as critical elements in preventing algal blooms downstream from wastewater treatment plants. Part of the problem in designing the wastewater process is control of the re-release of these compounds. Nitrogen can be reduced back to a gas, but Phosphorous has to be treated by precipitation to remove it Irom the wastewater stream. The same is true for almost any of the heavy toxic metals such as Arsenic, Lead, Copper, Uranium, and Cadmium to name a few. Safe to say, this is also a common problem with phyto-remediation systems. 

For removing low levels of priority metal pollutants from wastewater, using ferric chloride has been shown to be an effective and economical method [41]. The ferric salt forms iron oxyhydroxide, an amorphous precipitate in the wastewater. Pollutants are adsorbed onto and trapped within this precipitate, which is then settled out, leaving a clear effluent. The equipment is identical to that for metal hydroxide precipitation. Trace elements such as arsenic, selenium, chromium, cadmium, and lead can be removed by this method at varying pH values. Alternative methods of metals removal include ion exchange, oxidation or reduction, reverse osmosis, and activated carbon. 

In all applications where finely divided powders are used (such as talcum, cement, charcoal powder), the property of these will depend mainly on the surface area per gram (varying from a few square meters [talcum] to over 1000 m2/g [charcoal]). For example, if one needs to use charcoal to remove some chemical (such as coloring substances) from wastewater, then it is necessary to know the amount of absorbent needed to fulfill the process. In other words, if a 1000 m2 area is needed for adsorption when using charcoal, then 1 g of solid will be required. In fact, under normal conditions, swallowing charcoal would be considered dangerous because it would lead to the removal of essential substances from the stomach lining (such as lipids and proteins). 

Sometimes we have to precipitate one ion of a sparingly soluble salt. For example, heavy metal ions such as lead and mercury can be removed from municipal wastewater by precipitating them as the hydroxides. However, because the ions are in dynamic equilibrium with the solid salt, some heavy metal ions remain in solution. How can we get rid of the remaining ions ... 

Groffman, A., Peterson, S., and Brookins, D. (1992). Removing lead from wastewater using zeolite. Water Environ. Tech., 5, 54. 

Releases to Land. Wastewater from the grid paste mixing scrubber is discharged to a surface impoundment and evaporated. Although your facility historically has removed lead sludge from the surface impoundment each year, this has not been done for the past two years, as process changes have caused the sludge to accumulate more slowly than in previous years. Therefore, the impoundment must be considered an on-site land disposal unit, and releases to the impoundment must be reported in Part III, Section 5.5.1, of the form, and not in Part III, Section 5.3. 

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