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environmental aluminum hydroxide dust catcher in mwanza

the environmental impact of anodizing

the environmental impact of anodizing

The process ofanodizingwith a sulfuric acid bath produces two byproducts: degraded sulfuric acid and aluminum hydroxide. Aluminum hydroxide is a compound of aluminum from the anodized part, and hydrogen and oxygen from the acid. Classified by theEPAas hazardous, aluminum hydroxide wastewater cannot simply be dumped into a municipal wastewater system. The EPA has strict standards for the highest allowable aluminum concentration level upon disposal; degraded sulfuric acid must also be neutralized before disposal to a ph of between six and eight.

Through give and take between the industry and the EPA, the EPA sets up guidelines and standards called Best Available Technology Economically Achievable (BAT). BAT standards are then mandated for waste disposal. Some very innovative solutions to waste management have since been introduced that not only reduce the waste that needs disposal, but also reclamation and recycling of the aluminum metal itself.

The first step in dealing withwastewateris to produce less of it; this is the idea behind electrodialysis. Electrodialysis is a process of extending the life of theanodizingelectrolyte by removing the aluminum ions from the bath. Electricity charges the ions that are then driven through an ionic sensitive membrane on their way to an oppositely charged electrode. The membrane picks up the aluminum and allows the acid electrolyte to pass through and continue on back to the bath. The collected aluminum hydroxide is sludge, and the acid bath is then cleaned of it.

In another process calledacid sorption, the exact opposite takes place. In acid sorption, ion exchange resins absorb the sulfuric acid while the metals pass by. The resins then release the acids in a water wash, and the metals are collected for disposal.

In another method, flocculating agents separate the aluminum from the electrolyte. These polymer additives combine with the aluminum hydroxide and congeal, creating a wooly mass that is skimmed away.The only equipment needed is the agents themselvesthis makes it an attractive process to both large and small businesses.

In all of the above processes, heavy aluminum hydroxide sludge is left. Presses can squeeze out water, and sludge dryers further concentrate the sludge making it up to 75 percent solid. Small producers (less than 100 kilograms per month) are exempt from EPA guidelines in the disposal of hazardous waste and may take it to a general municipal landfill. Larger producers, though, must adhere to EPA regulations in the storage, transportation, and disposal of their waste. Similar in size to the U.S. Tax Code, there are literally thousands and thousands of pages on rules and regulations pertaining to hazardous waste in the U.S. Code Title 40, Protection of Environment.

Section 261.31 of U.S. Code Title 40, titled Hazardous Wastes from Non-specific Sources calls wastewater treatment sludge from the chemical conversion coating of aluminum by the name Industry and EPA Hazardous Waste No. F019. This simply means that if an anodizer is not an exempt small producer as described above, the anodizer must comply with EPA hazardous waste regulations in the disposal of aluminum sludge.

Air pollutionis a concern in the anodizing shop. In the anodizing bath, sulfuric acid fumes are released that can be hazardous not only to the air, but to employees in the plant. Local exhaust ventilation removes the fumes at the source point and a scrubber provides additional cleaning before release into the atmosphere. The concentration in the electrolyte bath may be only 10 to 20 percent, but long-term exposure causes permanent health problems if precautions are not taken. In the atmosphere, released sulfuric acid subsequently falls back to the ground as acid rain, which adversely affects flora, fauna, soils and surface waters.The Clean Air Actregulates the release of sulfuric acid into the atmosphere, not only controls its release, but also record keeping and reporting.

Besides the electrolyte bearing sludge, other wastes are generated in the anodizing process. The solvents and cleaners used in the pre-treating process, as well as the materials removed from the aluminum, must be collected and properly disposed of. After anodizing, there are also dyes and sealants that need additional disposal.

Hazardous waste contractors are an expensive way to deal with disposal, but save the anodizer from compliance errors that can be even more costly.Hazardous disposalcontractors services range from simpleconsultingto complete handling of thewaste. Once in hand, the waste isrecycled, incinerated, ortaken to a landfill.

If sludge contains high enough levels of aluminum, it can be removed from sludge and sent off for use in the manufacturing of bricks and clays, cosmetics, and paper products. This process often proves unfeasible due either to the contaminants in the sludge or its low metal content per volume.

Aluminum sludge is often taken for disposal to a Resource Conservation and Recovery Act (RCRA) landfill. RCRA landfills are lined with six inches of synthetic membranes that sit on top of at least five feet of solid clay. Monitors at different levels detect leaching and all collected leachate is processed and treated.

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