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Monday, February 22, 2016

Heavy Metal Contamination

Hastelloy is a common alloy that used in sewage pipe due to it's high corrosive resistance and high tensile strength. The sewage from city will flow to suburb through pipe. In the sewage, it contain a lot of chemicals that produced by citizens. With the time goes by, the impurity in the sewage will come closer together and shape precipitate attach inside the pipe. Which will jam the normal circulation of sewage. To solve this problem, people usually add some acid in the sewage to dissolve the precipitates.

Specifically, the common precipitate is CaCO3 and the common acid used is HCl.
Chemical Equation:
2HCl(aq)+CaCO3(solid)àH2O(liquid)+CO2(gas)+CaCl2(aq)


As we see, by reacting with acid, the precipitate will decompose to CO2 gas and soluble salt.
Image from url
However, this solution caused another unperceived problem. That is heavy metal pollution. In each joint of 2 pipes, people will use high temperature fire to burn the metal and solder them together. Notice that in the solder process, the heavy metal in the pipe will be oxides and expose outside, and directly contact with sewage. When people add acid to dissolve the precipitates, at the same time, those heavy metals will be dissolved too. They will exist in sewage flow into river and sea in form of ion and enter the recycling of nature. Fortunately, people realized that and do some change in pipe to reduce the contamination of heavy metal right now.

Check out this website for more information:
https://www.nlm.nih.gov/medlineplus/ency/article/002822.htm

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2 comments:

  1. Aryn ThomasMarch 5, 2016 at 1:13 PM

    I never considered how acids used to clean pipes could dissolve harmful metals. What are the effects of heavy metals entering river systems and oceans? What threats do they pose to aquatic ecosystems and can they be removed once they enter the water cycle? Great post!

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  2. UnknownApril 6, 2016 at 1:11 PM

    Thanks for your response. First, when heavy metal ion enter the river or ocean, some of them will sink to the bottom of river and ocean, and deposit into the mud of seabed. Those in the mud will effect normal biological reaction of some marine plants. Also, the heavy metal in the water will broke the bio-system of marine animal. Another way harmful effect passed by food chain. The fish in the river or ocean eat the plants that contain heavy metal, the big fish eat small fish that contain heavy metal, and our human eat the big fish that contain heavy metal. The toper position of food chain means more heavy metal that creature absorbed. Actually, it is kind of hard to eliminate the entire heavy metal in river or ocean. But there are still some ways, like by use precipitation ways in chemistry or plant certain plants to absorb heavy metal. But I think the most important ways is not pollute the heavy metal into river or ocean. People literally can do some clean process before discharge. Hope this response can help you figure out your haze!!!!!!!

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