Removal Of Arsenic And Other Heavy Metals From Semi-conductor Industry Waste Water

As an important heavy-metal element on earth, arsenic is on and on showing its two-side character in people's life.In the beginning, arsenic was used as an ingredient of the effective pesticide. Later it was broadly used in industry, stock-raising, medicine and food-making.But because of people's lack of self-protection and environmental protection in the early days, they didn't notice the toxicity of arsenic and didn't have good self-protection and environmental protection. So the arsenic compound was discharged into the environment because of people's ignorance of its toxicity, and more and more lives were killed and the environment was polluted more severely.As to the source of arsenic, there are two big kinds of sources: natural source and man-made source. Arsenic pollution caused by nature can't be controlled by human being, such as the blast of volcano. Man-made sources are those arsenic compound mat are used in people's life and work and discharge as waste into the environment.Arsenic pollution is becoming an more and more serious environmental and social problem. Now man-made pollution is the most severe. Today, more and more drinking water in different country and district are polluted by arsenic compound that is threatening people's life. So many countries have made relevant standard of drinking water. In all these standards, the American standard is the most strict(As concentration is no more than 10pp).When the technology goes ahead, semi-conductor industry has got full development. But as the main component of semi-conductor industry, gallium, indium and arsenic will be discharged into the waste water in the process of etching, cutting and grinding, and the waste water will have high toxicity. If the waste water are discharged directly into the environment without disposal, it will pollute the environment and threaten people's life.So the purpose of the experiment is to reduce the concentration of arsenic and other heavy metals to the much lower level that will reach the safe standard for discharge. Now, there are so many different methods for arsenic removal, such as: precipitation,adsorption, oxidation, ion exchange, reverse osmosis, electrolysis and so on. As to the method of adsorption, materials that have good absorbing ability such as bentonite, red mud and active carbon can be used as adsorbent.But the waste water discharged by semi-conductor industry is different from other kinds of waste water, because the concentration of arsenic in the waste water from semi-conductor is not very high(from 1 to100ppm),and it was blended with indium and gallium. So after considering all the factors above comprehensively and experimenting repeatedly, the author find an easier and more economic way to reduce the concentration of arsenic in the waste water, and the efficiency of this method is high to 99.6%. Because all the materials used in the experiment is cheap and familiar, there will not be economy problem and second pollution.