The Solidify Performance And Effect Mechanism Of Waste Containing Heavy Metals

With the great progress of society there are piles of solid wastes which were produced inevitably by industry and daily life including urban construction waste, industrial waste and municipal solid waste and so on. Most of them contain heavy metal element and other a range of toxic substances. In accordance with the provisions of nation in China that this kind of materials must be disposed in order to reusing. If these materials were handled improperly, there will have an impact on the living conditions of mankind. The method of cement solidification for its low-cost, simple treatment process and operation, a very good advantage of the fixed heavy metal, which has been widely used.This dissertation is for MSWI fly ash and slag as the research object studying solid waste. With the development of society and the increasing municipal solid waste, Incineration method practices quickly. In recent years, China's solid waste incineration increase with the scale rate of 5 percent. At present, the disposal of solid waste and final safe disposal have become a serious problem. Solidifing heavy metals, MSWI fly ash and MSWI slag was for the subject investigated of this dissertation. And the mechanism of cement solidifing heavy metals was studied; the effect of cement solidifing MSWI fly ash and slag was discussed; and the toxicity characteristic leaching of cement block was investigated.Studies have shown that under laboratory conditions, in the leaching solution pH value of 2.88, the solid-liquid ratio of 20:1, with oscillation of 18h, the maximum concentration of heavy metals is up to most leaching volume. In the laboratory using the largest amount of 2.0% and solidifing heavy metal elements, cement can solidify heavy metals effectively. After the leaching toxicity, the hydration of cement block did not reach the national emission standards and the effect of solidifing heavy metals by sulphoaluminate cement was better than which was by ordinary Portland cement.Under the condition of leaching test, MSWI fly ash has some leaching toxicity. If MSWI fly ash was exposed in the environment, even the threshold level was lower than leaching value which was in laboratory, under the natural condition including acid rain, hailstone and some adverse conditions, heavy metals could be leached much, which can be dangerous to environment, therefore, they still need to be solidified. After studying in the laboratory, cement can be effective in curing of the heavy metals of MSWI fly ash. With the increase in fly ash, the trend in solidifing heavy metal with cement increased, which was less than the national standard. In 40% and 50% of the cases, the curing performance was stability, therefore, in the use of MSWI fly ash which can be considered 80% or less.MSWI slag as a major by-product of dealing with municipal refuse by burning method has smaller leaching toxicity than MSWI fly ash. Many studies have shown that the activity of MSWI slag was more than MSWI fly ash, which can be used as blended material. When the introduction was 30%, MSWI slag had evident influence for the setting timen of cement; when the introduction was 50%, the final setting of cement extended more than 2 h; mixing waste incineration slag to Portland cement, with the amount of MSWI slag increasing, the strength of cement declined. When the content was 20%, the grade of cement dropped one grade; when the content was up to 50%, the 3 d compressive strength dropped more than 20%, and 28 d compressive strength had fallen by 40%. ICP tested the leaching toxicity of the MSWI slag and fly ash blended cement, results showed that the qualtity of MSWI slag and fly ash blended cement was little.