Study On Eletrochemistrcal Leaching Behavior Of Heavy Metal Ion From Cement-based Materials

The heavy metal pollution problem closely involved with environmental governance has been highly valued by many countries,because it is widely distributed in the atmosphere, water and soil, of strong toxicity, and degrades difficultly, tends to accumulate in nature. There are many methods for the determination of heavy metals leaching, which are mainly based on short-term crushing and leaching methods, and each country has its corresponding measurement standards. In view of the leaching behavior of heavy metals from the cement-based materials, there is no unified method at home and abroad, and the method for determination of solid waste is often adopted in China. The method needs to be broken sample, oscillation leaching and so on, which can lead to the damage of the solidified body, and the leaching method and the actual situation does not match, and the pertinence is not strong. Under this background, a method for testing the leaching of heavy metals is established in this paper. That is electrochemical accelerated leaching method, and the leaching behavior of heavy metal ions in cement based materials was studied by the method.First, by using the self-made electrochemical accelerating device, the 30 V DC voltage is applied to the ends of the specimen in the deionized water environment, accelerate the migration and leaching of ions in solidified body, and use the titration based on complesation reaction or inductively coupled plasma emission spectrometry for the determination of dissolution results. Characterizing by the concentration of leaching, rate of leaching and the change of the p H in the anode and cathode, the effects of the kinds, content and valence state of heavy metals on the solidification characteristics of cement- based materials are analyzed. Also, the feasibility and effectiveness of the method is demonstrated from the macroscopic and microscopic aspects.Second, the effects of 8 kinds of modified concrete on the short-term result of solification and characteristics of the specific heavy metals are further studied by using electrochemical accelerated leaching method for 60 hours. The relationship between the leaching content and the type and dosage of the reagent is established.Finally, after short-term accelerated leaching method,4 Pb2+ samples adding different agentia are taken from the groups, and dissolution test goes on to be carrying out without limiting time until the dissolution rate reacheshe maximum value. According to the static leaching theory and diffusion mechanisms, the cumulative leaching fraction, Periodic leaching rate, the effective diffusion coefficient are analyzed. We come to the conclusion that the long curing effect of 2 group specimens of adding calcium-based bentonite bentonite and silica fume together with cement on Pb2+ is better. At the same time,the test result of leaching are used to fit the data, and it is found that the reliability of the linear function fitting is high(correlation coefficient is above 0.96). In addition, the error between the maximum leaching mass,which is obtained by the numerical fitting of the samples with silica fume and DTCR,and the actual results of the 2 samples is less than 2%.