Release Mechanism Of Heavy Metal In Sintered Brick

Using solid waste to produce sintered bricks is an effective way to fix hazardoussubstances and achieve resource recycling. However, heavy metals in the sintered bricks arelikely released into the environment in the course of long-term use, which may do harm to theenvironment and human health. Therefore, it is necessary to do research on the release andrelease mechanism of heavy metals in sintered bricks. Environment safety assessment ofsintered bricks is also very important.In this article, sintered bricks were made by simulation experiments, which were in theline with the quality standards. Release characteristics of heavy metals in sintered bricks andscenario were analyzed. The experiment data combined with environmental parameters ofChina’s acid rain area can identify that the sintered brick road as the simulate scene. Therelease laws of heavy metals were studied under this simulated scene and release model wasdeveloped. The results showed that:Leaching ability of heavy metals in sintered bricks was related to the content of heavymetals. The leaching amount was the highest when the heavy metal content was0.8%, andwas lowest when the content was0.05%. The pH of leaching reagent was an important factorimpacting the leachability of heavy metals from bricks. In the investigated pH range, differentheavy metals had different leaching characteristics. Changes in pH had no significant effecton the release of Cr and As. The leaching amount of Ni and Cd decreased when pH increased.Leaching amount of Pb was larger in strong acid and alkaline condition, but very low in therange of pH from5.59to9.86. The leaching method impacted the release of heavy metals insintered brick. The release amount of Cr、Ni、Cd and Pb were higher in continuous conditionthan that in intermittent condition, but the release amount of As had no significant differencein these two conditions. The reason of this phenomenon might be that the intermittent storagereduced the concentration gradient between the pore water and leach solution, so continuousleaching conditions was easier for heavy metals leaching. And the carbonation in intermittentstorage changed the mineral phase of the sintered bricks. The parameters of the simulation experiment were: extraction solvent was a blend ofthick HNO3and H2SO4, and its weight ratio was1to2, acidity of extraction solvent was3.20(pH); liquid to solid ratio (L/S ratio) was20to1; and the leaching method was continuousleaching.In the leaching experiment, the leachate concentration of Cr, Ni and As achievedequilibrium after16days, Pb needed4days, and the release of Cd ascended all the times. Themajor release mechanism of Cr, Ni and As was diffusion control. Leaching of Cd wascontrolled by solution. Releasing of Pb appeared to be surface wash-off.Release models were made by fitting the experiment data. The second-order equationcould well describe the release of Cr、Ni and As. The parabolic equation could be used todescribe the release of Cd. And the double constant equation was more suitable to describe therelease of Pb.