Study On The Release And Transfer Law Of Pb And Cd In Pyrite Smelting Slag

In this paper, the author takes smelting slag of a sulfonated sulfur factory in Chongqing as the research object to carry out special study. The study includes: The properties of the waste slag were characterized, and research on the morphological structure and migration regularity of Pb and Cd under the effect of electric field; Research on the migration and removal rate of heavy metals under three-dimensional electrode conditions; Analysis the electrokinetic removal mechanism and mass transfer pattern. Now get the following conclusion:Waste slag samples contain a variety of heavy metal elements which the main existing forms of the heavy metals are oxide and silicate, and the slag shows slightly acid. This shows that acid leaching could increase the released amount of heavy metals when doing the research on electrokinetic removal. The results of leaching toxicity test showed that release is a long term accumulation process and the released elements are a small quantity of heavy metal. It is evidenced from the speciation analysis that the extractable content of Cd is lower than Pb in the waste residue and Cd is dissolved more easily and makes pollution to environment.Electrokinetic removal experimental study shows that the removal rate of Pb and Cd in waste residue increased gradually with the increase of the voltage gradient and the decrease of the p H value, and under the same conditions, the removal rate of Cd was smaller than that of Pb. The change of p H value was mainly affected by the acid extractable state of Pb, and the change of the voltage gradient mainly affected the Pb’s reduction state. Therefore, the acid extractable state and the reduced state of Pb in the waste residue are the two main factors influencing the Pb removal rate. The change of voltage gradient and p H value mainly affect the oxidation state of Cd, which has little effect on the extraction and the reduction of the acid. Accordingly, the oxidation state of Cd in the waste residue is the main factor affecting the removal efficiency of Cd.After the addition of three-dimensional Electrode, the voltage drop and p H value have insignificant impact on the sample zone, and the current change has the same tendency, but the current in the system reaches maximum value about 24 hours advanced than before, the overall current becomes large. The removal rate of Pb and Cd in the waste residue was significantly improved, the maximum removal rate of Pb was increased by 31.88 % and Cd maximum removal rate increased by 24.5 % among the two groups of experiments. The dissolution of heavy metals has been increased, and it increases the heavy metal elements in some slag transfer from residue to non residue state, thus reducing the environmental activity of heavy metal elements. Therefore, the energy consumption of unit mass of the waste residue is obviously decreased.This paper has obtained the following innovative achievements:(1) The speciation analysis was first used for the study on electrokinetic removal of heavy metals in pyrite slag. Raises the electrokinetic removal efficiency of Cd and Pb is closely connected with the morphological structure of elements, so as to provide support to the study of chemical mechanism of the dissolution and migration of Pb and Cd.(2) Based on the conservation of mass, this paper creats a model for mass transfer with the migration of heavy metal in the process of electrokinetic removal, and introduces electrokinetic effects and physical mechanism of Pb and Cd dissolution migration.(3) It is the first time that the method of three-dimensional electrode applied to electrokinetic removal of heavy metals, this can enhance the removal efficiency of heavy metal and reduce the energy consumption to a large extent.