Study On Environmental Toxicity And Electrokinetic Removal Technology Of Mining Slag

In recent years, China has seen a rapid increase in pollution incidents resulting from heavy metal due to intensive development and exploitation of various kinds of mineral resources. In this dissertation, the environmental effect of an old smelting slag piled in Fengdu county since Ming and Qing Dynasty, southwestern China of Chongqing has been investigated. The environmental activity and pollution prevention techniques of heavy metal in smelting slag have been systemically studied. The following conclusions are drawn:1.The result of X-ray diffraction analysis shows that oxidate and silicate are the major components of heavy metals in mining slag.Through SEM analysis we can observe that the surface of residue particle is rough and the holes in residue particle surface indicate the signs of natural weathering or corrosion2. The heavy metal content in mining slag is high. The average content of heavy metal (zinc plus plumbum) is up to 82381.4mg/kg. For hundreds of years, over 26.4% of lead plus zinc has been released into the surroundings.3.The optimized BCR sequential extraction procedure was used to analyze speciation distribution of heavy metals in mining slag. The results of speciation analysis test showes that two-thirds content of zinc and cadmium in mining slag are contained in a non-residual state with a moderate environmental risk.4. Roll over leaching procedure was adopted to carry out extraction toxicity test. The extraction quantity of lead, arsenic and cadmium all is lower than the"Identification standard for hazardous wastes - Leaching Toxicity identification". The extraction quantity of zinc is 10.1～28.7 times than the value of the"Identification standard for hazardous wastes - Leaching Toxicity identification", which suggests that the mining slag is a hazardous waste with its extraction toxicity. The correlation analysis result shows that the extraction toxicity of smelting slag and heavy metal species distribution are closely related.5. Fixed-dose procedure was adopted to carry out acute toxicity test with clean KM mouse as animal subject.In the experimental process, KM mouse appear no abnormal behavior and spirit At the end of the test ,the KM mouse were dissected. The organs of the KM mouse are normal.6. Two mainly steps controlling the electrokinetic removal of heavy metal from ancient pyrometallurgical slag: heavy metal extracted from the pyrometallurgical slag; the migration and enrichment of the metal ions. The experimental data show that 1.0～2.0 V/㎝ is an effective and economical voltage range for electrokinetic removal. Enhanced reagent addition and conversion electrodes can improve electrokinetic removal performance. The latter is more obviously. The use of cation exchange membrane to control the pH of cathode compartment could effectively solve the focusing effect and reduce environmental activity of heavy metals in mining slag. Furthermore, the extraction toxicity of mining slag is also greatly reduced.7. The chemical reaction rate of the leaching and release of heavy metals in electrokinetic removal system are controlled by three conditions: external diffusion resistance,internal diffusion resistance and chemical reaction resistance. Though reduction of the particle size and the improvement of electroosmotic flow,it could enhance the leaching efficiency of heavy metals in electrokinetic removal system. Mathematical model of transport in electrokinetic removal system is upbuilded.The following partial differential equation for transport of pollutants in electrokinetic removal system is proposed. Through the numerical simulation of transport of pollutants in electrokinetic removal system, the uneven distribution of electroosmotic flow was observed.