Dong Wei Li

Review of Contaminated Sites Remediation Technology

The contaminated site remediation is an important content of site management. Plans for the introduction of measures and requirements to prevent and remediate soil contamination, particularly through the development of inventories of contaminated sites and the definition of targets for prioritization of remediation actions, are expected to have important consequences for site management practice and national site policies. Nowadays contaminated soil and groundwater treatment technologies can be sorted as three categories, that is bioremediation, chemical treatment and physical treatment. Biodegradation generally refers to the breakdown of organic compounds by living organism eventually resulting in the formation of carbon dioxide and water or methane. Chemical remediation is a kind of method that chemical reagent, chemical reaction and chemistry principles are used to reduce the mobility, organisms use ratio of heavy metals and decrease the heavy metals in the soil so as to remediate and repair the soil. Physical treatments in the remediation of contaminated site contains revising methods, capping methods, stabilization methods, electrokinetic methods and so on.

Enhanced Electrokinetic Removal of Heavy Metals in MSWI Fly Ash Assisted by Cation Exchange Membranes

Since MSWI fly ash enriches heavy metals and many toxic components and these components would potentially leach when the ashes are land filled, it is regulated as hazardous waste in many countries. Electrokinetic removal, an electrochemically assisted extraction method, has recently been adopted as a new method for removal of heavy metals from MSWI fly ashes. But the generation of metal hydroxide precipitation near the cathode decreased conductivity of electrokinetic removal system and limited metal extraction from the sample area. In this study, cation exchange membrane was used in electrokinetic removal experiment to improve this method. After 192 hours of electrokinetic removal, about 15%Cd,20%Pb, 30% Zn, and 10% As was removed from 2.850kg MSWI fly ash. It showed positive effect compared to the trial test. But there still exists some problems, such as low removal efficiency. Further work should be done to solve it.Moreover, the high conductivity in fly ash limits the current , which in turn causes low electroosmotic flow. While electroosmotic flow is the main factor leting the heavy meatals release from fly ash, it would become the focus in further experiment to look for ways increasing the electroosmotic flow in sample cell.

Heavy Metal’s Potential Harm for Environment of Ancient Pyrometallurgical Slag

The total content of heavy metal in solid waster is usually used to forecast heavy metal’s potential harm for environment.This work was to study the potential harm for environment of ancient pyrometallurgical slag.The heavy metal content in ancient pyrometallurgical slag is high and the average content of heavy metal (zinc plus plumbum) is up to 6.97%.But the leachable quantity of Zn,Pb,Cr and Cd are all very low.It shows that the total content of heavy metal could not represent the harm for environment. Meanwhile,leaching behavior of heavy metal in pyrometallurgical slag was discussed through extraction toxicity test in different pH. The results showed that in neutral condition,the leachable quantity of Zn,Pb,Cr and Cd is at the lowest level and their migration ability were weak.

The Effects of Static Magnetic Field in Leaching Cadmium and Arsenic by Acidthiobacillus ferrooxidans

In view of the pollution of heavy metals in tailings of mining area, considering some metal recycling, in this paper, the method which was environmental friendly, mild reaction, short process, low energy consumption was applied to leaching As and Cd in tailings. Before leaching, Static Magnetic Field was used to deal with leach liquor, to research the effect of leaching rate for As and Cd. The results showed that under the conditions of pulp density 5%, inoculum 10%, leaching temperature 30°C, pH 2.0, magnetic induction intensity separately were 2mT , 5mT , 8mT and 11mT, the leaching rates of As and Cd were increased respectively about 8% and 2%. Besides, magnetic induction intensity also effected. The best magnetic induction intensity in bioleaching of As and Cd were respectively 2mT and 8mT.

Environmental Characteristical Study on Pyrite Smelting Slag

The pyrite smelting slag as industry waste residue was always fully studied in the present research. Due to the complexity of the property of the waste residue,which the environmental hazards of has been discussed in the experiment. Firstly, the complex composition of the waste residue and the primary contamination of heavy metals which included the Copper, Cadmium, Zinc, Nickel, Lead, Chromium and Arsenic usually were determined by XRF scanning. the result of XRF scanning also showed the value for reuse of the waste residue.Secondly,the test investigated the leaching toxicity of the waste residue,the results indicated that the heavy metal of the residue was in low concentration ,in the other words,the slag lixivium was in the range of the required standard, the pyrite smelting slag does not belong to hazardous wastes. The Copper, Zinc and Nickel had not exceeded the standard limit,however, the waste residue could contaminate the surrounding environment if it didn’t been disposed with proper methods.based on the further study, the residue belongs to Class Ⅱ General Industrial Solid Waste and the main phase present in pyrite smelting slag were silicon oxide. Thirdly, through XRD spectra analysis,it can be indicated that waste oxides and sulfate facies were the major phases of heavy metals. So,in order to prevent these potential risks,some effective protection measures should be taken.

The Effect of Silver Ion Catalysis on Bioleaching of Chalcopyrite Tailings

The bioleaching effect of different concentrations of silver ion catalysis on chalcopyrite tailings has been investigated in shaking flasks. In this paper, A.t ferrooxidans were selected for conducting the bioleaching process. Experiments were carried out under the condition of pulp density 150 g/L, inoculation amount 106~7 cells/mL, pH around 2.0, culture temperature 30°C, rotation speed 150 r/min. The silver ion concentrations varied from 0 to 0.05g/L. After a bioleaching time of 24 days, 82% and 55% of copper was dissolved from the ore for the silver ion concentration of 0.01 g/L and 0.001 g/L respectively, compared with only 37% and 13% recovery for the silver ion concentration of 0 and 0.05 g/L. Preliminary tests showed that the silver ion concentration had a markedly catalytic effect on the copper extraction. The experimental results also showed that high silver ion concentration would inhibit the copper extraction. That was because the silver ions at high concentrations are toxic and they can suppress the bacteria growth and oxidation activity.

Environmental Activity of Heavy Metals in Slags Treated by Electrokinetic Removal Technology

Ancient pyrometallurgical zinc generated large amounts of slag. Natural leaching from ancient pyrometallurgical zinc sites had contaminated the soil closed to the deposits. Enhanced electrokinetic removal technology was adopted to treat these slags. In this paper, atomic fluorescence spectrometer and scanning electronic microscope were used to investigate the total metal concentration and the surface topography of slags. The results showed that the heavy metals content in slags was high. The content of zinc in slags was up to 114550mg/kg. The surface topography of slags indicated that that the slags were corroded obviously by rainwater and lots of poisoning elements had released to the surroundings. The optimized BCR sequential extraction procedure was used to analyze the chemical speciation of heavy metals in slags. It could be determined that the evironmental activity of ancient pyrometallurgical slag decreased obviously after the treatment with electrokinetic removal technology and part of the residual fraction of heavy metals in slags transformed to the other fractions during the electrokinetic removal process.

Assessment of Potential Ecological Hazard of Heavy Metals in Farmland Based on GIS

This paper includes the analysis of total content of Cd element of 102 samples in the surface soil of farmland around the slag field. We evaluated the contamination of Cd of each samples and the space distribution with the potential ecological risk index method based on ArcGIS soft. The results showed that: average of potential ecological risk index of Cd is 241.4, Moderate ecological risk area accounted for 2.7% of the study area, strong ecological risk area of the region accounted for 30.1% of the study area, 22.2% of the study area had the considerable ecological risk, and the rest 39% of the study area had the extremely strong ecological risk.

Heavy Metals Leaching Experiment from the Pyritic Tailings by the T.F and T.T Bacterias

The produced and extraction process of pyritic would generate a large amount of pyritic mineral processing solid waste. This kind of waste can lead to land occupation, and contaminate the local water, air and soil. Therefore, in this paper, Thiobacillus ferrooxidans and Thiobacillus thiooxidans are used to deal with the pyritic mineral processing solid waste. The particles, catalysts and bioleaching products between microorganism and pyritic mineral processing solid wast were studied. It is indicated that the microorganism growth and the heavy metals leaching efficiency involve biological and chemical interactions. The experimental results suggested that the T.t was best to bioleach the pyritic mineral processing solid waste, and the efficiency of T.f was worse than that of T.t. The leaching effect of mixed bacterias of T.t and T.f fell in between, the leaching rate would decrease when the pulp density increased. The micro-morphology of bacteria was observed by SEM detector, the single cellular dimension of bioleaching bactreia was about (1~2) μm × (0.2~0.5) μm.

The Isolation and Purification of Sulfur Bacteria Originated from Stockpiling Area of Pyritic Smelting Solidwaste

It was found that there were some kinds of sulfur-oxidizing bacteria in the acidic mine water, and these bacteria could promote the dissolution behavior of heavy metals in the mining smelting waste slags. In this paper we collected a bacterium sample form a mining-water of an abandoned pyrite mine in the southwest of China and named it as FJ strain. We isolated and purified the FJ strain by 9K medium, and then made a primary identification of the purified strain. The FJ strain was gram-negative and in the shape of short rod. The strain was chemoautotrophic and aerobic bacterium, and it could oxidize the ferrous ion or the reduced sulfur as energy source to main the metabolism. The optimum growth temperature and pH is 30 °C and 2.0 separately. And we also found the strain had a considerable acid-producing ability and was eosinophilic. After a comparison and analysis, we confirmed that the physiological and biochemical characteristics of the isolated FJ strains were consistent with that of thiobacillus ferrooxidans, T ferroxidans for short. Therefore we drew a conclusion that the FJ strain we purified was just the target strains T ferrooxidans, the isolation-purification of the bacterium sample was successive.