Study On Species Of Heavy Metals And The Chemical Remediation Technology By Solidification And Solubilization For Sewage-irrigated Soil

There are currently many sites that contain soils contaminated with heavy metals because of incresement of population, rapid development of industry, leacheat and run off from waste solids on soil surface, hazardous material in atmosphere fall on the ground and irrigated by sewage water, et, al. Heavy metal-contaminated soil is one of most common problem and much need of recognition and settlement. There are mainly five kinds of soil pollution: heavy metal-contaminated soil, rdionclides of metal, pesticides and hazardous organic compounds and biologic containment. It is not only hard to degrade and also retain in surface of soil, which easy to assimilate by crop, and tranfer in food chain. Heavy metal pollution is the important reasons for degrading of soil quality, and comparing with orther pollutants the particularity of metal pollution is that it is hard to biotic degrad and etire died away. When reached a high concentration, it can be detrimental and destroy the soil-plant system.It was only focus on developing of our national economy in long-term, and people hold viewpoint of contamination first, then remediation on environmental pollution. So the environmental protect against pollution has been ignored, which lead to reduce of environmental quality. Nowdays survive and development of people maintain close ties with the environment and the proposition of sustainable development strategy is to enhance the knowledge that human protect the ecological environment to a new height, it is also required that doesn't influence the survival ability of offspring while meeting contemporary people's demands. So it is necessary for us to take effect measure to effectively increase the resistance to bioavailability and toxicity of heavy metals in sewage farm in the light of situaion of metal-contaminated soil in Baiyin.Chapter 1.Situation of soils contaminated by heavy metals and the chemicalremediation technology by solidification and solubilizationA review with 75 references is given on characteristics and current situation of contaminated by heavy metals and the relation between species and bioavailability of heavy metals in soil. There are two main type of remediation for metal contaminated soil: solidification/stabilization and desorption/solubilization, which mainly are discussed. In addition, some kinds of agents for solidification and desorption of heavy metals in soil also dicussed in these section.Chapter 2.The effect of humic acid on species of Cu,Cd,Pb,Zn in sewage farm.The superfluous heavy metals are harm for health of human being and the different speciation of heavy metals has direct influence on tranfer and transform and toxicity of heavy metals in soils. Humic acid is the most common natural organic matter in soil, and it is about 60% in soil organic matter. It has an important influence on toxicity and bioavailability of heavy metals in soil environment because of its complex structure and high activity of functional groups. Although, natural organic matter and its effect on tranfer and tranform of heavy metals have been studied, it mainly about sorption and desorption of heavy metals, but the effect of humic acid on speciation of heavy metals has not studied in previous work. To investigate the effects of humic acid on the speciations of heavy metals, such as Cu, Pb, Zn and Cd in sewage farm in Baiyin, four kinds of organic matters including humic acid, EDTA, citric acid and acetic acid were added, respectively, in polluted soil with a method of successive extraction performed to determine the species of heavy metals. The results showed that humic acid could remarkably decrease the content of soluble heavy metals with about60—80 %, while increase the fractions of Fe+Al+MnO_x and carbonate, which demonstrated clearly that huimc substance, under certain conditions, could effectively increase the resistance to bioavailability and toxicity of heavy metals in sewage farm.Chapter 3.Study on sorption of Cd on loess soil affected by humic acid.Humic acid is the most common natural organic matter in soil, and it has some engernic groups. It can be sorption and complexing with heavy metals because of its special structure and high activity of functional groups. Natural organic matter and its effect on tranfer and tranform of heavy metals has been studied, mainly about sorption and desorption of heavy metals, In this section vibration-centrifuge experiments were chosen to study on adsorption isotherms and adsorption thermodynamics of Cd on loess soil affected by humic acid in order to study the tranfer and transform regulation of heavy metal in soil. The results showed that the adsorption of Cd on loess soils fitted well with Freundlich isothermal equation no matter with or without humic acid, and the adsorption capacity of Cd increased from 29.22 mmol·kg^-1 to 31.39 mmol·kg^-1 by adding 10ml 55mg·L^-1 humic acid solution at 25°C, The adsorption quantity of Cd were reduced with increasing of environmental temperature, which indicated that adsorption of Cd was an excergic process, meanwhile, the respective adsorption standard free energy wereâ–³G₂^θ=-0.9497kJ·mol^-1 andâ–³G₁^θ=-0.8885kJ·mol^-1 with or without humic acid. The adsorption kinetics of Cd fitted with Evolich kinetics equation the best, and then was Double constant equation, but it changed to Double constant equation at present of humic acid. The adsorption speed of Cd is faster then no humic acid at present. The adsorption capability of Cd increased with an increase in the humic acid concentration and the solution pH. The adsorption quantity of Cd was high at low pH then high pH.Chapter 4.Surfactants enhanced soils washing efficiency of heavy metal with EDTA.Soil washing is common used to treat soils contaminated with heavy metal that separated heavy from soils in an aqueous-based system. The wash water may be augmented with a basic leaching agent, acid, surfactant, pH adjustments, or chealting agents in order to separate heavy metals that absorbed on soil surface. The most common chelating agent studied in the literature is ethylenediamine-tetraacetic acid (EDTA) because of its strong chelation nature, and little influence on soil nature. Meanwhile, the most study on desorption of organic pollutants in soils by surfactants carried out, but not mainly about heavy metals desorption. In this section, the effects of sodium dodecyl sulfate(SDS),laural polooxyethylene ether(Brij35) and Ethylenediaminetetraacetic acid(EDTA) on desorption of Cd and Pb from the soil contaminated by the wastewater irrigation are studied in laboratory, respectively, while the influence of adding SDS and Brij35 on EDTA desorption capacity is certified. The changes of the heavy metal's species before and after desorption in the soil matrix are certified too. The experimental results show that the removal of Cd from the soil increases from 61.67% by using EDTA alone to 79.68% if adding SDS, meantime, the removal of Pb increases from 57.25% to 79.68%. However, the addition of the surfactants could restrain the desorption capacity of EDTA, if EDTA has a lower concentration. SDS can significantly enhance the synergetic solubilization of Cd and Pb by an increase of EDTA concentrations. Brij35 has the same effect on the enhanced solubilization of Cd and Pb, but its efficiency appears to be little weaker than SDS. With a comparison of the changes of the heavy metal species in the desorption processes, the contents of soluble and carbonate species were decreased by 60-90% compared to that measured before desorption. It is said that bioavailability and toxicity of heavy metals in sewage farm have been decreased. The research results not only could theoretically provide the approach how to use surfactants to enhance the complexing capacity of EDTA for desorption of heavy metals from soil media, but also could extensively be used in the in-situ flushing technique for heavy metal contaminated soils. The research results not only could theoretically provide the approach how to use surfactants to enhance the complexing capacity of EDTA for desorption of heavy metals from soil media, but also could extensively be used in the in-situ flushing technique for heavy metal contaminated soils.Chapter 5.Study on desorption of heavy metal in sewage-irrigated soil bycomplexing with saponin.Biosurfactant which contains a hydrophobic portion and a hydrophilic group from qullaja bark seemed to be an attractive cleaning agent in environmental applications for researchers because of its biodegradability, low loxicity, possibility of reuse, and high economic value.In this section, the vibration-centrifuge experiments were performed to evaluate the feasibility of using saponin for the removal of heavy metals from the soil contaminated by the wastewater irrigation in laboratory, respectively, the sequential extraction procedure were selected to determine the speciation of heavy metal, at the same time, recovery of heavy metals and recycle of used saponin were also studied as a method for decreasing the costs of remediation processes. The results showed that desorption efficiency could be enhanced with the increase of the added Saponin concentrations, and could finally reach 43.9%, 95.1%, 83.5% and 20.7% for Cu,Cd,Pb,and Zn, respectively, by adding 3.0% of Saponin, while desorption by water alone was less than 5%. It was also found that the desorbed amount gradually decreased with the increase of pH values of the soil, which indicated that the high removal only take place in the week acidic environment. The ionic strength slightly had a negative influence on the desorption of Cd,Cu, but no efforts on Pb,Zn. Comparing the spices transformation of heavy metals before and after desorption in the soil matrix by Tesseri method, it was evident that soluble spices and carbonated fractions of Cu,Cd,Pb,Zn adsorbed on the soil surfaces were washed away tremendously but oxidant-combined and residual spices only reduced little. As a result, the toxicity and bio-reusability of the heavy metals were significantly decreased.