| Many studies paid more attention to the pollutions caused by heavy metals at home and abroad. Most of the previous scholars have been limited merely by means of total amount of heavy metals, however, hazards and toxicity of heavy metals not only depended on their physical and chemical properties and speciation, but also on the valence states and the chemical forms of the heavy metals. Against this background, it was important to identify and analyze the speciation of heavy metals in solid wastes. Available state of heavy metal was considered as a standard to evaluate the harmfulness to human beings and eco-environment, therefore, the research for heavy metals has important practical significance.Based on the research of heavy metals in environmental samples in documents, novel methods have been developed for the separation/preconcentration and speciation of cadmium and zinc in solid wastes. These methods combined liquid-liquid extraction and cloud point extraction of high preconcentration factors with flame atomic absorption spectrometry (FAAS) of high sensitive. Moreover, a research was conducted to analyze and leach Cr (Ⅵ) in chromic slag by a right extractant. The major contents were described as follows:(1)Determination of water-soluble and acid-soluble Zinc by flame atomic absorption spectrometry after ligandless cloud point extractionA ligandless cloud point extraction (CPE) procedure has been developed for determination of water-soluble and acid-soluble zinc in solid wastes by flame atomic absorption spectrometry. The proposed approach was based on cloud point extraction of zinc without ligand using polyethylene glycol octyl phenyl ether (OP) as surfactant. The surfactant-rich phase was dissolved with1.0mL0.1mol·L-1HNO3in ethanol to decrease the viscosity. The effects of experimental conditions pH, concentration of buffer solution and OP, equilibration temperature and time on cloud point extraction were studied. Interference of coexistent ions and their elimination were also discussed in detail. Under the optimized conditions, the calibration graph was linear in the range of0～0.20μg·mL-1for Zn with a correlation coefficient (r) of0.9985. The linear equation was A (absorbance)=1.1657C (μg·mL-1)-0.0016and the limit of detection was4.4×10-3μg·mL-1. The relative standard deviation (R.S.D) was2.4%for nine replicate measurements of0.10μg·mL-1Zn. The relative recoveries of available Zn of the samples were ranged from94%to113%. The results demonstrated that the environmental sample matrices, in our present context, had little interference on the analysis of available Zn by FAAS after CPE. These results indicated this method was reasonable for trace analysis of zinc.(2) Determination of trace cadmium in environmental samples by flame atomic absorption spectrometry after triple complex extractionIn this study, a new analytical procedure was developed for determination of trace cadmium in environmental samples by flame atomic absorption spectrometry. In the proposed approach,1,10-phenanthroline mono hydrate and alizarin yellow R were used as chelating agents, and methyl isobutyl ketone (MIBK) was selected as extractant. The samples were injected in flame atomic absorption spectrometry in form of organic phase, and the sensitivity of determination of cadmium was greatly improved. The effects of experimental conditions pH, concentration of chelating agent and buffer solution on liquid-liquid extraction were studied. Interference of coexistent elements and their elimination were also discussed in detail. Our experiments showed that interference could be eliminated with potassium sodium tartrate. Under the optimized conditions, the calibration graph was linear in the range of3.0×10-3-0.25μg·mL-1and the detection limit was1.7×10-3μg·mL-1. The relative standard deviation was1.1%. This analytical method could be applied for the determination of environmental samples with satisfactory results because of its simpleness and convenience.(3)A research for leaching chromium residue after the detoxification of hexavalent chromiumIn this part, a suitable extraction method was found through the lenching and determination of hexavalent chromium in the chromium slag after detoxification. A series experiment was conducted to research the extract efficiency of doubly deionized water, KCl、Na2CO3、Na2CO3/NaOH、Na3PO4on the extraction of hexavalent chromium in the solid wastes, finally,0.08mol·L-1Na3PO4was chosen as the leaching agent, in the meanwhile, FAAS was considered as the testing methods. This analytical method could be applied for the determination of solid waste samples with satisfactory results. This study to understand the detoxification of hexavalent chromium in the chromium slag pollution provided an important reference for comprehensive evaluation of leaching technology and rational utilization of this technology for remediation of heavy metal pollution. |
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