Studies On The Adsorption Characteristics Of Lead, Cadmium And Copper Onto Solid Phases And Their Main Components In Natural Waters

Heavy metals are released into aquatic and soil environments largely from various anthropogenic activities and pose a serious threat to plants, animals and human beings because of their bioaccumulation, non-biodegradable properties and toxicity even at low concentrations. Adsorption of heavy metals to aquatic solid phases are considered very important in controlling heavy metal behaviors in natural waters. Solid phases as surface coatings (SC),suspended particulate (SPM) and deposited sediment (DS), together with water phases, constitute the multi-phases system deciding the activities of heavy metals in the aquatic environment. However, distinct spatial position and forming conditions like temperature, sunlight and microorganisms etc. make the three solid phases have great difference in contents of main components (Fe oxides, Mn oxides and organic matters). Moreover, microbial composition, crystalline structure, and surface property of corresponding components in these solid phases aren't the same completely, even distinct evidently. The chemically reactive components in different solid phases have diverse binding abilities for trace metals and accordingly affect metal transportation, bioavailability and fate significantly. At present, many researches have been undertaken to investigate the heavy metals' reaction with SPM, DS or other solid phase, but a comprehensive study about heavy metals adsorption onto solid phases, as SC, SPM and DS in the same natural waters have not been found. So in this paper, Nanhu Lake, Jingyue Lake and Songhua River were chosen as natural waters for collecting solid phases samples and adsorption characteristics of Pb, Cd and Cu onto solid phases and their main components were assessed and compared, including adsorption capacity of the solid phases for Pb, Cd and Cu, distribution of these heavy metals to main components in different solid phases and adsorption ability of corresponding components in them. Also, comparison of adsorption characteristics and enrichment characteristics of SPM for heavy metals was investigated too. In addition, the kinetic characteristics of Pb, Cd and Cu adsorption to natural solid phases were compared. Finally, the effects of pH value and organiochlorine pesticide on adsorption of Pb, Cd and Cu to solid phases were studied and some elementary conclusion about associated contamination of heavy metals with organic pollutants was made.The microorganism phases on SC, SPM and DS were analyzed qualitatively and quantificationally. The microbial species, including algae, protoza and the metazoan on solid phases were determined. The results showed that species of microorganisms on the solid phases include Bacillariophyta, Chlorophyta, Cyanophyta, Ciliated Protozoa, Sarcodina etc. SC contains large amounts of vital organic matters such as alga, protozoa, metazoan, which could form orderly layers and consequently constitute minitype ecosystem. Though abundant algae are observed on the SPM as well, the species and quantity of protoza and the metazoan are still inferior to SC greatly. As far as DS, organic matters in the DS consist of non-vital organic matters such as humus (21) and less algae. The preponderant species on the SC was Fragilaria Lyngby in the Bacillariophyta and Genus Vorticella in the Ciliated Protozoa. According to the indication of algae, it was deduced that Jingyue Lake was contaminated with organic pollutants.Selective extraction followed by heavy metal adsorption and statistical analysis was employed to study the thermodynamic characteristics of Pb, Cd and Cu adsorption to solid phases and their main components. The results suggested that adsorption capacity of solid phases for Pb, Cd and Cu in all of three natural waters followed the same order of SC≥SPM>DS. Adsorption contribution of main components in SC for heavy metals in Nanhu Lake was similar with Jingyue Lake. At relatively low concentration, Mn oxides in SC contributed most to Pb adsorption, but Fe oxides contributed most of Pb adsorption at higher concentrations. For Cd adsorption onto SC, contribution of organic matters was the highest, but contribution of Ferromanganese oxides was higher than organic matters. Organic matters were most important contributor to Cu adsorption onto SC regardless of low or high concentration. Adsorption contribution of main components in DS for heavy metals in Nanhu Lake was similar with Jingyue Lake too. For both Pb and Cd adsorption onto DS, Fe oxides were absolute primary contributor, while contribution from the other components was very little. Just for Cu adsorption onto DS, contribution from organic matters was greater than Ferromanganese oxides evidently in Nanhu Lake, but contribution from Fe oxides was greater than organic matters in Jingyue Lake. As far as SPM, adsorption contribution of main components in two natural waters was dissimilar. Fe oxides and organic matters primarily contributed to Pb and Cd adsorption onto SPM in Nanhu Lake, but Fe oxides and Mn oxides contributed to the Pb and Cd adsorption onto SPM in Jingyue Lake.For Pb and Cd adsorption onto solid phases in both natural waters, contribution of Fe oxides in solid phases followed the order as: SC≤SPMSPM>DS. Contribution of Mn oxides followed the order as: SC>SPM>DS in Nanhu Lake, but SPM > SC > DS in Jingyue Lake. As far as Cu adsorption, contribution of corresponding component among solid phases was assumably equivalent.Contrary to adsorption contribution, adsorption ability was used to estimate the metal adsorption to per unit mass of component. Adsorption ability of main components in the same solid phase for heavy metals decreased in the order of Mn oxides>Fe oxides>organic materials in spite of Nanhu or Jingyue Lake. In both natural waters, adsorption ability of Mn oxides in solid phases followed the order as SC≥SPM>DS. Adsorption ability of Fe oxides in solid phases in Nanhu Lake followed the same order with Mn oxides, but adsorption ability of Fe oxides in Jingyue Lake was very close. In addition, for Nanhu Lake, adsorption ability of organic matters in DS was highest, but for Jingyue Lake, SC was the highest. Among Pb, Cd, Cu and Co, Pb tends to associate with both of Mn oxides and Fe oxides, and Co has preferential associations with Mn oxides too. However, Cu was more prone to chelated with organic matters. As far as Cd, adsorption ability of any components for it was relatively lower.Selective extraction followed by heavy metal adsorption and statistical analysis was employed to study the adsorption characteristics of solid phases for heavy metals and direct extraction method was employed to study enrichment characteristics of suspended particulate. By comparison of adsorption characteristic and enrichment characteristic, roles of main components in suspended particulate for Pb and Cu adsorption onto suspended particulate were confirmed. The results indicated that adsorption characteristics of components were comparable to enrichment characteristics of them. Pb tends to bind with Fe oxides in suspended particulate. Organic materials were most important adsorbents for Cu adsorption and enrichment. Enrichment contribution of Mn oxides was higher than adsorption contribution, which may be resulted from higher K value of Mn oxides.The kinetic characteristics of Pb, Cd and Cu adsorption onto solid phases in both natural waters were studied in the thesis. The result showed that adsorption of Pb, Cd and Cu onto solid phases often experienced two stages, i.e. preliminary fast adsorption process and continued relative slow adsorption process. Among Pb, Cd and Cu, Cd was adsorbed the fastest by the same solid surface, while Pb was a little faster than Cu. Among SC, SPM and DS, DS adsorbed the same heavy metal faster than SPM and SC.With pH value rising, all of Pb, Cd and Cu adsorption onto solid phases increased evidently, which might be partly resulted from dissolution of Mn oxides in solid phases at lower pH value. Among Pb, Cd and Cu, the effect of pH value on the Pb adsorption onto these solid phases is most remarkable probably owing to the strong association of Pb with Mn oxides. In addition, the effect of pH value on the SPM is more remarkable than SC and DS, which was probably relevant with higher content of Mn oxides in SPM.The adsorption of Pb, Cd to the SC after and before treated with the organiochlorine pesticide and the competitive adsorption between organiochlorine pesticide and Pb, Cd onto SC were conducted, in order to study the effects of the organiochlorine pesticide on the adsorption of heavy metals onto the natural surface coatings. Furthermore, the mechanism causing these effects was also assayed. The result showed that the organiochlorine pesticide could influence Pb and Cd adsorption to solid phases and organiochlorine pesticide could restrain the Pb adsorption, but promote Cd adsorption. Moreover, effect of organiochlorine pesticide on Cd adsorption onto SC was more prominent than Pb. Owing to the lower concentration of organiochlorine pesticide in natural waters, SC could adsorb organiochlorine pesticide and heavy metals synchronously.