The Effect Mechanism Of Dissolved Organic Matter On Cu²⁺ And Pb²⁺ Adsorption By Different Types Of Soil

Dissolved organic matter (DOM) was the most active component of organic fertilizer. After entering soil with organic fertilizer application, DOMs may bring a series of important influences on the bioavailability of heavy metals through the reaction such as adsorption, desorption, transformation and complexation with heavy metals in soil. Therefore, it is significant for evaluating the effect of organic fertilizer, advising the application of organic fertilizer, investigating the relation between organic fertilizer and soil fertility and the agricultural non-point source pollution.A series of experiments were carried on to research the effects of dissolved organic matter (DOM) which extracted from wheat straw and pig manure on the adsorption of Cu2+ and Pb2+ by three typical soils (black soil, red soil and fluvo-aquic soil) and other different kinds of agricultural soils. Furthermore, the multiple methods such as elemental analysis, FTIR spectroscopy and solid-state 13C NMR spectroscopy were jointly conducted to reveal the spectroscopic characterization of DOMs and DOMs-Cu2+ and DOMs-Pb2+ complexes, and then to elucidate the mechanism of Cu adsorption by typical soils.The main results of this thesis were listed as follows:Isothermal adsorption experiment of Cu2+ adsorption by the black, red and fluvo-aquic soils showed that the order of maximum adsorption capacity of Cu2+ was:fluvo-aquic soil> black soil> red soil. Cu2+ adsorption capacity was promoted by the DOMs in the black and red soils at the 350 mg L-1 of DOM concentration, while the Cu2+ adsorption capacity decreased in the fluvo-aquic soil. The influence of DOMp was more obviously higher than that of DOMw; for Pb2+ adsorption, DOMp and DOMw played an enhancement function in the black and fluvo-aquic soils, and an inhibitory function in the red soil.The different concentrations of DOMs promoted the adsorption of Cu2+ in the black and red soils, but the promoting ability weakened with increasing DOMs concentrations in the black and red soils. Meanwhile, in the fluvo-aquic soil, the exogenous DOMp inhibited the adsorption of Cu2+ obviously. For the adsorption of Pb2+, DOMw inhibited Pb2+ adsorption in the black and fluvo-aquic soils with increasing the DOMw concentrations, but in red soil, the promoted effect was more and more obviously with DOMw concentrations increasing. The effect of different concentrations of DOMp in black and fluvo-aquic soils was generally inhibitory trend, but with concentrations increasing the effect of DOMp on adsorption of Pb2+ in red soil changed from promoted action to inhibitory action.Resulted of FTIR showed that both DOMw and DOMp contained many active functional groups such as -C≡C-H,-COOH, N-H,-OH,-C=O,-NO2,C-O,C-Nand C=C, and they are mainly composed of carbohydrate material, and there was a reciprocal activation between Cu2+ and function groups of DOMs. In the process of Cu2+ adsoption by soils, after Cu2+ combined with DOMp, the number and area of peaks at 1400-1650 cm-1 and 500-1000 cm-1 were markedly stronger. But there was only a peaks at 1400-1650 cm-1 become stronger after Cu2+ combined with DOMw. And after Pb2+combined with DOMw, the peaks at 1110 cm-1 which formed of stretching vibration of C-O in polysaccharide and kind was become stronger, but after Pb2+combined with DOMp, the most obvious change was the peaks at 1383 cm-1 because of the C=O and C-O stretching vibration. And the peaks at 2398-2432 cm-1 was become not obvious after they combined with Pb2+. It showed that Pb2+ is easy to combine with the triple bond which make the peaks disappear.Solid-state 13C NMR spectrum analysis showed that both DOMw and DOMp contain-CH2-S-(25-45 ppm),-C-O-(60-86 ppm),-COOH(155-185 ppm). DOMw also contained-CH2-N-(40-60 ppm),-C-CΞC-(70-110 ppm) andα- halogenated aldehyde (170-190 ppm), while DOMp contained -CH-N-(50-70 ppm),-C=C-(110-150 ppm),-CHO (175-210 ppm). After the two DOMs combined with Cu2+, many characteristic peaks were changed except for CH3-S-(26 ppm), which showed these function groups may action with Cu2+, thereby they are no longer the characteristic adsorption peaks of NMR. Alkyl-C was incresed of DOMw but O-alkyl-C and aromatic-C was decreased afer DOMw combined with Pb2+. Each type of C was decreased after DOMp combined with Pb2+, which showed function groups of DOMp can complex or chelate with heavy metals more easily.The adsorbance range of Cu2+ and Pb2+ in twenty-seven types of agricultural soil was 0.61-2.10 mg g-1 and 3.26-6.25 mg g-1, respecticly. Adsorbance of Cu2+ and Pb2+ by Shenzhen soil was minimum while Zhaotong and Tianjin soil were maxmum. There was an exponential regression relationship between Kd of the two heavy metals and soil pH. Both Fe2O3 and Al2O3 were polynomial correlated with Kd of Cu2+. There were different effect on Cu2+ and Pb2+ adsorption by different soil after addition DOMw and DOMp. Both DOMw and DOMp promoted the adsorption of Cu2+ in Shanghai, Yanji, Xuzhou, Shenzhen, Guiyang, Yingtan, Fujian, Linzhi, Danzhou and Gongzhuling, and inhitited the adsorption of Cu2+ in other soils, and in spite of promoted action or inhibitory action, the influence of DOMp was more obviously than that of DOMw. For Pb2+, both DOMw and DOMp promoted the adsorption of Pb2+ in Shanghai, Shenzhen, Yingtan and Danzhou. But in Yanji, Xuzhou, Ningbo, Changsha, Guiyang, Fujian, Linzhi and Gongzhuling soil, DOMw promted Pb2+ adsorption while DOMp inhibited Pb2+ adsorption. Both DOM can inhibit the adsorption of Pb2+ in other thirteen types of soil.